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Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters
We present new (B, I) photometry for the globular cluster systems ineight brightest cluster galaxies (BCGs), obtained with the ACS/WFCcamera on the Hubble Space Telescope. In the very rich cluster systemsthat reside within these giant galaxies, we find that all have stronglybimodal color distributions that are clearly resolved by themetallicity-sensitive (B-I) index. Furthermore, the mean colors andinternal color range of the blue subpopulation are remarkably similarfrom one galaxy to the next, to well within the +/-0.02-0.03 maguncertainties in the foreground reddenings and photometric zero points.By contrast, the mean color and internal color range for the redsubpopulation differ from one galaxy to the next by twice as much as theblue population. All the BCGs show population gradients, with muchhigher relative numbers of red clusters within 5 kpc of their centers,consistent with their having formed at later times than the blue,metal-poor population. A striking new feature of the color distributionsemerging from our data is that for the brightest clusters(MI<-10.5) the color distribution becomes broad and lessobviously bimodal. This effect was first noticed by Ostrov et al. andDirsch et al. for the Fornax giant NGC 1399; our data suggest that itmay be a characteristic of many BCGs and perhaps other large galaxies.Our data indicate that the blue (metal-poor) clusters brighter thanMI~=-10 become progressively redder with increasingluminosity, following a mass/metallicity scaling relationZ~M0.55. A basically similar relation has been found for M87by Strader et al. (2005). We argue that these GCS characteristics areconsistent with a hierarchical-merging galaxy formation picture in whichthe metal-poor clusters formed in protogalactic clouds or densestarburst complexes with gas masses in the range107-1010 Msolar, but where the moremassive clusters on average formed in bigger clouds with deeperpotential wells where more preenrichment could occur.
| Peculiarities and populations in elliptical galaxies. III. Dating the last star formation event
Using 6 colours and 4 Lick line-indices we derive two-component modelsof the populations of ellipticals, involving a "primary" and a"juvenile" population. The first component is defined by the regressionsof indices against the central velocity dispersion found in Papers I andII for the {Nop} sample of non-peculiar objects. The second one isapproximated by an SSP, and the modeling derives its age A, metallicityZ and fractional V-luminosity q_V, the fractional mass qMbeing found therefrom. The model is designed for "blueish" peculiargalaxies, i.e. the {Pec} sample and NGC 2865 family in the terminologyof Paper I. The morphological peculiarities and the population anomalyare then believed to involve the same event, i.e. a merger plusstarburst. It is possible to improve the models in a few cases byintroducing diffuse dust (as suggested by far IR data), and/or by takinginto account the fact that Lick- and colour indices do not relate toidentical galaxy volumes. In most of the cases, the mass ratio of youngstars qM seems too small for the product of a recent majormerger: the events under consideration might be minor mergers bringing"the final touch" to the build-up of the structure of the E-type object.The same modeling has been successfully applied to blueish galaxies ofthe {Nop} sample, without morphological peculiarities however, tosupport the occurence of a distinct perturbing event. A few reddishobjects of the {Pec} sample (NGC 3923 family) and of the {Nop} sampleare also modeled, in terms of an excess of high metallicity stars, ordiffuse dust, or both, but the results are inconclusive.
| Group, field and isolated early-type galaxies - II. Global trends from nuclear data
We have derived ages, metallicities and enhanced-element ratios[α/Fe] for a sample of 83 early-type galaxies essentially ingroups, the field or isolated objects. The stellar-population propertiesderived for each galaxy correspond to the nuclear re/8aperture extraction. The median age found for Es is 5.8+/-0.6 Gyr andthe average metallicity is +0.37+/-0.03 dex. For S0s, the median age is3.0+/-0.6 Gyr and [Z/H]= 0.53+/-0.04 dex. We compare the distribution ofour galaxies in the Hβ-[MgFe] diagram with Fornax galaxies. Ourelliptical galaxies are 3-4 Gyr younger than Es in the Fornax cluster.We find that the galaxies lie in a plane defined by [Z/H]= 0.99logσ0- 0.46 log(age) - 1.60, or in linear terms Z~σ0× (age) -0.5. More massive (largerσ0) and older galaxies present, on average, large[α/Fe] values, and therefore must have undergone shorterstar-formation time-scales. Comparing group against field/isolatedgalaxies, it is not clear that environment plays an important role indetermining their stellar-population history. In particular, ourisolated galaxies show ages differing by more than 8 Gyr. Finally weexplore our large spectral coverage to derive log(O/H) metallicity fromthe Hα and NIIλ6584 and compare it with model-dependent[Z/H]. We find that the O/H abundances are similar for all galaxies, andwe can interpret it as if most chemical evolution has already finishedin these galaxies.
