Exploring molecular complexity with ALMA (EMoCA): Detection of three new hot cores in Sagittarius B2(N)
M. Bonfand, A. Belloche, K. M. Menten, R. T. Garrod, H. S. P. Mueller
AAstronomy & Astrophysics manuscript no. Detection_hot_cores_SgrB2 c (cid:13)
ESO 2017March 29, 2017
Exploring molecular complexity with ALMA (EMoCA):Detection of three new hot cores in Sagittarius B2(N)
M. Bonfand , A. Belloche , K. M. Menten , R. T. Garrod , H. S. P. Müller Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, Bonn, Germany Departments of Chemistry and Astronomy, University of Virginia, Charlottesville, VA 22904, USA I. Physikalishes Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
ABSTRACT
Context.
The Sagittarius B2 molecular cloud contains several sites forming high-mass stars. Sgr B2(N) is one of its main centersof activity. It hosts several compact and ultra-compact HII regions, as well as two known hot molecular cores (Sgr B2(N1) andSgr B2(N2)) in the early stage of the high-mass star formation process, where complex organic molecules (COMs) are detected in thegas phase.
Aims.
Our goal is to use the high sensitivity of the Atacama Large Millimeter / submillimeter Array (ALMA) to characterize the hotcore population in Sgr B2(N) and thereby shed a new light on the star formation process in this star-forming region. Methods.
We use a complete 3 mm spectral line survey conducted with ALMA to search for faint hot cores in the Sgr B2(N)region. The chemical composition of the detected sources and the column densities are derived by modelling the whole spectra underthe assumption of local thermodynamic equilibrium. Population diagrams are constructed to fit rotational temperatures. Integratedintensity maps are produced to derive the peak position and fit the size of each molecule’s emission distribution. The kinematicstructure of the hot cores is investigated by analyzing the line wing emission of typical outflow tracers. The H column densities arecomputed from ALMA and SMA continuum emission maps. Results.
We report the discovery of three new hot cores in Sgr B2(N) that we call Sgr B2(N3), Sgr B2(N4), and Sgr B2(N5). The threesources are associated with class II methanol masers, well known tracers of high-mass star formation, and Sgr B2(N5) also with aUCHII region. Their H column densities are found to be ∼
16 up to 36 times lower than the one of the main hot core Sgr B2(N1). Thespectra of these new hot cores have spectral line densities of 11 up to 31 emission lines per GHz above the 7 σ level, assigned to 22–25molecules plus 13–20 less abundant isotopologs. We derive rotational temperatures around 140–180 K for the three new hot coresand mean source sizes of 0.4 (cid:48)(cid:48) for Sgr B2(N3) and 1.0 (cid:48)(cid:48) for Sgr B2(N4) and Sgr B2(N5). The chemical composition of Sgr B2(N3),Sgr B2(N4), and Sgr B2(N5) is very similar, but it di ff ers from that of Sgr B2(N2). Finally, Sgr B2(N3) and Sgr B2(N5) show highvelocity wing emission in typical outflow tracers, with a bipolar morphology in their integrated intensity maps suggesting the presenceof an outflow, like in Sgr B2(N1). No sign of an outflow is found around Sgr B2(N2) and Sgr B2(N4). We derive statistical lifetimesof 4 × yr for the class II methanol maser phase and 6 × yr for the hot core phase in Sgr B2(N). Conclusions.
The associations of the hot cores with class II methanol masers, outflows, and / or UCHII regions tentatively suggest thefollowing age sequence: Sgr B2(N4), Sgr B2(N3), SgrB2(N5), Sgr B2(N1). The status of Sgr B2(N2) is unclear. It may contain twodistinct sources, a UCHII region and a very young hot core. Key words. stars: formation – ISM: individual objects: Sagittarius B2(N) – astrochemistry – ISM: molecules
1. Introduction
The Sagittarius B2 molecular cloud (Sgr B2 hereafter) is oneof the most prominent regions forming high-mass stars in ourGalaxy, with a mass of ∼ M (cid:12) in a diameter of ∼
40 pc (Lis& Goldsmith 1990). It is located in the Central Molecular Zone,close to the Galactic center ( ∼
100 pc from the central super-massive black hole Sgr A ∗ in projection) and at a distance of8.34 ± ∼ (cid:48)(cid:48) in the North-South direction (corresponding to 0.2 pc inprojection, Belloche et al. 2008; Qin et al. 2011). They are bothin the early stage of star formation when a high-mass protostarhas already formed and started to warm up its circumstellar en-velope, and is producing ionizing radiation that creates an ultra-compact HII region around it. The earliest stages of the forma-tion process of high-mass stars are still poorly understood since,first, the high dust content of high-mass protostellar cores makesobservations at infrared and shorter wavelengths impossible and,second, because of the small angular sizes of these faraway re-gions. However, it is in these stages that many molecules areformed, directly in the gas phase or at the surface of dust grains.These molecules can readily be studied by their rotational spec-trum and now, with the Atacama Large Millimeter / submillimeterArray (ALMA), at exquisite angular resolution and sensitivity.While the newly ignited protostar increases the temperature ofits surroundings, the molecules frozen in the ice mantles of the Article number, page 1 of 25 a r X i v : . [ a s t r o - ph . GA ] M a r & A proofs: manuscript no. Detection_hot_cores_SgrB2 dust grains are released in the gas phase, explaining the largenumber of molecules detected toward Sgr B2.Over the past five decades, nearly 200 molecules have beendiscovered in the interstellar medium (ISM) or in circumstel-lar envelopes of evolved stars (see, e.g., http: // / cdms / molecules). Among them, about 60 are com-posed of six atoms or more and are called Complex OrganicMolecules (COMs) in the field of astrochemistry (Herbst &van Dishoeck 2009). Most species have been discovered to-ward the warm and dense parts of star forming regions andmany of the first detections of interstellar molecules at radio and(sub)millimeter wavelengths were made toward Sgr B2, suchas acetic acid CH COOH (Mehringer et al. 1997), glycolalde-hyde CH (OH)CHO (Hollis et al. 2000), acetamide CH CONH (Hollis et al. 2006), and aminoacetonitrile NH CH CN (Bel-loche et al. 2008); see also the overview by Menten (2004).Sgr B2(N) thus appears to be one of the best targets for studyingCOMs and searching for new molecules, and thus expanding ourview of the chemical complexity of the ISM.Through the investigation of the chemical composition ofSgr B2(N), we wish to characterize its hot core population toshed a new light on the star formation process in this region. Tothis aim we analyze a spectral line survey recently conductedwith ALMA in its cycles 0 and 1 at high angular resolution.We take advantage of the high sensitivity of the EMoCA survey(standing for "Exploring Molecular Complexity with ALMA")to search for fainter hot cores in Sgr B2(N) in order to extendour view of the distribution of active star forming regions in thisoutstanding cloud. The article is structured as follows. The ob-servations and method of analysis are presented in Sect. 2. Theresults are given in Sect. 3 and discussed in Sect. 4. Finally theconclusions are presented in Sect. 5.
2. Observations and method of analysis
The ALMA observations that provided the data used here tar-get Sgr B2(N) with the phase center located half way betweenSgr B2(N1) and Sgr B2(N2), at α J2000 = h m s , δ J2000 = -28 o (cid:48) (cid:48)(cid:48) . It is a complete spectral line survey between84.1 GHz and 114.4 GHz, conducted at high angular resolution( ∼ (cid:48)(cid:48) ) and with a high sensitivity ∼ / beam per 488 kHz(1.7 to 1.3 km s − ) wide channel. The spectral line survey is di-vided into five spectral setups, each one delivering four spectralwindows. Details about the di ff erent setups and the data reduc-tion are presented in Belloche et al. (2016). The size (HPBW)of the primary beam of the 12 m antennas varies between 69 (cid:48)(cid:48) at84 GHz and 51 (cid:48)(cid:48) at 114 GHz (Remijan 2015). Qin et al. (2011) observed the Sgr B2 region using the SMAin the compact and very extended configurations, reporting thefirst high-angular-resolution submillimeter continuum observa-tions of this region. The continuum map used here was obtainedat 342.883 GHz, with a synthesized beam of 0.4 (cid:48)(cid:48) × (cid:48)(cid:48) and aposition angle of 14.4 o . The map has been corrected for the pri-mary beam attenuation. More details can be found in Qin et al.(2011). Given the high densities observed in the Sgr B2(N) region (Bel-loche et al. 2008, 2014; Qin et al. 2011), it is appropriate to workunder the local thermodynamic equilibrium (LTE) approxima-tion. We use Weeds (Maret et al. 2011), which is part of theCLASS software , to perform the line identification and mod-elling of the spectra, after correction for the primary beam atten-uation. A synthetic spectrum is produced for each species solv-ing the radiative transfer equation and taking into account thefinite angular resolution of the interferometer, the line opacity,and line blending. Each molecule is modelled separately adjust-ing the following parameters: column density, rotational temper-ature, angular size of the emitting region (assumed to be Gaus-sian), velocity o ff set with respect to the systemic velocity of thesource, and linewidth (FWHM). For each species, population di-agrams are plotted to derive the rotational temperature and 2DGaussians are fitted to integrated intensity maps to measure thesize of the emitting region. The linewidth and velocity o ff set arederived from 1D-Gaussian fits to the lines detected in the spec-tra. All parameters are then adjusted manually until a good fit tothe data is obtained. Finally, contributions from all species areadded to obtain the complete synthetic spectrum. Through thismodelling process, a line is assigned to a given molecule onlyif all lines from this molecule emitted in the frequency range ofthe survey are detected with the right intensity predicted by themodel and if no line is missing in the observed spectrum. Moreinformation about the modelling procedure can be found in Bel-loche et al. (2016). The spectroscopic predictions used to modelthe spectra are the same as in Belloche et al. (2016, 2017), andMüller et al. (2016). They originate mainly from the CDMS andJPL catalogs (Endres et al. 2016; Pearson et al. 2010).
3. Results
The high sensitivity of our ALMA data set allows us to search forfainter hot cores in the vicinity of Sgr B2(N1) and Sgr B2(N2).To this aim, we counted the channels with continuum-subtractedflux densities above the 7 σ level (1 σ ∼ / beam) over thewhole frequency range for each pixel in the field of view. In thiscount we excluded setup 3 which has the lowest angular resolu-tion (HPBW > (cid:48)(cid:48) , see Table 2 in Belloche et al. 2016) and wecounted only once the channels located in frequency ranges over-lapped by adjacent spectral windows. The analyzed ranges cover47296 channels, i . e . σ threshold, i . e higher contours reflect the presence of moreemission lines. The figure clearly shows the two main hot coresSgr B2(N1) and Sgr B2(N2). It also reveals high spectral linedensities toward three other positions, unveiling the presence ofthree new sources that we call Sgr B2(N3), Sgr B2(N4), andSgr B2(N5). The region inside the contour located South-East ofSgr B2(N5) shows emission lines only in setups 2 and 5 (4 spec-tral windows) with line intensities lower than toward Sgr B2(N5)but a line content that is very similar. We think this structure is adeconvolution artifact.We fit 2D Gaussians to the channel count map with theGILDAS procedure GAUSS-2D in order to derive the peak po-sition of the five sources. The results of the fits are listed in Ta-ble 1 and the position of the spectral line density peaks of each See http: // / IRAMFR / GILDAS.Article number, page 2 of 25. Bonfand et al.: Detection of three new hot cores in Sgr B2(N)
Fig. 1.
Contour map of the number of channels with continuum-subtracted flux density above the 7 σ level (1 σ ∼ / beam). The con-tour levels are: 500, 1000, 2000, 5000, 10000, 20000, 30000, and 40000.The blue crosses mark the peaks of spectral line density. Red crossesrepresent the 6.7 GHz class II methanol masers (Caswell 1996). Greencrosses represent the compact and ultra-compact HII regions (Gaumeet al. 1995; De Pree et al. 2015). The o ff sets are defined with respect tothe phase center (see Sect. 2.1). source is marked with a blue cross in Fig. 1. These positionsare adopted as reference positions of the hot cores. Known HIIregions (Gaume et al. 1995; De Pree et al. 2015) and class IImethanol masers (Caswell 1996) are shown in Fig. 1 as greenand red crosses, respectively. The distance of each hot core tothe closest UCHII region and the distance to the closest class IImethanol maser are given in Table 1. Sgr B2(N1), Sgr B2(N2),and Sgr B2(N5) are associated with UCHII regions. All the newhot cores, Sgr B2(N3), Sgr B2(N4), and Sgr B2(N5) happen tobe associated with class II methanol masers. In order to calculate H column densities from the dust thermalemission arising from the hot cores embedded in Sgr B2(N) weneed to know the dust mass opacity coe ffi cient κ ν , which dependson the dust emissivity exponent β . To derive these parameters weneed observations at at least two frequencies. Here we use theALMA and SMA data after processing them in the followingway: the flux densities measured in the ALMA continuum mapsneed to be corrected for the contribution of the free-free emissionand the SMA continuum map has to be smoothed to the ALMAresolution. We investigate 20 continuum maps obtained at di ff erent fre-quencies over the whole frequency range of the ALMA survey. Fig. 2.
