SDSS-IV MaNGA: Blueberry Candidates Associated with LSB Galaxies - Merger or Tidal Dwarf Systems ?
DD RAFT VERSION F EBRUARY
17, 2021Typeset using L A TEX twocolumn style in AASTeX63
SDSS-IV MaNGA: Blueberry Candidates Associated with LSB Galaxies − Merger or Tidal Dwarf Systems ? A BHISHEK P ASWAN , K ANAK S AHA , AND S URAJ D HIWAR Inter-University Centre for Astronomy and Astrophysics, Ganeshkhind, Post Bag 4, Pune 411007, India Dayanand Science College, Latur 413512, India (Received — xxx; Revised — xxx; Accepted — xxx)
ABSTRACTWe report here our finding of two new blueberry galaxies using optical IFU spectroscopic data from theMaNGA survey. Both the blueberries are found to be compact ( < − ∼ M (cid:12) amongst the locally known blueberry galaxies. We find a significantly large mean metallicity difference ( ∼ Keywords:
Galaxy evolution — Starburst galaxies — H II regions — Interstellar medium — Tidal interactions— Compact galaxies INTRODUCTIONOne of the most important events in the history of ourearly Universe is the cosmic re-ionization, which is still ob-servationally not well-constrained due to limited sample ofobserved ionizing sources. In recent years, a lot of effortshave been therefore made to search for the sources responsi-ble for the re-ionization of the Universe at high redshifts z (cid:38)
6. The general outcome of these studies suggests that faint,low-mass, compact and clumpy starburst systems with anescape of ionizing radiation above 10 −
20% are the primarysources to the ionizing budget of the early Universe (e.g.,Ouchi et al. 2009; Robertson et al. 2013; Dressler et al. 2015;Finkelstein et al. 2019).However, direct observation of such objects at high red-shifts are difficult due to various reasons e.g., due to limi-tation of observational facilities available at the present day,faintness of the sources (Robertson et al. 2013; Bouwenset al. 2015; Alavi et al. 2020), contamination by low redshift
Corresponding author: Abhishek [email protected] interlopers (e.g., Vanzella et al. 2010, 2012; Siana et al. 2015)and attenuation of ionizing photons by neutral intergalacticmedium (IGM; Inoue et al. 2014). As a consequence of theselimitations, so far a very few reliable high-redshift compactstarburst galaxies with leaking ionizing photons are knowne.g.,
Ion ion
3, Q1549-C25 and A2218-Flanking, AUDFs-01 as studied in Vanzella et al. (2015, 2018); de Barros et al.(2016); Shapley et al. (2016); Bian et al. (2017) and Sahaet al. (2020). But there has been a significant increase inthe number of sources, in particular the Green Peas (GPs;Cardamone et al. 2009) and blueberries (Yang et al. 2017),with leaking ionizing radiation with an escape fraction of2 −
98% in the low-redshift ( z ≤ .
4) Universe (e.g., Izotovet al. 2016a,b, 2018a,b; Jaskot et al. 2019; Wang et al. 2019).These sources are low-mass, compact ( < . −
100 M (cid:12) yr − ), highEW[OIII] (500 − ≡ [OIII]/[OII] ≥ B − V ) = 0 − . . − . a r X i v : . [ a s t r o - ph . GA ] F e b P ASWAN ET AL .ertheless, they are still statistically less in number limitingour understanding of their physical nature in general. Sev-eral questions such as their formation scenario and spatiallyresolved properties remain unanswered.Previous studies of GPs and blueberries have explicitlyshown that they reside in low galaxy-density environments(Cardamone et al. 2009; Yang et al. 2017). This might bethe case due to their selection effect, as they are primarilyselected based on their visual inspection as compact greenand blue isolated galaxies in the Galaxy Zoo catalogue. Buttheir environment dependence is yet to be understood. Ofthese two class of galaxies, blueberries are relatively nearbyobjects with z < .
