Disentangling the near infrared continuum spectral components of the inner 500 pc of Mrk 573: two-dimensional maps
M. R. Diniz, R. A. Riffel, R. Riffel, D. M. Crenshaw, T. Storchi-Bergmann, C. Fischer, H. R. Schmitt, S. B. Kraemer
aa r X i v : . [ a s t r o - ph . GA ] A p r Mon. Not. R. Astron. Soc. , 1–10 (2013) Printed 7 October 2018 (MN L A TEX style file v2.2)
Disentangling the near infrared continuum spectral components ofthe inner 500 pc of Mrk 573: two-dimensional maps
M. R. Diniz ⋆ , R. A. Ri ff el , R. Ri ff el , D. M. Crenshaw , T. Storchi-Bergmann ,T. C. Fischer , , H. R. Schmitt , S. B. Kraemer Universidade Federal de Santa Maria, Departamento de F´ısica, Centro de Ciˆencias Naturais e Exatas, 97105-900, Santa Maria, RS, Brazil Universidade Federal do Rio Grande do Sul, Instituto de F´ısica, CP 15051, Porto Alegre 91501-970, RS, Brazil Astrophysics Science Division, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771, USA Department of Physics and Astronomy, Georgia State University, Astronomy O ffi ces, 25 Park Place, Suite 605, Atlanta, GA 30303, USA Naval Research Laboratory, Washington, DC 20375, USA 0000-0001-7376-8481 Institute for Astrophysics and Computational Sciences, Department of Physics, The Catholic University of America, Washington,DC 20064, USA.
ABSTRACT
We present a near infrared study of the spectral components of the continuum in theinner 500 ×
500 pc of the nearby Seyfert galaxy Mrk 573 using adaptive optics near-infraredintegral field spectroscopy with the instrument NIFS of the Gemini North Telescope at aspatial resolution of ∼
50 pc. We performed spectral synthesis using the starlight code andconstructed maps for the contributions of di ff erent age components of the stellar population:young ( age
100 Myr), young-intermediate (100 < age
700 Myr), intermediate-old(700 Myr < age age > ∼
20% within the inner ∼
70 pc,while hot dust emission and featureless continuum components are also necessary to fit thenuclear spectrum, contributing up to 20% of the K-band flux there. The radial distribution ofthe di ff erent age components in the inner kiloparsec of Mrk 573 is similar to those obtainedby our group for the Seyfert galaxies Mrk 1066, Mrk 1157 and NGC 1068 in previous worksusing a similar methodology. Young stellar populations (
100 Myr) are seen in the inner200–300 pc for all galaxies contributing with >
20% of the K-band flux, while the near-IRcontinuum is dominated by the contribution of intermediate-age stars ( t =
100 Myr–2Gyr) atlarger distances. Older stellar populations dominate in the inner 250 pc.
Keywords : galaxies: individual (Mrk 573) – galaxies: Seyfert – infrared: galaxies –galaxies: stellar population
Stellar population (SP) synthesis using multi-wavelength spectrahas being used to constrain the star formation history (SFH) ofhost galaxies of active galactic nuclei (AGN), looking in particularfor the presence of recent star formation close to the AGN, sup-porting the so-called AGN-Starburst connection (Perry & Dyson1985; Terlevich & Melnick 1985; Norman & Scoville 1988). In-deed, previous studies have shown that massive star-forming re-gions are commonly detected in the inner kiloparsec of activegalaxies (Imanishi & Dudley 2000; Storchi-Bergmann et al. 2000;Imanishi 2002; Rodr´ıguez-Ardila & Viegas 2003; Ri ff el et al.2007; Dors et al. 2008; Ri ff el et al. 2009). Both, nuclear activityand star formation can be fed by gas inflows towards the nucleus,providing a gas reservoir in the central region of the galaxy. In-deed, inflows of gas have been observed using optical and near-infrared (near-IR) integral field spectroscopy of nearby galax-ies (e.g. Fathi et al. 2006; Ri ff el et al. 2008; Fischer et al. 2015).This feeding process is associated with the presence of nuclear bars or non-axis-symmetric features, spiral arms, or tidal interac-tions (Knapen et al. 2000; Maciejewski et al. 2002; Maciejewski2004a,b).The SFH of galaxies can be used as a constraint for their for-mation and evolution, being a fundamental ingredient of theoreti-cal models. Many studies of galaxy evolution in the infrared spec-tral range are strongly based on Evolutionary Population Synthesis(EPS) models (Capozzi et al. 2016). The main parameters of thestellar populations (SPs), as their ages, SFHs and stellar massesare derived through the EPS models. However, these models arestill being refined and of particular importance is the contributionof Thermally Pulsing Asymptotic Giant Branch (TP-AGB) starsthat play an important role in defining the shape of the spectra inthe near-IR wavelengths (e.g. Maraston 2005; Marigo et al. 2008;Salaris et al. 2014; Ri ff el et al. 2015). Construct EPS models forevolved stars, such as TP-AGB stars, is not an easy task due totheir complex inner structures, convection, and the eventual massejections. c (cid:13) Diniz et al.
