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The Calibration of Monochromatic Far-Infrared Star Formation Rate Indicators
Spitzer data at 24, 70, and 160 ?m and ground-based H? imagesare analyzed for a sample of 189 nearby star-forming and starburstgalaxies to investigate whether reliable star formation rate (SFR)indicators can be defined using the monochromatic infrared dust emissioncentered at 70 and 160 ?m. We compare recently published recipes forSFR measures using combinations of the 24 ?m and observed H?luminosities with those using 24 ?m luminosity alone. From thesecomparisons, we derive a reference SFR indicator for use in ouranalysis. Linear correlations between SFR and the 70 ?m and 160 ?mluminosity are found for L(70) >~ 1.4 × 1042 ergs-1 and L(160) >~ 2 × 1042 ergs-1, corresponding to SFR >~ 0.1-0.3 Msun yr-1, and calibrations of SFRs based onL(70) and L(160) are proposed. Below those two luminosity limits, therelation between SFR and 70 ?m (160 ?m) luminosity is nonlinearand SFR calibrations become problematic. A more important limitation isthe dispersion of the data around the mean trend, which increases forincreasing wavelength. The scatter of the 70 ?m (160 ?m) dataaround the mean is about 25% (factor ~2) larger than the scatter of the24 ?m data. We interpret this increasing dispersion as an effect ofthe increasing contribution to the infrared emission of dust heated bystellar populations not associated with the current star formation.Thus, the 70 (160) ?m luminosity can be reliably used to trace SFRsin large galaxy samples, but will be of limited utility for individualobjects, with the exception of infrared-dominated galaxies. Thenonlinear relation between SFR and the 70 and 160 ?m emission atfaint galaxy luminosities suggests a variety of mechanisms affecting theinfrared emission for decreasing luminosity, such as increasingtransparency of the interstellar medium, decreasing effective dusttemperature, and decreasing filling factor of star-forming regionsacross the galaxy. In all cases, the calibrations hold for galaxies withoxygen abundance higher than roughly 12 +log(O/H) ~ 8.1. At lowermetallicity, the infrared luminosity no longer reliably traces the SFRbecause galaxies are less dusty and more transparent.Based on observations obtained with the Spitzer Space Telescope, whichis operated by JPL, CalTech, under NASA Contract 1407.
| 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.
| Optical Spectroscopy and Nebular Oxygen Abundances of the Spitzer/SINGS Galaxies
We present intermediate-resolution optical spectrophotometry of 65galaxies obtained in support of the Spitzer Infrared Nearby GalaxiesSurvey (SINGS). For each galaxy we obtain a nuclear, circumnuclear, andsemi-integrated optical spectrum designed to coincide spatially withmid- and far-infrared spectroscopy from the Spitzer Space Telescope. Wemake the reduced, spectrophotometrically calibrated one-dimensionalspectra, as well as measurements of the fluxes and equivalent widths ofthe strong nebular emission lines, publically available. We use opticalemission-line ratios measured on all three spatial scales to classifythe sample into star-forming, active galactic nuclei (AGNs), andgalaxies with a mixture of star formation and nuclear activity. We findthat the relative fraction of the sample classified as star formingversus AGN is a strong function of the integrated light enclosed by thespectroscopic aperture. We supplement our observations with a largedatabase of nebular emission-line measurements of individual H IIregions in the SINGS galaxies culled from the literature. We use theseancillary data to conduct a detailed analysis of the radial abundancegradients and average H II-region abundances of a large fraction of thesample. We combine these results with our new integrated spectra toestimate the central and characteristic (globally averaged) gas-phaseoxygen abundances of all 75 SINGS galaxies. We conclude with an in-depthdiscussion of the absolute uncertainty in the nebular oxygen abundancescale.
| Diffuse Tidal Structures in the Halos of Virgo Ellipticals
We use deep V-band surface photometry of five of the brightestelliptical galaxies in the Virgo Cluster to search for diffuse tidalstreams, shells, and plumes in their outer halos (r>50 kpc). We fitand subtract elliptical isophotal models from the galaxy images toreveal a variety of substructure, with surface brightnesses in the range? V = 26-29 mag arcsec-2. M49 possessesan extended, interleaved shell system reminiscent of the radialaccretion of a satellite companion, while M89's complex system of shellsand plumes suggests a more complicated accretion history involvingeither multiple events or a major merger. M87 has a set of longstreamers as might be expected from stripping of low luminosity dwarfson radial orbits in Virgo. M86 also displays a number of small streamsindicative of stripping of dwarf companions, but these comprise muchless luminosity than those of M87. Only M84 lacks significant tidalfeatures. We quantify the photometric properties of these structures,and discuss their origins in the context of each galaxy's environmentand kinematics within the Virgo Cluster.
| The Accretion of Dwarf Galaxies and Their Globular Cluster Systems
The question of where the low-metallicity globular clusters inearly-type galaxies came from has profound implications for theformation of those galaxies. Our work supports the idea that themetal-poor globular cluster systems of giant early-type galaxies formedin dwarf galaxies that have been subsumed by the giants. To support thishypothesis, two linear relations, one involving globular clustermetallicity versus host galaxy luminosity and one involving metallicityversus velocity dispersion were studied. Tentatively, these relationsshow that the bright ellipticals do not obey the same trend as thedwarfs, suggesting that the low-metallicity globular clusters did notform within their parent bright ellipticals.
| A Relationship Between AGN Jet Power and Radio Power
Using Chandra X-ray and Very Large Array radio data, we investigate thescaling relationship between jet power, P jet, andsynchrotron luminosity, P radio. We expand the samplepresented in Bîrzan et al. to lower radio power by incorporatingmeasurements for 21 giant elliptical galaxies (gEs) to determine if theBîrzan et al. P jet-P radio scalingrelations are continuous in form and scatter from gEs up to brightestcluster galaxies. We find a mean scaling relation of P jet? 5.8 × 1043(Pradio/1040)0.70 ergs–1 which is continuous over ~6-8 decades in Pjet and P radio with a scatter of ? 0.7 dex.Our mean scaling relationship is consistent with the model presented inWillott et al. if the typical fraction of lobe energy in non-radiatingparticles to that in relativistic electrons is gsim100. We identifyseveral gEs whose radio luminosities are unusually large for their jetpowers and have radio sources which extend well beyond the densest partsof their X-ray halos. We suggest that these radio sources are unusuallyluminous because they were unable to entrain appreciable amounts of gas.