05 and provide us with a better likelihoodto explore their spatially resolved properties. To that, we per-form a systematic search for possible blueberry candidates inthe Mapping Nearby Galaxies at Apache Point Observatory(MaNGA; Bundy et al. 2015) Integral Field Unit (IFU) sur-vey. In this paper, we report on two new blueberry galaxieswith lowest stellar mass known to date and they are phys-ically located at the outer most region of their associatedlow-surface-brightness (LSB) galaxies. In the rest of thepaper, we discuss their possible formation mechanism andspatially resolved physical properties using MaNGA IFUdata.The paper is organized as follows: Section 2 describes theMaNGA observation and our source selection criteria. Insection 3, we discuss the host galaxy properties and the selec-tion of H II regions in it. Section 4 describes the photomet-ric and spectroscopic properties of the blueberries. In sec-tion 5, we show the metallicity and its gradient while in sec-tion 4.4, we study their stability properties. Section 6 dealswith the formation scenario. The summary and conclusionsare presented in section 7. Throughout this work, we haveconsidered the flat cosmological parameters of H o = 70 kms − Mpc − , Ω m = 0.3 and Ω Λ = 0.7. DATA AND SOURCE SELECTIONThe data used in this work are mainly taken from 16 th data release (DR16) of the MaNGA survey. This survey isan ongoing optical IFU observing program under the fourthgeneration Sloan Digital Sky Survey (SDSS-IV; Bundy et al.2015). It uses the same spectrograph as used in the BaryonOscillation Spectroscopic Survey (BOSS; Smee et al. 2013)mounted on 2.5-m Sloan Foundation Telescope (Gunn et al.2006) at Apache Point Observatory (APO). Here the IFUsize is selected such that it covers 1.5 R e of the galaxy ex-tent (Law et al. 2016). This survey has a target to observeabout 10,000 nearby (0.01 < z < M (cid:12) (Wake et al. 2017). The observedspectra have a wavelength coverage of 3600 − Table 1.
Summary of the galaxy properties studied in this work.MaNGA ID 8716 − − h m s h m s Dec +52 d m s +26 d m s Redshift (z) 0.0403 0.0141m g (mag) 21.808 21.901m r (mag) 22.933 23.126m i (mag) 22.599 24.264 r equ (kpc) 2.14 0.74 r ef f (kpc) 1.00 0.37 R a (kpc) 10.39 3.67 σ ∗ (km s − ) 101 67 M Blueberry ∗ (M (cid:12) ) 2.48 × × M host LSB ∗ (M (cid:12) ) 3.2 × × M tidal (M (cid:12) ) 8.39 × × EW(H α ) [Å] 332 206L(H α )[erg s − ] 1.10 × × SFR [M (cid:12) yr − ] 0.087 0.01212 + log(O/H) 8.05 8.07 a Projected distance between blueberries and their respective hostLSB galaxies a spectral resolution of R ∼ σ ∼
60 km s − . The MaNGA surveyprovides the data with an effective spatial resolution of 2.5"full width at half maximum (FWHM). The observed raw dataare reduced and calibrated using the Data Reduction Pipeline(DRP; Law et al. 2016). The science ready data are thenprovided after analysing the DRP’s output products usingData Analysis Pipeline (DAP; Westfall et al. 2019).In this study, we have used the DAP products given in theMaNGA DR16. Here DAP uses the pPXF code (Cappellari& Emsellem 2004) along with MILES stellar library to fitboth the stellar continuum and spectral line features presentin the spectra. In this fitting, single Gaussian function is usedto model the individual emission and absorption featuresand provide the emission and absorption line fluxes afterstellar continuum subtraction. It also gives stellar and gaskinematics parameter such as v stellar , σ stellar , v gas and σ gas .All the emission line fluxes used in the present study arecorrected for both the Galactic and internal extinctions us-ing corresponding reddening E ( B − V ) values. First Galacticforeground reddening correction was applied by assumingreddening law provided in O’Donnell (1994). Then internalreddening correction to the target galaxy was applied usingthe flux ratio of f H α /f H β emission lines by assuming the OMPACT STAR - FORMING GALAXIES : B
LUEBERY MaNGA: 871612705 MaNGA: 894112705SDSS image SDSS imageMaNGA: 871612705 MaNGA: 894112705DeCAL image DeCAL image griband color composite host LSBs Zoomedview ZoomedviewBlueberrycandidates Blueberrycandidates
Figure 1.