Continuum map of the Sgr B2(N) region obtained with ALMAat 108 GHz. Contour levels (positive in black solid line and negativein dashed line) start at 5 times the rms noise level, σ , of 3.0 mJy / beamand double in value up to 320 σ . The filled ellipse shows the synthe-sized beam (1.65 (cid:48)(cid:48) × (cid:48)(cid:48) , PA = -83.4 o ). The black cross represents thephase center. The blue crosses mark the positions of the five hot coresembedded in Sgr B2(N) derived from Fig. 1. The red crosses representthe average peak positions of the continuum emission derived from 2D-Gaussian fits to all ALMA continuum maps. The green crosses markthe compact and ultra-compact HII regions. The dotted red circle rep-resents the size (HPBW) of the primary beam of the 12 m antennas at108 GHz. The map is not corrected for the primary beam attenuation. As an example, Fig. 2 shows the continuum map obtained at108 GHz with ALMA. Only four of the five hot cores embeddedin Sgr B2(N) are detected above the 5 σ level in this map. Overthe whole frequency range, Sgr B2(N1) and Sgr B2(N2) showa strong continuum emission while Sgr B2(N4) and Sgr B2(N5)appear clearly weaker. Sgr B2(N3) is not detected at all; for thissource we can only derive an upper limit to its H column densityfrom the measurement of the noise level in the maps. In this case,noise histograms are plotted from all pixels using the commandGO NOISE of the GILDAS software to derive the rms noise levelin each map. For the other hot cores we measure the peak fluxdensity S beam ν (Jy / beam) by fitting a 2D-Gaussian to the contin-uum maps at di ff erent frequencies (using the GAUSS-2D taskof the GILDAS software). The derived flux density is then cor-rected for the primary beam attenuation. We note that the com-pact continuum source detected to the North of Sgr B2(N2) cor-responds to the UCHII region K4. It does not have a high spectralline density (see Fig. 1) and thus does not harbor a hot core.The average peak position of the continuum emission as-sociated to each hot core, derived from the 2D-Gaussian fit, ismarked with a red cross in Fig. 2. These positions are also givenin Table 2 as well as the distances to the closest hot core andUCHII region. The o ff set between the continuum peak positionand the hot core reference position is at most one fourth of thebeam. Article number, page 3 of 25 & A proofs: manuscript no. Detection_hot_cores_SgrB2
Table 1.
Position and spectral line density of the hot cores embedded in Sgr B2(N), and distance to UCHII regions and class II methanol masers.
Source ∆ α ; ∆ δ a α J2000 ; δ J2000 b N channels c n l d d l − maser e d l − UCHII e FWHM
UCHII f ( (cid:48)(cid:48) ) 17 h m ; -28 o (cid:48) (GHz − ) ( (cid:48)(cid:48) ) ( (cid:48)(cid:48) ) ( (cid:48)(cid:48) )N1 + s ; 18.40(0.01) (cid:48)(cid:48) + s ; 13.42(0.01) (cid:48)(cid:48) + s ; 14.91(0.06) (cid:48)(cid:48) s ; 32.41(0.05) (cid:48)(cid:48)
932 14 0.25(0.41) _ _N5 + s ; 41.34(0.01) (cid:48)(cid:48) < Notes. ( a ) Equatorial o ff sets of the spectral line density peak with respect to the phase center (see Sect. 2.1). The uncertainties in parentheses comefrom the 2D-Gaussian fit to the contour map. They are only statistical. ( b ) Same position given in J2000 Equatorial coordinates. ( c ) Number ofchannels with continuum-subtracted flux densities above 7 σ . ( d ) Estimation of the spectral line density above 7 σ (excluding setup 3) assumingmean linewidths of ∼ − for Sgr B2(N1) and ∼ − for the others hot cores (see Sect. 3.7 and Belloche et al. 2016). ( e ) Distance betweenthe hot core and the closest class II methanol maser or UCHII region. The uncertainties given in parentheses are calculated based on the errorsgiven by the Gaussian fits. In the case of the methanol masers, they also take into account the uncertainty on the maser positions (0.4 (cid:48)(cid:48) ) given byCaswell (1996). ( f ) Deconvolved angular size of the UCHII region (De Pree et al. 2015; Gaume et al. 1995).
Table 2.
Position and size of the ALMA continuum sources, and distances to hot cores and UCHII regions.
Source ∆ α ; ∆ δ a α J2000 ; δ J2000 b FWHM cc d c − l d d c − UCHII e ( (cid:48)(cid:48) ) 17 h m ; -28 o (cid:48) ( (cid:48)(cid:48) ) ( (cid:48)(cid:48) ) ( (cid:48)(cid:48) )N1 + s ; 18.48(0.05) (cid:48)(cid:48) + s ; 13.50(0.15) (cid:48)(cid:48) s ; 32.69(0.65) (cid:48)(cid:48) + s ; 41.38(0.18) (cid:48)(cid:48) Notes. ( a ) Equatorial o ff sets of the continuum peak with respect to the phase center (see Sect. 2.1). The uncertainties in parentheses represent thestandard deviation weighted by the errors given by the 2D-Gaussian fit. ( b ) Same position given in J2000 Equatorial coordinates. ( c ) Average decon-volved angular size of the continuum source derived from 2D-Gaussian fits to the ALMA continuum maps. The uncertainty given in parenthesescorresponds to the standard deviation. ( d ) Distance between the continuum peak position and the position of the closest hot core derived fromFig. 1. The uncertainty given in parentheses is calculated based on the errors given by the 2D-Gaussian fits. ( e ) Distance between the continuumpeak position and the peak position of the closest UCHII region (Gaume et al. 1995; De Pree et al. 2015). The uncertainty given in parentheses iscalculated based on the errors given by the 2D-Gaussian fit.
Usually (sub)millimeter continuum emission observed to-ward Sgr B2(N) is attributed to thermal emission from interstel-lar dust (Kuan & Snyder 1996), while at wavelength ≥ ∼
17% at 85 GHz and ∼
9% at 114 GHz. The free-free contribu-tion is higher toward Sgr B2(N2), from ∼
75% at 85 GHz, downto ∼
32% at 113.5 GHz, and it varies between 40% and 60% to-ward Sgr B2(N5). The flux densities measured in the 20 ALMAcontinuum maps and corrected for the free-free contribution arepresented in Tables B.1-B.5. We do not make any correction forSgr B2(N3) and Sgr B2(N4) because they are not associated withany known UCHII region.
We use the SMA map obtained by Qin et al. (2011) to derivethe dust emissivity index β in a joint ALMA / SMA analysis. Tothis aim we first need to smooth the SMA map to the ALMAresolution. We use the task GAUSS-SMOOTH of the GILDASsoftware. Figure 3 shows as an example the SMA map smoothedto the same resolution as the ALMA map shown in Fig. 2. Weproceed in the same way to smooth the SMA map to the 20 dif-ferent angular resolutions corresponding to the five ALMA se-tups (20 spectral windows, 4 per setup; see Belloche et al. 2016,for details about the angular resolution).Figure 3 shows that only the two main hot cores Sgr B2(N1)and Sgr B2(N2) are detected in the SMA map. To derive peakflux densities toward these two sources we fit 2D Gaussians tothe smoothed maps. For the other hot cores that are not detected,we measure in each map the noise level inside the polygons plot-ted in red in Fig. 3. Each square has a dimension of 6 (cid:48)(cid:48) and anarea of about twice the beam size is excluded in the middle.The flux densities or rms derived from the 20 maps are listedin Tables B.1-B.5. At 343 GHz, the contribution of the free-freeemission to the flux density is lower than 0.1% and can safely beignored (Qin et al. 2011).
To derive H column densities from the SMA map at its orig-inal resolution ( ∼ (cid:48)(cid:48) ), we measure the peak flux densities to- Article number, page 4 of 25. Bonfand et al.: Detection of three new hot cores in Sgr B2(N)
Fig. 3.
Continuum map of the Sgr B2(N) region obtained with the SMAat 343 GHz (Qin et al. 2011) and smoothed to the ALMA resolution.The new beam is shown in the bottom left corner (1.65 (cid:48)(cid:48) × (cid:48)(cid:48) , PA = -83.4 o ). The contour levels (positive in solid line, negative in dashed line)start at 8 σ and double up to 128 σ with σ = / beam, the noise levelmeasured inside the polygon defined around Sgr B2(N3). The blackcross represents the SMA phase center. The red crosses mark the peakpositions of the ALMA continuum emission derived from Fig. 2. Theposition of Sgr B2(N3) (blue cross) is derived from Fig. 1. The reddashed circle represents the size (HPBW) of the primary beam of theSMA 6 m antennas at 343 GHz. The map is corrected for the primarybeam attenuation. ward Sgr B2(N1) and Sgr B2(N2) with 2D-Gaussian fits to themap. For the fainter hot cores Sgr B2(N3), Sgr B2(N4), andSgr B2(N5) not detected in the SMA map, we measure the av-erage noise level inside a polygon of 6 (cid:48)(cid:48) excluding an area ofabout twice the beam size in the middle. column densities We assume a dust temperature T d ∼ T gas ∼
150 K (see Sect. 3.6).Neglecting the cosmic microwave background temperature, theradiative transfer equation can be written as follows: S beam ν = Ω beam B ν ( T d )(1 − e − τ ) , (1)with Ω beam = π × HPBW max × HPBW min the solid angle of thesynthesized beam, B ν ( T d ) the Planck function at the dust tem-perature, and τ the dust opacity. S beam ν is the peak flux densitymeasured in the continuum maps in Jy / beam. S beam ν is correctedfor the primary beam attenuation and, in the case of the ALMAdata, for the free-free contribution.From this equation we can calculate the dust opacity as fol-lows: τ = − ln (cid:32) − S beam ν Ω beam B ν ( T d ) (cid:33) . (2) The results of the opacity calculations for both the ALMA andSMA data are summarized in Table 3. The emission is opticallythin for all cores except Sgr B2(N1) at the SMA frequency. In theSMA map at its original resolution (0.3 (cid:48)(cid:48) ), the dust emission ofSgr B2(N1) is optically thick and inconsistent with a temperatureof 150 K. From Eq. 1 and assuming optically thick emission, wederive a lower limit to the dust temperature of 200 K at a scaleof 0.3 (cid:48)(cid:48) .The dust opacity, τ , is related to the H column density, N H ,via: τ = µ H m H κ ν N H , (3)with µ H = ff mann et al. 2008), m H the mass of atomic hy-drogen, and κ ν the dust mass opacity (in cm g − ) given by thepower law: κ ν = κ χ d (cid:32) νν (cid:33) β , (4)with χ d =
100 the standard gas-to-dust ratio, β the dust emissivityexponent, and κ the mass absorption coe ffi cient at frequency ν .We derive the dust emissivity index β from the ALMA andSMA data. From Eqs. 1, 3, and 4 we can write: S ALMA ν = Ω ALMA B ALMA ν ( T d ) − exp − µ H m H κ χ d (cid:32) ν ALMA ν (cid:33) β N H and S SMA ν = Ω SMA B SMA ν ( T d ) − exp − µ H m H κ χ d (cid:32) ν SMA ν (cid:33) β N H , which can also be written as: N H (cid:32) ν ALMA ν (cid:33) β = − µ H m H κ χ d × ln (cid:32) − S ALMA ν Ω ALMA B ALMA ν (cid:33) and N H (cid:32) ν SMA ν (cid:33) β = − µ H m H κ χ d × ln (cid:32) − S SMA ν Ω SMA B SMA ν (cid:33) . Then β is given by: β = ln ln (cid:18) − S ALMA ν Ω ALMA B ALMA ν (cid:19) ln (cid:18) − S SMA ν Ω SMA B SMA ν (cid:19) × (cid:16) ν ALMA ν SMA (cid:17) , (5)which only depends on the peak flux density measured on thecontinuum maps, the beam solid angle, the Planck function,and the frequency. We perform the calculations using the fluxdensities measured toward Sgr B2(N1) and Sgr B2(N2) in theALMA maps and in the SMA maps smoothed to the ALMA res-olution, excluding setup 3 (low angular resolution). We obtain β = ± β = ± β to-ward Sgr B2(N1) is underestimated due to these high opacities.It could also be that we have underestimated the contribution of Article number, page 5 of 25 & A proofs: manuscript no. Detection_hot_cores_SgrB2
Table 3.
Dust opacity of the five hot cores for a dust temperature of150 K.
