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AMUSE-Virgo. II. Down-sizing in Black Hole Accretion
We complete the census of nuclear X-ray activity in 100 early-type Virgogalaxies observed by the Chandra X-ray Telescope as part of theAMUSE-Virgo survey, down to a (3?) limiting luminosity of 3.7× 1038 erg s-1 over 0.5-7 keV. Thestellar mass distribution of the targeted sample, which is mostlycomposed of formally "inactive" galaxies, peaks below 1010 Msun, a regime where the very existence of nuclearsupermassive black holes (SMBHs) is debated. Out of 100 objects, 32 showa nuclear X-ray source, including 6 hybrid nuclei which also host amassive nuclear cluster as visible from archival Hubble Space Telescopeimages. After carefully accounting for contamination from nuclearlow-mass X-ray binaries based on the shape and normalization of theirX-ray luminosity function (XLF), we conclude that between 24% and 34% ofthe galaxies in our sample host an X-ray active SMBH (at the 95%confidence level). This sets a firm lower limit to the black hole (BH)occupation fraction in nearby bulges within a cluster environment. Thedifferential logarithmic XLF of active SMBHs scales with the X-rayluminosity as L X -0.4±0.1 up to1042 erg s-1. At face value, the activefraction—down to our luminosity limit—is found to increasewith host stellar mass. However, taking into account selection effects,we find that the average Eddington-scaled X-ray luminosity scales withBH mass as M BH ^{-0.62^{+0.13}_{-0.12}}, with an intrinsicscatter of 0.46+0.08 -0.06 dex. This findingcan be interpreted as observational evidence for "down-sizing" of BHaccretion in local early types, that is, low-mass BHs shine relativelycloser to their Eddington limit than higher mass objects. As aconsequence, the fraction of active galaxies, defined as those above afixed X-ray Eddington ratio, decreases with increasing BH mass.
| Homogeneous UGRIZ Photometry for ACS Virgo Cluster Survey Galaxies: A Non-parametric Analysis from SDSS Imaging
We present photometric and structural parameters for 100 ACS VirgoCluster Survey (ACSVCS) galaxies based on homogeneous, multi-wavelength(ugriz), wide-field SDSS (DR5) imaging. These early-type galaxies, whichtrace out the red sequence in the Virgo Cluster, span a factor of nearly~103 in g-band luminosity. We describe an automated pipelinethat generates background-subtracted mosaic images, masks field sourcesand measures mean shapes, total magnitudes, effective radii, andeffective surface brightnesses using a model-independent approach. Aparametric analysis of the surface brightness profiles is also carriedout to obtain Sérsic-based structural parameters and mean galaxycolors. We compare the galaxy parameters to those in the literature,including those from the ACSVCS, finding good agreement in most cases,although the sizes of the brightest, and most extended, galaxies arefound to be most uncertain and model dependent. Our photometry providesan external measurement of the random errors on total magnitudes fromthe widely used Virgo Cluster Catalog, which we estimate to be?(BT )? 0.13 mag for the brightest galaxies, risingto ? 0.3 mag for galaxies at the faint end of our sample(BT ? 16). The distribution of axial ratios of low-mass("dwarf") galaxies bears a strong resemblance to the one observed forthe higher-mass ("giant") galaxies. The global structural parameters forthe full galaxy sample—profile shape, effective radius, and meansurface brightness—are found to vary smoothly and systematicallyas a function of luminosity, with unmistakable evidence for changes instructural homology along the red sequence. As noted in previousstudies, the ugriz galaxy colors show a nonlinear but smooth variationover a ~7 mag range in absolute magnitude, with an enhanced scatter forthe faintest systems that is likely the signature of their more diversestar formation histories.
| Unusual PAH Emission in Nearby Early-type Galaxies: A Signature of an Intermediate-age Stellar Population?
We present the analysis of Spitzer-IRS spectra of four early-typegalaxies (ETGs), NGC 1297, NGC 5044, NGC 6868, and NGC 7079, allclassified as LINERs in the optical bands. Their IRS spectra present thefull series of H2 rotational emission lines in the range 5-38?m, atomic lines, and prominent polycyclic aromatic hydrocarbon (PAH)features. We investigate the nature and origin of the PAH emission,characterized by unusually low 6-9/11.3 ?m interband ratios. Afterthe subtraction of a passive ETG template, we find that the 7-9 ?mspectral region requires dust features not normally present instar-forming galaxies. Each spectrum is then analyzed with the aim ofidentifying their components and origin. In contrast to normalstar-forming galaxies, where cationic PAH emission prevails, our 6-14?m spectra seem to be dominated by large and neutral PAH emission,responsible for the low 6-9/11.3 ?m ratios, plus two broad dustemission features peaking at 8.2 ?m and 12 ?m. These broadcomponents, observed until now mainly in evolved carbon stars andusually attributed to pristine material, contribute approximately30%-50% of the total PAH flux in the 6-14 ?m region. We propose thatthe PAH molecules in our ETGs arise from fresh carbonaceous materialthat is continuously released by a population of carbon stars, formed ina rejuvenation episode that occurred within the last few Gyr. Theanalysis of the MIR spectra allows us to infer that, in order tomaintain the peculiar size and charge distributions biased to large andneutral PAHs, this material must be shocked and excited by the weak UVinterstellar radiation field of our ETGs.
| The Nuclear X-ray Emission of Nearby Early-type Galaxies
Nuclear hard X-ray luminosities (L X,nuc) for a sample of 112early-type galaxies within a distance of 67 Mpc are used to investigatetheir relationship with the central galactic black hole mass MBH (coming from direct dynamical studies or the MBH-? relation), the inner galactic structure (using theparameters describing its cuspiness), the hot gas content, and the coreradio luminosity. For this sample, L X,nuc ranges from1038 to 1042 erg s–1, and theEddington ratio L X,nuc/L Edd from10–9 to 10–4, with the largest valuesbelonging to four Seyfert galaxies. Together with a trend for LX,nuc to increase on average with the galactic luminosityLB and M BH, there is a wide variation of LX,nuc (and L X,nuc/L Edd), by up to 4orders of magnitude, at any fixed LB > 6 ×109 L B,sun or M BH >107 M sun. This large observed range shouldreflect a large variation of the mass accretion rate \dot{M}_BH, andpossible reasons for this difference are searched for. On thecircumnuclear scale, in a scenario where accretion is (quasi) steady,\dot{M}_BH at fixed LB (or M BH) could vary due todifferences in the fuel production rate from stellar mass return linkedto the inner galactic structure; a trend of L X,nuc withcuspiness is not observed, though, while a tendency for LX,nuc/L Edd to be larger in cuspier galaxies ispresent. In fact, \dot{M}_BH is predicted to vary with cuspiness by afactor exceeding a few only in hot gas-poor galaxies and for largedifferences in the core radius; for a subsample with thesecharacteristics the expected effect seems to be present in the observedL X,nuc values. L X,nuc does not show a dependenceon the age of the stellar population in the central galactic region, forages >3 Gyr; less luminous nuclei, though, are found among theyoungest galaxies or galaxies with a younger stellar component. On theglobal galactic scale, L X,nuc shows a trend with the totalgalactic hot gas cooling rate (L X,ISM): it is detected bothin gas-poor and gas-rich galaxies, and on average increases with L X,ISM, but again with a large scatter. The observed lack of atight relationship between L X,nuc and the circumnuclear andtotal gas content can be explained if accretion is regulated by factorsovercoming the importance of fuel availability, as (1) the gas is heatedby black hole feedback and \dot{M}_BH varies due to an activity cycle,and (2) the mass effectively accreted by the black hole can be largelyreduced with respect to that entering the circumnuclear region, as inradiatively inefficient accretion with winds/outflows. Finally,differently from L X,nuc, the central 5 GHz VLA luminosityshows a clear trend with the inner galactic structure that is similar tothat shown by the total soft X-ray emission; therefore, it is suggestedthat they could both be produced by the hot gas.