Upper panel shows the MaNGA footprint overlaid on the SDSS- gri color composite images of galaxies in the present study. Lowerpanel shows the corresponding higher-resolution deep color composite images in the DeCAL survey. The identified blueberry sources aremarked by red circles whose zoomed views in each panel are also shown. expected theoretical value of 2.86 (i.e., the Case-B recom-bination (Osterbrock & Bochkarev 1989) with an electrontemperature of ∼ K and electron density of 100 cm − ).For some spaxels, the flux ratio of f H α /f H β emission lineswas found less than the expected theoretical value of 2.86.A low value of f H α /f H β is often associated with intrinsicallylow reddening, and hence we assumed an internal E ( B − V )values as zero for such cases.The MaNGA DR16 contains a total of ∼ II gas emitting regions(as confirmed through their H α emission maps) withtheir peak [OIII]/[OII] emission line ratio of spaxel’s asequal or above 5 (i.e., [OIII]/[OII] ≥
5) in the MaNGADR16 survey, which also simultaneously satisfy twoother criteria as mentioned below. • The peak H β emission line equivalent width ofspaxel’s is high, EW(H β ) ≥
100 Å, so that the selectedobjects justify the presence of young starbursts withages of 3 − λ λ ≥
500 Å.It is to note here that the above spectroscopic selectioncriteria are similar to that which were previously applied byCardamone et al. (2009) and Yang et al. (2017) for spec-troscopic selection of GPs and blueberries, respectively.Although they also used photometric criteria, we have alsochecked the same photometric criteria for our spectroscopi-cally selected sources to confirm them as blueberry sources(see Section. 4.1 for more details). With our search cri-teria as mentioned above, we found a total of 50 galaxiessatisfying the first criteria. Out of these 50 galaxies, wefound only three potential blueberry candidates satisfyingthe last two criteria. Of these three candidates, one blue-berry candidate was found as an isolated dwarf system andis presented somewhere else by Paswan et al. (2020a,b; in P
ASWAN ET AL .preparation). It is important to note that this identified iso-lated blueberry candidate has already been characterized asLAE (Lyman- α Emitter) with showing a Ly α escape fractionof ∼
10% as obtained using direct ultra-violate (UV) ob-servations with the Cosmic Origins Spectrograph (COS) onboard
Hubble Space Telescope ( HST ). Whereas, two otherpotential blueberry candidates are separately selected andpresented here. Because they are located at the outer mostregion of large LSB galaxies. Therefore, they may providethe possible clue about the formation scenario of blueberrysources.Apart from the MaNGA data, other ancillary data are takenfrom the publicly available SDSS survey. As per our require-ments, the obtained science ready data are further analyzedusing various standard packages available in Python, SEx-tractor and Image Reduction and Analysis Facilities (IRAF)to derive our final results which are presented below. HOST GALAXY PROPERTY AND HII REGIONSIn order to first characterize the nature of host galaxies asshown in Fig. 1, we have presented their
SDSS r − band sur-face brightness profiles in Fig. 2. In this figure, solid circlesrepresent the observed profile derived using ELLIPSE fittingroutine available in IRAF. The dashed and dot-dashed linesare the two (bulge + disk) components fitted to the observedprofiles using Sersic and Exponential functions, respectively.Additionally, some of spiral features seen in the host galaxiesare fitted with Gaussian models as shown by dotted-line. Thesolid line shows the total models fit to the observed profiles.All these fittings are performed under the PROFILER envi-ronments (Ciambur 2016), after taking the image PSF (pointspread function − moffat) convolution into account. This pro-vides the value of central surface brightness of disk compo-nents ( µ , disk ) as 21.554 ± − ± − (MaNGA: 8941 − − .As the criteria used for classification of a galaxy into an high-surface-brightness (HSB) or LSB based on its µ , disk suggeststhat a disk galaxy can be considered as an LSB, if its µ , disk in the r -band is 21 mag arcsec − or fainter than the quotedvalue (Brown et al. 2001; Adami et al. 2006; Pahwa & Saha2018). According to this criteria, the host galaxies presentedhere are therefore LSB galaxies.3.1. Selection of H II region of interest In the presented LSBs, it can be clearly seen that they hostseveral H II regions which are appeared as blue regions in thecolor composite images (see Fig. 1), and also as bright H α emitting knots in the H α emission maps (see first column inFig. 