Recently, SP studies of nearby Seyfert galaxies using near-IRspectroscopy have become more frequent (e.g. Ri ff el et al. 2009,and references therein). The near-IR spectral range, besides allow-ing us to access regions highly obscured by dust, also hosts spec-tral fingerprints originated in massive and evolved stars, as thosefound in the Red Supergiant (RSG) and TP-AGB phases. Thesephases are responsible for a large fraction of the near-IR stellarcontinuum and can be used as tracers of young to intermediate SPswith ages between 200 Myr and 2 Gyr (Maraston 2005; Ri ff el et al.2007, 2008; Salaris et al. 2014; Ri ff el et al. 2015). Additionally, inthis spectral range, one can detect hot dust emission associated tothe putative torus surrounding the central AGN, and some contribu-tion also from the AGN featureless continuum (FC) emission, orig-inated in the accretion disk (Ri ff el et al. 2009b). The detection andcharacterization of these components is fundamental to understandthe AGN spectral energy distribution and investigate the impact ofthe AGN in the evolution of its host galaxy.For the reasons pointed out above, near-IR spectroscopy isa powerful tool to investigate both the stellar populations and theunresolved emission from the dusty torus and accretion disk sur-rounding the supermassive black hole (SMBH). With the aid of theintegral field capability at 8-10 meter telescopes, it is also possi-ble to map the spatial distribution of the stellar population in thecircumnuclear region of nearby active galaxies, a study that ourgroup – AGNIFS – has been doing using the instrument NIFS(Near-Infrared Integral Field Spectrograph) at the Gemini NorthTelescope.In a recent work, we have used near-IR integral field spec-troscopy and optical long-slit spectra to map the emission-line andstellar kinematics of the inner 700 × of Mrk 573 using theNIFS at Gemini North and Dual Imaging Spectrograph (DIS) atApache Point Observatory, respectively (Fischer et al. 2017). Fromthis work, we found that flux distributions of ionized and molecu-lar gas, while distinctly di ff erent, were morphologically related asarcs of molecular H gas connected ionized [S iii ] gas features fromoutside the NLR bicone. We also found that molecular gas kinemat-ics outside the NLR, and ionized gas kinematics at great distancesfrom the nucleus in the extended NLR (ENLR), show signatures ofrotation as observed from our stellar kinematics analysis. These ob-servations suggest that the ionized gas kinematics and morphologyin Mrk 573 can largely be attributed to material originating in therotating disk of the host galaxy. Deviations from pure rotation wereobserved along the NLR projected axis at radii r <
750 pc and inter-preted as being due to the radiative acceleration of material in thehost disk. As the radiatively accelerated gas in the host disk goes todistances smaller than the length of the full NLR / ENLR, we con-cluded that these outflows may have a smaller range of impact thanpreviously expected. The host disk galaxy presents an inclinationof i = ◦ , with the north edge corresponding to the side nearest us(Fischer et al. 2017).The stellar content of the central region of Mrk 573 was stud-ied by Raimann et al. (2003) using long-slit spectra obtained withthe 4-m Mayall telescope of Kitt Peak National Observatory. Theyoriented the 1 . ′′ = ◦ and mapped the stel-lar populations in the inner 8 ′′ (2.7 kpc). They found that the fluxat 4020 Å is dominated by an old SP component. Within the in-ner 2 ′′ up to 70 % of the flux is due to emission of 10 Gyr SPs,while the contribution of these populations decreases at larger dis-tances, being responsible for about 40 % of the observed flux at8 ′′ from the nucleus. Intermediate-age (1 Gyr) SPs contribute withabout 20 % of the nuclear flux, and their contribution increases toat larger distances, reaching 60 % outwards. The contribution of younger SPs is very small at all locations. The SP reddening val-ues are in the range E ( B − V ) = − .