| Accretion and nuclear activity in Virgo early-type galaxies
We use Chandra observations to estimate the accretion rate of hot gasonto the central supermassive black hole in four giant (of stellar massM_* 1011-1012 Msun) early-typegalaxies located in the Virgo cluster. They are characterized by anextremely low radio luminosity, in the range L ?3×1025-1027 erg s-1Hz-1. We find that, accordingly, accretion in these objectsoccurs at an extremely low rate, 0.2-3.7×10-3M? yr-1, and that they smoothly extend therelation accretion-jet power found for more powerful radio-galaxies.This confirms the dominant role of hot gas and of the galactic coronaein powering radio-loud active galactic nuclei across 4 orders ofmagnitude in luminosity. A suggestive trend between jet power andlocation within the cluster also emerges.Appendix is only available in electronic form at http://www.aanda.org
| The SAURON project - XV. Modes of star formation in early-type galaxies and the evolution of the red sequence
We combine SAURON integral field data of a representative sample oflocal early-type, red sequence galaxies with Spitzer/Infrared ArrayCamera imaging in order to investigate the presence of trace starformation in these systems. With the Spitzer data, we identify galaxieshosting low-level star formation, as traced by polycyclic aromatichydrocarbon emission, with measured star formation rates that comparewell to those estimated from other tracers. This star formation proceedsaccording to established scaling relations with molecular gas content,in surface density regimes characteristic of disc galaxies andcircumnuclear starbursts. We find that star formation in early-typegalaxies happens exclusively in fast-rotating systems and occurs in twodistinct modes. In the first, star formation is a diffuse process,corresponding to widespread young stellar populations and high moleculargas content. The equal presence of co- and counter-rotating componentsin these systems strongly implies an external origin for thestar-forming gas, and we argue that these star formation events may bethe final stages of (mostly minor) mergers that build up the bulges ofred sequence lenticulars. In the second mode of star formation, theprocess is concentrated into well-defined disc or ring morphologies,outside of which the host galaxies exhibit uniformly evolved stellarpopulations. This implies that these star formation events representrejuvenations within previously quiescent stellar systems. Evidence forearlier star formation events similar to these in all fast-rotatingearly-type galaxies suggests that this mode of star formation may becommon to all such galaxies, with a duty cycle of roughly 1/10, andlikely contributes to the embedded, corotating inner stellar discsubiquitous in this population.
| Exploring the star formation history of elliptical galaxies: beyond simple stellar populations with a new line strength estimator
We study the stellar populations of a sample of 14 elliptical galaxiesin the Virgo cluster. Using spectra with high signal-to-noise ratio (S/N>~ 100Å-1) we propose an alternative approach to thestandard side-band method to measure equivalent widths (EWs). Ourboosted median continuum is shown to map the EWs more robustly than theside-band method, minimizing the effect from neighbouring absorptionlines and reducing the uncertainty at a given S/N. Our newly definedline strengths are more successful at disentangling the age-metallicitydegeneracy. We concentrate on Balmer lines (H?, H?,H?), the G band and the combination [MgFe] as the main age andmetallicity indicators. We go beyond the standard comparison of theobservations with simple stellar populations (SSPs) and consider fourdifferent models to describe the star formation histories, either with acontinuous star formation rate or with a mixture of two different SSPs.These models improve the estimates of the more physically meaningfulmass-weighted ages. Composite models are found to give more consistentfits among individual line strengths and agree with an independentestimate using the spectral energy distribution. A combination of age-and metallicity-sensitive spectral features allows us to constrain theaverage age and metallicity. For a Virgo sample of elliptical galaxiesour age and metallicity estimates correlate well with stellar mass orvelocity dispersion, with a significant threshold around 5 ×1010Msolar above which galaxies are uniformly oldand metal rich. This threshold is reminiscent of the one found byKauffmann et al. in the general population of Sloan Digital Sky Surveygalaxies at a stellar mass 3 × 1010Msolar.In a more speculative way, our models suggest that it is formation epochand not formation time-scale what drives the mass-age relationship ofelliptical galaxies.
| The ACS Fornax Cluster Survey. VIII. The Luminosity Function of Globular Clusters in Virgo and Fornax Early-type Galaxies and Its Use as a Distance Indicator
We use a highly homogeneous set of data from 132 early-type galaxies inthe Virgo and Fornax clusters in order to study the properties of theglobular cluster luminosity function (GCLF). The globular cluster systemof each galaxy was studied using a maximum likelihood approach to modelthe intrinsic GCLF after accounting for contamination and completenesseffects. The results presented here update our Virgo measurements andconfirm our previous results showing a tight correlation between thedispersion of the GCLF and the absolute magnitude of the parent galaxy.Regarding the use of the GCLF as a standard candle, we have found thatthe relative distance modulus between the Virgo and Fornax clusters issystematically lower than the one derived by other distance estimators,and in particular, it is 0.22 mag lower than the value derived fromsurface brightness fluctuation measurements performed on the same data.From numerical simulations aimed at reproducing the observed dispersionof the value of the turnover magnitude in each galaxy cluster weestimate an intrinsic dispersion on this parameter of 0.21 mag and 0.15mag for Virgo and Fornax, respectively. All in all, our study shows thatthe GCLF properties vary systematically with galaxy mass showing noevidence for a dichotomy between giant and dwarf early-type galaxies.These properties may be influenced by the cluster environment assuggested by cosmological simulations.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute (STScI), which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555.
| A census of nuclear stellar discs in early-type galaxies
Nuclear stellar discs (NSDs), of a few tens to hundreds of parsecacross, are a common and yet poorly studied feature of early-typegalaxies. Still, such small discs represent a powerful tool to constrainthe assembling history of galaxies, since they can be used to trace tothe epoch when galaxies experienced their last major merger event. Bystudying the fraction and stellar age of NSDs, it is thus possible totest the predictions for the assembly history of early-type galaxiesaccording to the current hierarchical paradigm for galaxy formation. Inthis paper we have produced the most comprehensive census of NSDs innearby early-type galaxies by searching for such discs in objects within100 Mpc and by using archival images from the Hubble Space Telescope. Wefound that NSDs are present in approximately 20 per cent of early-typegalaxies, and that the fraction of galaxies with NSDs depends neither ontheir Hubble type nor on their galactic environment, whereas theincidence of NSDs appears to decline in the most massive systems.Furthermore, we have separated the light contribution of 12 such discsfrom that of their surrounding stellar bulge in order to extract theirphysical properties. This doubles the number of decomposed NSDs andalthough the derived values for their central surface brightness andscalelength are consistent with previous studies, they also give a hintof possible different characteristics due to different formationscenario between nuclear discs and other kinds of large galactic discs.
| The effect of dust extinction on the observed properties of galaxies in the near-infrared
Galaxies behind the Milky Way suffer size reduction and dimming due totheir obscuration by dust in the disc of our Galaxy. The degree ofobscuration is wavelength dependent. It decreases towards longerwavelengths. Compared to the optical, the near-infrared (NIR)Ks-band extinction is only ~10 per cent that of the B band.This makes NIR surveys well suited for galaxy surveys close to theGalactic plane, where extinction is severe.While Galactic obscuration is less prominent in the NIR, it is notnegligible. In this paper, we derive empirical relations to correctisophotal radii and magnitudes of galaxies observed in the NIR forforeground absorption. We simulate extinction in the J, H andKs bands on 64 (unobscured) galaxies from the Two Micron AllSky Survey Large Galaxy Atlas. We propose two methods for the extinctioncorrection, the first is optimized to provide the most accuratecorrection and the second provides a convenient statistical correctionthat works adequately in lower extinction regions. The optimizedcorrection utilizes the galaxy surface brightness, either the disccentral surface brightness, ?0, or the combined disc plusbulge central surface brightness, elliptical and disc/spiral Hubbletypes. A detailed comparison between the different methods and theiraccuracy is provided.
| A Population of Compact Elliptical Galaxies Detected with the Virtual Observatory
Compact elliptical galaxies are characterized by small sizes and highstellar densities. They are thought to form through tidal stripping ofmassive progenitors. However, only a handful of them were known,preventing us from understanding the role played by this mechanism ingalaxy evolution. We present a population of 21 compact ellipticalgalaxies gathered with the Virtual Observatory. Follow-up spectroscopyand data mining, using high-resolution images and large databases, showthat all the galaxies exhibit old metal-rich stellar populationsdifferent from those of dwarf elliptical galaxies of similar masses butsimilar to those of more massive early-type galaxies, supporting thetidal stripping scenario. Their internal properties are reproduced bynumerical simulations, which result in compact, dynamically hot remnantsresembling the galaxies in our sample.