3). Of all these H II regions, our regions of interest are se-lected as the brightest region in the H α emission line, having the largest H α emission line equivalent width (EW) and situ-ated at the outer most regions of associated LSB galaxies. Assuch H II regions at outskirts of large galaxies are often iden-tified as merging and/or tidally interacting low mass compactstarburst galaxies (Duc & Mirabel 1998; Meurer et al. 1995;Melo et al. 2005; Bastian et al. 2006). In Fig. 3, second col-umn shows the EW maps of H α emission line of the galaxiesin our study. The H α emission line and its EW clearly in-dicate that the marked H II regions (as shown in Fig. 1) havethe largest H α flux and EW amongst all the H II regions seenin LSB galaxies. These H II regions are also situated at theouter most region of LSB galaxies. In Fig. 4, we have shownthe rest-frame optical spectra of these H II regions at outskirt(blue; marked ones in Fig. 1) and LSB galaxies at center(red), after applying the same redshift correction as measuredfor LSB galaxies. Both of these spectra are closely comparedin the inset images of Fig. 4. In both the cases, the rest-frameH α and [NII] λλ II regions and LSB galaxies fall at similar wavelengths havinga small radial velocity difference of ∼
30 km s − , indicatingthat the selected outer most H II regions are indeed closelyassociated with their respective host LSB galaxies. PHYSICAL PROPERTIES OF THE BLUEBERRIES4.1.
Photometric characteristic: color-color diagram
Following the SDSS g − r vs. r − i color-color criteria asdefined by Yang et al. (2017) to classify the blueberry candi-dates at lower redshift (z ≤ II regions as marked by circle in color-compositeimages of LSB galaxies. In this figure, the previously classi-fied blueberry galaxies and defined color boundaries in Yanget al. (2017) are also shown by blue solid circle and orangedash-dotted line, respectively. The compact H II regions inthe present work are shown by star symbol. Interestingly, thelocation of the selected H II regions on the color-color plot arein consistent with the previous identified blueberry galaxies,showing their location inside of the color boundaries definedfor classifying the blueberry galaxies. This implies that theselected compact H II regions are potential blueberry sources.This hypothesis is also verified by their spectroscopic prop-erties as presented below.4.2. Spectroscopic characteristic
The spatially resolved spectroscopic properties such asEW([OIII] λ ≡ O parameter, dust ex-tinction E ( B − V ) and gas-phase metallicity 12 + log(O/H) ofthe selected compact H II regions as marked by red circle inthe 2D IFU maps are presented in Fig. 6. In Fig. 7, the sameproperties are also shown in the form of histogram distribu-tions and then compared with the spectroscopic properties OMPACT STAR - FORMING GALAXIES : B
LUEBERY µ r ( m a g / a r c s e c ) R maj (arcsec) − ∆ µ ∆ rms = µ r ( m a g / a r c s e c ) R maj (arcsec) − ∆ µ ∆ rms = Figure 2.
The Surface brightness profiles of host galaxies MaNGA: 8716 − − of previous known GPs and blueberry galaxies, respectively,studied in Cardamone et al. (2009) and Yang et al. (2017).In this figure, GP and blueberry galaxies are shown by solidgreen and dashed blue histograms, respectively, while thespaxels from compact H II regions in the present work arerepresented by solid-red line (MaNGA: 8941-12705) andspacefilled-blue (MaNGA: 8716-12705) histograms. FromFig. 6 and 7, it is interesting to note that the derived spec-troscopic properties of the selected compact H II regions arein consistent with properties of GP and blueberry galaxies -suggesting that these compact H II regions are found with ex-tremely high values of EW([OIII] λ parameter,and with low values dust extinction and gas-phase metallic-ity, similar to typical spectroscopic properties of GPs andblueberries. Therefore, in consistent with our observed pho-tometric color-color property that indicates the compact H II regions as blueberry candidates, our analysed spectroscopicproperties also support the fact that the selected compact H II regions are indeed blueberry sources.4.3. Sizes and projected distances
Since the identified blueberry sources in photometric bandimages (see Fig. 1) suffer a possible faint and diffuse lightcontamination due their host LSB galaxies, it thereforemakes difficult to define the actual extent or sizes of ourblueberry sources. In order to follow a systematic approachand compare with the sizes of other extragalactic sources, wedefine the size of a given blueberry source as the area encir-cled the largest extent of H α emitting region seen in the 2DH α emission map centered at the peak emission associatedwith that region. This provides us an estimate of the totalsize of the blueberry region by defining an equivalent radiusof r equ = (cid:112) Area /π . Similarly, an effective radius ( r e f f ) is also defined as the radius that contains half of the total fluxwithin the area covered by circle of radius r equ . The values of r equ and r e f f of our identified blueberry sources are listed inTable 1, which range from a few hundreds of pc (i.e., ∼ ∼ r equ with the sizes of other extragalactic H II regions studied in the literature (e.g., Kennicutt 1984; Mayya1994) which have typical radii of ∼ −
900 pc, the presentblueberry sources are comparable to the largest Gaint H II re-gions. Also our estimated r e f f of the blueberry sources (i.e.,0 . − r e f f of 0.2 ≤ r e f f ≤ ∼ ASWAN ET AL .