4, with the highest valuesseen at 2 ′′ southeast of the nucleus. On the other hand, Ri ff el et al.(2009) found that the near-IR continuum in the inner 0 . ′′ × . ′′ µ m and is diluted by a fea-tureless continuum (FC) component, which contributes with 22 %of the continuum. Ramos Almeida, P´erez Garc´ıa & Acosta-Pulido(2009) found also that intermediate age stars dominate the near-IRnuclear continuum, but they did not found an evidence for the FCcomponent.This paper is organized as follows: in Section 2 we discuss theobservations and data reduction procedures, Section 3 shows mapsof the flux and mass-weighted contribution of each SP, which arediscussed in Section 4. Section 5 summarizes the conclusions ofthis work. In this paper we use the spectral synthesis technique to mapthe ages of the stellar populations of the inner 500 pc radiusof the Seyfert 2 galaxy Mrk 573. Mrk 573 is a nearly face-on, early-type galaxy, morphologically classified as RSAB(rs) + (de Vaucouleurs et al. 1991), presenting a bright extended emis-sion line region ( ∼ ff et al. 1988) and high-ionizationemission-lines (Storchi-Bergmann et al. 1996). Three radio contin-uum sources were first detected by Ulvestad & Wilson (1984), onein the nucleus of the galaxy and the two radio lobes along positionangle PA = ◦ . It harbors a Seyfert 2 nucleus (Tsvetanov et al.1992) and is located at a distance of ∼
73 Mpc (Springob et al.2005), for which 1 ′′ corresponds to 350 pc at the galaxy.Z, J and K band integral-field spectroscopy (IFS) of Mrk 573have been obtained with the Gemini-north Near-Infrared Integral-Field Spectrograph (NIFS– McGregor et al. 2003) operating withGemini North Adaptive Optics system ALTAIR. Observations ofMrk 573 were obtained under the Gemini programme GN-2010B-Q-8 (PI: Michael Crenshaw) in 2010B and 2011A semesters, fol-lowing the standard Object-Sky-Object dither sequence. Six expo-sures of 600s each were performed in the K-band, centred at 2 . µ mand covering the spectral range from 2 . µ m to 2 . µ m, 5 exposuresof 600 s for J-band, centred at 1 . µ m, covering the spectral regionfrom 1 . µ m to 1 . µ m and 6 exposures of 500 s for Z-band, cen-tred at 1 . µ m and covering the spectral region from 0 . µ m to1 . µ m.The NIFS has a square field of view of 3 . ′′ × . ′′
0, dividedinto 29 slices with an angular sampling of 0 . ′′ × . ′′
04, and wasoriented along the position angle PA = ◦ , measured relative tothe orientation of the slices.The data reduction was accomplished using tasks containedin the nifs package, which are part of gemini iraf package, as wellas standard iraf tasks and Interactive Data Language (IDL) rou-tines. The process followed the standard procedure of near-IR spec-troscopic data reduction, including trimming of the images, flat-fielding, sky subtraction, wavelength and s-distortion calibrations.The telluric absorption bands were removed by dividing the spec-tra of the galaxy by a normalized spectrum of a telluric standardstar, observed just before and / or after the galaxy exposures. Thefinal spectra were then flux calibrated by interpolating a black-body function to the spectrum of the telluric standard star. Individ- c (cid:13) , 1–10 D stellar populations in Mrk573 ual exposure datacubes were created with an angular sampling of0 . ′′ × . ′′
05, which were combined to obtain a single cube for eachband, using the nucleus of the galaxy as reference for the astrom-etry. The final data cubes cover the inner ≈ . ′′ × . ′′ ∼ × at the galaxy.The spatial resolution is ∼
45 pc for the J and K bands, asestimated from the full width at half maximum (FWHM) of thebrightness profile of the telluric standard star, while for the Z bandthe performance of ALTAIR is worse and the resulting spatial res-olution is about 55 pc. The spectral resolution is ∼ − for allbands, as obtained from the typical FWHM of arc lamp lines.Since the performance of the adaptive optics at the Z bandis worse, compared with the J and K bands, and the signal-to-noise ratio of the Z band continuum spectra is also lower, we usedonly the J and K band datacubes to perform the spectral synthesis.These cubes were combined to a single datacube with a constantspectral bin of 5 Å and 0 . ′′ × . ′′
15 angular sampling. More detailsabout the observations and data reduction procedure can be foundin Fischer et al. (2017).