| Multiband photometric decomposition of nuclear stellar disks
Context. Small, bright stellar disks with scale lengths of a few tens ofparsec are known to reside in the center of galaxies. They are believedto have formed in a dissipational process as the end result of starformation in gas either accreted during a merging (or acquisition) eventor piled up by the secular evolution of a nuclear bar. Only a few ofthem have been studied in detail to date. Aims: Using archivalHubble Space Telescope (HST) imaging, we investigate the photometricparameters of the nuclear stellar disks hosted by three early-typegalaxies in the Virgo cluster, NGC 4458, NGC 4478, and NGC 4570, toconstrain the process that forms their stars. Methods: Thecentral surface brightness, scale length, inclination, and positionangle of the nuclear disks were derived by adopting the photometricdecomposition method introduced by Scorza & Bender and assuming thedisks to be infinitesimally thin and exponential. Results: Thelocation, orientation, and size of the nuclear disks is the same in allthe images obtained with the Wide Field Planetary Camera 2 and AdvancedCamera for Surveys and available in the HST Science Archive. The scalelength, inclination, and position angle of each disk are constant withinthe errors in the observed U, B, V, and I passbands, independently oftheir values and the properties of the host spheroid. Conclusions: We interpret the absence of color gradients in the stellarpopulation of the nuclear disks as the signature that star formationhomogeneously occurred along their length. An inside-out formationscenario is, instead, expected to produce color gradients and istherefore ruled out.
| Evolutionary stellar population synthesis with MILES - I. The base models and a new line index system
We present synthetic spectral energy distributions (SEDs) forsingle-age, single-metallicity stellar populations (SSPs) covering thefull optical spectral range at moderately high resolution [full width athalf-maximum (FWHM) = 2.3Å]. These SEDs constitute our basemodels, as they combine scaled-solar isochrones with an empiricalstellar spectral library [Medium resolution INT Library of EmpiricalSpectra (MILES)], which follows the chemical evolution pattern of thesolar neighbourhood. The models rely as much as possible on empiricalingredients, not just on the stellar spectra, but also on extensivephotometric libraries, which are used to determine the transformationsfrom the theoretical parameters of the isochrones to observationalquantities. The unprecedented stellar parameter coverage of the MILESstellar library allowed us to safely extend our optical SSP SEDpredictions from intermediate- to very-old-age regimes and themetallicity coverage of the SSPs from super-solar to [M/H] = -2.3. SSPswith such low metallicities are particularly useful for globular clusterstudies. We have computed SSP SEDs for a suite of initial mass functionshapes and slopes. We provide a quantitative analysis of the dependenceof the synthesized SSP SEDs on the (in)complete coverage of the stellarparameter space in the input library that not only shows that our modelsare of higher quality than those of other works, but also in which rangeof SSP parameters our models are reliable. The SSP SEDs are a usefultool to perform the analysis of stellar populations in a very flexiblemanner. Observed spectra can be studied by means of full spectrumfitting or by using line indices. For the latter, we propose a new lineindex system to avoid the intrinsic uncertainties associated with thepopular Lick/IDS system and provide more appropriate, uniform, spectralresolution. Apart from constant resolution as a function of wavelength,the system is also based on flux-calibrated spectra. Data can beanalysed at three different resolutions: 5, 8.4 and 14Å (FWHM),which are appropriate for studying globular cluster, low- andintermediate-mass galaxies, and massive galaxies, respectively.Furthermore, we provide polynomials to transform current Lick/IDS lineindex measurements to the new system. We provide line index tables inthe new system for various popular samples of Galactic globular clustersand galaxies. We apply the models to various stellar clusters andgalaxies with high-quality spectra, for which independent studies areavailable, obtaining excellent results. Finally, we designed a web pagefrom which not only these models and stellar libraries can be downloadedbut which also provides a suite of on-line tools to facilitate thehandling and transformation of the spectra.
| Spitzer Observations of Passive and Star-Forming Early-Type Galaxies: An Infrared Color–Color Sequence
We describe the infrared properties of a large sample of early-typegalaxies, comparing data from the Spitzer archive with Ks-band emissionfrom the Two Micron All Sky Survey. While most representations of thisdata result in correlations with large scatter, we find a remarkablytight relation among colors formed by ratios of luminosities inSpitzer-Multiband Imaging Photometer bands (24, 70, and 160 μm) andthe Ks band. Remarkably, this correlation among E and S0 galaxiesfollows that of nearby normal galaxies of all morphological types. Inparticular, the tight infrared color-color correlation for S0 galaxiesalone follows that of the entire Hubble sequence of normal galaxies,roughly in order of galaxy type from ellipticals to spirals toirregulars. The specific star formation rate (SFR) of S0 galaxiesestimated from the 24 μm luminosity increases with decreasing K-bandluminosity (or stellar mass) from essentially zero, as with most massiveellipticals, to rates typical of irregular galaxies. Moreover, theluminosities of the many infrared-luminous S0 galaxies can significantlyexceed those of the most luminous (presumably post-merger) E galaxies.SFRs in the most infrared-luminous S0 galaxies approach 1-10 solarmasses per year. Consistently, with this picture we find that while mostearly-type galaxies populate an infrared red sequence, about 24% of theobjects (mostly S0s) are in an infrared blue cloud together withlate-type galaxies. For those early-type galaxies also observed at radiofrequencies, we find that the far-infrared luminosities correlate withthe mass of neutral and molecular hydrogen, but the scatter is large.This scatter suggests that the star formation may be intermittent orthat similar S0 galaxies with cold gaseous disks of nearly equal masscan have varying radial column density distributions that alter thelocal and global SFRs.
| A Very Large Array Radio Survey of Early-Type Galaxies in the Virgo Cluster
We present the results of an 8.4 GHz Very Large Array radio survey ofearly-type galaxies extracted from the sample selected byCôté and collaborators for the Advanced Camera for SurveysVirgo Cluster Survey. The aim of this survey is to investigate theorigin of radio emission in early-type galaxies and its link with thehost properties in an unexplored territory toward the lowest levels ofboth radio and optical luminosities. Radio images, available for all 63galaxies with B T < 14.4, show the presence of a compactradio source in 12 objects, with fluxes spanning from 0.13 mJy to 2700mJy. The remaining 51 galaxies, undetected at a flux limit of ~0.1 mJy,have radio luminosities L lsim 4 × 1018 WHz–1. The fraction of radio-detected galaxies are astrong function of stellar mass, in agreement with previous results:none of the 30 galaxies with M sstarf < 1.7 ×1010 M sun is detected, while 8 of the 11 mostmassive galaxies have radio cores. There appears to be no simplerelation between the presence of a stellar nucleus and radio emission.In fact, we find radio sources associated with two nucleated galaxies,but the majority of nucleated objects are not a radio emitter above ourdetection threshold. A multiwavelength analysis of the active galacticnucleus (AGN) emission, combining radio and X-ray data, confirms thelink between optical surface brightness profile and radio loudness inthe sense that the bright core galaxies are associated with radio-loudAGNs, while non-core galaxies host radio-quiet AGNs. Not allradio-detected galaxies have an X-ray nuclear counterpart (and viceversa). A complete census of AGNs (and supermassive black holes, SMBHs)thus requires observations, at least, in both bands. Nonetheless, thereare massive galaxies in the sample, expected to host a large SMBH (MBH ~ 108 M sun), whose nuclear emissioneludes detection despite their proximity and the depth and the spatialresolution of the available observations. Most likely this is due to anextremely low level of accretion onto the central SMBH.
| The SAURON project - XIII. SAURON-GALEX study of early-type galaxies: the ultraviolet colour-magnitude relations and Fundamental Planes
We present Galaxy Evolution Explorer far-ultraviolet (FUV) andnear-ultraviolet (NUV) imaging of 34 nearby early-type galaxies from theSAURON representative sample of 48 E/S0 galaxies, all of which haveground-based optical imaging from the MDM Observatory. The surfacebrightness profiles of nine galaxies (~26 per cent) show regions withblue UV-optical colours suggesting RSF. Five of these (~15 per cent)show blue integrated UV-optical colours that set them aside in the NUVintegrated colour-magnitude relation. These are objects with eitherexceptionally intense and localized NUV fluxes or blue UV-opticalcolours throughout. They also have other properties confirming they havehad RSF, in particular Hβ absorption higher than expected for aquiescent population and a higher CO detection rate. This suggests thatresidual star formation is more common in early-type galaxies than weare used to believe. NUV blue galaxies are generally drawn from thelower stellar velocity dispersion (σe <200kms-1) and thus lower dynamical mass part of the sample.We have also constructed the first UV Fundamental Planes and show thatNUV blue galaxies bias the slopes and increase the scatters. If they areeliminated, the fits get closer to expectations from the virial theorem.Although our analysis is based on a limited sample, it seems that adominant fraction of the tilt and scatter of the UV Fundamental Planesis due to the presence of young stars in preferentially low-massearly-type galaxies. Interestingly, the UV-optical radial colourprofiles reveal a variety of behaviours, with many galaxies showingsigns of RSF, a central UV-upturn phenomenon, smooth but large-scale ageand metallicity gradients and in many cases a combination of these. Inaddition, FUV-NUV and FUV-V colours even bluer than those normallyassociated with UV-upturn galaxies are observed at the centre of somequiescent galaxies. Four out of the five UV-upturn galaxies are slowrotators. These objects should thus pose interesting challenges tostellar evolutionary models of the UV upturn.