| Group, field and isolated early-type galaxies - I. Observations and nuclear data
This is the first paper of a series on the investigation of stellarpopulation properties and galaxy evolution of an observationallyhomogeneous sample of early-type galaxies in groups, field and isolatedgalaxies.Here we present high signal-to-noise ratio (S/N) long-slit spectroscopyof 86 nearby elliptical and S0 galaxies. Eight of them are isolated,selected according to a rigorous criterion, which guarantees a genuinelow-density subsample. The present survey has the advantage of coveringa larger wavelength range than normally found in the literature, whichincludes [OIII]λ5007 and Hα, both lines important foremission correction. Among the 86 galaxies with S/N >= 15 (perresolution element, for re/8 central aperture), 57 have theirHβ-index corrected for emission (the average correction is 0.190Åin Hβ) and 42 galaxies reveal [OIII]λ5007 emission,of which 16 also show obvious Hα emission. Most of the galaxies inthe sample do not show obvious signs of disturbances nor tidal featuresin the morphologies, although 11 belong to the Arp catalogue of peculiargalaxies; only three of them (NGC 750, 751 and 3226) seem to be stronglyinteracting. We present the measurement of 25 central line-strengthindices calibrated to the Lick/IDS system. Kinematic information isobtained for the sample. We analyse the line-strength index versusvelocity dispersion relations for our sample of mainly low-densityenvironment galaxies, and compare the slope of the relations withcluster galaxies from the literature. Our main findings are that theindex-σ0 relations presented for low-density regionsare not significantly different from those of cluster E/S0s. The slopeof the index-σ0 relations does not seem to change forearly-type galaxies of different environmental densities, but thescatter of the relations seems larger for group, field and isolatedgalaxies than for cluster galaxies.
| Detection of Radial Surface Brightness Fluctuations and Color Gradients in Elliptical Galaxies with the Advanced Camera for Surveys
We study surface brightness fluctuations (SBFs) in a sample of eightelliptical galaxies using the Advanced Camera for Surveys (ACS) WideField Channel (WFC) data drawn from the Hubble Space Telescope archive.SBF magnitudes in the F814W bandpass and galaxy colors from F814W,F435W, and F606W images, when available, are presented. Galaxy surfacebrightness profiles are determined as well. We present the firstSBF-broadband color calibration for the ACS WFC F814W bandpass and(relative) distance moduli estimates for seven of our galaxies. Wedetect and study in detail the SBF variations within individual galaxiesas a probe of possible changes in the underlying stellar populations.Inspecting both the SBF and color gradients in comparison to modelpredictions, we argue that SBFs and SBF gradients can in principle beused for unraveling the different evolutionary paths taken by galaxies,although a more comprehensive study of this issue would be required. Weconfirm that the radial variation of galaxy stellar populationproperties is mainly connected to the presence of radial chemicalabundance gradients, with the outer galaxy regions being more metal-poorthan the inner ones.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555. These observations areassociated with programs 9427, 9293, and 9399.