| Cosmic Evolution of Size and Velocity Dispersion for Early-type Galaxies
Massive (stellar mass M sstarf >~ 3 ×1010 M sun), passively evolving galaxies atredshifts z >~ 1 exhibit on average physical sizes smaller, byfactors ?3, than local early-type galaxies (ETGs) endowed with thesame stellar mass. Small sizes are in fact expected on theoreticalgrounds, if dissipative collapse occurs. Recent results show that thesize evolution at z <~ 1 is limited to less than 40%, while most ofthe evolution occurs at z >~ 1, where both compact and alreadyextended galaxies are observed and the scatter in size is remarkablylarger than it is locally. The presence at high redshift of asignificant number of ETGs with the same size as their localcounterparts, as well as ETGs with quite small size (lsim1/10 of thelocal one), points to a timescale for reaching the new, expandedequilibrium configuration of less than the Hubble time tH(z). We demonstrate that the projected mass of compact, high-redshiftgalaxies and that of local ETGs within the same physical radius, thenominal half-luminosity radius of high-redshift ETGs, differsubstantially in that the high-redshift ETGs are on averagesignificantly denser. This result suggests that the physical mechanismresponsible for the size increase should also remove mass from centralgalaxy regions (r <~ 1 kpc). We propose that quasar activity, whichpeaks at redshift z ~ 2, can remove large amounts of gas from centralgalaxy regions on a timescale shorter than the triggering a puffing upof the stellar component at constant stellar mass (or a timescale on theorder of the dynamical one); in this case, the size increase goestogether with a decrease in the central mass. The size evolution isexpected to parallel that of the quasars and the inverse hierarchy, ordownsizing, seen in the quasar evolution is mirrored in the sizeevolution. Exploiting the virial theorem, we derive the relation betweenthe stellar velocity dispersion of ETGs and the characteristic velocityof their hosting halos at the time of formation and collapse. Bycombining this relation with the halo formation rate at z >~ 1, wepredict the local velocity dispersion distribution function. Oncomparing it to the observed one, we show that velocity dispersionevolution of massive ETGs is fully compatible with the observed averageevolution in size at constant stellar mass. Less massive ETGs (withstellar masses M sstarf <~ 3 × 1010 Msun) are expected to evolve less both in size and in velocitydispersion, because their evolution is essentially determined bysupernova feedback, which cannot yield winds as powerful as thosetriggered by quasars. The differential evolution is expected to leaveimprints in the size versus luminosity/mass, velocity dispersion versusluminosity/mass, and central black hole mass versus velocity dispersionrelationships, as observed in local 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.
| 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.
| 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.
| Orbital Structure of Merger Remnants. I. Effect of Gas Fraction in Pure Disk Mergers
Since the violent relaxation in hierarchical merging is incomplete,elliptical galaxies retain a wealth of information about their formationpathways in their present-day orbital structure. Recent advances inintegral field spectroscopy, multi-slit infrared spectroscopy, andtriaxial dynamical modeling techniques have greatly improved our abilityto harvest this information. A variety of observational and theoreticalevidence indicates that gas-rich major mergers play an important role inthe formation of elliptical galaxies. We simulate 1:1 disk mergers atseven different initial gas fractions (f gas) ranging from 0%to 40%, using a version of the TreeSPH code Gadget-2 that includesradiative heating and cooling, star formation, and feedback fromsupernovae and active galactic nuclei. We classify the stellar orbits ineach remnant and construct radial profiles of the orbital content,intrinsic shape, and orientation. The dissipationless remnants aretypically prolate-triaxial, dominated by box orbits within rc~ 1.5 Re , and by tube orbits in their outer parts. As fgas increases, the box orbits within rc areincreasingly replaced by a population of short-axis tubes (z-tubes) withnear zero net rotation, and the remnants become progressively moreoblate and round. The long-axis tube (x-tube) orbits are highlystreaming and relatively insensitive to f gas, implying thattheir angular momentum is retained from the dynamically cold initialconditions. Outside rc , the orbital structure is essentiallyunchanged by the gas. For f gas >~ 15%, gas that retainsits angular momentum during the merger re-forms a disk that appears inthe remnants as a highly streaming z-tube population superimposed on thehot z-tube distribution formed by the old stars. In the 15%-20% gasremnants, this population appears as a kinematically distinct core (KDC)within a system that is slowly rotating or dominated by minor-axisrotation. These remnants show an interesting resemblance, in both theirvelocity maps and intrinsic orbital structure, to the KDC galaxy NGC4365. At 30%-40% gas, the remnants are rapidly rotating, with sharpembedded disks on ~1 Re scales. We predict a characteristic,physically intuitive orbital structure for 1:1 disk merger remnants,with a distinct transition between 1 and 3 Re that will bereadily observable with combined data from the two-dimensionalkinematics surveys SAURON and SMEAGOL. Our results illustrate the powerof direct comparisons between N-body simulations and dynamical models ofobserved systems to constrain theories of galaxy formation.
| X-ray Properties of Young Early-type Galaxies. I. X-ray Luminosity Function of Low-mass X-ray Binaries
We have compared the combined X-ray luminosity function (XLF) oflow-mass X-ray binaries (LMXBs) detected in Chandra observations ofyoung, post-merger elliptical galaxies with that of typical oldelliptical galaxies. We find that the XLF of the "young" sample does notpresent the prominent high-luminosity break at LX > 5× 1038 erg s-1 found in the oldelliptical galaxy XLF. The "young" and "old" XLFs differ with a 3?statistical significance (with a probability less than 0.2% that theyderive from the same underlying parent distribution). Young ellipticalgalaxies host a larger fraction of luminous LMXBs (LX > 5× 1038 erg s-1) than old ellipticalgalaxies and the XLF of the young galaxy sample is intermediate betweenthat of typical old elliptical galaxies and that of star-forminggalaxies. This observational evidence may be related to the lastmajor/minor mergers and the associated star formation.
| Decreased Frequency of Strong Bars in S0 Galaxies: Evidence for Secular Evolution?