| The SAURON Project - XIV. No escape from Vesc: a global and local parameter in early-type galaxy evolution
We present the results of an investigation of the local escape velocity(Vesc) - line strength index relationship for 48 early-typegalaxies from the SAURON sample, the first such study based on a largesample of galaxies with both detailed integral field observations andextensive dynamical modelling. Values of Vesc are computedusing multi-Gaussian expansion (MGE) photometric fitting andaxisymmetric, anisotropic Jeans' dynamical modelling simultaneously onHubble Space Telescope and ground-based images. We determine linestrengths and escape velocities at multiple radii within each galaxy,allowing an investigation of the correlation within individual galaxiesas well as amongst galaxies. We find a tight correlation betweenVesc and the line-strength indices. For Mgb, we find thatthis correlation exists not only between different galaxies but alsoinside individual galaxies - it is both a local and global correlation.The Mgb-Vesc relation has the form: log(Mgb/4Å) = (0.32+/- 0.03) log(Vesc/500km s-1) - (0.031 +/- 0.007)with an rms scatter σ = 0.033. The relation within individualgalaxies has the same slope and offset as the global relation to a goodlevel of agreement, though there is significant intrinsic scatter in thelocal gradients. We transform our line strength index measurements tothe single stellar population (SSP) equivalent ages (t), metallicity([Z/H]) and enhancement ([α/Fe]) and carry out a principalcomponent analysis of our SSP and Vesc data. We find that inthis four-dimensional parameter space the galaxies in our sample are toa good approximation confined to a plane, given by log (Vesc/500 kms -1) = 0.85 [Z/H] + 0.43 log (t/Gyr) -0.29. It is surprising that a combination of age and metallicity isconserved; this may indicate a `conspiracy' between age and metallicityor a weakness in the SSP models. How the connection between stellarpopulations and the gravitational potential, both locally and globally,is preserved as galaxies assemble hierarchically may provide animportant constraint on modelling.
| A Hertzsprung-Russell-like Diagram for Galaxies: The M • Versus M Gσ2 Relation
We show that the relation between the mass of supermassive black holeslocated in the center of the host galaxies and the kinetic energy ofrandom motions of the corresponding bulges is a useful tool to study theevolution of galaxies. In the form \log_{10}(M_{\bullet })=b+m\log_{10}(M_G\sigma^2/c^2), the best-fitting results for a sample of 64galaxies of various morphological types are the slope m = 0.80 ±0.03 and the normalization b = 4.53 ± 0.13. We note that, inanalogy with the Hertzsprung-Russell diagram for stars, eachmorphological type of galaxy generally occupies a different area in theM •-(M Gσ2)/c 2plane. In particular, we find elliptical galaxies in the upper part ofthe line of best fit, the lenticular galaxies in the middle part, andthe late-type galaxies in the lower part, the mass of the central blackhole giving an estimate of the age, whereas the kinetic energy of thestellar bulges is directly connected with the temperature of eachgalactic system. Finally, the values of the linear correlationcoefficient, the intrinsic scatter, and the χ2 obtainedby using the M •-M Gσ2relation are better than the corresponding ones obtained from the M•-σ or the M •-M Grelation.
| The Herschel Reference Survey
The Herschel Reference Survey is a Herschel guaranteed time key projectand will be a benchmark study of dust in the nearby universe. The surveywill complement a number of other Herschel key projects including largecosmological surveys that trace dust in the distant universe. We willuse Herschel to produce images of a statistically-complete sample of 323galaxies at 250, 350, and 500 ?m. The sample is volume-limited,containing sources with distances between 15 and 25 Mpc and flux limitsin the band to minimize the selection effects associated with dust andwith young high-mass stars and to introduce a selection in stellar mass.The sample spans the whole range of morphological types (ellipticals tolate-type spirals) and environments (from the field to the center of theVirgo Cluster) and as such will be useful for other purposes than ourown. We plan to use the survey to investigate (i) the dust content ofgalaxies as a function of Hubble type, stellar mass, and environment;(ii) the connection between the dust content and composition and theother phases of the interstellar medium; and (iii) the origin andevolution of dust in galaxies. In this article, we describe the goals ofthe survey, the details of the sample and some of the auxiliaryobserving programs that we have started to collect complementary data.We also use the available multifrequency data to carry out an analysisof the statistical properties of the sample.
| Revisiting the "Fundamental Plane" of Black Hole Activity at Extremely Low Luminosities
We investigate the origin of the X-ray emission in low-luminosity activegalactic nuclei (LLAGNs). Yuan and Cui predicted that the X-ray emissionshould originate from jets rather than an advection-dominated accretionflow (ADAF) when the X-ray luminosity L X of the source isbelow a critical value of L X,crit ≈ 10–6L Edd. This prediction implies that the X-ray spectrum insuch sources should be fitted by jets rather than ADAFs. Furthermore,below L X,crit the correlation between radio (L R)and X-ray (L X) luminosities and the black hole mass(M)—the so-called fundamental plane of black holeactivity—should deviate from the general correlation obtained byMerloni et al. and become steeper. The Merloni et al. correlation isdescribed by logL R = 0.6logL X + 0.78logM + 7.33,while the predicted correlation is logL R = 1.23logLX + 0.25logM – 13.45. We collect data from theliterature to check the validity of these two expectations. We find thatamong the 16 LLAGNs with good X-ray and radio spectra, 13 are consistentwith the Yuan and Cui prediction. For the 22 LLAGNs with L X< L X,crit, the fundamental plane correlation is describedby logL R = 1.22logL X + 0.23logM – 12.46,also in excellent agreement with the prediction.
| Fractal Dimension of Galaxy Isophotes
In this paper we investigate the use of the fractal dimension of galaxyisophotes in galaxy classification. We have applied two differentmethods for determining fractal dimensions to the isophotes ofelliptical and spiral galaxies derived from CCD images. We conclude thatfractal dimension alone is not a reliable tool but that combined withother parameters in a neural net algorithm the fractal dimension couldbe of use. In particular, we have used three parameters to segregate theellipticals and lenticulars from the spiral galaxies in our sample.These three parameters are the correlation fractal dimension Dcorr, the difference between the correlation fractaldimension and the capacity fractal dimension D corr – Dcap, and, thirdly, the B – V color of the galaxy.