| Probing the Dust Obscuration in Seyfert Galaxies using Infrared Spectroscopy. II. Implication for the Unification of Seyfert Galaxies
We report near-IR spectroscopic observations of 11 Seyfert galaxies (sixSeyfert 1s, one Seyfert 1.9, and four Seyfert 2s) and additionalgalaxies (four LINERs, two H II, and one type 2 transition) forcomparison, obtained using the Gemini twin-channel near-IR camera on theShane 3 m telescope at Lick Observatory. With the unique design of theGemini camera, full J and K spectra were taken simultaneously throughthe same slit. This produced accurate line ratios of hydrogenrecombination lines over a large wavelength baseline. For the Seyfert 1s(<=1.5), the line ratios of Paβ/Brγ are not onlycomparable in both broad- and narrow-line regions but also consistentwith case B recombination, indicating little or no reddening in bothnarrow- and broad-line regions. Seyfert 2 (>1.5) galaxies, however,show substantial reddening toward the narrow-line regions. We compareoptical reddening data from the literature and find significant supportfor the dichotomy between Seyfert 1s and Seyfert 2s, at least inlow-luminosity objects. Two different scenarios are explored to explainthe observed difference in reddening: a difference in reddening due toan extended dusty torus under active galactic nucleus unification, and adifference due to a different grain size distribution between the twoSeyfert types. We also discuss a similar potential difference found inthe strength of the 9.7 μm silicate line, along with a possiblecorrelation between the narrow-line reddening and the strength of thesilicate absorption line. We also analyzed CO band head absorptionfeatures longward of 2.3 μm to look for nonstellar contamination andevidence of recent star formation activity. The CO band head in Seyfert1s shows heavy contamination from nonstellar radiation, which iscorrelated with an H-K nuclear color excess. We confirm that the COspectroscopic indices in both Seyfert types do not show evidence ofrecent star formation. Taking the nonstellar contamination into account,there is little evidence from the CO index for a difference in starformation rates in the nuclei of Seyfert 1s and Seyfert 2s in ourlow-luminosity sample.
| The Centers of Early-Type Galaxies with Hubble Space Telescope. V. New WFPC2 Photometry
We present observations of 77 early-type galaxies imaged with the PC1CCD of the Hubble Space Telescope (HST) WFPC2. ``Nuker-law'' parametricfits to the surface brightness profiles are used to classify the centralstructure into ``core'' or ``power-law'' forms. Core galaxies aretypically rounder than power-law galaxies. Nearly all power-law galaxieswith central ellipticities ɛ>=0.3 have stellar disks,implying that disks are present in power-law galaxies withɛ<0.3 but are not visible because of unfavorable geometry. Afew low-luminosity flattened core galaxies also have disks; these may betransition forms from power-law galaxies to more luminous core galaxies,which lack disks. Several core galaxies have strong isophote twistsinterior to their break radii, although power-law galaxies have interiortwists of similar physical significance when the photometricperturbations implied by the twists are evaluated. Central colorgradients are typically consistent with the envelope gradients; coregalaxies have somewhat weaker color gradients than power-law galaxies.Nuclei are found in 29% of the core galaxies and 60% of the power-lawgalaxies. Nuclei are typically bluer than the surrounding galaxy. Whilesome nuclei are associated with active galactic nuclei (AGNs), just asmany are not; conversely, not all galaxies known to have a low-level AGNexhibit detectable nuclei in the broadband filters. NGC 4073 and 4382are found to have central minima in their intrinsic starlightdistributions; NGC 4382 resembles the double nucleus of M31. In general,the peak brightness location is coincident with the photocenter of thecore to a typical physical scale of <1 pc. Five galaxies, however,have centers significantly displaced from their surrounding cores; thesemay be unresolved asymmetric double nuclei. Finally, as noted byprevious authors, central dust is visible in about half of the galaxies.The presence and strength of dust correlates with nuclear emission;thus, dust may outline gas that is falling into the central black hole.The prevalence of dust and its morphology suggest that dust clouds form,settle to the center, and disappear repeatedly on ~108 yrtimescales. We discuss the hypothesis that cores are created by thedecay of a massive black hole binary formed in a merger. Apart fromtheir brightness profiles, there are no strong differences between coregalaxies and power-law galaxies that demand this scenario; however, therounder shapes of core, their lack of disks, and their reduced colorgradients may be consistent with it.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS 5-26555. These observations are associated withGO and GTO proposals 5236, 5446, 5454, 5512, 5943, 5990, 5999, 6099,6386, 6554, 6587, 6633, 7468, 8683, and 9107.