30 20 10 0 10 20 30X-Offset ["]3020100102030 Y - O ff s e t [ " ] MaNGA: 8716-12705 H Map H f l u x [ × e r g / c m / s ]
30 20 10 0 10 20 30X-Offset ["]3020100102030 Y - O ff s e t [ " ] H EW Map H E W [ Å ]
30 20 10 0 10 20 30X-Offset ["]3020100102030 Y - O ff s e t [ " ] MaNGA: 8941-12705 H Map H f l u x [ × e r g / c m / s ]
30 20 10 0 10 20 30X-Offset ["]3020100102030 Y - O ff s e t [ " ] H EW Map H E W [ Å ] Figure 3.
First column shows the H α emission line maps of the galaxies chosen for our study. Similarly, second column shows the equivalentwidth maps of H α emission line. Å ]0.00.20.40.60.81.01.21.4 F l u x [ x e r g / s / c m / Å ] MaNGA: 8716-12705Host LSB galaxyBlueberry 6500 6550 6600 66500.00.10.20.30.40.5 H [ N II ] [ N II ] Å ]0.00.20.40.60.81.01.21.4 F l u x [ x e r g / s / c m / Å ] MaNGA: 8941-12705Host LSB galaxyBlueberry 6500 6525 6550 6575 66000.00.10.20.30.40.5 H [ N II ] [ N II ] Figure 4.
The central optical spectra of blueberry (blue) and host LSB galaxies (red). The inset plot in each panel represents the wavelengthcomparison of identified H α +[NII] emission lines from the host LSBs and blueberries. OMPACT STAR - FORMING GALAXIES : B
LUEBERY g r r i MaNGA 8716-12705: BlueberryMaNGA 8941-12705: BlueberryYang et al. (2017): Blueberries
Figure 5.
The g − r vs r − i color-color diagram of blueberry sourcesidentified in this work as shown by star symbol. The blue dots areblueberry galaxies from Yang et al. (2017). The orange dot-dashedline represents the color-color boundary defined for selecting blue-berry galaxies in Yang et al. (2017). by their stable dynamical structure as present in the next sec-tion. 4.4. Stability against internal motions
In order to test that if the identified blueberry-like H II re-gions constitute themselves as self-gravitating entities to sur-vive as a dwarf systems, we studied their locations on theradius-velocity dispersion (i.e., r − σ ) relation measured forelliptical and globular clusters. For this purpose, we haveplotted the classical fits to the r equ − σ plane for ellipticalgalaxies, globular cluster and H II regions taken from Ter-levich & Melnick (1981) along with our identified blueberrysources as shown in Fig. 8. In this plot, different symbols rep-resent the samples of various type of objects taken from theliterature: dots − galactic globular clusters from Trager et al.(1993), Pryor & Meylan (1993); crosses − massive globu-lar clusters in NGC 5128 from Martini & Ho (2004); plus − dwarf elliptical galaxies from Geha et al. (2003); square − intermediate ellipticals; solid circles − giant ellipticals; dia-mond − compact ellipticals; triangles − dwarf ellipticals andhexagonals − bulges all these are from Bender et al. (1992).Objects in this work are shown by star symbols. Here, thecontinuous line represents the fit for extragalactic H II regionstaken from Terlevich & Melnick (1981) while the dashed anddotted lines show the fits for elliptical galaxies and globularclusters + elliptical galaxies, respectively. Based on the po-sition of our blueberry sources on the r equ − σ plane, it ap-pears that they are indeed self-gravitating entities. Further-more, they are also in a region close to other dwarf and in-termediate elliptical galaxies and much far from the regionsoccupied by globular clusters and extragalactic H II regions. Therefore, our analysis suggests that these blueberry sourcesin the present study are indeed typical compact dwarf sys-tems which are associated with LSB galaxies either througha merger or tidal interaction event.4.5. Main sequence relation for our blueberries