| Elliptical Galaxies: Rotationally Distorted, After All
On the basis of earlier investigations on homeoidally striated MacLaurin spheroids and Jacobi ellipsoids (Caimmi and Marmo 2005, Caimmi2006a, 2007), different sequences of configurations are defined andrepresented in the ellipticity-rotation plane, ({O}hat{e}?_v^2). The rotation parameter, ?_v^2, is defined as the ratio,E_{rot}/E_{res}, of kinetic energy related to the mean tangentialequatorial velocity component, M(overline{v_?})^2/2, to kineticenergy related to tangential equatorial component velocity dispersion,M?_{??}^2/2, and residual motions,M(?_{ww}^2+?_{33}^2)/2. Without loss of generality (above athreshold in ellipticity values), the analysis is restricted to systemswith isotropic stress tensor, which may be considered as adjointconfigurations to any assigned homeoidally striated density profile withanisotropic stress tensor, different angular momentum, and equalremaining parameters. The description of configurations in the({O}hat{e}?_v^2) plane is extended in two respects, namely (a) fromequilibrium to nonequilibrium figures, where the virial equations holdwith additional kinetic energy, and (b) from real to imaginary rotation,where the effect is elongating instead of flattening, with respect tothe rotation axis. An application is made to a subsample (N=16) ofelliptical galaxies extracted from richer samples (N=25, N=48) of earlytype galaxies investigated within the SAURON project (Cappellari et al.2006, 2007). Sample objects are idealized as homeoidally striatedMacLaurin spheroids and Jacobi ellipsoids, and their position in the({O}hat{e}?_v^2) plane is inferred from observations following aprocedure outlined in an earlier paper (Caimmi 2009b). The position ofrelated adjoint configurations with isotropic stress tensor is alsodetermined. With a single exception (NGC 3379), slow rotators arecharacterized by low ellipticities (0? hat{e}<0.2), low anisotropyparameters (0??<0.15), and low rotation parameters(0??_v^2<0.15), while fast rotators show large ellipticities(0.2? hat{e}<0.65), large anisotropy parameters(0.15??<0.35), and large rotation parameters(0.15??_v^2<0.5). An alternative kinematic classificationwith respect to earlier attempts (Emsellem et al. 2007) requires largersamples for providing additional support to the above mentioned results. A possible interpretation of slow rotators as nonrotating at all andelongated due to negative anisotropy parameters, instead of flatteneddue to positive anisotropy parameters, is exploited. Finally, theelliptical side of the Hubble morphological sequence is interpreted as asequence of equilibrium (adjoint) configurations where the ellipticityis an increasing function of the rotation parameter, slow rotatorscorrespond to early classes (E0-E2 in the oblate limit and E2-E0 in theprolate limit) and fast rotators to late classes (E3-E6). In this view,boundaries are rotationally distorted regardless of angular momentum andstress tensor, where rotation has to be intended as due to additionalkinetic energy of tangential equatorial velocity components, withrespect to spherical configurations with isotropic stress tensor.
| Infrared-red cores in nearby elliptical galaxies
We present the Spitzer Space Telescope Infrared Array Cameraobservations for a sample of local elliptical galaxies to study laterstages of active galactic nucleus (AGN) activity. A sample of 36elliptical galaxies is selected from the Palomar spectroscopic survey.We detect nuclear non-stellar infrared emission in nine of them. Thereis unambiguous evidence of circumnuclear dust in these nine galaxies intheir optical images. We also find a remarkable correlation between theinfrared excess emission and the nuclear radio/X-ray emission,suggesting that infrared excess emission is tightly related to nuclearactivity. The possible origin of infrared excess emission from hot dustheated by the central AGN is supported by the spectral indices of theinfrared excess emission.
| Tidal Stripping of Globular Clusters in the Virgo Cluster
With the aim of finding evidence of tidal stripping of globular clusters(GCs) we analyzed a sample of 13 elliptical galaxies taken from the ACSVirgo Cluster Survey (VCS). These galaxies belong to the mainconcentration of the Virgo Cluster (VC) and present absolute magnitudes–18.5 < Mz < –22.5. We used the public GCcatalog of Jordán et al. and separated the GC population intometal poor (blue) and metal rich (red) according to their integratedcolors. The galaxy properties were taken from Peng et al. We found thefollowing. (1) The specific frequencies (SN ) of total andblue GC populations increase as a function of the projected galaxydistances rp to M87. A similar result is observed whenthree-dimensional distances r 3D are used. The same behaviorsare found if the analysis is made using the number of GCs per10^9\;{\mathcal {M}_{\odot }} (T). No correlations between SNor T and rp or r 3D is observed for the red GCpopulation. The correlations for the blue GCs (typically more extended)and the lack of correlations for the red GCs (more concentrated) withthe clustocentric distance of the host galaxy are interpreted asevidence of GCs stripping due to tidal forces. (2) No correlation isfound between the slope of GC density profiles of host galaxies and thegalaxy distance to M87 (Virgo central galaxy). The lack of such acorrelation is interpreted in terms of a shrinkage of the GCdistribution after the stripping of GCs in the outermost region ofgalaxies. (3) We also computed the local density of GCs(ρout) located further than 6.2 kpc from the galaxycenter for nine galaxies of our sample. We find that the GC populationaround most of these galaxies is mainly composed of blue GCs. The twohighest values of ρout are found in the core of the VC(up to 100 kpc) and correspond to the two lowest values of SN. Our results suggest that the number and the fraction of blue and redGCs observed in elliptical galaxies located near the centers of massiveclusters could be significantly different from the underlying GCpopulation. These differences could be explained by tidal strippingeffects that occur as galaxies approach the centers of clusters.
| A Search for "Dwarf" Seyfert Nuclei. VII. A Catalog of Central Stellar Velocity Dispersions of Nearby Galaxies
We present new central stellar velocity dispersion measurements for 428galaxies in the Palomar spectroscopic survey of bright, northerngalaxies. Of these, 142 have no previously published measurements, mostbeing relatively late-type systems with low velocity dispersions(lsim100 km s–1). We provide updates to a number ofliterature dispersions with large uncertainties. Our measurements arebased on a direct pixel-fitting technique that can accommodate compositestellar populations by calculating an optimal linear combination ofinput stellar templates. The original Palomar survey data were takenunder conditions that are not ideally suited for deriving stellarvelocity dispersions for galaxies with a wide range of Hubble types. Wedescribe an effective strategy to circumvent this complication anddemonstrate that we can still obtain reliable velocity dispersions forthis sample of well-studied nearby galaxies.
| Radiatively Inefficient Accretion in Nearby Galaxies
We use new central stellar velocity dispersions and nuclear X-ray andHα luminosities for the Palomar survey of nearby galaxies toinvestigate the distribution of nuclear bolometric luminosities andEddington ratios for their central black holes (BHs). This informationhelps to constrain the nature of their accretion flows and the physicaldrivers that control the spectral diversity of nearby active galacticnuclei. The characteristic values of the bolometric luminosities andEddington ratios, which span over 7-8 orders of magnitude, from Lbol lsim 1037 to 3 × 1044 ergs–1 and L bol/L Edd≈10–9 to 10–1, vary systematicallywith nuclear spectral classification, increasing along the sequenceabsorption-line nuclei → transition objects → low-ionizationnuclear emission-line regions → Seyferts. The Eddington ratio alsoincreases from early-type to late-type galaxies. We show that the verymodest accretion rates inferred from the nuclear luminosities can bereadily supplied through local mass loss from evolved stars and Bondiaccretion of hot gas, without appealing to additional fueling mechanismssuch as angular momentum transport on larger scales. Indeed, we arguethat the fuel reservoir generated by local processes should produce farmore active nuclei than is actually observed. This genericluminosity-deficit problem suggests that the radiative efficiency inthese systems is much less than the canonical value of 0.1 fortraditional optically thick, geometrically thin accretion disks. Theobserved values of L bol/L Edd, all substantiallybelow unity, further support the hypothesis that massive BHs in mostnearby galaxies reside in a low or quiescent state, sustained byaccretion through a radiatively inefficient mode.