Source τ ALMA a τ SMA(1 . (cid:48)(cid:48) ) b τ SMA(0 . (cid:48)(cid:48) ) c N1 0.36 0.95 _ * N2 0.05 0.19 0.61N3 < < < < < < < Notes. ( a ) Dust opacity calculated based on the ALMA data. S beam ν hasbeen corrected for the primary beam attenuation and the free-free con-tamination. ( b ) Dust opacity calculated based on the SMA map smoothedto the ALMA resolution ( ∼ (cid:48)(cid:48) ). ( c ) Dust opacity calculated based onthe SMA map at its original resolution ( ∼ (cid:48)(cid:48) ). ( * ) Optically thick andinconsistent with a temperature of 150 K. free-free emission toward Sgr B2(N1) at the ALMA frequencies.Therefore, we consider the value obtained toward Sgr B2(N2) asmore reliable, and we adopt β = . ffi cient κ = . g − (ofdust) at λ = . ∼ × − relative to H for Sgr B2(N2) (see Sect. 3.8), consis-tent with the peak gas-phase abundance of methanol predicted byour chemical models (Garrod et al. 2009; Müller et al. 2016). Ahigher value of κ would imply lower H column densities and,in turn, higher methanol abundances that would not be realisticanymore.From Eqs. 1 and 3 we can now calculate the H column den-sity for each hot core using the following equation: N H = − µ H m H κ ν × ln (cid:32) − S beam ν Ω beam B ν ( T d ) (cid:33) . (6)Figure 4 shows the results of the H column density calculationsat T d =
150 K, from both the SMA and ALMA data as a functionof ALMA frequency. The figure shows that Sgr B2(N4) is notsystematically detected over the whole frequency range of theALMA survey. All upper limits correspond to 5 times the noiselevel. All the results are also listed in Tables B.1-B.5. One shouldkeep in mind that the beam is slightly di ff erent as a function offrequency, especially in the frequency range covered by setup 3which has the lowest angular resolution (HPBW > (cid:48)(cid:48) ). We thuscalculate the average peak H column density of each hot corefrom both the SMA (smoothed to the ALMA resolution) andALMA data excluding setup 3. Table 4 summarizes the resultsobtained from the ALMA data before and after correction forthe free-free contribution and for the SMA data after and beforesmoothing to the ALMA resolution. This table shows that theH column densities of Sgr B2(N2), Sgr B2(N3), Sgr B2(N4),and Sgr B2(N5) are, respectively, 8, >
36, 28, and 16 times lowerthan the one of the main hot core Sgr B2(N1). Within the uncer-tainties, the column densities or upper limits obtained from theALMA data for the faint hot cores Sgr B2(N3), Sgr B2(N4), andSgr B2(N5) are consistent with the upper limits derived from theSMA smoothed maps.
85 90 95 100 105 1100.40.60.81.01.21.41.61.82.0 N H ( c m − ) Setup 3 Setup 3 N1
85 90 95 100 105 1100.00.51.01.52.02.53.03.54.04.5 N H ( c m − ) N2
85 90 95 100 105 11012345678 N H ( c m − ) N3
85 90 95 100 105 1102345678 N H ( c m − ) N4
85 90 95 100 105 110Freq (GHz)0.40.60.81.01.21.41.61.8 N H ( c m − ) N5 Fig. 4. H column densities as a function of frequency for the fivehot cores embedded in Sgr B2(N). The values obtained based on theALMA data before and after correction for the free-free contribution areshown as black and red crosses respectively. The green crosses representthe results obtained based on the SMA map at 343 GHz smoothed tothe angular resolution of the ALMA maps. Error bars are calculatedfrom the error on S beam ν given by the GAUSS-2D routine and take intoaccount the uncertainty on the correction for the free-free emission. Thetriangles represent 5 σ upper limits. The dashed line in each panel is theaverage H column density (or upper limit) excluding setup 3. Table 4. H column densities for a dust temperature of 150 K. Source N H (10 cm − )ALMA a ALMA dust b SMA (1 . (cid:48)(cid:48) ) c SMA (0 . (cid:48)(cid:48) ) d N1 15.4(2.2) 13.1(2.2) 8.1(0.9) _ * N2 3.6(0.2) 1.6(0.5) 1.7(0.2) 5.1(0.4)N3 < < < < < < < < Notes.
The uncertainties are given in parentheses and correspond to thestandard deviations weighted by the error on S beam ν and on the correc-tion factor for the free-free emission. ( a ) H column densities calculatedbased on the ALMA data after correction for the primary beam atten-uation, for a mean synthesized beam size of ∼ (cid:48)(cid:48) . ( b ) ALMA dust is inaddition corrected for the free-free contribution. ( c ) H column densitiescalculated based on the SMA map smoothed to the ALMA resolution( ∼ (cid:48)(cid:48) ). ( d ) H column densities calculated based on the SMA map at itsoriginal resolution ( ∼ (cid:48)(cid:48) ) . ( * ) The dust emission toward Sgr B2(N1)being optically thick we cannot derive its H column density. Table 1 clearly shows that the spectral line density is muchlower toward Sgr B2(N3), Sgr B2(N4), and Sgr B2(N5) thanfor Sgr B2(N1) and Sgr B2(N2), reducing considerably the oc-
Article number, page 6 of 25. Bonfand et al.: Detection of three new hot cores in Sgr B2(N)
Table 5.
Statistics of the lines detected toward the three new hot cores.Source N l a n l b N species c N iso c N exc c U-lines d (GHz − ) (%)N3 714 31 23 20 19 9N4 249 11 22 13 9 11N5 508 22 25 16 12 7 Notes. ( a ) Total number of emission lines detected above the 7 σ level(rms ∼ / beam) excluding setup 3. ( b ) Line density above 7 σ , ex-cluding setup 3. ( c ) Number of identified molecules, less abundant iso-topologs, and vibrationally excited states. ( d ) Fraction of remainingunidentified lines above 7 σ . curence of line blending. This is also illustrated in Fig. 5 wherea portion of the ALMA spectrum of each hot core is shown. Weuse Weeds as described in Sect. 2.3 to perform the line identi-fication and model the spectra observed toward the three newhot cores in order to derive their chemical composition. Table 5shows the total number of emission lines detected above the 7 σ level, counted manually toward the peak position of each hotcore, excluding setup 3. It also summarises the number of speciesidentified so far and the fraction of remaining unidentified linesabove 7 σ (U-lines hereafter). The line density derived here issomewhat lower than reported in Table 1. In Table 1, we di-vided the number of channels derived from Fig. 1 by the typicalFWHM of an emission line. This was a rough estimate becausea faint line may have only a single channel emitting above the7 σ threshold while a strong line will have more channels above7 σ than the number of channels covered by its FWHM. Thissuggests that Sgr B2(N1) and Sgr B2(N2) probably contain lessemission lines than indicated in Table 1.Table 5 also shows that Sgr B2(N4) has a low spectral linedensity compared to the other hot cores although roughly thesame number of molecules were identified. This di ff erence canbe explain by the low number of less abundant isotopologs andvibrationally excited states detected in Sgr B2(N4) compared toSgr B2(N3) and Sgr B2(N5). In order to get information about the spatial structure of the threenew hot cores, we investigate for each identified molecule theintegrated intensity maps produced from its vibrationnal groundstate transitions that are well detected and free of contamina-tion from other species. The position of the emission peak ofeach spectral line is derived from a 2D-Gaussian fit to its mapusing the GAUSS-2D task of the GILDAS software. Figure 6shows the spatial distribution of the molecules identified so fartoward Sgr B2(N3), Sgr B2(N4), and Sgr B2(N5). Each crossrepresents the mean peak position of a given species. Figure 6ashows that almost all species identified toward Sgr B2(N3) peakwithin a distance of ∼ (cid:48)(cid:48) from the reference position of the hotcore. Only SO, CH CCH, and HC N peak beyond 0.5 (cid:48)(cid:48)
South-West of this position. In the case of Sgr B2(N4) (Fig. 6b) andSgr B2(N5) (Fig. 6c), all molecules peak within distances ofabout 0.6 (cid:48)(cid:48) and 0.4 (cid:48)(cid:48) from the hot core position, respectively.For both Sgr B2(N4) and Sgr B2(N5), HC N in its vibrationalground state shows broad lines contaminated by other species.For this reason we used transitions in its first vibrationally ex-cited state, (cid:51) =
1. They peak close to the reference positionof each hot core, in particular toward Sgr B2(N3) for which the
Table 6.
Rms noise levels and contour levels used in Fig. 7.
Source Transition σ a Levels b N3 OCS(7-6) 49.8 4, 8, 16, 22OCS(8-7) 50.8C H CN(10 , -10 , ) 37.2C H CN(11 , -11 , ) 37.5N4 CH OH(13 -12 ) 23.5 4, 6, 8, 10, 12CH CN(6 -5 ) 30.2H CCO(5 , -4 , ) 17.1CH CCH(6 -5 ) 20.8N5 C H CN(11 , -11 , ) 36.0 4, 8, 16, 32, 64CH CN(6 -5 ) 47.4OCS(9-8) 20.0CH OH(6 -7 ) 28.0 Notes. ( a ) Rms noise level measured in the integrated intensity map inmJy beam − km s − . ( b ) Contour levels in unit of σ . emission peak of the vibrational ground state transitions is o ff setto the South-West by ∼ (cid:48)(cid:48) . For each hot core we select the transitions that are well repro-duced by the model, are not severely contaminated by otherspecies, and have a high signal-to-noise ratio (typically ≥ ∼
99) to fit 2D Gaussians to their integrated intensity maps andderive their emission size.It is di ffi cult to constrain the size of Sgr B2(N3) because theemission is unresolved for most species. Only four transitions ofOCS and C H CN show spatially resolved emission. The firstrow of Fig. 7 shows their integrated intensity maps. The result ofthe Gaussian fit is displayed in blue and the red ellipse shows thedeconvolved emission size. The middle row of Fig. 7 shows themaps of four transitions for which the emission of Sgr B2(N4)is resolved. In total for this source, 12 transitions from sevendistinct species show resolved emission with a strong signal-to-noise ratio ( ≥ ∼ ∼
10 to 99. We decided tofocus only on species showing compact emission, for this reasonwe did not take into account the transitions of CH CCH detectedtoward Sgr B2(N5), also spatially resolved but showing extendedemission, with a deconvolved size of ∼ (cid:48)(cid:48) , around the positionof the hot core.Table 7 gives the results of the Gaussian fits to the integratedintensity maps of the lines discussed above that show resolvedemission. These results are also plotted in Figs. C.1, C.2, andC.3 for Sgr B2(N3), Sgr B2(N4), and Sgr B2(N5), respectively.For each transition, the deconvolved major and minor diame-ters of the emission ( θ maj and θ min ), given in columns 10 and 11of Table 7, allow us to calculate the average deconvolved sizeof the emitting region ( (cid:112) θ ma j × θ min ). The results are given incolumn 13 of Table 7. The mean deconvolved size of each hotcore is derived from these values. We obtain sizes of 0.4 ± (cid:48)(cid:48) for Sgr B2(N3), 1.0 ± (cid:48)(cid:48) for Sgr B2(N4), and 1.0 ± (cid:48)(cid:48) forSgr B2(N5). Article number, page 7 of 25 & A proofs: manuscript no. Detection_hot_cores_SgrB2 T a b l e . R e s u lt s o f e lli p ti ca l D - G a u ss i a n fi t s t o t h e i n t e g r a t e d i n t e n s it y m a p s o f t h e t r a n s iti on s w it h r e s o l v e d e m i ss i on . S ou r ce M o l ec u l e T r a n s iti on F r e q . E up I p ea k a r m s a S N R b B ea m c P A c m a j . d m i n . d P A d ∆ α e ∆ β e θ m a j f θ m i n f P A f D l g ( M H z )( K )( J yb ea m − k m s − )( (cid:48)(cid:48) × (cid:48)(cid:48) )( o )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( o )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( (cid:48)(cid:48) )( o )( (cid:48)(cid:48) ) N O C S - . . . ( ) . . . × . - . . ( ) . ( ) + . ( )- . ( ) . ( ) . . + . . - . . . ( ) . . . × . - . . ( ) . ( ) + . ( )- . ( ) . ( ) . . + . . C H C N , - , . . . ( ) . . . × . - . . ( ) . ( ) + . ( )- . ( ) . ( ) . . + . . , - , . . . ( ) . . . × . - . . ( ) . ( ) + . ( )- . ( ) . ( ) . . - . . N O C S - . . . ( ) . . . × . - . . ( ) . ( )- . ( )- . ( )- . ( ) . . - . . - . . . ( ) . . . × . - . . ( ) . ( )- . ( )- . ( )- . ( ) . . - . . C H OH - . . . ( ) . . . × . - . . ( ) . ( )- . ( )- . ( )- . ( ) . . - . . C H O C H , - , * . . . ( ) . . . × . - . . ( ) . ( )- . ( )- . ( )- . ( ) . . - . .