The integrated spectrum of an active galaxy comprises a set of com-ponents such as stellar, gas, dust, as well as nuclear componentssuch as a black-body (from the torus) and power-law emission fromthe accretion disk. One way to disentangle these components is bythe technique of spectral synthesis, which allows to quantify thecontributions of each one these components to the spectrum.A widely used code is the starlight (Asari et al. 2007;Cid Fernandes et al. 2004, 2005a,b), which fits the continuumsearching for the best description of the observed spectrum by re-producing it with di ff erent proportions of the supposed componentsthat sum up to the observed spectrum. These components comprisethe base of spectral elements. In this way, the “key” of the spec-tral synthesis technique is to provide a base of elements includingall possible components observed in galaxies (Cid Fernandes et al.2004, 2005a,b; Ri ff el et al. 2009a). When fitting near-IR spectraldata one needs to have in mind that this region host characteris-tic absorption features, being the most common the CN, CO, VO,ZrO and TiO absorptions bands, which are attributed to evolvedstars, as those in the RGB and TP-AGB phases (e.g. Maraston2005; Ri ff el et al. 2007, 2015). Thus, the simple stellar population(SSP) models used to fit near-IR data need to include these fea-tures. Therefore, we selected the Maraston (2005) SSP models, thatinclude empirical data for the the TP-AGB evolutionary phase.The set of spectral elements used here is composed by the SSPmodels of Maraston (2005) and are described in Ri ff el et al. (2009).In short, they include 12 ages ( t = = . , . , , ⊙ ). Wealso included black-body functions for temperatures in the range700 − F λ ∼ λ − . ), inorder to account for possible contributions from hot dust emissionand from a featureless continuum (FC) in the nucleus of the galaxy.For details see Ri ff el et al. (2009a).The fit is carried out in starlight by minimizing the followingequation: χ = X λ [( O λ − M λ ) ω λ ] , (1)where O λ is the observed spectrum, M λ is the fitted model, ω λ = / e λ and e λ corresponds to the associated uncertainties to the ob-served spectrum. The emission lines and spurious data were excluded from thefit by setting their weight as zero. Each model spectrum is obtainedby: M λ = M λ N ⋆ X j = x j b j ,λ r λ ⊗ G ( υ ⋆ , σ ⋆ ) , (2)where M λ is the synthetic flux at the normalization wavelength freeof any emission or absorption line, ~ x is the population vector, whosecomponents x j ( j = , ... , N ⋆ ) represent the fractional contributionof each SSP in the spectral base, b j ,λ is the normalized spectrum ofthe j th SSP component of the base, ⊗ corresponds the convolutionoperator and G ( υ ⋆ , σ ∗ ) is the Gaussian distribution used to modelthe line of sight velocity distribution, centered at velocity υ ⋆ withdispersion σ ∗ . The extinction due to dust is modeled as an uniformscreen following the extinction law of Cardelli et al. (1989). An optical image of Mrk 573 obtained with the Hubble Space Tele-scope (HST) Wide Field Planetary Camera 2 (WFPC2) through thefilter F606W is shown in the top-left panel of Fig.1. The centralblack square indicates the FOV of the NIFS observations. The rightpanel shows a continuum image of the nuclear region, in logarith-mic flux units per pixel, acquired from the NIFS datacube in thespectral range between 2.25 and 2.28 µ m, without emission or ab-sorption lines. Spectra from two positions (N and A), extractedwithin an aperture of 0 . ′′ × . ′′
15, are shown in the bottom pan-els. The central “cross” corresponds to the location of the nucleus,which was defined as the peak of continuum emission.The bottom panels of Fig.1 show the results of the spectralsynthesis overploted to the observed spectrum (black), for the nu-cleus (N) and for position A, indicated on the continuum map (top-right panel). In the spectral synthesis, we masked out emission linesand spurious features, fitting only the regions with stellar absorp-tion features and featureless continua.The fits for all spaxels are very similar to those shown inFig. 1. The quality of the fits can be evaluated using the rightmostpanel of Fig.3, where we show the map of the mean percent devia-tion over all fitted pixels (Adev = | O λ − M λ | / O λ ).Since small stellar population di ff erences in the spectra arewashed away due to the uncertainties on the observations, we havefollowed Cid Fernandes et al. (2004) and binned the contributionof the individual SSP, x j , into a coarser population vector as fol-lows (Ri ff el et al. 2010, 2009): young ( x y : t
100 Myr); young-intermediate ( x yi : 100 < t
700 Myr); intermediate-old (x io :700 Myr < t old (x o : 2 < t
15 Gyr).Fig. 2 (top) shows the results of the spectral synthesis in mapsof the main stellar population components (SPCs) percent con-tributions to the 2.2 µ m continuum light within inner ∼
500 pc ofMrk 573. Grey regions in these maps correspond to masked loca-tions where we were not able to get good fits, with adev >
15. Thex y map shows that the young population contributes with up to 50%of the continuum within ∼ . ′′
5, with the highest contribution seen at0 . ′′ ∼ ′′ from the nucleus in a partial ring structure showingvalues of up to 100% to the south and south-east. The rest of thering is dominated by the contribution from the x yi population thatreaches up to 100% at the ring. The last two panels (x io and x o )show a flux contribution of old SPs in the central region of up to60% mostly inside the ring. c (cid:13) , 1–10 Diniz et al.
Figure 1.