| Structure and Formation of Elliptical and Spheroidal Galaxies
New surface photometry of all known elliptical galaxies in the Virgocluster is combined with published data to derive composite profiles ofbrightness, ellipticity, position angle, isophote shape, and color overlarge radius ranges. These provide enough leverage to show thatSérsic log I vprop r 1/n functions fit the brightnessprofiles I(r) of nearly all ellipticals remarkably well over largedynamic ranges. Therefore, we can confidently identify departures fromthese profiles that are diagnostic of galaxy formation. Two kinds ofdepartures are seen at small radii. All 10 of our ellipticals with totalabsolute magnitudes MVT <= –21.66 have cuspycores—"missing light"—at small radii. Cores are well knownand naturally scoured by binary black holes (BHs) formed indissipationless ("dry") mergers. All 17 ellipticals with –21.54<= MVT <= –15.53 do not have cores. We find a newdistinct component in these galaxies: all coreless ellipticals in oursample have extra light at the center above the inward extrapolation ofthe outer Sérsic profile. In large ellipticals, the excess lightis spatially resolved and resembles the central components predicted innumerical simulations of mergers of galaxies that contain gas. In thesimulations, the gas dissipates, falls toward the center, undergoes astarburst, and builds a compact stellar component that, as in ourobservations, is distinct from the Sérsic-function main body ofthe elliptical. But ellipticals with extra light also containsupermassive BHs. We suggest that the starburst has swamped corescouring by binary BHs. That is, we interpret extra light components asa signature of formation in dissipative ("wet") mergers.Besides extra light, we find three new aspects to the ("E-E") dichotomyinto two types of elliptical galaxies. Core galaxies are known to beslowly rotating, to have relatively anisotropic velocity distributions,and to have boxy isophotes. We show that they have Sérsic indicesn > 4 uncorrelated with MVT . They also areα-element enhanced, implying short star-formation timescales. Andtheir stellar populations have a variety of ages but mostly are veryold. Extra light ellipticals generally rotate rapidly, are moreisotropic than core Es, and have disky isophotes. We show that they haven sime 3 ± 1 almost uncorrelated with MVT and youngerand less α-enhanced stellar populations. These are new clues togalaxy formation. We suggest that extra light ellipticals got their lowSérsic indices by forming in relatively few binary mergers,whereas giant ellipticals have n > 4 because they formed in largernumbers of mergers of more galaxies at once plus later heating duringhierarchical clustering.We confirm that core Es contain X-ray-emitting gas whereas extra lightEs generally do not. This leads us to suggest why the E-E dichotomyarose. If energy feedback from active galactic nuclei (AGNs) requires a"working surface" of hot gas, then this is present in core galaxies butabsent in extra light galaxies. We suggest that AGN energy feedback is astrong function of galaxy mass: it is weak enough in small Es not toprevent merger starbursts but strong enough in giant Es and theirprogenitors to make dry mergers dry and to protect old stellarpopulations from late star formation.Finally, we verify that there is a strong dichotomy between ellipticaland spheroidal galaxies. Their properties are consistent with ourunderstanding of their different formation processes: mergers forellipticals and conversion of late-type galaxies into spheroidals byenvironmental effects and by energy feedback from supernovae.In an appendix, we develop machinery to get realistic error estimatesfor Sérsic parameters even when they are strongly coupled. And wediscuss photometric dynamic ranges necessary to get robust results fromSérsic fits.Based in part on observations obtained with the Hobby-Eberly Telescope(HET), which is a joint project of the University of Texas at Austin,the Pennsylvania State University, Stanford University,Ludwig-Maximilians-Universität München, andGeorg-August-Universität Göttingen.
| The stellar content of low redshift radio galaxies from near-infrared spectroscopy
Context: We present medium spectral resolution near-infrared (NIR)HK-band spectra for eight low redshift (z < 0.06) radio galaxies tostudy the NIR stellar properties of their host galaxies. The sample wasselected from a radio galaxy sample imaged previously in the B- andR-band. They were found to be bluer than inactive elliptical galaxies,possibly indicating a recent star formation episode. As a homogeneouscomparison sample, we used nine inactive elliptical galaxies that wereobserved with the same telescope and detector with similar resolutionand wavelength range. Aims: The aim of the study is, by using theadvantage of NIR absorption features, to compare the NIR spectralproperties of radio galaxies to those of inactive early-type galaxiesand, furthermore, produce the first NIR HK-band spectra for low redshiftradio galaxies. Methods: For the radio galaxy and inactive ellipticalsamples, spectral indices of several diagnostic absorption features,namely SiI(1.589 μm), CO(1.619 μm) in the H-band and NaI(2.207μm), CaI(2.263 μm), CO(> 2.29 μm) in the K-band, weremeasured. The strength of absorption lines depends on the luminosityand/or temperature of stars and, therefore, spectral indices can be usedto trace the stellar population of galaxies. To characterize the age ofthe populations, the measured EWs of the absorption features were fittedwith the corresponding theoretical evolutionary curves of the EWscalculated by the stellar synthesis model. Results: On average, EW(CO2.29) of radio galaxies is somewhat greater than that of inactiveellipticals. Most likely, EW(CO 2.29) is not significantly affected bydilution, thus indicating that elliptical galaxies containing AGN are ina different stage in their evolution than inactive ellipticals. This isalso supported by comparing other NIR absorption line features, such asCaI and NaI, with each other. Based on the theoretical evolutionarycurves of EWs, absorption features are consistent with the intermediateage stellar population, suggesting that host galaxies contain both oldand intermediate age components. An intermediate age population is alsoconsistent with previous optical spectroscopy studies, which have shownevidence of an intermediate age (~2 Gyr) stellar population in radiogalaxies, and also in some of the early-type galaxies. Conclusions: Anintermediate stellar population component indicates that radio galaxieshave experienced a star formation epoch relatively recently. Theexistence of an intermediate stellar population is a link between thestar formation episode, possibly induced by an interaction or mergingevent, and triggering of nuclear activity.
| Evidence of Star Formation in Local S0 Galaxies: Spitzer Observations of the Sauron Sample
We discuss infrared Spitzer observations of early-type galaxies in theSAURON sample at 24, 60, and 170 μm. When compared with 2MASS Ks bandluminosities, lenticular (S0) galaxies exhibit a much wider range ofmid-to-far-infrared luminosities than elliptical (E) galaxies. Mid- andfar-infrared emission from E galaxies is a combination of circumstellaror interstellar emission from local mass-losing red giant stars, dustbuoyantly transported from the galactic cores into distant hotinterstellar gas and dust accreted from the environment. The source ofmid- and far-IR emission in S0 galaxies is quite different and isconsistent with low levels of star formation, 0.02-0.2 Msun yr–1, in cold, dusty gaseous disks. Theinfrared 24 μm-70 μm color is systematically lower for (mostly S0)galaxies with known molecular disks. Our observations support theconjecture that cold dusty gas in some S0 galaxies is created by stellarmass loss at approximately the same rate that it is consumed by starformation, so the mass depletion of these disks by star formation willbe slow. Unlike E galaxies, the infrared luminosities of S0 galaxiescorrelate with both the mass of molecular gas and the stellar Hβspectral index, and all are related to the recent star formation rate(SFR). However, star formation rates estimated from theHβ-emission-line luminosities L Hβ in SAURON S0galaxies are generally much smaller. Since L Hβ does notcorrelate with 24 μm emission from dust heated by young stars,optical emission lines appear to be a poor indicator of SFRs in SAURONS0 galaxies. The absence of Hβ emission may be due to a relativeabsence of OB stars in the initial mass function or to dust absorptionof Hβ emission lines.
| Early-type galaxies in the near-infrared: 1.5-2.4 μm spectroscopy
Context: Near-infrared (hereafter NIR) data may provide complementaryinformation to the traditional optical population synthesis analysis ofunresolved stellar populations because the spectral energy distributionof the galaxies in the 1-2.5 μm range is dominated by different typesof stars than at optical wavelengths. Furthermore, NIR data are lessaffected by dust absorption and hence could constrain the stellarpopulations in dust-obscured galaxies. Aims: We attempt to developobservational constraints on the stellar populations of unresolvedstellar systems in the NIR. Methods: To achieve this goal, we requirebenchmark NIR spectra of “simple” early-type galaxies, totest and calibrate the outputs of population synthesis models. Weobtained low-resolution (R ~ 1000) long-slit spectra between 1.5 and 2.4μm for 14 nearby early-type galaxies using SofI at the ESO 3.5-m NewTechnology Telescope and higher resolution (R ~ 3000) long-slit spectra,centered on Mgi at ~1.51 μm for a heterogeneous sample of 5 nearbygalaxies observed with ISAAC at Antu, one of the 8.2-m ESO Very LargeTelescope. Results: We defined spectral indices corresponding to CO,Nai, Cai and Mgi absorption lines and measured their strengths in thegalaxies spectrum. We defined a new global NIR metallicity index,suitable for abundance measurements in low-resolution spectra. Finally,we created an average-combined NIR spectrum of an early-type galaxy,from a homogeneous subset of our data set. Conclusions: The NIR galaxyspectra are similar to each other and some of the line index strengthscorrelate with both the iron abundance [Fe/H] and optical metal lineindices of the galaxies. The data suggest that the NIR metal features,in combination with a hydrogen absorption feature, may break theage-metallicity degeneracy in a similar way the Mg and Fe features inthe rest-frame optical wavelength range.Based on observations made with ESO Telescopes at the La Silla andParanal Observatory under programmes 69.B-0311 and 077.B-0163. FullTable 5 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/497/41
| Dissipation and Extra Light in Galactic Nuclei. II. "Cusp" Ellipticals
We study the origin and properties of "extra" or "excess" central lightin the surface brightness profiles of cusp or power-law ellipticalgalaxies. Dissipational mergers give rise to two-component profiles: anouter profile established by violent relaxation acting on stars alreadypresent in the progenitor galaxies prior to the final stages of themerger, and an inner stellar population comprising the extra light,formed in a compact central starburst. By combining a large set ofhydrodynamical simulations with data that span a broad range of profilesat various masses, we show that observed cusp ellipticals appearconsistent with the predicted "extra light" structure, and we use oursimulations to motivate a two-component description of the observationsthat allows us to examine how the properties and mass of this componentscale with, e.g., the mass, gas content, and other properties of thegalaxies. We show how to robustly separate the physically meaningfulextra light and outer, violently relaxed profile, and demonstrate thatthe observed cusps and "extra light" are reliable tracers of the degreeof dissipation in the spheroid-forming merger. We show that the typicaldegree of dissipation is a strong function of stellar mass, roughlytracing the observed gas fractions of disks of the same mass over theredshift range z ~ 0-2. We demonstrate a correlation between thestrength of this component and effective radius at fixed mass, in thesense that systems with more dissipation are more compact, sufficient toexplain the discrepancy in the maximum phase-space and mass densities ofellipticals and their progenitor spirals. We show that the outer shapeof the light profile in simulated and observed systems (when fit toproperly account for the central light) does not depend on mass, with amean outer Sérsic index ~2.5. We also explore how this relatesto, e.g., the shapes, kinematic properties, and stellar populationgradients of ellipticals. Extra light contributes to making remnantsrounder and diskier, and imprints stellar population gradients.Simulations with the gas content needed to match observed surfacebrightness profiles reproduce the observed age, metallicity, and colorgradients of cusp ellipticals, and we make predictions for how these canbe used as tracers of the degree of dissipation in spheroid formation.