In Fig. 9, we have presented the main sequence ( M ∗ - SFR)relation for our identified blueberries (star symbols) togetherwith other blueberries (blue circles) and GPs (green circles),respectively, taken from Yang et al. (2017) and Cardamoneet al. (2009). Here, SFRs are estimated from extinction cor-rected H α luminosity using SFR calibrator SFR(M (cid:12) yr − )= 7.9 × − L H α (erg s − ) provided by Kennicutt (1998).Stellar-masses are estimated from ( g − r ) colors and r-bandmagnitudes using relation given by Bell & de Jong (2001).The resulting SFRs and stellar-masses are provided in Ta-ble 1. In Fig. 9, dotted red line shows typical constant sSFRof 10 − yr − observed for nearby normal star-forming galax-ies in the SDSS survey. It can be clearly seen that blueber-ries and GPs from Yang et al. (2017) and Cardamone et al.(2009), respectively, are higher by 2 − ∼ GAS-PHASE METALLICITY AND ITS GRADIENTIn Fig. 10, we have presented the radial profile of gas-phase metallicity for both the host LSB and blueberry galax-ies. The gas-phase metallicity [i.e., 12 + log(O/H)] is derivedusing the N2 calibrator proposed by Pettini & Pagel (2004) -based on the ratio between the [NII] λ α emissionlines. In Fig. 10, red and blue solid circles show the metal-licity profiles for LSB and blueberry galaxies, respectively.Their respective linear fits to observed data are also shownby dot-dashed (black) and dashed (pink) lines. In this figure,black solid circles show the metalicity profile of LSB galax-ies along their major axis (i.e., perpendicular to the profileshown by red solid circles which is drawn along the minoraxis of LSBs, in the direction of identified blueberry galax-ies).Interestingly, it is noticeable that the gas-phase metallicitygradients of LSB and blueberry galaxies are significantly dif-ferent to each other. In each case, we found an appreciable P ASWAN ET AL . Figure 6.
The spatially resolved 2D-map of EW[OIII] (first column), O a proxy for ionization parameter (second column), gas-phasemetallicity [12 + log(O/H)] (third column) and E( B − V ) (fourth column) of each studied galaxy. In each panel, the identified blueberry sourcesare marked by red circles. mean metallicity difference of ∼ − , with an average gradient of -0.024 dex kpc − having a scatter of 0.010 at 1 σ level (Bresolin & Kennicutt2015). In consistent with the study of Bresolin & Kenni-cutt (2015), our derived metallicity gradient for both the LSBgalaxies under this study are found as ∼ -0.03 dex kpc − .Nevertheless, the metallicity gradient of blueberry galax-ies are found as -0.18 ± ± ∼ POSSIBLE FORMATION SCENARIO 6.1.
Merger or TDG blueberry candidates?
In previous sections, most of the observational propertiesof our studied blueberry galaxies such as sizes, projected dis-tances to the host LSB galaxies and test for stability againsttheir internal dynamics place them in the category of com-pact dwarf galaxies. Interestingly, the observed gas-phasemetallicity gradient of blueberries are significantly differentthan their respective host LSB galaxies, and mean metallic-ity differences between blueberries and their host LSBs arealso appreciably large (i.e., ∼ M tidal = 3 M (cid:18) RD (cid:19) (1)In Eq. 1, M is the mass of host galaxy. R and D are theradius of blueberries (here used as r equ ) and their distanceto the host LSB galaxies, respectively. If tidal masses esti-mated from Eq. 1 are smaller than the masses of blueberrysources then only they are stable against the forces exercisedby their host LSB galaxies, and hence they can survive as OMPACT STAR - FORMING GALAXIES : B
LUEBERY Figure 7.