Using data from the Near-Infrared S0 Survey of nearby, early-typegalaxies, we examine the distribution of bar strengths in S0 galaxies ascompared to S0/a and Sa galaxies, and as compared to previouslypublished bar strength data for Ohio State University Bright SpiralGalaxy Survey spiral galaxies. Bar strengths based on the gravitationaltorque method are derived from 2.2 ?m Ks -band images fora statistical sample of 138 (98 S0, 40 S0/a,Sa) galaxies having a meantotal blue magnitude lang BT rang <= 12.5 and generallyinclined less than 65°. We find that S0 galaxies have weaker bars onaverage than spiral galaxies in general, even compared to their closestspiral counterparts, S0/a and Sa galaxies. The differences aresignificant and cannot be entirely due to uncertainties in the assumedvertical scale heights or in the assumption of constant mass-to-lightratios. Part of the difference is likely simply due to the dilution ofthe bar torques by the higher mass bulges seen in S0s. If spiralgalaxies accrete external gas, as advocated by Bournaud & Combes,then the fewer strong bars found among S0s imply a lack of gas accretionaccording to this theory. If S0s are stripped former spirals, or elseare evolved from former spirals due to internal secular dynamicalprocesses which deplete the gas as well as grow the bulges, then theweaker bars and the prevalence of lenses in S0 galaxies could furtherindicate that bar evolution continues to proceed during and even aftergas depletion.
| 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
| Detection of a Large-Scale Structure of Intracluster Globular Clusters in the Virgo Cluster
Globular clusters are usually found in galaxies, and they are excellenttracers of dark matter. Long ago it was suggested that intraclusterglobular clusters (IGCs) may exist that are bound to a galaxy clusterrather than to any single galaxy. Here we present a map showing thelarge-scale distribution of globular clusters over the entire Virgocluster. It shows that IGCs are found out to 5 million light years fromthe Virgo center and that they are concentrated in several substructuresthat are much larger than galaxies. These objects might have been mostlystripped off from low-mass dwarf galaxies.
| Demography of Sloan Digital Sky Survey Early-Type Galaxies from the Perspective of Radial Color Gradients
We have investigated the radial g – r color gradients ofearly-type galaxies in the Sloan Digital Sky Survey (SDSS) DR6 in theredshift range 0.00 <= z <= 0.06. The majority of massiveearly-type galaxies show a negative color gradient (red-cored) asgenerally expected for early-type galaxies. On the other hand, roughly30% of the galaxies in this sample show a positive color gradient(blue-cored). These "blue-cored" galaxies often show strong H?absorption-line strengths and/or emission-line ratios that areindicative of the presence of young stellar populations. Combining theoptical data with Galaxy Evolution Explorer (GALEX) ultravioletphotometry, we find that all blue-cored galaxies show UV–opticalcolors that can only be explained by young stellar populations. Thisimplies that most of the residual star formation in early-type galaxiesis centrally concentrated. Blue-cored galaxies are predominantlylow-velocity dispersion systems, and tend to live in lower densityregions. A simple model shows that the observed positive color gradients(blue-cored) are visible only for a billion years after a star formationepisode for the typical strength of recent star formation. The observedeffective radius decreases and the mean surface brightness increases dueto this centrally concentrated star formation episode. As a result, themajority of blue-cored galaxies may lie on different regions in thefundamental plane (FP) from red-cored ellipticals. However, the positionof the blue-cored galaxies on the FP cannot be solely attributed torecent star formation but requires substantially lower velocitydispersion. Our results based on the optical data are consistent withthe residual star formation interpretation of Yi and collaborators whichwas based on GALEX UV data. We conclude that a low-level of residualstar formation persists at the centers of most low-mass early-typegalaxies, whereas massive ones are mostly quiescent systems withmetallicity-driven red cores.
| Spectral Energy Distributions of Weak Active Galactic Nuclei Associated with Low-Ionization Nuclear Emission Regions
We present a compilation of spectral energy distributions (SEDs) of 35weak active galactic nuclei (AGNs) in low-ionization nuclear emissionregions (LINERs) using recent data from the published literature. Wemake use of previously published compilations of data, aftercomplementing and extending them with more recent data. The mainimprovement in the recent data is afforded by high-spatial-resolutionobservations with the Chandra X-Ray Observatory andhigh-spatial-resolution radio observations utilizing a number offacilities. In addition, a considerable number of objects have beenobserved with the Hubble Space Telescope in the near-IR through near-UVbands since the earlier compilations were published. The data includeupper limits resulting from either non-detections or observations at lowspatial resolution that do not isolate the AGN. For the sake ofcompleteness, we also compute and present a number of quantities fromthe data, such as optical-to-X-ray spectral indices(αox), bolometric corrections, bolometric luminosities,Eddington ratios, and the average SED. We anticipate that these datawill be useful for a number of applications. In a companion paper, weuse a subset of these data ourselves to assess the energy budgets ofLINERs.
| The SAURON project - XVI. On the sources of ionization for the gas in elliptical and lenticular galaxies
Following our study on the incidence, morphology and kinematics of theionized gas in early-type galaxies, we now address the question of whatis powering the observed nebular emission. To constrain the likelysources of gas excitation, we resort to a variety of ancillary data wedraw from complementary information on the gas kinematics, stellarpopulations and galactic potential from the SAURON data, and use theSAURON-specific diagnostic diagram juxtaposing the [OIII]?5007/H? and [NI] ??5197, 5200/H? lineratios. We find a tight correlation between the stellar surfacebrightness and the flux of the H? recombination line across oursample, which points to a diffuse and old stellar source as the maincontributor of ionizing photons in early-type galaxies, withpost-asymptotic giant branch (pAGB) stars being still the best candidatebased on ionizing balance arguments. The role of AGN photoionization isconfined to the central 2-3arcsec of an handful of objects with radio orX-ray cores. OB-stars are the dominant source of photoionization in 10per cent of the SAURON sample, whereas for another 10 per cent theintense and highly ionized emission is powered by the pAGB populationassociated to a recently formed stellar subcomponent. Fast shocks arenot an important source of ionization for the diffuse nebular emissionof early-type galaxies since the required shock velocities can hardly beattained in the potential of our sample galaxies. Finally, in the mostmassive and slowly or non-rotating galaxies in our sample, which canretain a massive X-ray halo, the finding of a spatial correlationbetween the hot and warm phases of the interstellar medium (ISM)suggests that the interaction with the hot ISM provides an additionalsource of ionization besides old ultraviolet-bright stars. This is alsosupported by a distinct pattern towards lower values of the[OIII]/H? ratio. These results lead us to investigate the relativerole of stellar and AGN photoionization in explaining the ionized gasemission observed in early-type galaxies by the Sloan Digital Sky Survey(SDSS). By simulating how our sample galaxies would appear if placed atfurther distance and targeted by the SDSS, we conclude that only in veryfew, if any, of the SDSS galaxies which display modest values for theequivalent width of the [OIII] line (less than ~2.4 Å) andlow-ionization nuclear emission-line region like [OIII]/H? valuesthe nebular emission is truly powered by an AGN.