| The ACS Fornax Cluster Survey. V. Measurement and Recalibration of Surface Brightness Fluctuations and a Precise Value of the Fornax-Virgo Relative Distance
We present (g 475 – z 850) color and z850-band surface brightness fluctuations (SBFs) measurementsfor 43 early-type galaxies in the Fornax cluster imaged with the HubbleSpace Telescope Advanced Camera for Surveys. These are combined with ourearlier measurements for Virgo cluster galaxies to derive a revised,nonlinear calibration of the z 850-band SBF absolutemagnitude \overline{M}_z as a function of (g 475 – z850) color, valid for the AB color range 0.8 < (g475 – z 850) < 1.6. In all, we tabulaterecalibrated SBF distances for 134 galaxies in Virgo, Fornax, the VirgoW' group, and NGC 4697 in the Virgo Southern Extension. The calibrationprocedure yields a highly precise relative distance modulus for Fornaxwith respect to Virgo of Δ(m – M) FV = 0.42± 0.03 mag, or a distance ratio dF /dV =1.214 ± 0.017. The resulting Fornax distance modulus is (m– M)For = 31.51 ± 0.03 ± 0.15 mag,corresponding to dF = 20.0 ± 0.3 ± 1.4 Mpc,where the second set of error bars reflects the total systematicuncertainty from our assumed Virgo distance of 16.5 Mpc. The rmsdistance scatter for the early-type Fornax cluster galaxies isσ d = 0.49+0.11 –0.15 Mpc,or a total line-of-sight depth of 2.0+0.4–0.6 Mpc, consistent with its compact appearance on thesky. This translates to a depth scatter smaller than the intrinsic, or"cosmic," scatter σcos in the SBF calibration, unlikethe case for the larger Virgo cluster. As a result, we are able to placethe first tight constraints on the value of σcos. Wefind σcos = 0.06 ± 0.01 mag, with a firm upperlimit of σcos < 0.08 mag, for the subsample ofgalaxies with (g 475 – z 850)>1.02, butit is about twice as large for bluer galaxies. We also present analternative SBF calibration based on the "fluctuation count" parameter\overline{N}= \overline{m}- m_tot, a proxy for galaxy mass. This gives aconsistent relative distance but with larger intrinsic scatter, and weadopt the result from the calibration on (g 475 – z850) because of its basis in stellar population propertiesalone. Finally, we find no evidence for systematic trends of the galaxydistances with position or velocity (e.g., no current infall); theFornax cluster appears both compact and well virialized.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| An optimized H? index for disentangling stellar population ages
We have defined a new H? absorption index definition,H?o, which has been optimized as an age indicator forold and intermediate age stellar populations. Rather than using stellarspectra, we employed for this purpose a library of stellar populationspectral energy distributions of different ages and metallicities atmoderately high resolution. H?o provides us withimproved abilities for lifting the age-metallicity degeneracy affectingthe standard H? Lick index definition. The new index, which hasalso been optimized against photon noise and velocity dispersion, isfully characterized with wavelength shift, spectrum shape, dustextinction and [?/Fe] abundance ratio effects. H?orequires spectra of similar qualities as those commonly used formeasuring the standard H? Lick index definition. Aiming atillustrating the use and capabilities of H?o as an ageindicator we apply it to Milky Way globular clusters and to a wellselected sample of early-type galaxies covering a wide range in mass.The results shown here are particularly useful for applying this indexand understand the involved uncertainties.
| The ACS Virgo Cluster Survey XVI. Selection Procedure and Catalogs of Globular Cluster Candidates
We present catalogs of globular cluster candidates for the 100 galaxiesof the Advanced Camera for Surveys Virgo Cluster Survey, a large programto carry out imaging of early-type members of the Virgo Cluster usingthe Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. Wedescribe the procedure used to select bona fide globular clustercandidates out of the full list of detections based on model-basedclustering methods with the use of expected contamination catalogsconstructed using blank field observations and which are customized foreach galaxy. We also present the catalogs of expected contaminants foreach of our target galaxies. For each detected source we measure itsposition, magnitudes in the F475W (≈ Sloan g) and F850LP (≈ Sloanz) bandpasses, and half-light radii by fitting point-spread functionconvolved King models to the observed light distribution. Thesemeasurements are presented for 20,375 sources, of which 12,763 arelikely to be globular clusters. Finally, we detail the calculation ofthe aperture corrections adopted for the globular cluster photometry.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| Low-Mass X-Ray Binaries and Globular Clusters in Early-Type Galaxies. II. Globular Cluster Candidates and Their Mass-Metallicity Relation
We present an astrometry and photometry catalogue of globular cluster(GC) candidates detected with the Hubble Space Telescope Wide FieldPlanetary Camera 2 in a sample of 19 early-type galaxies, appropriatefor comparison with the low-mass X-ray binary populations observed withChandra. In a companion paper, we present the Chandra data andinvestigate the relation between these populations. We demonstrate that,although there is little evidence of a color-magnitude correlation forthe GCs, after estimating mass and metallicity from the photometry underthe assumption of a single-age simple stellar population, there is asignificant positive correlation between mass and metallicity. Weconstrained [Z/H] = (-2.1 ± 0.2) + (0.25 ±0.04)log10M, with a 1σ intrinsic scatter of 0.62 dex inmetallicity. If GCs are bimodal in metallicity, this relation isconsistent with recent suggestions of a mass-metallicity relation onlyfor metal-poor clusters. Adopting a new technique to fit the GCluminosity function (GCLF) accounting for incompleteness and theEddington bias, we compute the V-band local GC specific frequency(SN ) and specific luminosity (SL ) of eachgalaxy. We show that SL is the more robust measure of therichness of a GC population where a significant fraction is undetecteddue to source detection incompleteness. We find that the absolutemagnitude of the GCLF turnover exhibits intrinsic scatter from galaxy togalaxy of ~0.3 mag (1σ), limiting its accuracy as a standarddistance measure.