| A dichotomy in the orientation of dust and radio jets in nearby low-power radio galaxies
We examine the properties of central dust in nearby quiescent and activeearly-type galaxies. The active galaxies are low-power radio galaxieswith Fanaroff & Riley type I or I/II radio jets. We focus on (a) thecomparison of the dust distributions in the active and quiescent galaxysamples; and (b) the relation between the radio jet and dustorientations. Our main observational conclusions are: (i) in line withprevious studies, the dust detection rate is higher in radio-jetgalaxies than in non radio-jet galaxies; (ii) radio galaxies contain ahigher fraction of regular dust “ellipses” compared toquiescent galaxies which contain more often irregular dustdistributions; (iii) the morphology, size and orientation of dustellipses and lanes in quiescent early-types and active early-types withkpc-scale radio jets is very similar; (iv) dust ellipses are alignedwith the major axis of the galaxy, dust lanes do not show a preferredalignment except for large (>kpc) dust lanes which are aligned withthe minor axis of the galaxy; and (v) as projected on the sky, jets donot show a preferred orientation relative to the galaxy major axis (andhence dust ellipses), but jets are preferentially perpendicular to dustlanes. We show that the dust ellipses are consistent with being nearlycircular thin disks viewed at random viewing angles. The lanes arelikely warped dust structures, which may be in the process of settlingdown to become regular disks or are being perturbed by anon-gravitational force. We use the observed dust-jet orientations toconstrain the three-dimensional angle θDJ between jetand dust. For dust-lane galaxies, the jet is approximately perpendicularto the dust structure, while for dust-ellipse galaxies there is a muchwider distribution of θDJ. We discuss two scenariosthat could explain the dust/jet/galaxy orientation dichotomy. If lanesare indeed settling, then the jet orientation apparently is roughlyaligned with the angular momentum of the dust before it settles. Iflanes are perturbed by a jet-related force, it appears that it causesthe dust to move out of its equilibrium plane in the galaxy into a planewhich is perpendicular to the jet.
| Peculiarities and populations in elliptical galaxies. II. Visual-near IR colours as population indices
As a complement to the data collected and discussed in Paper I of thisseries, 2MASS near-IR images have been used, in connection withavailable V light aperture photometry, to derive the colours V-J, V-K,J-H and J-K within the effective aperture A_e: nearly the same completesample of 110 E-type galaxies is treated. In Paper I these wereclassified, based on morphological criteria, into the ``peculiar'' (orPec) and ``normal'' (or Nop) subsamples. For the Nop subsample, thederived colour indices are tightly related to the galaxy masses, asmeasured by the central velocity dispersion σ0,although with rather small slopes as regards J-H and J-K. For the Pecsubsample, the V-J and V-K colours behave as UBV and line-indices: partof the objects show blue residuals from the appropriatecolour-σ0 regression, which is evidence of a youngerpopulation mixed with the ``normal'' one traced by the Nop regressions;the other shows no deviations from the Nop subsample. The distinctionamong Pec objects between the YP family (NGC 2865 type), and the NP one(NGC 3923 type), is statistically supported, and generally confirmed inspecific cases.Based in part on observations collected at the Observatoire deHaute-Provence.Table 4 is only available in electonic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/819
| Nuclear activity and the dynamics of elliptical galaxies
This Letter looks for any correlation between the internal dynamics ofelliptical galaxies and the relatively mild nuclear activity found inmany such systems. We show that there is such a relation in the sensethat the active ellipticals tend to be significantly less rotationallysupported than their inactive cousins. The correlation can partly berelated to the galaxies' luminosities: the brightest galaxies tend to bemore active and less rotationally supported. However, even at lowerluminosities the active and inactive galaxies seem to havesystematically different dynamics. This variation suggests that thereare significant large-scale structural differences between active andinactive elliptical galaxies, and hence that the existence of both typesof system cannot just be the result of random sporadic nuclear activity.
| Core Depletion from Coalescing Supermassive Black Holes
New measurements of the stellar-mass deficits at the centers of luminouselliptical galaxies are presented. These were derived considering thefollowing observational facts. First, ``core'' galaxies, which arethought to have had their inner region depleted from the coalescence ofsupermassive black holes, show an abrupt downward deviation of theirinner light profile relative to their outer Sérsic profile.Second, ``power-law'' galaxies, having undisturbed profiles and nopartially depleted core, have inner light profiles that display nodeparture from the inward extrapolation of their outer Sérsicprofile. The central stellar deficits have therefore been derived fromthe difference in flux between the Hubble Space Telescope observedgalaxy light profiles and the inward extrapolation of each galaxy'souter Sérsic profile. This approach gives flux deficits ~0.1% ofthe total galaxy light and mass deficits that are ~2 times each galaxy'scentral supermassive black hole mass. These results are in agreementwith the theoretical expectations of mass ejection from binary blackhole mergers and also with popular ΛCDM models of hierarchicalgalaxy formation. It is also explained why this result is some 10 timessmaller than current observational estimates of the central mass deficitand therefore implies a merger history for giant elliptical galaxiesthat is 1 order of magnitude less violent than previously suggested.