| The Mysterious Merger of NGC 6868 and NGC 6861 in the Telescopium Group
We use Chandra X-ray observations of the hot gas in and around NGC 6868and NGC 6861 in the Telescopium galaxy group (AS0851) to probe theinteraction history between these galaxies. Mean surface brightnessprofiles for NGC 6868 and NGC 6861 are each well described by doubleβ-models, suggesting that they are each the dominant galaxy in agalaxy subgroup about to merge. Surface brightness and temperature mapsof the brightest group galaxy NGC 6868 show a cold front edge ~23 kpc tothe north, and a cool 0.62 keV spiral-shaped tail to the south. Analysisof the temperature and density across the cold front constrains therelative motion between NGC 6868 and the ambient group gas to be at mosttransonic; while the spiral morphology of the tail strongly suggeststhat the cold front edge and tail are the result of gas sloshing due tothe subgroup merger. The cooler central region of NGC 6861 is surroundedby a sheath of hot gas to the east and hot, bifurcated tails of X-rayemission to the west and northwest. We discuss supersonic infall of theNGC 6861 subgroup, sloshing from the NGC 6868 and NGC 6861 subgroupmerger, and AGN heating as possible explanations for these features, anddiscuss possible scenarios that may contribute to the order of magnitudediscrepancy between the Margorrian and black hole mass-σpredictions for its central black hole.
| Nearby early-type galaxies with ionized gas. IV. Origin and powering mechanism of the ionized gas
Aims: A significant fraction of early-type galaxies (ETGs)exhibit emission lines in their optical spectra. We attempt to identifythe producing the emission mechanism and the ionized gas in ETGs, andits connection with the host galaxy evolution. Methods: Weanalyzed intermediate-resolution optical spectra of 65 ETGs, mostlylocated in low density environments and exhibiting spectros-copicdiagnostic lines of ISM from which we had previously derived stellarpopulation properties. To extract the emission lines from the galaxyspectra, we developed a new fitting procedure that accurately subtractsthe underlying stellar continuum, and accounts for the uncertaintiescaused by the age-metallicity degeneracy. Results: Opticalemission lines are detected in 89% of the sample. The incidence andstrength of emission correlate with neither the E/S0 classification, northe fast/slow rotator classification. By means of the classical[OIII]/H? versus [NII]/H? diagnostic diagram, the nucleargalaxy activity is classified such that 72% of the galaxies withemission are LINERs, 9% are Seyferts, 12% are composite/transitionobjects, and 7% are non-classified. Seyferts have youngluminostiy-weighted ages (?5 Gyr), and appear, on average,significantly younger than LINERs and composites. Excluding the Seyfertsfrom our sample, we find that the spread in the ([OIII], H?, or[NII]) emission strength increases with the galaxy central velocitydispersion ?_c. Furthermore, the [NII]/H? ratio tends toincrease with ?_c. The [NII]/H? ratio decreases withincreasing galactocentric distance, indicative of either a decrease inthe nebular metallicity, or a progressive “softening” of theionizing spectrum. The average nebular oxygen abundance is slightly lessthan solar, and a comparison with the results obtained in Paper III fromLick indices shows that it is ?0.2 dex lower than that of stars. Conclusions: The nuclear (r < re/16) emission can beattributed to photoionization by PAGB stars alone only for ?22% ofthe LINER/composite sample. On the other hand, we cannot exclude animportant role of PAGB star photoionization at larger radii. For themajor fraction of the sample, the nuclear emission is consistent withexcitation caused by either a low-accretion rate AGN or fast shocks(200-500 km s-1) in a relatively gas poor environment (n? 100 cm-3), or both. The derived [SII]6717/6731 ratiosare consistent with the low gas densities required by the shock models.The derived nebular metallicities are indicative of either an externalorigin of the gas, or an overestimate of the oxygen yields by SN models.Based on observations obtained at the European Southern Observatory, LaSilla, Chile.Appendix and Tables 2 and 3 are only available inelectronic form at http://www.aanda.org
| An Assessment of the Energy Budgets of Low-Ionization Nuclear Emission Regions
Using the spectral energy distributions (SEDs) of the weak activegalactic nuclei (AGNs) in 35 low-ionization nuclear emission regions(LINERs) presented in a companion paper, we assess whetherphotoionization by the weak AGN can power the emission-line luminositiesmeasured through the large (few-arcsecond) apertures used inground-based spectroscopic surveys. Spectra taken through such aperturesare used to define LINERs as a class and constrain non-stellarphotoionization models for LINERs. Therefore, our energy budget test isa self-consistency check of the idea that the observed emission linesare powered by an AGN. We determine the ionizing luminosities and photonrates by integrating the observed SEDs and by scaling a template SED. Wefind that even if all ionizing photons are absorbed by the line-emittinggas, more than half of the LINERs in this sample suffer from a deficitof ionizing photons. In 1/3 of LINERs the deficit is severe. If only 10%of the ionizing photons are absorbed by the gas, there is an ionizingphoton deficit in 85% of LINERs. We disfavor the possibility thatadditional electromagnetic power, either obscured or emitted in theunobservable far-UV band, is available from the AGN. Therefore, weconsider other power sources such as mechanical heating by compact jetsfrom the AGN and photoionization by either young or old stars.Photoionization by young stars may be important in a small fraction ofcases. Mechanical heating can provide enough power in most cases but itis not clear how this power would be transferred to the emission-linegas. Photoionization by post asymptotic giant branch stars is animportant power source; it provides more ionizing photons than the AGNin more than half of the LINERs and enough ionizing photons to power theemission lines in 1/3 of the LINERs. It appears likely that theemission-line spectra of LINERs obtained from the ground include the sumof emission from different regions where different power sourcesdominate.