| Low-Mass X-Ray Binaries and Globular Clusters in Early-Type Galaxies. I. Chandra Observations
We present a Chandra survey of LMXBs in 24 early-type galaxies.Correcting for detection incompleteness, the X-ray luminosity function(XLF) of each galaxy is consistent with a power law with negativelogarithmic differential slope, β~2.0. However, β stronglycorrelates with incompleteness, indicating the XLF flattens atlow-LX. The composite XLF is well fitted by a power law witha break at (2.21+0.65-0.56)×1038ergs s-1 and β=1.40+0.10-0.13 and2.84+0.39-0.30 below and above it, respectively.The break is close to the Eddington limit for a 1.4 Msolarneutron star, but the XLF shape rules out its representing the divisionbetween neutron star and black hole systems. Although the XLFs aresimilar, we find evidence of some variation between galaxies. Thehigh-LX XLF slope does not correlate with age, but maycorrelate with [α/Fe]. Considering only LMXBs withLX>1037 ergs s-1, matching the LMXBswith globular clusters (GCs) identified in HST observations of 19 of thegalaxies, we find the probability a GC hosts an LMXB is proportional toLαGCZγFe whereα=1.01+/-0.19 and γ=0.33+/-0.11. Correcting for GCluminosity and color effects, and detection incompleteness, we find noevidence that the fraction of LMXBs withLX>1037 ergs s-1 in GCs (40%), orthe fraction of GCs hosting LMXBs (~6.5%) varies between galaxies. Thespatial distribution of LMXBs resembles that of GCs, and the specificfrequency of LMXBs is proportional to the GC specific luminosity,consistent with the hypothesis that all LMXBs form in GCs. If the LMXBlifetime is τL and the duty cycle is Fd, ourresults imply ~1.5(τL/108yr)-1F-1d LMXBs are formed per gigayearper GC, and we place an upper limit of one active LMXB in the field per3.4×109 Lsolar of V-band luminosity.
| Populating the Galaxy Velocity Dispersion - Supermassive Black Hole Mass Diagram: A Catalogue of (Mbh, σ) Values
An updated catalogue of 76 galaxies, with direct measurements ofsupermassive black-hole mass (Mbh) plus, when available, thecentral velocity dispersion (σ0) of their host bulge isprovided. Fifty of these mass measurements are considered reliable,while the others remain somewhat uncertain at this time. An additionalnine stellar systems, including one stellar cluster and three globularclusters, are listed as hosting potential intermediate mass black holes<106 Msolar. With this larger data set, thedemographics within the Mbh-σ0 diagram arebriefly explored. Many barred galaxies are shown to be offset from theMbh-σ0 relation defined by the non-barredgalaxies, in the sense that their velocity dispersions are too high.Furthermore, including 88 AGN with black-hole mass estimates fromreverberation mapping studies, we speculate that barred AGN may followthis same general trend. We also show that some AGN withσ0 < 100 km s-1 tend to reside up to(~0.6 dex) ~1.0 dex above the (barless)Mbh-σ0 relation. Finally, it is shown that`core galaxies' appear not to define an additional subdivision of theMbh-σ0 diagram, although improved methodsfor measuring σ0 values may be valuable.
| The Hot Interstellar Medium in Normal Elliptical Galaxies. III. The Thermal Structure of the Gas
This is the third paper in a series analyzing X-ray emission from thehot interstellar medium in a sample of 54 normal elliptical galaxiesobserved by Chandra. We focus on a subset of 36 galaxies with sufficientsignal to compute radial temperature profiles. We distinguish fourqualitatively different types of profile: positive gradient (outwardlyrising), negative gradients (falling), quasi-isothermal (flat), andhybrid (falling at small radii and rising at larger radii). We measurethe mean logarithmic temperature gradients in two radial regions: from 0to 2 J-band effective radii RJ (excluding the central pointsource), and from 2 to 4 RJ. We find the outer gradient to beuncorrelated with intrinsic host galaxy properties, but stronglyinfluenced by the environment: galaxies in low-density environments tendto show negative outer gradients, while those in high-densityenvironments show positive outer gradients, suggesting the influence ofcircumgalactic hot gas. The inner temperature gradient, however, islargely unaffected by the environment, but strongly correlated withintrinsic host galaxy characteristics: negative inner gradients are morecommon for smaller, optically faint, low radio luminosity galaxies,whereas positive gradients are found in bright galaxies with strongerradio sources. There is no evidence for bimodality in the distributionof inner or outer gradients. We propose three scenarios to explain theinner temperature gradients: (1) weak AGNs heat the ISM locally, whilehigher luminosity AGNs heat the system globally through jets inflatingcavities at larger radii; (2) the onset of negative inner gradientsindicates a declining importance of AGN heating relative to othersources, such as compressional heating or supernovae; or (3) the varietyof temperature profiles are snapshots of different stages of atime-dependent flow, cyclically reversing the temperature gradient overtime.
| The correlation of black hole mass with metallicity index of host spheroid
We investigate the correlation between the mass of the supermassiveblack holes (SMBHs) and metal abundance, using existing data sets. TheSMBH mass Mbh is well correlated with integrated stellarfeature of Mgb. For 28 galaxies, the best-fitting Mbh-Mgbrelation has a small scatter, which is an equivalent level with otherwell-known relation, such as a correlation between the stellar velocitydispersion and the mass. An averaged iron index alsopositively correlates with Mbh, but the best-fittingMbh- relation has a larger scatter. The differencecomes from the synthesis and evolution mechanisms, and may be importantfor the SMBH and star formation history in the host spheroid.
| The SAURON project - XII. Kinematic substructures in early-type galaxies: evidence for discs in fast rotators
We analysed two-dimensional maps of 48 early-type galaxies obtained withthe SAURON and OASIS integral-field spectrographs using kinemetry, ageneralization of surface photometry to the higher order moments of theline-of-sight velocity distribution (LOSVD). The maps analysed include:reconstructed image, mean velocity, velocity dispersion, h3and h4 Gauss-Hermite moments. Kinemetry is a good method torecognize structures otherwise missed by using surface photometry, suchas embedded discs and kinematic subcomponents. In the SAURON sample, wefind that 31 per cent of early-type galaxies are single componentsystems. 91 per cent of the multicomponents systems have two kinematicsubcomponents, the rest having three. In addition, 29 per cent ofgalaxies have kinematically decoupled components, nuclear componentswith significant kinematic twists. We differentiate between slow andfast rotators using velocity maps only and find that fast-rotatinggalaxies contain discs with a large range in mass fractions to the mainbody. Specifically, we find that the velocity maps of fast rotatorsclosely resemble those of inclined discs, except in the transitionregions between kinematic subcomponents. This deviation is measured withthe kinemetric k5/k1 ratio, which is large andnoisy in slow rotators and about 2 per cent in fast rotators. In termsof E/S0 classification, this means that 74 per cent of Es and 92 percent of S0s have components with disc-like kinematics. We suggest thatdifferences in k5/k1 values for the fast and slowrotators arise from their different intrinsic structure which isreflected on the velocity maps. For the majority of fast rotators, thekinematic axial ratios are equal to or less than their photometric axialratios, contrary to what is predicted with isotropic Jeans models viewedat different inclinations. The position angles of fast rotators areconstant, while they vary abruptly in slow rotators. Velocity dispersionmaps of face-on galaxies have shapes similar to the distribution oflight. Velocity dispersion maps of the edge-on fast rotators and allslow rotators show differences which can only be partially explainedwith isotropic models and, in the case of fast rotators, often requireadditional cold components. We constructed local (bin-by-bin)h3-V/σ and h4-V/σ diagrams from SAURONobservations. We confirm the classical anticorrelation of h3and V/σ, but we also find that h3 is almost zero insome objects or even weakly correlated with V/σ. The distributionof h4 for fast and slow rotators is mildly positive onaverage. In general, fast rotators contain flattened componentscharacterized by a disc-like rotation. The difference between slow andfast rotators is traceable throughout all moments of the LOSVD, withevidence for different intrinsic shapes and orbital contents and, hence,likely different evolutionary paths.
| Measuring the inclination and mass-to-light ratio of axisymmetric galaxies via anisotropic Jeans models of stellar kinematics
We present a simple and efficient anisotropic generalization of thesemi-isotropic (two-integral) axisymmetric Jeans formalism, which isused to model the stellar kinematics of galaxies. The following isassumed: (i) a constant mass-to-light ratio (M/L) and (ii) a velocityellipsoid that is aligned with cylindrical coordinates (R, z) andcharacterized by the classic anisotropy parameter . Our simple modelsare fit to SAURON integral-field observations of the stellar kinematicsfor a set of fast-rotator early-type galaxies. With only two freeparameters (βz and the inclination), the modelsgenerally provide remarkably good descriptions of the shape of the first(V) and second () velocity moments, once a detailed description of thesurface brightness is given. This is consistent with previous findingson the dynamical structure of these objects. With the observationallymotivated assumption that βz >~ 0, the method is ableto recover the inclination. The technique can be used to determine thedynamical M/L and angular momenta of early-type fast-rotators and spiralgalaxies, especially when the quality of the data does not justify moresophisticated modelling approaches. This formalism allows for theinclusion of dark matter, supermassive black holes, spatially varyinganisotropy and multiple kinematic components.
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