The left panel shows an optical HST image of Mrk 573 through the filter F606W, with the NIFS FOV indicated by the central square. The rightpanel displays a continuum image in the K-band, in logarithmic flux units per pixel. The central cross on the panels indicate the position of the nucleus. Thebottom panels show the synthesis results (red) for two spectra (black): the nucleus and position A identified in the top right panel. The flux was normalized at21955 Å and emission lines were masked. The HST image has been rotated to the same orientation of NIFS data (PA = ◦ ), indicated in the top-left cornerof the top-left panel. Once the SSPs are in the form L ⊙ Å − M − ⊙ , thus a light-to-mass-ratio spectrum, the starlight code computes the mass frac-tions based on the L / M ratio . The maps with the mass fractionsfor each binned age group are shown in the bottom panels of Fig. 2.The spatial distribution of each mass contribution, as expected, issimilar to that observed to the light fractions, however, due to thenonlinear M / L relation, the m o maps show higher contributions inmass than in flux, with values of up to 95%.In Fig. 3 we present the maps for the FC and BB componentsthat contribute to the observed continuum emission within 0 . ′′ E ( B − V ) reddening map, which displays values of upto 0 . Adev map with most of the values . Studies of the stellar populations in nearby Seyfert galaxiesbased on near-IR long-slit spectra show a substantial fractionof intermediate-age SPs in the inner few hundreds of par-secs (e.g. Ri ff el et al. 2009), while at optical wavelengths sig-natures of recent episodes of star formation are seen for about40-50 % of nearby bright Seyfert 2 galaxies at similar spatialscales (e.g. Storchi-Bergmann et al. 2001; Raimann et al. 2003;Cid Fernandes et al. 2004; Sarzi et al. 2007). Young and inter-mediate age stellar populations in the inner few hundreds ofparsecs of Seyfert galaxies are also detected in recent near-IRIFS studies (e.g. Davies et al. 2007; Ri ff el et al. 2010, 2011b;Storchi-Bergmann et al. 2012). In addition, a correlation betweenthe distribution of intermediate-age stars with low-stellar veloc-ity dispersion ( σ ∗ ∼ −
70 km s − ) rings has been observed forsome objects (Ri ff el et al. 2010, 2011b), indicating that these low- c (cid:13) , 1–10 D stellar populations in Mrk573 Figure 2.
From left to right we show the distributions of: in the top row, percent contributions to the 2.2 µ m continuum of young (x y
100 Myr), young-intermediate (100 < x yi
700 Myr), intermediate-old (700 Myr < x io < x o
13 Gyr) age components; In the bottom row, we show thecorresponding percent mass contributions (m y , m yi , m io and m o ). The spatial orientation (PA = ◦ ) is indicated in the left panels. Contours in the BB and FCpanels correspond to 10 and 20 % flux contribution. Figure 3.
From left to right: percent contributions to the 2.2 µ m continuum of the FC and BB emission, Adev and Av maps. The spatial orientation (PA = ◦ )is indicated in the left panel. σ ∗ rings are originated from SPs that still preserve the “cold” kine-matics of the gas they were formed (being thus younger than thesurroundings), as claimed to explain the σ ∗ -drops commonly re-ported for more than 20 years (e.g. Emsellem 2001; M´arquez et al.2003).Our results for Mrk 573 show that old SPs are dominantin the inner 0 . ′′ ≈ . ′′ ′′ × ′′ and their result is in agreement with other studies of thestellar populations in optical wavelengths (Raimann et al. 2003;Storchi-Bergmann et al. 2001). On the other hand, near-IR spec-tral synthesis of the nucleus for an aperture of 0 . ′′ × . ′′ ff el et al. 2009a), being also in agreement with results ob-tained by Ramos Almeida, P´erez Garc´ıa & Acosta-Pulido (2009),who found that the nuclear H and K band emission is dominated bylate-type giants with ages between 100 Myr and 1 Gyr.The simplest way to represent the mixture of stellar popula-tions of a galaxy is estimating its mean light ( < log t ⋆ > L ) and mass( < log t ⋆ > M ) weighted stellar age. Following Cid Fernandes et al.(2005b), < log t ⋆ > L = N X J = x j log t j (3)and < log t ⋆ > M = N X J = m j log t j . (4) c (cid:13) , 1–10 Diniz et al.
Figure 4.
Logarithm of the mean age weighted by flux (left) and stellarmass (right).
Figure 5.
Map of the young SPC with green contours overlaid showingthe H λ . µ m emission-line flux distribution (left panel), and stellar ve-locity dispersion map (right panel) with overlaid contours of the young-intermediate SPCs distributions in green. While the former is more representative of younger ages, the lat-ter is enhanced by the old SPC (Ri ff el et al. 2009). In Fig. 4 weshow the maps for the mean age light- (left panel) and mass- (rightpanel) weighted in logarithmic units (years). The mean light- andmass-weighted ages over whole field of view are < log t ⋆ > L = . < log t ⋆ > M = .