78 7 , - , * . . . ( ) . . . × . - . . ( ) . ( ) + . ( )- . ( )- . ( ) . . + . . H CC O , - , . . . ( ) . . . × . - . . ( ) . ( )- . ( )- . ( )- . ( ) . . - . . , - , . . . ( ) . . . × . - . . ( ) . ( )- . ( )- . ( )- . ( ) . . - . . C H C N - . . . ( ) . . . × . - . . ( ) . ( ) + . ( )- . ( )- . ( ) . . + . . - . . . ( ) . . . × . - . . ( ) . ( ) + . ( )- . ( )- . ( ) . . + . . C H CC H - . . . ( ) . . . × . + . . ( ) . ( ) + . ( )- . ( )- . ( ) . . + . . - . . . ( ) . . . × . + . . ( ) . ( ) + . ( )- . ( )- . ( ) . . + . . C H O C HO , - , . . . ( ) . . . × . - . . ( ) . ( )- . ( )- . ( )- . ( ) . . - . . N C H C N , - , . . . ( ) . . . × . - . . ( ) . ( )- . ( ) . ( )- . ( ) . . - . . , - , . . . ( ) . . . × . - . . ( ) . ( ) + . ( ) . ( )- . ( ) . . - . . , - , . . . ( ) . . . × . - . . ( ) . ( ) + . ( ) . ( )- . ( ) . . - . . , - , . . . ( ) . . . × . - . . ( ) . ( ) + . ( ) . ( )- . ( ) . . - . . C H O C H , - , * . . . ( ) . . . × . + . . ( ) . ( ) + . ( ) . ( )- . ( ) . . + . . C H C N - . . . ( ) . . . × . + . . ( ) . ( ) + . ( ) . ( )- . ( ) . . + . . - . . . ( ) . . . × . - . . ( ) . ( ) + . ( ) . ( )- . ( ) . . - . . - . . . ( ) . . . × . - . . ( ) . ( ) + . ( ) . ( )- . ( ) . . + . . O C S - . . . ( ) . . . × . - . . ( ) . ( ) + . ( ) . ( )- . ( ) . . - . . - . . . ( ) . . . × . - . . ( ) . ( ) + . ( ) . ( )- . ( ) . . + . . C H OH - . . . ( ) . . . × . - . . ( ) . ( )- . ( ) . ( )- . ( ) . . - . . - . . . ( ) . . . × . - . . ( ) . ( )- . ( ) . ( )- . ( ) . . - . . , - , . . . ( ) . . . × . - . . ( ) . ( )- . ( ) . ( )- . ( ) . . - . . C H O C HO , - , ( E ) ** . . . ( ) . . . × . - . . ( ) . ( ) + . ( ) . ( )- . ( ) . . + . . , - , ( A ) . . . ( ) . . . × . - . . ( ) . ( ) + . ( ) . ( )- . ( ) . . - . . , - , ( A ) . . . ( ) . . . × . - . . ( ) . ( )- . ( ) . ( )- . ( ) . . - . . , - , ( E ) . . . ( ) . . . × . - . . ( ) . ( )- . ( ) . ( )- . ( ) . . - . . , - , ( A ) . . . ( ) . . . × . + . . ( ) . ( ) + . ( ) . ( )- . ( ) . . - . . , - , ( E ) . . . ( ) . . . × . + . . ( ) . ( )- . ( ) . ( )- . ( ) . . + . . , - , ( A ) . . . ( ) . . . × . + . . ( ) . ( ) + . ( ) . ( )- . ( ) . . + . . , - , ( E ) . . . ( ) . . . × . - . . ( ) . ( )- . ( ) . ( )- . ( ) . . - . . , - , ( E ) . . . ( ) . . . × . - . . ( ) . ( ) + . ( ) . ( )- . ( ) . . - . . N o t e s . N u m b e r s i np a r e n t h e s e s a r e un ce r t a i n ti e s g i v e nby t h e fi tti ng r ou ti n e GAU SS - D i nun it s o f t h e l a s t d i g it s . ( a ) P ea k fl uxd e n s it y a ndno i s e l e v e l m ea s u r e d i n t h e i n t e g r a t e d i n t e n s it y m a p . ( b ) S i gn a l - t o - no i s e r a ti o . ( c ) S i ze o f s yn t h e s i ze db ea m ( H P B W ) a ndpo s iti on a ng l e ( E a s t fr o m N o r t h ) . ( d ) S i ze ( F W H M ) a ndpo s iti on a ng l e o f t h e fi tt e d G a u ss i a n . ( e ) E qu a t o r i a l o ff s e t w it h r e s p ec tt oph a s ece n t e r( s ee S ec t . . ) . ( f ) D ec onvo l v e d m a j o r a nd m i no r d i a m e t e r s o f t h ee m i ss i on ( F W H M ) a ndpo s iti on a ng l e . ( g ) A v e r a g e d ec onvo l v e d s i ze o f t h ee m itti ng r e g i on . ( * ) T h e li n e i s a g r oupo f t r a n s iti on s fr o m t h e s a m e m o l ec u l e b l e nd e d t og e t h e r . ( ** ) T h e A a nd E l a b e l s m a r k t h e t w o s ub s t a t e s o f t h e g r ound t o r s i on a ll e v e l o f m e t hy l f o r m a t e . Article number, page 8 of 25. Bonfand et al.: Detection of three new hot cores in Sgr B2(N)
Fig. 5.
Part of the continuum-subtracted ALMA spectra observed toward the hot cores embedded in Sgr B2(N). The spectra have been correctedfor the primary beam attenuation, and shifted along the y axis for display purposes. The spectra of Sgr B2(N1) and Sgr B2(N2) have been dividedby 10 and 6, respectively. The frequency axis corresponds to the systemic velocities derived in Sect. 3.7. ∆ α (arcsec)0.60.81.01.21.41.6 ∆ δ ( a r c s e c ) N3 a SO CH CCHHC N radius: 0.33 HC N( v =1 ) ∆ α (arcsec)17.016.516.015.5 N4 b radius: 0.63 HC N( v =1 ) ∆ α (arcsec)26.025.825.625.425.225.024.824.6 N5 c radius: 0.44 HC N( v =1 ) Fig. 6.
Spatial distribution of the molecules identified around Sgr B2(N3), Sgr B2(N4), and Sgr B2(N5). In each panel, the red star represents theposition of the hot core derived from Fig. 1. Blue crosses represent the mean peak position for each species. Error bars correspond to the standarddeviation weighted by the uncertainties given by the GAUSS-2D routine. The radius of the dashed circle is given in the top right corner. Theaverage peak position of HC N, (cid:51) = Population diagrams are plotted based on transitions that arewell detected and not severely contaminated by lines from otherspecies to derive rotational temperatures. We use the followingequation (Snyder et al. 2005) to compute ordinate values (up- per level column density divided by statistical weight, N u / g u ),assuming optically thin emission in first approximation:ln (cid:32) N u g u (cid:33) = ln (cid:32) π k b ν Whc A ul Bg u (cid:33) = − E u k b T rot + ln (cid:18) N mol Z (cid:19) , (7) Article number, page 9 of 25 & A proofs: manuscript no. Detection_hot_cores_SgrB2
Fig. 7.
Integrated intensity maps of selected transitions toward Sgr B2(N3) (top row), Sgr B2(N4) (middle row), and Sgr B2(N5) (bottom row).For each map the red cross shows the peak position of the emission and the black cross is the reference position of the hot core derived from Fig. 1.The blue ellipse represents the result of the Gaussian fit to the map while the red ellipse is the deconvolved emission size. The black filled ellipserepresents the synthesized beam. The rms and contour levels are indicated in Table 6. where k b is the Boltzmann constant, ν the frequency, W the in-tegrated intensity in brightness temperature scale, h the Planckconstant, c the speed of light, A ul the Einstein coe ffi cient forspontaneous emission, B = source size beam size + source size the beam fillingfactor, g u the statistical weight of the upper level, E u the upperlevel energy, T rot the rotational temperature, Z the partition func-tion, and N mol the molecular column density.We present here the results of this analysis for ethanol andmethyl formate, two species that have many well detected linesspread over a large energy range (see Table 11). To derive the ro-tational temperature of CH OCHO, we use both its ground andfirst vibrationally excited states, modelled with the same param-eters ( N mol , T rot , source size, v o ff , ∆ v ). Only the ground statetransitions are used for ethanol. Figures 8a,c, 9a,c, and 10a,cshow the population diagrams of both species for Sgr B2(N3),Sgr B2(N4), and Sgr B2(N5), respectively. In Figs. 8b,d, 9b,d,and 10b,d we applied to both the observed and synthetic popu-lations the opacity correction factor C τ = τ − e − τ (see Goldsmith& Langer 1999; Snyder et al. 2005) using the opacities of ourradiative transfer model. In all cases the opacity correction onlyslightly a ff ects the population diagram (see values of τ max in col- umn 5 of Table 8). Since a transition can be partially contami-nated by other species, we also subtracted from the measured in-tegrated intensities the contribution of contaminating moleculesusing our model that includes all species identified so far. Thesynthetic and observed points are closer to each other after thiscorrection, however the synthetic data points are globally belowthe observed ones. This can be explained by our modelling pro-cedure in which we try to not overestimate the observed peakflux density of each spectral line. The modelled spectrum canthen well reproduce the observed spectrum in terms of peak fluxdensity, but it will not necessarily exactly fit the whole line pro-file because we use a single linewidth to model all detected lines.In addition one has to keep in mind that even after removingthe contamination from other species, the measured integratedintensities can still be a ff ected by residual contamination fromU-lines.The synthetic data points are not a ff ected by contaminationfrom other species and should be strictly aligned. The residualdispersion of the synthetic data points seen in Figs. 8b,d, 9b,d,and 10b,d can be explained by the frequency boundaries set tointegrate the intensity which are a compromise between cover- Article number, page 10 of 25. Bonfand et al.: Detection of three new hot cores in Sgr B2(N) E u /k b (K) l n ( N u / g u ( c m − )) a C H OH E u /k b (K) b C H OH E u /k b (K) l n ( N u / g u ( c m − )) c CH OCHO E u /k b (K) d CH OCHO
Fig. 8.
Population diagrams of C H OH (panels a and b) andCH OCHO (panels c and d) for Sgr B2(N3). The black points are com-puted using the integrated intensities of the observed spectrum while thered points are computed using the integrated intensities of our syntheticmodel. The error bars on the observed data points are 1 σ uncertaintieson N u / g u . No correction is applied in panels a and c, while in panels band d the optical depth correction has been applied to both the observedand synthetic populations and the contamination from all other speciesincluded in the full LTE model has been removed from the observeddata points. The blue line is the weighted linear fit to the observed pop-ulations. ing the line as much as possible and limiting the contaminationfrom other species emitting at nearby frequencies in the observedspectrum.After correction for the opacity and contamination fromother species, the observed data points are roughly aligned andcan be fitted by a single straight line, meaning one single tem-perature component. The blue line in Figs. 8b,d, 9b,d, and 10b,dshows the weighted linear fit to the observed data points. Ac-cording to Eq. 7 and considering the LTE approximation, theinverse of the slope gives us the kinetic temperature of the hotcores. The results are presented in Table 8 and show that all hotcores have temperatures around 140 K, also consistent with thekinetic temperature of Sgr B2(N2) (Müller et al. 2016; Bellocheet al. 2016).For all the species emitting numerous lines spread over abroad energy range, we use the same method to plot population E u /k b (K) l n ( N u / g u ( c m − )) a C H OH E u /k b (K) b C H OH E u /k b (K) l n ( N u / g u ( c m − )) c CH OCHO E u /k b (K) d CH OCHO
Fig. 9.
Same as Fig. 8 but for Sgr B2(N4).
Table 8.
Rotational temperatures derived from population diagrams.
Source Species States a N l b τ max c T rot d (K)N3 C H OH (cid:51) = OCHO (cid:51) = (cid:51) t = H OH (cid:51) = OCHO (cid:51) = (cid:51) t = H OH (cid:51) = OCHO (cid:51) = (cid:51) t = * C H OH (cid:51) = OCHO (cid:51) = (cid:51) t = Notes. ( a ) Vibrational or torsional states taken into account to fit thepopulation diagrams. ( b ) Number of lines plotted in the population dia-gram. ( c ) Maximum opacity. ( d ) Rotational temperature derived from thefit. The standard deviation is indicated in parentheses. ( * ) Sgr B2(N2)’sparameters are from Müller et al. (2016) and Belloche et al. (2016) . diagrams and derive rotational temperatures. For the rest of themolecules, we set the temperature to 145 K in our LTE modelwhich allows in most cases to reproduce well the observed spec-tra of the three new hot cores.
Article number, page 11 of 25 & A proofs: manuscript no. Detection_hot_cores_SgrB2 E u /k b (K) l n ( N u / g u ( c m − )) a C H OH E u /k b (K) b C H OH E u /k b (K) l n ( N u / g u ( c m − )) c CH OCHO E u /k b (K) d CH OCHO
Fig. 10.
Same as Fig. 8 but for Sgr B2(N5).