| 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.
| A simplified model of ADAF with the jet driven by the large-scale magnetic field
We propose a simplified model of outflow/jet driven by theBlandford-Payne (BP) process from advection-dominated accretionflows (ADAF) and derive the expressions of the BP power and diskluminosity based on the conservation laws of mass, angular momentum andenergy. We fit the 2-10 keV luminosity and kinetic power of 15active galactic nucleus (AGNs) of sub-Eddington luminosity. It is foundthat there exists an anti-correlation between the accretion rate and theadvection parameter, which could be used to explain the correlationbetween Eddington-scaled kinetic power and bolometric luminosity of the15 samples. In addition, the Ledlow-Owen relation for FR I/IIdichotomy is re-expressed in a parameter space consisting of logarithmof dimensionless accretion rate versus that of the BH mass. It turns outthat the FR I/II dichotomy is determined mainly by the dimensionlessaccretion rate, being insensitive to the BH mass. And the dividingaccretion rate is less than the critical accretion rate for ADAFs,suggesting that FR I sources are all in the ADAF state.
| The Unusual X-Ray Morphology of NGC 4636 Revealed by Deep Chandra Observations: Cavities and Shocks Created by Past Active Galactic Nucleus Outbursts
We present Chandra ACIS-I and ACIS-S observations (~200 ks in total) ofthe X-ray luminous elliptical galaxy NGC 4636, located in the outskirtsof the Virgo cluster. A soft band (0.5-2 keV) image shows the presenceof a bright core in the center surrounded by an extended X-ray coronaand two pronounced quasi-symmetric, 8 kpc long, arm-like features. Eachof these features defines the rim of an ellipsoidal bubble. Anadditional bubble-like feature, whose northern rim is located ~2 kpcsouth of the northeastern arm, is detected as well. We present surfacebrightness and temperature profiles across the rims of the bubbles,showing that their edges are sharp and characterized by temperaturejumps of about 20%-25%. Through a comparison of the observed profileswith theoretical shock models, we demonstrate that a scenario where thebubbles were produced by shocks, probably driven by energy depositedoff-center by jets, is the most viable explanation to the X-raymorphology observed in the central part of NGC 4636. As a confirmationto this scenario, radio jets extending toward the bubbles and a centralweak X-ray and radio source are detected and are most likely the signsof active galactic nuclei activity which was more intense in the past. Abright dense core of ~1 kpc radius is observed at the center of NGC4636. A sharp decline in surface brightness from the core to the ambientgas is observed and is not accompanied by a variation in the temperatureand thus could not be in thermal pressure equilibrium. However, thebright core could be a long-lived feature if the radio jets are actingas a balancing factor to thermal pressure or if the bright core isproduced by steep abundance gradients.
| 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 ultraviolet flare at the center of the elliptical galaxy NGC 4278
Context: A large fraction of otherwise normal galaxies shows a weaknuclear activity. One of the signatures of the low-luminosity activegalactic nuclei (LLAGNs) is ultraviolet variability which wasserendipitously discovered in the center of some low-ionization nuclearemission-line region (LINER) galaxies. Aims: There is a pressingneed to acquire better statistics about UV flaring and variability ingalaxy nuclei, both in terms of the number and monitoring of targets.The Science Data Archive of the Hubble Space Telescope was queried tofind all the elliptical galaxies with UV images obtained in differentepochs with the Wide Field Planetary Camera 2 (WFPC2) and possibly withnuclear spectra obtained with the Space Telescope Imaging Spectrograph(STIS) in the region of the Hα emission line. These data werefound only for the elliptical radiogalaxy NGC4278. Methods: The UV flux of the nuclear source of NGC4278 was measured by means of aperture photometry on the WFPC2/F218Wimages obtained between June 1994 and January 1995. The mass of thecentral supermassive black hole (SBH) was estimated by measuring thebroad components of the emission lines observed in the STIS/G750Mspectrum and assuming that the gas is uniformly distributed in asphere. Results: The nucleus of NGC 4278 hosts a barely resolvedbut strongly variable UV source. Its UV luminosity increased by a factorof 1.6 in a period of 6 months. The amplitude and scale time of the UVflare in NGC 4278 are remarkably similar to those of the brightest UVnuclear transients which were found earlier in other LLAGNs. The mass ofthe SBH was found to be in the range between 7 × 107and 2 × 109 Mȯ. This is in agreementwith previous findings based on different assumptions about the gasdistribution and with the predictions based on the galaxy velocitydispersion. Conclusions: All the LINER nuclei with availablemulti-epoch UV observations and a detected radio core are characterizedby a UV variable source. This supports the idea that the UV variabilityis a relatively common phenomenon in galaxy centers, perhaps providingthe missing link between LINERs and true AGN activity.
| Radio and spectroscopic properties of miniature radio galaxies: revealing the bulk of the radio-loud AGN population
We explore radio and spectroscopic properties of a sample of 14miniature radio galaxies, i.e. early-type core galaxies hostingradio-loud AGN of extremely low radio power, 1027-29 ergs-1 Hz-1 at 1.4 GHz. Miniature radio galaxiessmoothly extend the relationships found for the more powerful FR I radiogalaxies between emission line, optical and radio nuclear luminositiesto lower levels. However, they have a deficit of a factor of ~100 inextended radio emission with respect to that of the classical example of3CR/FR I. This is not due to their low luminosity, since we found radiogalaxies of higher radio core power, similar to those of 3CR/FR I,showing the same behavior, i.e. lacking significant extended radioemission. Such sources form the bulk of the population of radio-loud AGNin the Sloan Digital Sky Survey. At a given level of nuclear emission,one can find radio sources with an extremely wide range, a factor of⪆100, of radio power. We argue that the prevalence of sources withluminous extended radio structures in flux limited samples is due to aselection bias, since the inclusion of such objects is highly favored.The most studied catalogues of radio galaxies are thus composed by theminority of radio-loud AGN that meet the physical conditions required toform extended radio sources, while the bulk of the population isvirtually unexplored.Based on observations made with the Italian Telescopio Nazionale Galileooperated on the island of La Palma by the Centro Galileo Galilei of INAF(Istituto Nazionale di Astrofisica) at the Spanish Observatorio delRoque del los Muchachos of the Instituto de Astrofisica de Canarias.