61, respectively. These values are also in goodagreement with those found in Ri ff el et al. (2009) for the nuclear0 . ′′ × . ′′ ff el et al. 2009; Ramos Almeida, P´erez Garc´ıa & Acosta-Pulido2009). These studies are based on measurements of a nuclear spec-trum that actually integrates the light within a few hundreds pc ofthe nucleus, what is comparable to the whole NIFS FOV. The NIFSadaptive optics observations allowed us to spatially resolve the dis-tribution of the stellar populations in the inner 600 pc of Mrk 573at a spatial resolution of ∼
50 pc, at least 5 times better than thatof the previous long-slit observations. We have shown that recent( t <
700 Myr) star formation dominates at distances larger than300 pc from the nucleus (at least up to ≈
500 pc from the nucleus),while at smaller distances older stars dominate the near-IR contin-uum emission and the stellar mass content of Mrk˙573. emission Our group AGNIFS (AGN Integral Field Spectroscopy) has startedto characterize the stellar population of the inner kiloparsec ofgalaxies using the starlight code (e.g. Cid Fernandes et al. 2004,2005a,b) via spectral synthesis of IFS obtained with the GeminiNear-infrared Integral Field Spectrograph (NIFS- McGregor et al.2003). To date, we studied four nearby Seyfert galaxies (Mrk 1066,Mrk 1157, NGC 1068 and NGC 5548). For NGC 1068, we foundtwo episodes of recent star formation: one at 300 Myr ago, extend-ing over the inner 300 pc of the galaxy and another at 30 Myr ago,observed in a ring at ∼
100 pc from the nucleus and being asso-ciated to an expanding ring observed in warm H gas emission(Storchi-Bergmann et al. 2012). For Mrk 1066 and Mrk 1157, ringsof intermediate age stars have been found, being correlated withlow stellar velocity dispersion values ( σ ∗ ∼ − ), and inter-preted as being originated by stars that still preserve the kinematicsof the gas from which they formed (Ri ff el et al. 2010, 2011b). Inthe case of NGC 5548, the stellar population is dominated by anold ( > ∼
25 % of the K-band nuclear flux for NGC 1068 and ∼
60 %for NGC 5548 (Ri ff el et al. 2010, 2011b; Storchi-Bergmann et al.2012; Sch¨onell et al. 2016).In order to look for similar correlations for Mrk 573, wepresent in the left panel of Fig. 5 contours (in green) of theH λ . µ m flux distribution (left panel) overlaid on the youngSPC distribution, while in the right panel we show the stellarvelocity dispersion map with overlaid contours in green of theyoung-intermediate SPC. The H λ . µ m fluxes were mea-sured by direct integration of the H line profile from the dat-acube and subtracting the adjacent continuum. The σ ∗ map wasobtained by using the penalised pixel-fitting (pPXF) method ofCappellari & Emsellem (2004) to fit the CO absorption band-headsat ∼ . µ m, using as templates spectra of late type stars fromWinge et al. (2009). The H flux distribution shows two arc-shapedstructures extended along the east-west, with the highest emissionobserved within a blob centred at 0 . ′′ σ ∗ map shows that most values range between 80 and180 km s − , with the lowest values being observed mainly to south,west and north-west of the nucleus at distances of 0 . ′′ emission line map for Mrk 573, except maybe at0 . ′′ flux shows someoverlap with the distribution of the young SPC around the nucleus.A similar trend is observed between low- σ ∗ values and the distribu-tion of the young-intermediate age SP, as shown by the green con-tours overploted to the sigma map. This support our previous sim-ilar findings for other active galaxies that the low- σ ∗ structures aredue to stars formed ∼ c (cid:13) , 1–10 D stellar populations in Mrk573 In order to compare the radial distribution of stellar populationcontributions in Mrk 573 with those of previous studies by ourAGNIFS team for other active galaxies, using similar data andtechnique, we have built radial profiles of the young, young-intermediate, intermediate-old and old population contributions tothe flux at 2.2 µ m for all studied galaxies so far. The results areshown in Fig. 6. The age bins for all galaxies are the same (asdescribed in Section 3) and the derived values for Mrk 1066,Mrk 1157 and NGC 1068, are described in Ri ff el et al. (2010),Ri ff el et al. (2011b) and Storchi-Bergmann et al. (2012), respec-tively. These plots were constructed by calculating the average con-tribution of each SPC to the flux at 2.2 µ m within circular rings with0 . ′′ Ψ ) and disk inclination ( i ) usedin the deprojection were obtained from the modeling of the stel-lar velocity field and presented in Fischer et al. (2017) for Mrk 573( Ψ = ◦ , i = ◦ ), Ri ff el et al. (2017) for Mrk 1066 ( Ψ = ◦ , i = ◦ ) and Mrk 1157 ( Ψ = ◦ , i = ◦ ) and Davies et al.