| Evidence for a New Elliptical-Galaxy Paradigm: Sérsic and Core Galaxies
We fitted the surface-brightness profiles of 21 elliptical galaxiesusing both the Sérsic function and a new empirical model thatcombines an inner power law with an outer Sérsic function. Theprofiles are combinations of deconvolved Hubble Space Telescope (HST)profiles from the literature and ellipse fits to the full WFPC2 mosaicimages and thus span a radial range from ~0.02" to about twice thehalf-light radius. We are able to accurately fit the entire profilesusing either the Sérsic function or our new model. In doing so,we demonstrate that most, if not all, so-called ``power-law'' galaxiesare better described as ``Sérsic galaxies''-they are well modeledby the three-parameter Sérsic profile into the limits of HSTresolution-and that ``core'' galaxies are best understood as consistingof an outer Sérsic profile with an inner power-law cusp, which isa downward deviation from the inward extrapolation of the Sérsicprofile. This definition of cores resolves ambiguities that result whenthe popular ``Nuker law'' is fitted to the profiles of ellipticals andbulges, particularly at lower luminosities. We also find that using theNuker law to model core-galaxy nuclear profiles systematicallyoverestimates the core radii by factors of 1.5-4.5 and underestimatesthe inner power-law slope by ~20%-40% or more.
| Peculiarities and populations in elliptical galaxies. I. An old question revisited
Morphological peculiarities, as defined from isophote asymmetries andnumber of detected shells, jets or similar features, have been estimatedin a sample of 117 E classified galaxies, and qualified by an ad hocΣ2 index. The overall frequency of ``peculiar'' objects(Pec subsample) is 32.5%. It decreases with the cosmic density of theenvironment, being minimal for the Virgo cluster, the densestenvironment in the sampled volume. This environmental effect is strongerfor galaxies with relatively large Σ2.The Pec subsample objects are compared with ``normal'' objects (Nopsubsample) as regards their basic properties. Firstly, theysystematically deviate from the Fundamental Plane and the Faber-Jacksonrelation derived for the Nop subsample, being too bright for their mass.Secondly, the dust content of galaxies, as estimated from IRAS fluxes,are similar in both subsamples. Third, the same is true of the frequencyof Kinematically Distinct cores (KDC), suggesting that KDC andmorphological peculiarities do not result from the same events in thehistory of E-galaxies.Using the Nop sample alone, we obtain very tight reference relationsbetween stellar population indicators (U-B, B-V, B-R, V-I,Mg2, Hβ, , Mgb) and the central velocitydispersion σ0. The discussion of the residuals of theserelations allows us to classify the Pec galaxies in two families i.e.the YP or NGC 2865 family, and the NP or NGC 3923 one. Galaxies in thefirst group show consistent evidence for a younger stellar populationmixed with the old one, in agreement with classical results (Schweizeret al. \cite{Schweizer1990}; Schweizer & Seitzer\cite{Schweizer1992}). The second group, however, has ``normal``, orreddish, populations. It is remarkable that a fraction (circa 40%) ofmorphologically perturbed objects do not display any signature of ayoung population, either because the event responsible for thepecularity is too ancient, or because it did not produce significantstar formation (or eventually that the young sub-population has highmetallicity).A preliminary attempt is made to interpret the populations of Pecobjects by combining a young Single Stellar Population with a Nopgalaxy, with only limited success, perhaps largely due to uncertaintiesin the SSP indices used.Based in part on observations collected at the Observatoire deHaute-Provence.Figures \ref{fig1}-\ref{fig3} are only available in electronic form athttp://www.edpsciences.orgTable 10 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/423/833
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| Galaxy cores as relics of black hole mergers
We investigate the hypothesis that the cores of elliptical galaxies andbulges are created from the binding energy liberated by the coalescenceof supermassive binary black holes during galaxy mergers. Assuming thatthe central density profiles of galaxies were initially steep powerlaws, ρ ~r -2 , we define the `mass deficit' as the massin stars that had to be removed from the nucleus in order to produce theobserved core. We use non-parametric deprojection to compute the massdeficit in a sample of 35 early-type galaxies with high-resolutionimaging data. We find that the mass deficit correlates well with themass of the nuclear black hole, consistent with the predictions ofmerger models. We argue that cores in haloes of non-interacting darkmatter particles should be comparable in size to those observed in thestars.