We derived the systemic velocity of the faint hot cores embed-ded in Sgr B2(N) by fitting 1D Gaussians to numerous well de-tected transitions over the whole spectrum. We obtained a veloc-ity of 74 km s − for Sgr B2(N3), 64 km s − for Sgr B2(N4), and60 km s − for Sgr B2(N5). Sgr B2(N3) and Sgr B2(N4) have thesame velocity as Sgr B2(N2) and Sgr B2(N1), respectively.These fits also give information on the typical linewidth ofeach species. The three hot cores have a median linewidth ofabout 5.0 km s − , ranging from 4.0 to 7.7 km s − for Sgr B2(N3),from 3.5 to 5.5 km s − for Sgr B2(N4), and from 3.5 to6.8 km s − for Sgr B2(N5) (see Table 11).The spectra observed toward the three new hot cores showsome broader lines with wing emission at high velocities whichcould suggest the presence of outflows. Investigating thesemolecular outflows can provide information on the evolutionarystage during the star formation process. To assess the presence ofoutflows and characterize their properties, we investigate spec-tral lines from molecules known as typical tracers of outflows.Figure 11 presents the spectra of some of these lines detected to-ward Sgr B2(N3) and Sgr B2(N5). All of them show broad wingemission at blue- and red-shifted velocities compared to the sys-temic velocity of the source. The top row of Fig. 11 shows twotransitions of SO and the OCS(8-7) transition observed toward Sgr B2(N3). The blue wing of the latter appears narrower be-cause its boundaries have been defined in order to avoid contam-ination from another species (see green spectrum in Fig. 11). Thebottom row of Fig. 11 presents the CS(2-1) transition and threetransitions of SO observed toward Sgr B2(N5). The SO transi-tion with the lowest upper energy level, SO(2 -1 ), shows a deepabsorption profile and strong broad wings in emission, like theCS(2-1) transition. For all lines, the wing boundaries are chosento avoid contamination from the line core emission predicted bythe LTE model (magenta spectrum in Fig. 11) and contamina-tion from other species (green spectrum in Fig. 11). The velocityranges used to integrate the blue- and red-shifted emission aresummarized in columns 6 and 7 of Table 9.The integrated intensity maps of blue- and red-shifted emis-sion are presented in Fig. 12 for each line along with the mapof the line core, or the continuum emission when the line coreis in absorption. All maps show a bipolar morphology for bothSgr B2(N3) and Sgr B2(N5) with distinct blue and red lobes,shifted compared to the line core, which could suggest the pres-ence of an outflow. The top row of Fig. 12 shows the integratedintensity maps of the SO lines observed toward Sgr B2(N3).Both maps are similar, showing the peak position of the bluewing clearly shifted North-East of the line core, while the redone is slightly shifted to the South. The map produced for theOCS(8-7) transition confirms the North-South velocity gradientobserved in the SO maps. The bottom row of Fig. 12 presents themaps of the line wings observed toward Sgr B2(N5). The mapsof the SO(2 -1 ) and CS(2-1) transitions, with the line core seenin absorption, show a clear bipolar structure oriented NE-SW.The other two transitions of SO exhibit a di ff erent morphology,with the red lobe shifted East of the continuum emission. Thereason for this behaviour is unclear but we note that the veloc-ities over which the red-shifted wing emission is integrated aresmaller than the ones used for SO(2 -1 ) and CS(2-1) (see Ta-ble 9).For each transtion the distance r between the peak positionsof the blue- and red-shifted outflow lobes and the hot core ref-erence positions are given in Table 9. In columns 8 and 9 wecalculated the maximum outflow velocities, V max , for the blueand red lobes as the di ff erence between the high end of the ve-locity range set to integrate the wing emission and the systemicvelocity of the source. From these values we calculate dynamicaltimescale of each outflow lobe as t dyn = rV max assuming that theinclination of the outflow axis with respect to the line of sight isabout 45 o as the maps show two distinct blue and red lobes. Theaverage dynamical times obtained from the blue- and red-shiftedlobes are on the order of a few thousand years (Table 9).Finally, we found no evidence for a bipolar structure aroundSgr B2(N4) and Sgr B2(N2). In the case of Sgr B2(N4), the samelines as those investigated in Sgr B2(N3) and Sgr B2(N5) are tooweak to show wing emission (see SO lines in Fig. C.4) or theyshow atypical shapes with blue-shifted wings but without red-shifted wings (see OCS lines in Fig. C.4). The same shape is alsoobserved in the lines of other species not considered as typicaltracers of outflows (see Fig. C.5). It is thus di ffi cult to concludewhether this broad blue-shifted emission in Sgr B2(N4) is due toan outflow or to a fainter component emitting at lower velocity. We use Weeds as described in Sect. 2.3 to model the emissionlines of ten (complex) organic molecules detected toward thethree new hot cores. For each molecule, the source size, rota-
Article number, page 12 of 25. Bonfand et al.: Detection of three new hot cores in Sgr B2(N)
Table 9.
Properties of molecular outflows toward Sgr B2(N3) and Sgr B2(N5).
Source Transition V LSR a r blue b r red b ∆ V blue c ∆ V red c V maxblue d V maxred d t dyn e (km s − ) ( (cid:48)(cid:48) ) ( (cid:48)(cid:48) ) (km s − ) (km s − ) (km s − ) (km s − ) (10 yr)N3 SO(2 -1 ) 74.0 1.07 (NE) 0.64 (SW) [61.1 ; 67.9] [79.8 ; 83.2] 12.9 9.2 3.0SO(3 -2 ) 74.0 1.04 (NE) 0.53 (SW) [63.2 ; 68.5] [80.7 ; 86.1] 10.8 12.1 2.8OCS(7-8) 74.0 0.48 (NE) 0.21 (SE) [66.4 ; 68.0] [79.8 ; 85.8] 7.6 11.8 1.6N5 SO(2 -1 ) 60.0 0.87 (NE) 0.35 (E) [44.0 ; 54.3] [66.1 ; 76.4] 16.0 16.4 1.5SO(3 -2 ) 60.0 1.37 (E) 0.83 (E) [40.4 ; 53.9] [65.9 ; 78.0] 19.6 18.0 2.3SO(2 -1 ) 60.0 1.86 (E) 3.17 (SW) [40.6 ; 58.4] [81.9 ; 96.7] 19.4 36.7 3.6CS(2-1) 60.0 1.86 (E) 3.00 (SW) [34.6 ; 53.9] [82.4 ; 98.8] 25.4 38.8 3.0 Notes. ( a ) Systemic velocity of the source. ( b ) Distance of the emission peak of the blue / red-shifted lobe compared to the reference position of thehot core. The direction is indicated in parentheses. ( c ) Velocity range adopted to integrate the emission from the blue / red-shifted wing. ( d ) Maximumoutflow velocity of the blue / red-shifted wing calculated as the di ff erence between the high end of the velocity range and V LSR . ( e ) Average dynamicaltime of the outflow, assuming an inclination of 45 ◦ ( r / V max ) . Fig. 11.
Spectra of the lines investigated to search for outflows toward Sgr B2(N3) (top row) and Sgr B2(N5) (bottom row). The dashed verticalline marks the systemic velocity of the source and the high velocity wings are highlighted in blue and red. The magenta spectrum represents ourbest-fit model while the green spectrum shows the model that contains all the identified species. The rest frequency and upper level energy (intemperature unit) of each transition are indicated in each panel. tional temperature, and velocity and linewidth are derived as de-scribed in Sects. 3.5, 3.6, and 3.7, respectively. All these parame-ters are listed in Table 11 along with the molecular column den-sities obtained from our best-fit LTE models toward the threehot cores. Column densities derived for Sgr B2(N2) are alsoshown for comparison (Müller et al. 2016; Belloche et al. 2016,2017). We investigated the isotopologs CH CN and CH
CNinstead of CH CN because the vibrational ground state transi-tions of the latter are optically thick. We assume the isotopic ratio[CH CN] / [ CH CN] = [CH CN] / [CH CN] =
21 derived byBelloche et al. (2016) to obtain the column density of CH CN.The resulting chemical composition of the four hot cores is dis-played in Fig. 13a. Figure 13b shows the column densties nor-malized to the column density of C H CN.We compute chemical abundances relative to H using theH column densities derived in Sect. 3.2. From the emissionlines detected toward Sgr B2(N3), we derived a deconvolvedsource size of 0.4 (cid:48)(cid:48) (see Sect. 3.5), therefore we use the upperlimit on the H column density derived from the SMA map atits original resolution of 0.3 (cid:48)(cid:48) (Table 4). This gives us lower lim-its to the chemical abundances of the molecules detected towardSgr B2(N3). In the case of Sgr B2(N2) and Sgr B2(N5) we de-rived deconvolved source sizes > (cid:48)(cid:48) from the ALMA contin- uum maps (see Table 2), larger than the ALMA angular reso-lution of 1.6 (cid:48)(cid:48) . For both hot cores, we thus extrapolate the H column density obtained at the ALMA angular resolution (Ta-ble 4) to the more compact region where the molecular emissioncomes from ( ∼ (cid:48)(cid:48) and 1.0 (cid:48)(cid:48) for Sgr B2(N2) and Sgr B2(N5)respectively, see Sect. 3.5). We assume spherical symmetry anda density profile proportional to r − . , which implies a columndensity scaling with r − . . Finally, the ALMA continuum mapsyield an average deconvolved source size of 0.7 (cid:48)(cid:48) for Sgr B2(N4),smaller than the ALMA resolution. Therefore, we correct the H column density obtained for Sgr B2(N4) in Sect. 3.2.4 for thebeam dilution, that is we multiply it by HPBW + θ s θ s = . + . . . Theresulting H column densities are listed in Table 12 and used inFig. 13c to derive chemical abundances.Figure 13 shows that the three new hot cores have simi-lar compositions but di ff er from Sgr B2(N2). Among the newhot cores, Sgr B2(N3) appears to be closer to Sgr B2(N5) thanSgr B2(N4) in terms of chemical content. Figure 13b shows in-deed that Sgr B2(N3) and Sgr B2(N5) have, within a factor of2, the same abundances relative to C H CN. It is also the casefor Sgr B2(N4), except for CH NCO and CH SH, which aremore abundant in this source. NH CHO is not detected towardSgr B2(N4). Relative to H , Sgr B2(N4) has COM abundances Article number, page 13 of 25 & A proofs: manuscript no. Detection_hot_cores_SgrB2
Fig. 12.
Integrated intensity maps of the lines shown in Fig. 11 toward Sgr B2(N3) (top row) and Sgr B2(N5) (bottom row). In each panel, mapsof the blue- and red-shifted wings are presented in blue and red contours, respectively, overlaid on the integrated emission of the line core (blackcontours). For the line cores a ff ected by absorption, the black contours represent the continuum emission. Rms noise levels and contour levels usedfor each map are listed in Table 10. Each cross corresponds to the peak position of the emission. The black triangle marks the position of the hotcore (Sgr B2(N3) or Sgr B2(N5)) derived from Fig. 1. C H C N C H C N C H C N C H O H C H O HC H O C H O N H C H O H N C O C H N C O C H S H N m o l ( c m − ) a N2N3N4N5 C H C N C H C N C H C N C H O H C H O HC H O C H O N H C H O H N C O C H N C O C H S H -2 -1 N m o l / N C H C N b N2N3N4N5 C H C N C H C N C H C N C H O H C H O HC H O C H O N H C H O H N C O C H N C O C H S H -9 -8 -7 -6 -5 N m o l / N H c N2N3N4N5
Fig. 13. a
Column densities of various molecules detected toward four of the five hot cores embedded in Sgr B2(N) (see Table 11). b Columndensities normalized to the column density of C H CN. c Chemical abundances with respect to H . In each panel, lower and upper limits areindicated with arrows. roughly one order of magnitude below that of Sgr B2(N5), whileSgr B2(N2) and Sgr B2(N3) lie roughly one order of magnitudeabove (Fig. 13c). C H CN and NH CHO are in particular muchmore abundant in Sgr B2(N2).
4. Discussion
In Sect. 3.1 we presented the detection of three new hot coresin Sgr B2(N), which we called Sgr B2(N3), Sgr B2(N4), andSgr B2(N5), based on the detection of high spectral line densityregions in Fig. 1. While Sgr B2(N3) is not detected in the ALMAcontinuum maps, Sgr B2(N4), and Sgr B2(N5) show a faintcontinuum level with H column densities about 28 and 16 timeslower than the one calculated for Sgr B2(N1). The two main hot cores Sgr B2(N1) and Sgr B2(N2) have high H columndensities of 1.3 × cm − and 1.6 × cm − at a resolutionof ∼ (cid:48)(cid:48) . In a previous analysis of Sgr B2(N) based on thesame ALMA survey, Belloche et al. (2014) calculated a peak H column density at 98.8 GHz of 4.2 × cm − for Sgr B2(N2),for a beam size of 1 . (cid:48)(cid:48) × . (cid:48)(cid:48) , which is about 3 times higherthan our result. This di ff erence results from the dust massopacity coe ffi cient they assumed ( κ . = × − cm g − ), ∼ ∼ column density. From the flux density measuredtoward Sgr B2(N2) in the SMA map at its original resolution we Article number, page 14 of 25. Bonfand et al.: Detection of three new hot cores in Sgr B2(N)
Table 10.
Rms noise levels and contour levels used in Fig. 12.