| X-ray Isophotes in a Rapidly Rotating Elliptical Galaxy: Evidence of Inflowing Gas
We describe two-dimensional gasdynamical computations of the X-rayemitting gas in the rotating elliptical galaxy NGC 4649 that indicate aninflow of ~1 M sun yr–1 at every radius.Such a large instantaneous inflow cannot have persisted over a Hubbletime. The central constant-entropy temperature peak recently observed inthe innermost 150 pc is explained by compressive heating as gas flowstoward the central massive black hole. Since the cooling time of thisgas is only a few million years, NGC 4649 provides the most acutelyconcentrated known example of the cooling flow problem in which thetime-integrated apparent mass that has flowed into the galactic coreexceeds the total mass observed there. This paradox can be resolved byintermittent outflows of energy or mass driven by accretion energyreleased near the black hole. Inflowing gas is also required atintermediate kpc radii to explain the ellipticity of X-ray isophotes dueto spin-up by mass ejected by stars that rotate with the galaxy and toexplain local density and temperature profiles. We provide evidence thatmany luminous elliptical galaxies undergo similar inflow spin-up. Asmall turbulent viscosity is required in NGC 4649 to avoid forming largeX-ray luminous disks that are not observed, but the turbulent pressureis small and does not interfere with mass determinations that assumehydrostatic equilibrium.
| An X-ray view of 82 LINERs with Chandra and XMM-Newton data
We present the results of a homogeneous X-ray analysis for 82 nearbylow-ionisation, narrow emission-line regions (LINERs) selected from thecatalogue of Carrillo et al. (1999, Rev. Mex. Astron. Astrofis., 35,187). All sources have available Chandra (68 sources) and/or XMM-Newton(55 sources) observations. This is the largest sample of LINERs withX-ray spectral data (60 out of the 82 objects), and it significantlyimproves our previous analysis based on Chandra data for 51 LINERs(Gonzalez-Martin et al. 2006b, A&A, 460, 45). It both increases thesample size and adds XMM-Newton data. New models permit the inclusion ofdouble absorbers in the spectral fits. Nuclear X-ray morphology isinferred from the compactness of detected nuclear sources in the hardband (4.5-8.0 keV). Sixty per cent of the sample shows a compact nuclearsource and are classified as active galactic nucleus (AGN) candidates.The spectral analysis indicates that best fits involve a compositemodel: 1) absorbed primary continuum and 2) soft spectrum below 2 keVdescribed by an absorbed scatterer and/or a thermal component. Theresulting median spectral parameters and their standard deviations are<Γ> = 2.11 ± 0.52, < kT> = 0.54 ± 0.30keV, < log(NH1) > } = 21.32 {± 0.71 and < log(NH2)> }= 21.93 {± 1.36. We complement our X-ray results with an analysisof HST optical images and literature data on emission lines, radiocompactness, and stellar population. After adding all thesemultiwavelength data, we conclude that evidence supports the AGN natureof their nuclear engine for 80% of the sample (66 out of 82 objects).Tables 1 to 15, and Appendices are only available in electronic form athttp://www.aanda.org
| The anticorrelation between the hard X-ray photon index and the Eddington ratio in low-luminosity active galactic nuclei
We find a significant anticorrelation between the hard X-ray photonindex Γ and the Eddington ratio Lbol/LEddfor a sample of low-ionization nuclear emission-line regions and localSeyfert galaxies, compiled from literature with Chandra or XMM-Newtonobservations. This result is in contrast with the positive correlationfound in luminous active galactic nuclei (AGN), while it is similar tothat of X-ray binaries (XRBs) in the low/hard state. Our result isqualitatively consistent with the spectra produced fromadvection-dominated accretion flows (ADAFs). It implies that the X-rayemission of low-luminosity active galactic nuclei (LLAGN) may originatefrom the Comptonization process in ADAF, and the accretion process inLLAGN may be similar to that of XRBs in the low/hard state, which isdifferent from that in luminous AGN.
| 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.
| 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.
| Every BCG with a Strong Radio Agn has an X-Ray Cool Core: Is the Cool Core-Noncool Core Dichotomy Too Simple?
The radio active galactic nucleus (AGN) feedback in X-ray cool cores hasbeen proposed as a crucial ingredient in the evolution of baryonicstructures. However, it has long been known that strong radio AGNs alsoexist in "noncool core" clusters, which brings up the question whetheran X-ray cool core is always required for the radio feedback. In thiswork, we present a systematic analysis of brightest cluster galaxies(BCGs) and strong radio AGNs in 152 groups and clusters from the Chandraarchive. All 69 BCGs with radio AGN more luminous than 2 ×1023 W Hz-1 at 1.4 GHz are found to haveX-ray cool cores. BCG cool cores can be divided into two classes: thelarge cool core (LCC) class and the corona class. Small coronae, easilyoverlooked at z > 0.1, can trigger strong heating episodes in groupsand clusters, long before LCCs are formed. Strong radio outburststriggered by coronae may destroy embryonic LCCs and thus provide anothermechanism to prevent the formation of LCCs. However, it is unclearwhether coronae are decoupled from the radio feedback cycles as theyhave to be largely immune to strong radio outbursts. Our sample studyalso shows the absence of groups with a luminous cool core while hostinga strong radio AGN, which is not observed in clusters. This points to agreater impact of radio heating on low-mass systems than clusters. Few L1.4 GHz > 1024 W Hz-1 radioAGNs (~16%) host an L 0.5-10 keV > 1042 ergs-1 X-ray AGN, while above these thresholds, all X-rayAGNs in BCGs are also radio AGNs. As examples of the corona class, wealso present detailed analyses of a BCG corona associated with a strongradio AGN (ESO 137-006 in A3627) and one of the faintest coronae known(NGC 4709 in the Centaurus cluster). Our results suggest that thetraditional cool core/noncool core dichotomy is too simple. A betteralternative is the cool core distribution function, with the enclosedX-ray luminosity or gas mass.
| Fitting Liner Nuclei within the Active Galactic Nucleus Family: A Matter of Obscuration?