| Nuclear Cusps and Cores in Early-Type Galaxies as Relics of Binary Black Hole Mergers
We present an analysis of the central cusp slopes and core parameters ofearly-type galaxies using a large database of surface brightnessprofiles obtained from Hubble Space Telescope observations. We examinethe relation between the central cusp slopes, core parameters, and blackhole masses in early-type galaxies, in light of two models that attemptto explain the formation of cores and density cusps via the dynamicalinfluence of black holes. Contrary to the expectations fromadiabatic-growth models, we find that the cusp slopes do not steepenwith increasing black hole mass fraction. Moreover, a comparison ofkinematic black hole mass measurements with the masses predicted by theadiabatic models shows that they overpredict the masses by a factor of~3. Simulations involving binary black hole mergers predict that boththe size of the core and the central mass deficit correlate with thefinal black hole mass. These relations are qualitatively supported bythe present data.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Relation between dust and radio luminosity in optically selected early type galaxies
We have surveyed an optical/IR selected sample of nearby E/S0 galaxieswith and without nuclear dust structures with the VLA at 3.6 cm to asensitivity of 100 mu Jy. We can construct a Radio Luminosity Function(RLF) of these galaxies to ~ 1019 W Hz-1 and findthat ~ 50% of these galaxies have AGNs at this level. The space densityof these AGNs equals that of starburst galaxies at this luminosity.Several dust-free galaxies have low luminosity radio cores, and theirRLF is not significantly less than that of the dusty galaxies.
| A synthesis of data from fundamental plane and surface brightness fluctuation surveys
We perform a series of comparisons between distance-independentphotometric and spectroscopic properties used in the surface brightnessfluctuation (SBF) and fundamental plane (FP) methods of early-typegalaxy distance estimation. The data are taken from two recent surveys:the SBF Survey of Galaxy Distances and the Streaming Motions of AbellClusters (SMAC) FP survey. We derive a relation between(V-I)0 colour and Mg2 index using nearly 200galaxies and discuss implications for Galactic extinction estimates andearly-type galaxy stellar populations. We find that the reddenings fromSchlegel et al. for galaxies with E(B-V)>~0.2mag appear to beoverestimated by 5-10 per cent, but we do not find significant evidencefor large-scale dipole errors in the extinction map. In comparison withstellar population models having solar elemental abundance ratios, thegalaxies in our sample are generally too blue at a given Mg2;we ascribe this to the well-known enhancement of the α-elements inluminous early-type galaxies. We confirm a tight relation betweenstellar velocity dispersion σ and the SBF `fluctuation count'parameter N, which is a luminosity-weighted measure of the total numberof stars in a galaxy. The correlation between N and σ is eventighter than that between Mg2 and σ. Finally, we deriveFP photometric parameters for 280 galaxies from the SBF survey data set.Comparisons with external sources allow us to estimate the errors onthese parameters and derive the correction necessary to bring them on tothe SMAC system. The data are used in a forthcoming paper, whichcompares the distances derived from the FP and SBF methods.
| Dusty Nuclear Disks and Filaments in Early-Type Galaxies
We examine the dust properties of a nearby distance-limited sample ofearly-type galaxies using WFPC2 of the Hubble Space Telescope. Dust isdetected in 29 out of 67 galaxies (43%), including 12 with small nucleardusty disks. In a separate sample of 40 galaxies biased for thedetection of dust by virtue of their detection in IRAS 100 μm band,dust is found in ~78% of the galaxies, 15 of which contain dusty disks.In those galaxies with detectable dust, the apparent mass of the dustcorrelates with radio and far-infrared luminosity, becoming moresignificant for systems with filamentary dust. A majority of IRAS andradio detections are also associated with dusty galaxies rather thandustless galaxies. This indicates that thermal emission from clumpy,filamentary dust is the main source of the far-IR radiation inearly-type galaxies. Dust in small disklike morphology tends to be wellaligned with the major axis of the host galaxies, while filamentary dustappears to be more randomly distributed with no preference for alignmentwith any major galactic structure. This suggests that, if the dustydisks and filaments have a common origin, the dust originates externallyand requires time to dynamically relax and settle in the galaxypotential in the form of compact disks. More galaxies with visible dustthan without dust display emission lines, indicative of ionized gas,although such nuclear activity does not show a preference for dusty diskover filamentary dust. There appears to be a weak relationship betweenthe mass of the dusty disks and central velocity dispersion of thegalaxy, suggesting a connection with a similar recently recognizedrelationship between the latter and the black hole mass. Based onobservations with the NASA/ESA Hubble Space Telescope, obtained at theSpace Telescope Science Institute, which is operated by the Associationof Universities for Research in Astronomy, Inc., under NASA contractNAS5-26555.