Source Transition Range a rms b Levels c blue 40.52N3 SO(2 -1 ) core 36.59 3,5,7,9red 15.45blue 23.75SO(3 -2 ) core 22.96 4,6,8,12,16,20red 15.00blue 16.86OCS(8-7) core 29.95 3,6,12,24,36,45red 13.53blue 45.30N5 SO(2 -1 ) core 44.90 4,6,10,14red 44.60blue 28.04SO(3 -2 ) core 28.27 4,6,10,14,16red 34.18blue 83.53SO(2 -1 ) core 87.83 4,8,15,23red 56.16blue 98.32CS(2-1) core 63.52 8,13,18,28,38,43red 102.02 Notes. ( a ) The velocity ranges are shown in Fig. 11. ( b ) Rms noise level, σ , in mJy beam − km s − measured in the integrated intensity map. ( c ) Contour levels in unit of σ . derived a H column density of 5.1 × cm − . Based on thesame map, Qin et al. (2011) calculated an H column densityof 1.5 × cm − toward Sgr B2(N2). They used the same dusttemperature, but they assumed optically thin emission and a dustmass opacity coe ffi cient κ = × − cm g − that is 3.8times smaller than the value we obtain at this frequency fromour combined ALMA / SMA analysis. In addition, we deriveda dust opacity of 0.61 for Sgr B2(N2) in the original SMAmap (see Table 3), which implies that they underestimated thecolumn density by a factor ∼ ff ects explain thefactor ∼ ff erence between the two studies.Sgr B2(N3), Sgr B2(N4), and Sgr B2(N5) are associated with6.7 GHz methanol masers (see Fig. 1). Indeed, column 8 of Ta-ble 1 shows that within the uncertainties, the peak positions ofline density of the three hot cores are consistent with the posi-tions of the class II methanol masers reported in Sgr B2(N) byCaswell (1996). The 6.7 GHz methanol transition is the strongestand most widespread of the class II methanol masers (Menten1993). It is known to be one of the best tracers of star formationand thought to be associated exclusively with regions forminghigh-mass stars (Minier et al. 2003; Xu et al. 2008). Indeed fora methanol transition to exhibit maser emission, both suitablephysical conditions and a su ffi cient abundance of methanol arerequired. Sobolev et al. (1997) showed that pumping requiresdust temperature >
150 K, high methanol column densities ( > × cm − ), and moderate densities ( n H < cm − ) to excitethe 6.7 GHz methanol maser transition. For these reasons lowmass stars are not expected to produce class II methanol masersand indeed such masers have not been detected toward regionsforming low-mass stars so far (see, e.g., Pandian et al. 2008).The specific conditions for masers to exist make them powerful probes of high-mass star formation sites and confirm the natureof the new hot cores discovered in Sgr B2(N).Methanol masers can also allow us to assess the evolutionarystages of these new sources as they are thought to trace evolu-tionary stages from the IR dark cloud (Pillai et al. 2006) to theUCHII phase. Urquhart et al. (2014) proposed an evolutionarysequence for high-mass star formation in which methanol masersand HII regions trace two di ff erent phases, with the masers prob-ing an earlier stage in the high-mass star formation process.Walsh et al. (1997) showed that methanol maser emission is de-tectable before radio continuum emission, that is before the for-mation of UCHII regions. The masers are thought to be asso-ciated with deeply embedded high-mass protostars not evolvedenough to ionize the surrounding gas and produce a detectableHII region. The maser emission remains active after first, a hy-per and then an ultra compact HII region has formed around thestar for a significant portion of the UCHII phase, during whichthe methanol molecules are shielded from the central UV radi-ation by the warm dust in the UCHII region’s slowly expand-ing molecular envelope whose emission also provides its mid-IR pumping photons. Finally, the maser emission stops as theUCHII region expands. This picture is supported by recent radioobservations with the greatly increased sensitivity of the newlyexpanded Karl G. Jansky Very Large Array (JVLA). Hu et al.(2016) find radio continuum emission in the vicinity of a thirdof their sample of 372 methanol masers. This is a significantlyhigher percentage than found by Walsh et al. (1998) with theAustralia Compact Array (ATCA), which is due to the fact thatthe new JVLA images are ∼
20 times deeper; ie., have a typ-ical rms noise level 45 µ Jy beam − at 4–8 GHz compared tothe ∼ − (at 8.64 GHz) of the Walsh et al. ATCAdata. Most likely, at the JVLA’s higher sensitivity, one is ableto detect the emission from hypercompact HII regions surround-ing the still accreting protostar exciting the masers (Keto 2007).Due to such regions’ compactness, their radio emission is veryweak. However, an increasing number of such objects is now be-ing detected with the JVLA (Rosero et al. 2016; Hu et al. 2016).van der Walt (2005) estimated the lifetime of class II methanolmasers between 2.5 × and 4.5 × yr (depending on theassumed IMF). After this period the HII region then exists with-out the maser emission. These last considerations suggest thatSgr B2(N1) and Sgr B2(N2) are already more evolved than thenew hot cores for which the maser emission still exists. Amongthem, Sgr B2(N5) is associated with both a UCHII region and aclass II methanol maser, which might suggest that it is in a phasebetween Sgr B2(N3) / Sgr B2(N4) and Sgr B2(N1) / Sgr B2(N2),when a UCHII region has formed and coexists with maser emis-sion.
Another way to assess the evolutionary stages of the hotcores is to compare their chemical compositions. Sgr B2(N3),Sgr B2(N4), and Sgr B2(N5) have spectral line densities of 31,11, and 22 lines per GHz above 7 σ , respectively (see Sect. 3.3),much lower than the two main hot cores Sgr B2(N1) andSgr B2(N2). Our LTE model allowed us to identify about 91%,89%, and 93% of the lines detected above 7 σ that have beenassigned to 22, 23, and 25 main species, respectively (see Ta-ble 5). This is much less than the 52 species identified so fartoward Sgr B2(N2) based on the EMoCA survey (Belloche, priv.comm.). Although Sgr B2(N3) has the highest spectral line den-sity among the new hot cores, Sgr B2(N5) contains the largestnumber of identified molecules. However fewer isotopologs and Article number, page 15 of 25 & A proofs: manuscript no. Detection_hot_cores_SgrB2
Table 11.
Parameters of our best-fit LTE model.
Source Species N l a N mol b C vib c T rot d D e v o ff f ∆ v g (cm − ) (K) ( (cid:48)(cid:48) ) (km s − ) (km s − )N3 C H CN, (cid:51) = × H CN, (cid:51) = × CH CN, (cid:51) = × CN, (cid:51) = × OH, (cid:51) = × H OH, (cid:51) = × OCHO, (cid:51) = × CHO, (cid:51) = × (cid:51) = × NCO, (cid:51) = × SH, (cid:51) = × H CN, (cid:51) = × H CN, (cid:51) = × CH CN, (cid:51) = × CN, (cid:51) = × OH, (cid:51) = × H OH, (cid:51) = × OCHO, (cid:51) = × CHO, (cid:51) = < × (cid:51) = × NCO, (cid:51) = × SH, (cid:51) = × H CN, (cid:51) = × H CN, (cid:51) = × CH CN, (cid:51) = × CN, (cid:51) = × OH, (cid:51) = × H OH, (cid:51) = × OCHO, (cid:51) = × CHO, (cid:51) = × (cid:51) = × NCO, (cid:51) = × SH, (cid:51) = × * C H CN, (cid:51) = × H CN, (cid:51) = × CH CN, (cid:51) = × CN, (cid:51) = × OH, (cid:51) = × H OH, (cid:51) = × OCHO, (cid:51) = × CHO, (cid:51) = × (cid:51) = × NCO, (cid:51) = × SH, (cid:51) = × Notes. ( a ) Number of lines detected above 3 σ . One line may mean a group of transitions of the same molecule blended together. ( b ) Total columndensity of the molecule. ( c ) Correction factor applied to the column density to account for the contribution of vibrationally or torsionally excitedstates not included in the partition function. ( d ) Rotational temperature (see Sect. 3.6). ( e ) Source diameter (FWHM) (see Sect. 3.5). ( f ) Velocityo ff set with respect to the assumed systemic velocity of the source: 74 km s − for Sgr B2(N2) and Sgr B2(N3), 64 km s − for Sgr B2(N4), and60 km s − , for Sgr B2(N5) (see Sect. 3.7). ( g ) Linewidth (FWHM) (see Sect. 3.7). ( * ) Sgr B2(N2)’s parameters are taken from Belloche et al. (2016);Müller et al. (2016); Belloche et al. (2017). vibrationally excited states of these molecules are detected to- ward Sgr B2(N5) than Sgr B2(N3). Sgr B2(N4)’s spectrum
Article number, page 16 of 25. Bonfand et al.: Detection of three new hot cores in Sgr B2(N)
Table 12. H column densities used to derive chemical abundances. Source θ sa N H b n c ( (cid:48)(cid:48) ) (10 cm − ) (10 cm − )N2 1.2 1.8 1.4N3 0.3 < < Notes. ( a ) Sizes for which the new H column densities are calculatedas described in Sect. 3.8. ( b ) H column density calculated for the sizeindicated in the previous column. This value is used in Fig. 13 to plotchemical abundances relative to H . ( c ) Mean particule density calcu-lated as n = N H2 θ s × µ H2 µ , with µ = ff mann et al. 2008). shows a low spectral line density and less species have beenidentified toward this source. Most of the remaining unidentifiedlines are thought to belong to vibrationally excited states of al-ready known molecules for which the spectroscopic predictionsare still missing (Belloche et al. 2013), but the presence of newmolecules in the ALMA spectra is not excluded.In order to assess whether the di ff erences reported above arereal or sensitivity limited, we need to compare in more detailsthe chemical content of the three new hot cores. In Sect. 3.8,we reported the chemical abundances of (complex) organicmolecules detected toward the new hot cores plus Sgr B2(N2)(Fig. 13). Sgr B2(N3), Sgr B2(N4), and Sgr B2(N5) have a sim-ilar chemical composition but di ff er from Sgr B2(N2). Accord-ing to our chemical model presented in Fig. 3 of Belloche et al.(2014), the chemical abundance of C H CN in the gas phaseafter sublimation is expected to decrease with time while theabundance of C H CN increases. The abundance of CH CNis also expected to increase with time after sublimation. Ta-ble 13 and Fig. 13 show that Sgr B2(N2) has the lowest ratios of[C H CN] / [C H CN] and [CH CN] / [C H CN] among the fourhot cores, which could suggest that it is less evolved than thethree new hot cores. According to our chemical model presentedin Fig. 5 of Belloche et al. (2017), the chemical abundances ofCH NCO and HNCO in the gas phase are also expected to in-crease with time after sublimation. Sgr B2(N2) also shows low[CH NCO] / [C H CN] and [HNCO] / [C H CN] ratios, consis-tent with the hypothesis made above. However, all these ratiosinvolve C H CN in the denominator, which may dominate thegeneral trend discussed above. A deeper analysis involving ra-tios of various molecules will be necessary to constrain the evo-lutionary stages of Sgr B2(N)’s hot cores from their chemistryin a more reliable way, especially because the conclusion drawnhere that Sgr B2(N2) appears chemically younger than the threenew hot cores is in contradiction with the conclusion drawn inSect. 4.1 from the associations of the hot cores with methanolmasers and / or UCHII regions (see discussion in Sect. 4.4, how-ever).One should also note that the chemical timescales ofmolecules within any single model may not relate directly tothe dynamical age of the source, as pointed out by Garrodet al. (2008). This may be exacerbated by the physical di ff er-ences between the sources, which will also a ff ect the chemicaltimescales. Only a more explicit and individualized treatment ofthe time- and space-dependent chemistry in each source is likelyto give an accurate explanation for the observed chemical di ff er-ences. Table 13.
Column density ratios of selected molecules.
Source [C H CN][C H CN] [CH CN][C H CN] [HNCO][C H CN] [CH NCO][C H CN]
N2 0.06 0.33 0.30 0.03N3 0.22 1.92 0.57 0.24N4 0.13 2.80 0.21 0.67N5 0.13 1.31 0.32 0.13
In Sect. 3.4 we investigated the spatial distribution of themolecules detected toward the three new hot cores. Most of theidentified species show compact emission with emission peakswithin distances of ∼ (cid:48)(cid:48) , 0.6 (cid:48)(cid:48) , and 0.4 (cid:48)(cid:48) of the positions ofSgr B2(N3), Sgr B2(N4), and Sgr B2(N5), respectively (seeFig. 6). This led us to define the reference position of eachhot cores as the position where their spectral line density peaks(Sect. 3.1). Within the uncertainties the emission peak of mostspecies is consistent with this position. Only three molecules,SO, HC N, and CH CCH, show significant o ff sets between theiremission peaks and the position of Sgr B2(N3). The transitionsof SO detected toward Sgr B2(N3) have an emission peak lo-cated ∼ (cid:48)(cid:48) South-West of the hot core on average (Fig. 6a andtop row of Fig. 12). Figures 14a,b present the integrated inten-sity maps of two vibrational ground state transitions of CH CCHand HC N. They both show the same elongated shape as the SOmaps. In both cases the peak positions of the emission given bythe 2D-Gaussian fit to the map is shifted beyond 0.5 (cid:48)(cid:48) from thehot core position, due to this extended emission. On the con-trary, transitions from within the first vibrationally excited stateof HC N have a compact emission that peaks at a position con-sistent with the position of Sgr B2(N3). The (cid:51) = N thus trace the hot core better than the (cid:51) = (cid:51) = N, SO, and CH CCH is unclear. It may be relatedto the outflow that is seen along the same direction (Fig. 12).