In this paper, we study the nuclear obscuration of galaxies hosting lowionization narrow emission regions (LINERs) based on their X-ray andoptical emission. They show column densities at soft energies (0.5-2keV) mostly related to the diffuse emission around the active galacticnucleus (AGN), showing a correlation with the optical extinction. Columndensities at hard energies (2-10 keV) seem to be much higher than whatwould be expected from the optical extinction. They might be associatedwith the inner regions of the AGN, buried at optical wavelengths. Themain result of this paper is that around 50% of our LINER sample showssignatures of Compton-thickness according to the most common tracers:the X-ray spectral index, {F_{X}(2\--10\;keV)/F([\mbox{O}\,\mathsc{iii}])} ratio, and FeKα equivalent width (EW). However, the EWsof the Compton-thick LINERs are significantly lower than in theCompton-thick Seyferts (sime200 eV against >=500 eV), suggesting thatthe 2-10 keV emission is dominated by electron scattering of theotherwise invisible AGN, or by emission from shocked gas associated withstar formation rather than by reflection from the inner wall of thetorus. However, no clear relation seems to exist between galaxies withoptical dust lanes and X-ray classified Compton-thick objects. This maysuggest that Compton-thick sources should be related to absorbingmaterial located at the very inner regions of the AGN, maybe in theputative dusty torus. Larger black hole masses and lower Eddingtonratios than Seyfert galaxies have been found. This effect can be betterattributed to LINER nuclei being hosted by earlier morphological typesthan Seyfert nuclei. However, it has to be noted that, once a propercorrection to the X-ray luminosity is applied, LINERs show Eddingtonratios overlapping those of type 2 Seyferts. We speculate with apossible scenario for LINER nuclei: an inner obscuring matter similar tothat of type 2 Seyfert, and an external obscuring matter responsible forthe optical extinction. Compton-thick sources appear to be more commonamong LINERs than Seyferts.
| A High Fidelity Sample of Cold Front Clusters from the Chandra Archive
This paper presents a sample of "cold front" clusters selected from theChandra archive. The clusters are selected based purely on the existenceof surface brightness edges in their Chandra images which are modeled asdensity jumps. A combination of the derived density and temperaturejumps across the fronts is used to select nine robust examples of coldfront clusters: 1ES0657 - 558, Abell 1201, Abell 1758N,MS1455.0+2232, Abell 2069, Abell 2142, Abell 2163, RXJ1720.1+2638, andAbell 3667. This sample is the subject of an ongoing study aimed atrelating cold fronts to cluster merger activity, and understanding howthe merging environment affects the cluster constituents. Here,temperature maps are presented along with the Chandra X-ray images. Adichotomy is found in the sample in that there exists a subsample ofcold front clusters which are clearly mergers based on their X-raymorphologies, and a second subsample of clusters which harbor coldfronts, but have surprisingly relaxed X-ray morphologies, and minimalevidence for merger activity at other wavelengths. For this secondsubsample, the existence of a cold front provides the sole evidence formerger activity at X-ray wavelengths. We discuss how cold fronts canprovide additional information which may be used to constrain mergerhistories, and also the possibility of using cold fronts to distinguishmajor and minor mergers.
| Radial Distribution of Stars, Gas, and Dust in SINGS Galaxies. I. Surface Photometry and Morphology
We present ultraviolet through far-infrared (FIR) surface brightnessprofiles for the 75 galaxies in the Spitzer Infrared Nearby GalaxiesSurvey (SINGS). The imagery used to measure the profiles includes GalaxyEvolution Explorer UV data, optical images from Kitt Peak NationalObservatory, Cerro Tololo Inter-American Observatory, and Sloan DigitalSky Survey, near-IR data from Two Micron All Sky Survey, and mid- andFIR images from Spitzer. Along with the radial profiles, we also providemulti-wavelength asymptotic magnitudes and several nonparametricindicators of galaxy morphology: the concentration index (C42), the asymmetry (A), the Gini coefficient (G), and thenormalized second-order moment of the brightest 20% of the galaxy's flux(\overline{M}_{20}). In this paper, the first of a series, we describethe technical aspects regarding the surface photometry, and present abasic analysis of the global and structural properties of the SINGSgalaxies at different wavelengths. The homogeneity in the acquisition,reduction, and analysis of the results presented here makes these dataideal for multiple unanticipated studies on the radial distribution ofthe properties of stars, dust, and gas in galaxies. Our radial profilesshow a wide range of morphologies and multiple components (bulges,exponential disks, inner and outer disk truncations, etc.) that vary notonly from galaxy to galaxy but also with wavelength for a given object.In the optical and near-IR, the SINGS galaxies occupy the same regionsin the C 42-A-G-\overline{M}_{20} parameter space as othernormal galaxies in previous studies. However, they appear much lesscentrally concentrated, more asymmetric, and with larger values of Gwhen viewed in the UV (due to star-forming clumps scattered across thedisk) and in the mid-IR (due to the emission of polycyclic aromatichydrocarbons at 8.0 μm and very hot dust at 24 μm). In anaccompanying paper by Muñoz-Mateos et al., we focus on theradial distribution of dust properties in the SINGS galaxies, providinga detailed analysis of the radial variation of the attenuation, the dustcolumn density, the dust-to-gas ratio, the abundance of PAHs, and theintensity of the heating starlight.
| 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.