The spaxel histogram distribution of EW[OIII] (top-left), O a proxy for ionization parameter (top-right), gas-phase metallicity[12 + log(O/H)] (bottom-left) and E( B − V ) (bottom-right) extracted over only blueberry region of each galaxy as marked by circles in Fig. 6.These distribution are also compared with the distribution of previously known blueberry and GP galaxies studied in Yang et al. (2017) andCardamone et al. (2009), respectively. In each plot, red (MaNGA: 8941 − − TDGs. The estimated tidal masses for each case are listedin Table 1. In this table, it is to note that the estimated tidalmasses in each case are found to be larger than the masses ofblueberries, implying that they would not have any chanceto be stable against the forces applied by LSB galaxies. Al-ternatively, this might also imply that they are in advancedstage of merger events.Moreover, other way to test the tidal origin of one dwarfsystem is the relation between absolute magnitude and gas-phase metallicity as proposed by Duc & Mirabel (1998). InFig. 11, M B vs 12 + log(O/H) relation is shown for normaldwarf galaxies (open circles) and TDGs (solid circles) takenfrom the literature. Here, blueberry sources in the currentstudy are represented by star symbols. Since it is well-knownthat TDGs are made up from processed material in their par-ent galaxies (Duc & Mirabel 1998), and hence they show high metallicity as also seen in Fig. 11. In this figure, ourstudied blueberries are however in consistent with the loca-tions of normal dwarf galaxies within 3 σ scatter (as shownby orange dot-dashed line) observed in the relation, show-ing low metallicity for a given absolute B -band magnitude ofblueberry galaxies. Therefore, our analyses performed hererule out the fact that blueberries are TDGs, suggesting thatthey are indeed merging dwarf galaxies associated with LSBgalaxies. 6.2. Local environment
It is worth examining the local galaxy environment of ourblueberries in a view of merger event as observed in thisstudy. For this purpose, we searched for neighbor galaxieswithin a projected radius of 1 Mpc and having a narrow ve-locity range of nearly ±
250 km s − from the recession ve-locity of host LSB galaxies. The reasons for selecting this0 P ASWAN ET AL . Log ( ) [km s ] L o g ( r ) [ p c ] Galactic globular clustersNGC 5128: massive globular clustersDwarf elliptical galaxiesIntermediate ellipticalsGiant ellipticalsCompact ellipticalsDwarf ellipticalsBulgesMaNGA 8716-12705: BlueberryMaNGA 8941-12705: Blueberry
Figure 8.
A comparison of our blueberries with different type ofobjects such as dwarfs, ellipticals, bulges on the r equ − σ plane (fordetails see the text). The blueberry galaxies in the present work arepresented by star (red and blue) symbols. log(M * /M ) l o g ( S F R / M y r ) sSFR = 10 yr sSFR = 10 yr sSFR = 10 yr sSFR = 10 yr Blueberries: Yang et al. (2017)Green Peas: Cardemone et al. (2009)MaNGA 8716-12705: BlueberryMaNGA 8941-12705: Blueberry
Figure 9.