In Sects. 3.5, 3.6, and 3.7, we presented basic physical proper-ties of the three new hot cores discovered in Sgr B2(N). Theyshow similarities with one of the already known hot cores,Sgr B2(N2). All of them have kinetic temperatures of ∼ ∼ − similar to the values derived by Belloche et al. (2016)for Sgr B2(N2), ranging from 4.7 to 6.5 km s − . Sgr B2(N4)and Sgr B2(N5) have mean molecular emission sizes of ∼ (cid:48)(cid:48) ,which is slightly smaller than the size of Sgr B2(N2) ( ∼ (cid:48)(cid:48) ,with values ranging between 0.8 (cid:48)(cid:48) and 1.5 (cid:48)(cid:48) ; Belloche et al. 2016,2017). Sgr B2(N3) is more compact, with a molecular emissionsize of 0.4 (cid:48)(cid:48) .In Table 11 we presented the parameters of our best fit mod-els for ten molecules. For each hot core we have decided to adoptthe mean angular size derived from the transitions showing re-solved emission. As the hot cores appear to be resolved for onlyfew species (especially Sgr B2(N3) for which transitions fromonly two species could be used to derive the source size, seeTable 7), we decided to use a single source size for each hotcore to model all molecules. One has to keep in mind this lastconsideration while comparing the chemical composition of thehot cores in Section 3.8 because the column densities derived Article number, page 17 of 25 & A proofs: manuscript no. Detection_hot_cores_SgrB2
Fig. 14.
Integrated intensity maps of selected transitions detected in Sgr B2(N3). The contour levels start at 3 σ (rms ∼ / beam) and increasewith a step of 3 σ . In each map the blue ellipse shows the result of the 2D-Gaussian fit. The black cross represents the position of the hot corederived from Fig. 1 and the red cross marks the peak position derived from the fit. The black filled ellipse represents the synthesized beam. Theupper level energy of each transition is indicated in temperature unit in each panel. from the model strongly depend on the adopted source size. Forinstance, we used a source size of 1.0 (cid:48)(cid:48) to model the spectrumtoward Sgr B2 (N5), although the results of the 2D-Gaussian fitto the integrated intensity maps of C H CN transitions suggestan average emission size of ∼ (cid:48)(cid:48) for this molecule (see Table7). The column density of C H CN in Sgr B2(N5) might thus beunderestimated.In Sect. 3.7 we highlighted bipolar structures in the inte-grated intensity maps of the wings of typical outflow tracers. TheNorth-South velocity gradient observed toward Sgr B2(N3) inthe maps of two SO lines and the OCS(8-7) transition most prob-ably suggests the presence of an outflow (Fig. 12). The SO(2 -1 ) and CS(2-1) transitions investigated toward Sgr B2(N5)show a clear bipolar structure also suggesting the presence ofan outflow. However, what the other transitions of SO trace to-ward this source is less clear. Nevertheless our interpretation thatSgr B2(N3) and Sgr B2(N5) drive outflows is reinforced by thefact that H O maser emission is found in the close vicinity ofboth sources (McGrath et al. 2004, see also Fig. C.6).Higuchi et al. (2015) have recently reported the presence ofa bipolar molecular outflow in the East–West direction in SgrB2(N1), on the basis of the SiO(2-1) and SO (12 , -13 , ) tran-sitions in the same data set used here. They derived an averagedynamical time of ∼ × years, similar to our results for SgrB2(N3) and Sgr B2(N5)( ∼ × yr). The fact that no out-flow has been detected toward Sgr B2(N4) does not necessarilymean a real lack of outflow motion but instead it might reflect theyouth of the source compared to the others. The outflow structurein this case might be too small to be detected at the resolution ofour ALMA survey.Codella et al. (2004) explored the possibility of using molec-ular outflows to estimate the age of the associated source. Theyinvestigated a large survey of outflows toward UCHII regions.They proposed an evolutionary scheme for regions forming high-mass stars in which class II methanol masers appear before anoutflow is detectable, then both coexist in the same phase be-fore the maser switches o ff as the UCHII region expands. Forthese reasons, the fact that no outflow has been detected towardSgr B2(N2) might suggest that it is more evolved than the othercores because a UCHII region is already detected in the sourceand no class II methanol maser has been reported. However, this hypothesis is in contradiction with the conclusion derived fromthe comparison of the chemical composition of Sgr B2(N2) andthe three new hot cores. An alternative explanation could be thatthere are two sources in Sgr B2(N2). Indeed, there is an o ff set of0.43 (cid:48)(cid:48) ( ∼ (cid:48)(cid:48) , a hypercompact HII region, W51e2-W, and a hot molec-ular core, W51e2-E (Shi et al. 2010; Ginsburg 2017). At the dis-tance of Sgr B2(N), these two objects would have a separationof 0.5 (cid:48)(cid:48) , similar to the o ff set seen between K7 and Sgr B2(N2).Observations at higher angular resolution with ALMA will benecessary to test this scenario. In a previous analysis of Sgr B2(N), Belloche et al. (2013) usedthe UCHII regions reported by Gaume et al. (1995) to estimatea star formation rate of 0.028-0.039 M (cid:12) yr − averaged over 10 years for the whole Sgr B2 complex. We assume a constant starformation rate to estimate the lifetime of Sgr B2(N)’s hot cores.Combining the results of Gaume et al. (1995) and De Pree et al.(2015), we count ten HII regions within the ALMA primarybeam centered between Sgr B2(N1) and Sgr B2(N2) (see Fig. 2).Eight of these sources are UCHII regions. Only five hot cores aredetected in the same area. Considering a lifetime of ∼ yr forthe UCHII regions (Peters et al. 2010), we estimate a lifetime of10 × ∼ × yr for Sgr B2(N)’s hot cores. In the same waywe derive a statistical lifetime of about 4 × yr for the class II6.7 GHz methanol masers detected in this area, which is, giventhe low number statistics of the Sgr B2(N) region, surprisinglyconsistent with the lifetime derived by van der Walt (2005) forclass II methanol masers (2.5 × to 4.5 × yr).Based on Fig. 5 of Codella et al. (2004) and the statisticallifetimes calculated above, we propose in Fig. 15 an evolution-ary sequence of the hot cores embedded in Sgr B2(N). Amongthe three new hot cores, Sgr B2(N5) would be the most evolvedone because it is associated with both an outflow and a classII methanol maser, and has already entered the UCHII phase. Article number, page 18 of 25. Bonfand et al.: Detection of three new hot cores in Sgr B2(N)
Sgr B2(N4) appears like the youngest core because it is onlyassociated with class II methanol maser emission. With an as-sociated methanol maser and a detected outflow but no associ-ated UCHII region, Sgr B2(N3) would be in-between. As men-tioned in Sect. 3.8, the status of Sgr B2(N2) is unclear. Its as-sociation with a UCHII region but no methanol maser and nooutflow would suggest that it is more evolved than the new hotcores, but its chemical composition seems to suggest the oppo-site. As discussed in Sect. 4.4, one reason for this apparent con-tradiction could be that Sgr B2(N2) actually contains two distinctsources, one associated with the UCHII region K7, and there-fore more evolved than all the other hot cores, and the other one,the hot core, with a line density peak shifted from K7, and stilltoo young to show outflow emission on the scales probed withALMA or to harbor a UCHII region.As shown in Table 2, the five hot cores detected in Sgr B2(N)have peak column densities that di ff er by more than one orderof magnitude. Therefore, they may form stars of di ff erent finalmasses and our attempt to classify them with a single evolution-ary sequence should be considered as tentative only. A deeperanalysis of their properties, in particular at higher angular reso-lution, will be necessary to improve our understanding of theirrespective evolutionary states.There is one complication to the evolutionary sequence pro-posed above: as discussed in Sects. 1.1 and 4.1 of Belloche et al.(2008) and shown here in Fig. C.6, Sgr B2(N1) coincides withthe centroid position of a powerful H O maser compact (4 (cid:48)(cid:48) × (cid:48)(cid:48) sized) outflow (Reid et al. 1988). For their (collisional) pump-ing, H O masers require temperatures of ∼
400 K and densities of ∼ cm − , much higher than the values derived in this paper forSgr B2(N1). These conditions are met in the post shock regionsof fast (J) shocks (Elitzur et al. 1989; Hollenbach et al. 2013).The compact H O maser outflow may originate from a di ff erentsource than that which drives the UCHII region K2, a situationreminiscent of the archetypical UCHII region W3(OH), whichhas powerful OH and methanol masers in its expanding envelope(Menten et al. 1992) and is separated by 5 (cid:48)(cid:48) from the multiple hotcore W3(OH)-H O (Wyrowski et al. 1999). Like Sgr B2(N1), thelatter drives a powerful bipolar H O maser outflow (Hachisukaet al. 2006), but shows no methanol maser emission.We also mention that several H O masers are associated witha faint peak of continuum emission in our ALMA data (seeFig. C.6), which also coincides with a region of moderately en-hanced spectral line density located ∼ (cid:48)(cid:48) West of Sgr B2(N5)(Fig. 1). This region probably harbors an additional (faint) hotcore that is not associated with any UCHII region or class IImethanol maser.
5. Conclusions
We used the 3 mm line survey EMoCA conducted with ALMAin its cylces 0 and 1 to search for new hot cores in theSgr B2(N) region, taking advantage of the high sensitivity ofthese observations. We report the discovery of three new hotcores that we called Sgr B2(N3), Sgr B2(N4), and Sgr B2(N5),located at ( α J2000 = h m s , δ J2000 = -28 o (cid:48) (cid:48)(cid:48) ),( α J2000 = h m s , δ J2000 = -28 o (cid:48) (cid:48)(cid:48) ), and ( α J2000 = h m s , δ J2000 = -28 o (cid:48) (cid:48)(cid:48) ) respectively. We an-alyzed the line survey to characterize their chemical compositionand physical structure, and we searched for outflows and associ-ations with UCHII regions or methanol masers. Our main resultsare summarized as follows: 1. Sgr B2(N3), Sgr B2(N4), and Sgr B2(N5) have spectral linedensities above 7 σ of 31, 11, and 22 lines per GHz respec-tively, which qualify them as hot cores. About 91%, 89%,and 93% of these lines have been identified and assigned to22, 23, and 25 main species, respectively.2. The typical linewidth of the three new hot cores is 5 km s − .They have rotational temperatures of ∼ (cid:48)(cid:48) for Sgr B2(N3) and 1.0 (cid:48)(cid:48) for Sgr B2(N4) and Sgr B2(N5).3. Assuming a dust temperature of 150 K similar to the rota-tional temperatures obtained from the emission lines, we de-rive a dust emissivity index β ∼ . column densities of < × ,3 × , and 1 × cm − for Sgr B2(N3), Sgr B2(N4), andSgr B2(N5), respectively, for the sizes listed above.4. We report the detection of outflows in Sgr B2(N3) andSgr B2(N5) based on the analysis of three SO lines, and theOCS(8-7) and CS(2-1) transitions. The outflow dynamicaltime is ∼ × yr for both sources. No outflow is detectedtoward Sgr B2(N4) and Sgr B2(N2).5. Each new hot core is associated with a 6.7 GHz class IImethanol maser. Sgr B2(N4) is also associated with a UCHIIregion.6. We derived the column densities and abundances often (complex) organic molecules toward Sgr B2(N3),Sgr B2(N4), and Sgr B2(N5). The three sources share asimilar chemical composition, with Sgr B2(N3) resemblingSgr B2(N5) a bit more than Sgr B2(N4). However, they di ff erfrom Sgr B2(N2) and several molecular ratios suggest thatSgr B2(N2) is chemically less evolved than the three newhot cores.7. Assuming a lifetime of 10 yr for UCHII regions, we de-rive statistical lifetimes of 4 × yr for the class IImethanol maser phase and 6 × yr for the hot core phase inSgr B2(N).Given that their peak column densities di ff er by more than oneorder of magnitude, the five hot cores may form stars of di ff er-ent final masses. Still, their associations with class II methanolmasers, outflows, and / or UCHII regions tentatively suggest thefollowing age sequence from the youngest to the oldest source:Sgr B2(N4), Sgr B2(N3), Sgr B2(N5), Sgr B2(N1). The statusof Sgr B2(N2) is puzzling. Its association with a UCHII regionbut no outflow and no methanol maser suggests that it shouldbe the oldest source in this sequence. However, this contradictsits youth suggested by its chemical composition. An explana-tion may be that Sgr B2(N2) contains two distinct sources, assuggested by the small angular o ff set separating its embeddedUCHII region from the line density peak of the hot core. On-going observations at higher angular resolution with ALMA willhelp understanding the status of this source. Acknowledgements.
We thank Sheng-Li Qin and Peter Schilke for pro-viding us the SMA map of Sgr B2(N) in electronic form. This papermakes use of the following ALMA data: ADS / JAO.ALMA / JAO.ALMA / NRAO, and NAOJ. The interferometric data are availablein the ALMA archive at https: // almascience.eso.org / aq / . This work has been inpart supported by the Deutsche Forschungsgemeinschaft (DFG) through the col-laborative research grant SFB 956 “Conditions and Impact of Star Formation”,project area B3. Article number, page 19 of 25 & A proofs: manuscript no. Detection_hot_cores_SgrB2
MASER
OUTFLOWand UCHII not detected ___
MASEROUTFLOWUCHII not detected ___
UCHIIOUTFLOWMASER UCHIIOUTFLOWNo MASER ___
UCHII
No MASER No OUTFLOW
N1N5N3N4
Methanol maser lifetime ~4 × yrHot core lifetime ~6 × yr ___ K7N2? time
UCHII region lifetime ~10 yr Fig. 15.
Proposed evolutionary sequence for all the hot cores embedded in Sgr B2(N) based on their associations with UCHII regions, class IImethanol masers, and outflows. K7 is the UCHII region located close to Sgr B2(N2) and may be a distinct source.