| 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 Globular Cluster System in M87: A Wide-Field Study with CFHT/Megacam
Canada-France-Hawaii Telescope Megacam data in (g', r', i') are used toobtain deep, wide-field photometry of the globular cluster system (GCS)around M87. A total of 6200 GCs brighter than i' = 23.0 (roughlyequivalent to MI = –8.5) are included in the study,essentially containing almost the entire bright half of the total GCpopulation in the galaxy. The classic bimodal metal-poor and metal-richsequences of GCs show up clearly. While the spatial distribution of theGCs can be traced detectably outward to R gc sime 100 kpc andperhaps further, the blue, metal-poor subpopulation is very much morespatially extended than the red subpopulation. Both the red and blue GCsubsystems have radial metallicity gradients, where mean heavy-elementabundance scales with a projected galactocentric distance as Z ~ R–0.12 (blue) and R –0.17 (red). Theblue sequence exhibits a strongly significant mass/metallicity relation(MMR) in which the mean metallicity gradually increases with clusterluminosity as Z ~ L 0.25 ± 0.05 for the luminosityrange MI lsim –10 and the assumption of a constant M/L.However, this relation is also clearly nonlinear: fainter than thislevel, the sequence is more nearly vertical. This mass/metallicity trendcan be understood as the result of self-enrichment within the mostmassive metal-poor GCs during their formation. The red sequence formallyexhibits a negatively sloped MMR, but the numerical solutions and testsshow that this red-GC slope is not very significant. In giant ellipticalgalaxies, the red GCs are likely to represent a broad compositepopulation formed during several major starbursts. If so, the redsequence might display a population-based MMR that could in principle beeither positive or negative.This research used the facilities of the Canadian Astronomy Data Centreoperated by the National Research Council of Canada with the support ofthe Canadian Space Agency. Based on observations obtained at theCanada-France-Hawaii Telescope (CFHT) which is operated by the NationalResearch Council of Canada, the Institut National des Sciences del'Univers of the Centre National de la Recherche Scientifique of France,and the University of Hawaii.
| 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.
| Radial Distribution of Stars, Gas, and Dust in Sings Galaxies. II. Derived Dust Properties
We present a detailed analysis of the radial distribution of dustproperties in the SINGS sample, performed on a set of ultraviolet (UV),infrared (IR), and H I surface brightness profiles, combined withpublished molecular gas profiles and metallicity gradients. The internalextinction, derived from the total-IR (TIR)-to-far-UV (FUV) luminosityratio, decreases with radius, and is larger in Sb-Sbc galaxies. TheTIR-to-FUV ratio correlates with the UV spectral slope β, followinga sequence shifted to redder UV colors with respect to that ofstarbursts. The star formation history (SFH) is identified as the maindriver of this departure. Both L TIR/L FUV andβ correlate well with metallicity, especially in moderately face-ongalaxies. The relation shifts to redder colors with increased scatter inmore edge-on objects. By applying physical dust models to our radialspectral energy distributions, we have derived radial profiles of thetotal dust mass surface density, the fraction of the total dust masscontributed by polycyclic aromatic hydrocarbons (PAHs), and theintensity of the radiation field heating the grains. The dust profilesare exponential, their radial scale length being constant from Sb to Sdgalaxies (only ~10% larger than the stellar scale length). Many S0/a-Sabgalaxies have central depressions in their dust radial distributions.The PAH abundance increases with metallicity for 12 + log(O/H) < 9,and at larger metallicities the trend flattens and even reverses, withthe SFH being a plausible underlying driver for this behavior. Thedust-to-gas ratio is also well correlated with metallicity and thereforedecreases with galactocentric radius. Although most of the total emittedIR power (especially in the outer regions of disks) is contributed bydust grains heated by diffuse starlight with a similar intensity as thelocal Milky Way radiation field, a small amount of the dust mass (~1%)is required to be exposed to very intense starlight in order toreproduce the observed fluxes at 24 μm, accounting for ~10% ofthe total integrated IR power.
| Gas Sloshing and Bubbles in the Galaxy Group NGC 5098
We present results from Chandra observations of the galaxy pair andassociated galaxy group NGC 5098, and find evidence for both gassloshing and active galactic nucleus (AGN) heating. The X-ray brightnessimages show diffuse emission with a spiral structure, centered on NGC5098a, and a sharp edge in the diffuse emission surrounding much of thegalaxy at about 30 kpc. The spiral structure in the X-ray surfacebrightness and temperature maps, the offset between the peak of the coolgas and the central AGN, and the structure of the cold front edges allsuggest gas sloshing in the core. The most likely perturber is thenearby galaxy NGC 5098b, which has been stripped of its gaseousatmosphere. Detailed images of the core reveal several X-ray cavities,two of which, just north and southeast of the central AGN, correlatewith radio emission and have bright X-ray rims, similar to buoyantbubbles seen in the intracluster medium of other systems. We estimatethe pressures in the bubbles and rims and show that they are roughlyequal, consistent with these being young features, as suggested by theirclose proximity to the central AGN. We assume that the other X-raycavities in the core, which show no correlation with existing radioobservations, are ghost cavities from previous AGN outbursts. Anestimate of the mechanical energy required to inflate the cavitiesindicates that it is sufficient to offset radiative cooling of the gasfor 15 Myr. Therefore, for a typical cycle time of 107yr, the central AGN energy output is enough to balance cooling over longtimescales.
| 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.
| Spitzer IRS Observations of k+a Galaxies: A Link Between Polycyclic Aromatic Hydrocarbon Emission Properties and Active Galactic Nucleus Feedback?
We have performed Spitzer InfraRed Spectrograph (IRS) low-resolution5-12 μm spectroscopy on a sample of galaxies selected to be at threedistinct poststarburst evolutionary stages based on their opticalspectral indices. The resulting IRS spectra show distinctive polycyclicaromatic hydrocarbon (PAH) emission line structures at 6.2, 7.7, 8.6,and 11.3 μm and little silicate absorption, indicative of ongoingstar formation. However, the PAH interline ratios, in particular the11.3/6.2 μm and 7.7/6.2 μm ratio, show large variations. Thesevariations are found to correlate with both time since the most recentstarburst and active galactic nucleus (AGN) activity. We speculate thatthe evolution observed in these PAH ratios is related to an increase inAGN activity with time since starburst.
| 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.
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