(2007) for NGC 1068 ( Ψ = ◦ , i = ◦ ).Although contribution of young stellar populations of at least20% are observed at the nucleus only for Mrk 573 and Mrk 1066,they are present for all studied galaxies within the inner 200–300 pc, in good agreement with results obtained from optical (e.g.Storchi-Bergmann et al. 2001; Sarzi et al. 2007) and near-IR stud-ies (e.g. Davies et al. 2007; Ri ff el et al. 2009a). These young starspossibly originate from a reservoir of gas recently accumulated inthe central region of active galaxies. One possibility is that thesereservoirs have been built by gas streaming motions along spiralarms and nuclear bars, seem at similar scales in many active galax-ies (e.g. Fathi et al. 2006; M¨uller S´anchez et al. 2009; Diniz et al.2015). The nuclear activity may also have been triggered by thepresence of this gas reservoir, due to gas directly accreted by theSMBH or to accretion of gas ejected by the recently formed youngstars (e.g. Davies et al. 2007; Ri ff el et al. 2009a).Some contribution of young SPs is also observed at distanceslarger than 500 pc from the nucleus, while the young-intermediateage SPs show their highest contribution at distances of 300–500 pcfrom it. The intermediate-old population is observed mainly withinthe inner 400 pc (with its highest contribution at ∼ We found that both the AGN FC (power-law) component and black-body emission contribute to up to 20 % of the observed K-bandnuclear flux of Mrk 573, as seen in Fig. 3. The nucleus of Mrk 573is classified as Seyfert 2 and the inclusion of these components isnecessary to fit the nuclear spectrum of at least 25 % of Seyfert2 galaxies, while more than 50 % of Seyfert 1 galaxies show FCand hot dust contribution (Ri ff el et al. 2009). The detection of thepower-law component for Mrk 573 suggests that radiation from theaccretion disk is coming out through the torus, in good agreementwith the detection of an obscured Narrow-Line Seyfert 1 nucleus as indicated by the presence of a broad component in the Pa β emissionline (Ramos Almeida et al. 2008).The spectral synthesis confirmed the presence of an unre-solved black-body component at the nucleus, previously detectedin the infrared (Ramos Almeida, P´erez Garc´ıa & Acosta-Pulido2009; Schlesinger et al. 2009; Ri ff el et al. 2009), and possibly dueto the dusty torus surrounding the SMBH. We have estimated themass of the hot dust following Ri ff el et al. (2009a) and using theformalism of Barvainis (1987), for dust composed by grains ofgraphite.The IR spectral luminosity of each dust grain, in erg s − Hz − ,can be written as L gr ν, ir = π a Q ν B ν ( T gr ) , (5)where a = . µ m is the grain radius, Q ν = . × − ν . is its ab-sorption e ffi ciency and B ν ( T gr ) is its spectral distribution assumedto be a Planck function for a temperature T gr .The total number of graphite grains can be obtained from N HD ∼ L HDir L grir , (6)where L HDir is the total luminosity of the hot dust, obtained by in-tegrating the flux of each black-body component contribution fromthe synthesis. Then, we multiplied the integrated normalized fluxby the normalization flux at 21955Å and convert it to the adequateunits (from erg s − cm − Å − to erg s − Hz − ). In order to obtain L grir ,we have integrated the Eq. 5 for all temperatures, ranging themfrom 700 to 1400 K, in steps of 100 K.Finally, the hot dust mass can be obtained by the equation (e.g.Rodr´ıguez-Ardila et al. 2005): M HD ∼ π a N HD ρ gr , (7)where ρ gr = .
26 g cm − is the density of the grain. The totaldust mass estimated for the nucleus of Mrk 573 by integratingover the entire field of view, is M HD = . × − M ⊙ , whichis within the range of masses observed for other active galaxies(e.g. Ri ff el et al. 2009, 2010, 2011b; Rodr´ıgues-Ardila & Mazzalay2006; Rodr´ıguez-Ardila et al. 2005). The E ( B − V ) map (Fig. 3) obtained for the stellar population showhigher values to the southwest side of the nucleus. We can com-pare this map with that for the gas extinction. A gas reddening mapcan be obtained by using the Pa β / Br γ emission line ratio via thefollowing equation: E ( B − V ) = .
74 log . F Pa β / F Br γ ! , (8)where F Pa β and F Br γ are the fluxes of Pa β and Br γ emission lines,respectively. This equation was obtained using the reddening law ofCardelli et al. (1989) and adopting the intrinsic ratio F Pa β / F Br γ = .
88 corresponding to case B recombination (Osterbrock & Ferland2006). The Pa β and Br γ emission-line flux distributions were ob-tained by fitting the line profiles at each spaxel by Gaussian curves,and as discussed in Fischer et al. (2017) these lines show similarflux distributions to those of the [S iii ] λ . µ m line. The resulting E ( B − V ) map for the gas is shown in Fig. 7.The median value of the reddening for the gas over the wholefield of view is E ( B − V ) ∼ . c (cid:13) , 1–10 Diniz et al.