The stellar-mass vs. SFR for blueberry sources in thepresent study as represented by star symbol. This plot also includesother blueberry (blue circles) and GP (green circles) galaxies fromYang et al. (2017) and Cardamone et al. (2009), respectively. Sev-eral straight lines in the plot represent constant sSFR of 10 − , 10 − ,10 − and 10 − yr − . parameter space are the following. A galaxy can travel up to ∼ ∼
250 km s − in the IGM, which is alsotypical velocity dispersion in groups of galaxies. The localgalaxy environment of each individual LSB/blueberry galax-ies is briefly discussed below.6.2.1. MaNGA: − Within the defined search parameters as mentioned above,a total of 39 galaxies are found in the vicinity of MaNGA:8716 − ∼ − . All the identified neighbouring galaxies are in avery narrow velocity range of ∼ − − , wherethe recession velocity of host LSB galaxy is 4207 km s − .Our observed galaxy density value here is similar to typi-cal group environments of galaxies as found in the literature(e.g., Omar & Dwarakanath 2005; Sengupta & Balasubra-manyam 2006). This analysis therefore suggests the pres-ence of a galaxy-rich dense environment around MaNGA:8716 − MaNGA: − In the vicinity of MaNGA: 8941 − ∼
11 Mpc − . The neighbouring galaxies are in a narrow veloc-ity range of ∼ − − , where the recessionvelocity of the host LSB galaxy is 12082 km s − . Similarto previous case, it seems that MaNGA: 8941 − ∼
12 Mpc − around blueberries studied here, indicating a likely higherinteraction/merger rate, it is obvious that tidal interactionsand/or merger events leading to intense starbursts are verycommon in this region. SUMMARY AND CONCLUSIONSIn this work, we studied two giant H II regions situatedat the outer most region of LSB galaxies observed in theMaNGA survey. They are selected being the brightest H II regions in H α emission with the highest H α EWs among allthe H II complexes seen in the LSB galaxies. They are alsofound to be closely associated with their host LSB galaxies.Further, the spatially resolved physical (e.g., optical color,size and distance to the LSBs, r − σ relation, dust extinction,luminosity, EW, ionization parameter and main sequence re-lation etc.) and chemical (e.g., gas-phase metallicity and itsgradient) properties of the selected H II regions are charac-terized using SDSS photometric and MaNGA IFU spectro-scopic data. Our main results are concluded as follows.• The two identified brightest giant H II regions at theouter most region of LSB galaxies are indeed compactdwarf galaxies (1 − r − σ relation. OMPACT STAR - FORMING GALAXIES : B
LUEBERY Radius [arcsec] + l o g ( O / H ) MaNGA: 8716-12705Linear fit: Host LSBHost: Minor axisHost: Major axis 2 0 27.87.98.08.18.3
Linear fit: BlueberryBlueberry
Radius [arcsec] + l o g ( O / H ) MaNGA: 8941-12705Linear fit: Host LSBHost: Minor axisHost: Major axis 2 0 27.67.88.08.2
Linear fit: BlueberryBlueberry
Figure 10.
The radial gas-phase metallicity gradient in galaxies studied here. The red and blue solid circles correspond to the host LSB andblueberry galaxies, respectively. The dot-dsahed (black) and dashed (magenta) lines are linear-fit to the radial metallicity profiles in the hostLSB and blueberry galaxies.
19 18 17 16 15 14 13 12 11 10 M B + l o g ( O / H ) Linear fit: Isolated dwarfs3 scatterIsolated dwarfsTDGsMaNGA 8716-12705: BlueberryMaNGA 8941-12705: Blueberry
Figure 11.
Oxygen abundance Vs. absolute B -band magnitude fora sample of isolated nearby dwarf galaxies (open circles; taken fromRicher & McCall (1995) and tidal dwarf galaxies (filled circles;taken from Duc (1995)). Blueberry sources in the present work areshown with star symbols. • Using photometric and spectroscopic characteristics,they are classified to be blueberry compact dwarfgalaxies, similar to that studied in the literature.• The studied blueberries follow the same main se-quence relation as known for other GPs and blueber-ries in the literature. Nevertheless, they lie at lowermass end of this relation, indicating that they are ex-tended fainter counterparts of other known blueber- ries and GPs. They also represent themselves as blue-berry galaxies having the lowest stellar masses i.e.,log( M ∗ / M (cid:12) ) ∼ I clouds in a dense galaxyenvironment.This pilot study using data from the MaNGA surveydemonstrates a great exploitation of IFU data to identify andcharacterize TDGs or merging compact systems located atoutskirt of underlying galaxies in dense environments. Simi-lar to this study, a systematic search using several other IFUsurveys such as MUSE, CALIFA and SAMI can further en-large our sample of different population of blueberry-likesystems formed through interaction and/or merger of galax-ies or H I clouds. Moreover, the ultra-violet (UV) observa-tions of such different sample of blueberries may identifythem as Lyman Continuum (LyC) leaking sources responsi-ble for re-ionizing our early Universe. Such study will helpus in a broad understanding about the characteristics of LyCleakers resided in the diverse environments.REFERENCES Adami, C., Scheidegger, R., Ulmer, M., et al. 2006, A&A, 459,679, doi: 10.1051/0004-6361:20053758 Alavi, A., Colbert, J., Teplitz, H. I., et al. 2020, arXiv e-prints,arXiv:2007.05519. https://arxiv.org/abs/2007.05519
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OMPACT STAR - FORMING GALAXIES : B
LUEBERY13