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Appendix A: Estimating the level of free-freeemission
Here we present the procedure used to estimate the contributionof free-free emission expected toward Sgr B2(N1), Sgr B2(N2),and Sgr B2(N5) in the ALMA continuum maps. As mentionedin Sect. 3.2.1, the overall shape of the extended continuum emis-sion detected with ALMA is similar to the shape of the 1.3 cmfree-free emission reported by Gaume et al. (1995) which sug-gests that the extended emission detected with ALMA is dom-inated by free-free emission. Figure A.1b shows the profileof the continuum emission along the direction going throughSgr B2(N2) indicated in red in Fig. A.1a. Because Sgr B2(N2)is located in the direction of extended 1.3 cm free-free emission,we decompose the profile shown in Fig. A.1b into a peak, whichwe attribute to dust emission associated with Sgr B2(N2), and apedestal, which we attribute to the extended free-free emission.We proceed in the same way for the 20 ALMA continuum maps.The results are plotted in Fig. A.2. The weighted linear fit to theresults excluding setup 3 gives us the correction to subtract fromthe measured peak density S beam ν as a function of frequency. Forthe maps belonging to the frequency range of setup 3 (with thelowest angular resolution), we directly apply the corrections es-timated from the plots of the continuum profile. The correctionsapplied here take into account the contamination from the ex-tended continuum emission detected in the ALMA continuummaps but a correction for the free-free emission arising from theUCHII region K7 that is associated with Sgr B2(N2) still has tobe applied. We estimate the flux expected from K7 based on theflux reported by De Pree et al. (2015). They measured an inte-grated flux of 30 mJy at 44.2 GHz for a source size of 0.08 (cid:48)(cid:48) . Weassume that the free-free emission of K7 is optically thin andthus that the measured flux is proportional to ν α , with α = − . ∼
28 mJy for the fre-quency range of the ALMA survey. This value is added to thecorrection for Sgr B2(N2) derived from Fig. A.2.We proceed in the same way for Sgr B2(N5), based on theflux reported by Gaume et al. (1995) toward Z10.24. They mea-sured an integrated flux of 36 mJy at 22.4 GHz for a source size < (cid:48)(cid:48) . We extrapolate this value to the ALMA frequency rangeassuming optically thin emission, and we and obtain ∼
31 mJy.This value is directly subtracted from the values of the peakflux density measured in the ALMA continuum maps towardSgr B2(N5).Finally in the case of Sgr B2(N1) we use the flux measuredby De Pree et al. (2015) toward K2 and K3 at 44.2 GHz. Theymeasured integrated flux densities of 80 mJy toward K2 for asource size of 0.12 (cid:48)(cid:48) and 242 mJy toward K3 for a source size of0.27 (cid:48)(cid:48) . K3 being located 1.3 (cid:48)(cid:48)
North-East of K2, we estimate thatonly ∼
15% of the free-free emission arising from this UCHII re-gion contributes to the total flux density measured in the ALMAsynthesized beam of ∼ (cid:48)(cid:48) centered on K2. We thus obtain atotal free-free contribution of ∼
116 mJy that we subtract fromthe flux densities measured toward Sgr B2(N1) in the ALMAcontinuum maps.
Appendix B: Additional tables : continuum analysisAppendix C: Additional figures
Table B.1.
Peak flux densities and H column densities towardSgr B2(N1). Freq. S ALMA ν (a) S SMA ν (b) N ALMAH N SMAH (GHz) (Jy / beam) (10 cm − )85.0 0.569(3) 24.15(11) 1.01(1) 0.67(1)86.5 0.594(3) 23.69(2) 1.05(1) 0.69(1)88.0 0.688(4) 24.35(3) 1.13(1) 0.70(1)90.5 0.789(3) 23.08(1) 1.38(1) 0.77(1)92.0 0.878(5) 25.67(2) 0.93(1) 0.50(1)94.5 0.942(7) 25.65(4) 0.93(1) 0.51(1)96.0 0.810(7) 21.57(3) 1.31(1) 0.82(1)97.0 0.776(5) 21.39(4) 1.21(1) 0.82(1)97.5 0.883(7) 20.93(2) 1.34(1) 0.84(1)98.5 0.809(6) 20.91(2) 1.27(1) 0.85(1)99.0 1.028(9) 21.58(14) 1.57(2) 0.83(1)100.0 1.022(7) 20.78(2) 1.68(1) 0.90(1)101.5 1.047(10) 21.11(2) 1.55(2) 0.86(1)102.5 1.051(11) 20.41(31) 1.65(2) 0.93(3)104.0 1.149(10) 23.40(6) 1.06(1) 0.60(1)106.5 1.220(11) 22.85(1) 1.11(1) 0.62(1)108.0 1.300(10) 18.80(9) 1.53(2) 0.98(1)109.5 1.012(10) 18.25(4) 1.51(2) 1.02(1)111.0 1.192(11) 19.44(3) 1.59(2) 0.97(1)113.5 1.161(14) 18.51(16) 1.55(2) 1.02(2) Notes.
Uncertainties in parentheses are given in units of the last digit.They take into account the error on S ν given by the Gaussian fittingprocedure and the uncertainty on the free-free correction factor. Re-sults obtained from maps belonging to the frequency range covered bysetup 3 are highlighted in grey. ( a ) Peak flux density derived from the2D-Gaussian fit to the continuum map, corrected for the primary beamattenuation and for the free-free contamination. ( b ) Peak flux densitymeasured on the SMA map obtained at 343 GHz and smoothed to theresolution of the ALMA map.
Table B.2.
Peak flux densities and H column densities towardSgr B2(N2). Freq S ALMA ν S SMA ν N ALMAH N SMAH (GHz) (Jy / beam) (10 cm − )85.0 0.051(8) 6.51(2) 0.82(13) 1.35(1)86.5 0.058(8) 6.42(2) 0.92(13) 1.38(1)88.0 0.070(8) 6.60(2) 1.03(12) 1.39(1)90.5 0.078(9) 6.34(1) 1.17(13) 1.52(1)92.0 0.073(7) 6.69(1) 0.69(7) 1.04(1)94.5 0.060(7) 6.69(1) 0.54(6) 1.06(1)96.0 0.103(16) 5.97(3) 1.43(22) 1.58(1)97.0 0.098(9) 5.97(2) 1.32(13) 1.60(1)97.5 0.114(9) 5.87(1) 1.59(13) 1.63(1)98.5 0.104(10) 5.87(4) 1.41(13) 1.65(1)99.0 0.138(9) 6.02(2) 1.76(12) 1.61(1)100.0 0.137(10) 5.88(6) 1.85(13) 1.73(2)101.5 0.152(9) 5.93(2) 1.87(12) 1.66(1)102.5 0.144(10) 5.80(2) 1.86(13) 1.77(1)104.0 0.169(9) 6.26(2) 1.38(8) 1.23(1)106.5 0.159(9) 6.16(2) 1.27(8) 1.28(1)108.0 0.163(10) 5.42(1) 2.00(13) 1.85(1)109.5 0.173(9) 5.30(1) 2.14(13) 1.91(1)111.0 0.198(10) 5.58(2) 2.15(11) 1.84(1)113.5 0.211(10) 5.39(1) 2.31(11) 1.92(1) Notes.
Same as Table B.1 but for Sgr B2(N2).Article number, page 21 of 25 & A proofs: manuscript no. Detection_hot_cores_SgrB2
Fig. A.1. a
Continuum map obtained at 86.5 GHz with ALMA. The contour levels are 20 σ , 40 σ , 60 σ , 100 σ , 140 σ , and 160 σ , with σ = (cid:48)(cid:48) × (cid:48)(cid:48) , PA = -83.3 o ). b Profile of the continuum emission alongthe direction plotted in red in panel a . The blue line marks the estimated level of free-free emission.
85 90 95 100 105 110 115
Frequency (GHz) F r a c t i on o f f r ee - f r ee e m i ss i on ( % ) Setup 3
Fig. A.2.
Fraction of free-free emission relative to the total flux densitymeasured toward Sgr B2(N2). This does not include the contribution ofK7. The blue line is the weighted linear fit to the results excluding setup3 that is shown in red.
Table B.3. H column density upper limits toward Sgr B2(N3). Freq rms
ALMA (a) rms
SMA (b) N ALMAH (c) N SMAH (c) (GHz) (mJy / beam) (Jy / beam) (10 cm − )85.0 5.3 0.12 < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < Notes.
Same as Table B.1 but for Sgr B2(N3). ( a ) Noise level measuredin the ALMA continuum map with GO NOISE. ( b ) Noise level measuredin the SMA map inside a polygon defined around Sgr B2(N3)’s positionas described in Sect. 3.2.2. ( c ) The upper limits correspond to 5 σ .Article number, page 22 of 25. Bonfand et al.: Detection of three new hot cores in Sgr B2(N) Table B.4.
Peak flux densities and H column densities towardSgr B2(N4). Freq S ALMA ν rms ALMA (a) rms
SMA (b) N ALMAH (c) N SMAH (d) (GHz) (mJy / beam) (Jy / beam) (10 cm − )85.0 _ 5.3 0.53 < < < < < < < < < < < < < < < < < < < < < < < < < < Notes.
Same as Table B.1 but for Sgr B2(N4). ( a ) Noise level measuredin the ALMA continuum map with GO NOISE. ( b ) Noise level mea-sured in the SMA map inside a polygon defined around Sgr B2(N4)’sposition as described in Sect. 3.2.2. ( c ) Where Sgr B2(N4) is not detectedin the ALMA maps, an upper limit to its H column density has beencalculated at the 5 σ level. ( d ) The upper limits correspond to 5 σ . Table B.5.
Peak flux densities and H column densities towardSgr B2(N5). Freq S ALMA ν rms SMA (a) N ALMAH N SMAH (b) (GHz) (Jy / beam) (10 cm − )85.0 0.073(1) 1.19 1.17(1) < < < < < < < < < < < < < < < < < < < < Notes.
Same as Table B.1 but for Sgr B2(N5). ( a ) Noise level measuredin the SMA map inside a polygon defined around Sgr B2(N5)’s positionas described in Sect. 3.2.2. ( b ) The upper limits correspond to 5 σ .
15 20 25 30 35 40 ∆ δ ( a r c s e c ) a reference ∆ δ
15 20 25 30 35 40 ∆ α ( a r c s e c ) b reference ∆ α
15 20 25 30 35 40 E up ( K ) θ ( a r c s e c ) c OCSC H CN
15 20 25 30 35 40 E up ( K ) s i ze ( a r c s e c ) d mean size Fig. C.1.
Results of the 2D-Gaussian fits to the integrated intensitymaps showing resolved emission toward Sgr B2(N3). a, b
Fitted posi-tion. The error bars are the uncertainties given by the Gaussian fits. c, d
Fitted size. The dots represent the deconvolved major and minor diam-eters of the emission ( c ) and the resulting average source size ( d ). Thesquares represent the major and minor axes of the synthesized beam ( c ).The dashed lines represent the reference position of the hot core ( a, b ),and the mean deconvolved angular size ( d ). E up ( K ) ∆ δ ( a r c s e c ) reference ∆ δ E up ( K ) ∆ α ( a r c s e c ) reference ∆ α E up ( K ) θ ( a r c s e c ) CH CNCH OCH CH OCHOCH OH
10 20 30 40 50 60 70 80 90 E up ( K ) θ ( a r c s e c ) CH CCHH CCOOCS E up ( K ) s i ze ( a r c s e c ) mean size Fig. C.2.
Same as Fig. C.1 but for Sgr B2(N4).Article number, page 23 of 25 & A proofs: manuscript no. Detection_hot_cores_SgrB2 E up ( K ) ∆ δ ( a r c s e c ) reference ∆ δ E up ( K ) ∆ α ( a r c s e c ) reference ∆ α
50 100 150 E up ( K ) θ ( a r c s e c ) C H CNCH OCH CH CNCH OH
15 20 25 30 35 40 E up ( K ) θ ( a r c s e c ) CH OCHOOCS E up ( K ) s i ze ( a r c s e c ) mean size Fig. C.3.
Same as Fig. C.1 but for Sgr B2(N5).Article number, page 24 of 25. Bonfand et al.: Detection of three new hot cores in Sgr B2(N)
Fig. C.4.
Lines of typical outflow tracers detected toward Sgr B2(N4). The red spectrum represents our LTE model fit to the complete observedspectrum of the molecule. The green spectrum shows the model that contains all the molecules identified so far toward Sgr B2(N4). The dashedhorizontal line shows the 3 σ level. The systemic velocity of the source is marked with the dashed vertical line. The rest frequency and upper levelenergy (in temperature unit) of each transition are indicated in each panel. Fig. C.5.
Same as Fig. C.4 but for species not considered as typical outflow tracers.
Fig. C.6.
Continuum map of the Sgr B2(N) region obtained withALMA at 108 GHz. Contour levels (positive in black solid line andnegative in dashed line) start at 5 times the rms noise level, σ , of3.0 mJy / beam and double in value up to 320 σ . The filled ellipse showsthe synthesized beam (1.65 (cid:48)(cid:48) × (cid:48)(cid:48) , PA = -83.4 o ). The black cross rep-resents the phase center. The red crosses mark the positions of the fivehot cores embedded in Sgr B2(N). The blue crosses represent H2