Figure 6.
Contribution to the flux at 2.2 µ m of each stellar population component as a function of the deprojected distance to the nucleus. Values for Mrk 573are shown in black lines, for Mrk 1157 in green, for Mrk 1066 in blue and for NGC 1068 in red. The dashed lines show the standard deviation of the azimuthalmean at each radius. See text for more details. Figure 7.
From left to right: E ( B − V ) map for the gas from the line ratios between Pa β and Br γ ; stellar E(B-V) map obtained from starlight and theH λ where both Br γ and Pa β emission lines were detected. For the stel-lar population we obtain a smaller value of E ( B − V ) ∼ ff el et al. (2006) presented the nuclear spectrum of Mrk 573 foran aperture of 0 . ′′ × . ′′ µ m. Using the their fluxvalues for Br γ and Pa β emission lines, we obtain an E ( B − V )value for the gas very similar to ours, while Ri ff el et al. (2009) ob- tained E ( B − V ) ≈ . ff erence may be due to the fact thatmost of the gas is located closer to the galaxy disk, where largeamount of dust is expected, while the near-IR continuum has animportant contribution from stars of the bulge of the galaxy.Comparing the gas and stellar E ( B − V ) maps, we note that c (cid:13) , 1–10 D stellar populations in Mrk573 they show a similar distribution near the nucleus, with higher val-ues observed to the southwest of the nucleus and values close tozero to the northeast of it. The observed extinction for the gas islarger than that of the stellar population, in good agreement withprevious studies (e.g. Ri ff el et al. 2008). A higher extinction to thesouthwest of the nucleus is also supported by the dust lanes seen inthe structure map presented in Fig. 7 of Fischer et al. (2017).The rightmost panel of Fig. 7 shows that the distribution of thehot molecular gas presents a good correlation with the gas E ( B − V ), confirming the known association between the molecular gasand dust. The highest apparent concentration of hot molecular gascoincides with the region of highest extinction in the gas and in thestars at 0 . ′′ We used near-IR integral field spectra at a spatial resolution of ∼
50 pc to map the stellar population distributions in the inner500 pc of the Seyfert galaxy Mrk 573, as well as featureless con-tinua contributions at the nucleus by combining the spectral syn-thesis technique with Maraston (2005) SSP models. The main con-clusions of this work are: • Although the old stellar population ( x i > ∼
250 pc (0 . ′′ ∼
70 pcfrom the nucleus there is up to 30% contribution from a young stel-lar population ( x i <
100 Myr). Beyond the inner ∼
250 pc and up tothe border of the FOV (500 pc), the young-intermediate age stellarpopulations (100–700 Myr) are dominant, in a structure resemblinga partial ring where its contribution to the continuum reaches up to ≈ • Unresolved power-law and black-body functions contribu-tions to the continuum are detected at the nucleus at the level of20 % in the K-band. The first is attributed to the accretion diskemission and the latter to the emission from the dusty torus. Wederive a hot dust mass of ∼ .
013 M ⊙ , consistent with values ob-served for other Seyfert 2 galaxies. • The distribution of intermediate age stars shows a weak corre-lation with locations where we observe low stellar velocity disper-sion values, supporting that these low- σ structures are originated instellar populations that still preserve the cold kinematics of the gasfrom which they were formed. • By comparing the radial distribution of each stellar populationcomponent observed in Mrk 573 with those of other three galaxiesstudied using similar data (Mrk 1066, Mrk 1157 and NGC 1068),we found that young stellar populations (contributing with > • The stellar population extinction is larger at the nucleus and tothe southwest of it, where we also observe higher gas extinction, asderived from the Pa β / Br γ line ratio. The high extinction region tothe southwest coincides also with a region of strong hot moleculargas emission. ACKNOWLEDGEMENTS
This work is based on observations obtained at the Gemini Ob-servatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreementwith the NSF on behalf of the Gemini partnership: the NationalScience Foundation (United States), the Science and Technol-ogy Facilities Council (United Kingdom), the National ResearchCouncil (Canada), CONICYT (Chile), the Australian ResearchCouncil (Australia), Minist´erio da Ciˆencia e Tecnologia (Brazil)and South-EastCYT (Argentina). This research has made use ofthe NASA / IPAC Extragalactic Database (NED) which is operatedby the Jet Propulsion Laboratory, California Institute of Tech-nology, under contract with the National Aeronautics and SpaceAdministration. This work has been partially supported by theBrazilian institution CNPq.
M.R.D. thanks financial support fromCNPq.
R.A.R. acknowledges support from FAPERGS (project N0.12 / / R.R. thanks toCNPq and FAPERGS for partially funding this work.
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