| WFPC2 Images of the Central Regions of Early-Type Galaxies. I. The Data
We present high-resolution R-band images of the central regions of 67early-type galaxies obtained with the Wide Field and Planetary Camera 2(WFPC2) aboard the Hubble Space Telescope (HST). This homogeneouslyselected sample roughly doubles the number of early-type galaxies thathave now been imaged at HST resolution and complements similar data onthe central regions of radio galaxies and the bulges of spiral galaxies.Our sample strikingly confirms the complex morphologies of the centralregions of early-type galaxies which have become apparent from previousstudies with HST. In particular, we detect dust, either in the form ofnuclear disks or with a filamentary distribution, in 43% of allgalaxies, in good agreement with previous estimates. In addition, wefind evidence for embedded stellar disks in a remarkably large fractionof 51%. In 14 of those galaxies the disklike structures are misalignedwith the main galaxy, suggesting that they correspond to stellar bars inS0 galaxies. We analyze the luminosity profiles of the galaxies in oursample and classify galaxies according to their central cusp slope. To alarge extent we confirm the results from previous HST surveys in thatearly-type galaxies reveal a clear dichotomy: the bright ellipticals(MB<~-20.5) are generally boxy and have luminosityprofiles that break from steep outer power laws to shallow inner cusps(referred to as ``core'' galaxies). The fainter ellipticals, on theother hand, typically have disky isophotes and luminosity profiles thatlack a clear break and have a steep central cusp (referred to as``power-law'' galaxies). The advantages and shortcomings ofclassification schemes utilizing the extrapolated central cusp slopeγ are discussed, and it is shown that γ might be aninadequate representation for galaxies whose luminosity profile slopechanges smoothly with radius rather than resembling a broken power law.Thus, we introduce a new, alternative parameter and show how thisaffects the classification. In fact, we find evidence for an``intermediate'' class of galaxies that cannot unambiguously beclassified as either core or power-law galaxies and that have centralcusp slopes and absolute magnitudes intermediate between those of coreand power-law galaxies. It is unclear at present, however, whether thesegalaxies make up a physically distinct class or whether distance and/orresolution effects cause them to lose their distinct core or power-lawcharacteristics.
| HI observations of loose galaxy groups. I. Data and global properties
At Nançay, 21-cm H I line observations were made of 15spiral-dominated loose groups of galaxies, divided into two samples: an``interacting'' sample containing at least one pair of interactinggalaxies, and a ``control'' sample having no optical evidence ofinteractions or morphological disturbances among the group members. Theinteracting sample consists of 62 galaxies representing 9 differentgroups, and the control sample contains 40 galaxies representing 6groups. Of the 91 galaxy and galaxy pairs observed, 74 were detected,while upper limits were placed on the remaining 17 objects. Thesehomogeneous H I data, which will be used in future analyses, providecomparative information on the H I content of groups and serve as aprobe of the vicinity of the target spirals for H I clouds or very lowsurface brightness gas-rich galaxies.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| Probing the Dust Obscuration in Seyfert Galaxies Using Infrared Spectroscopy
We present near-infrared spectroscopy of four Seyfert 1 galaxies, oneSeyfert 1.9 galaxy, and one Seyfert 2 galaxy, obtained using the Geminiinfrared camera at the Lick Observatory 3 m Shane telescope. With theunique design of the Gemini camera, full J- and K-band spectra weretaken simultaneously through the same slit. This produced a moreaccurate comparison of hydrogen recombination line fluxes than previousinfrared studies. We have also used template galaxies to remove stellarfeatures from the infrared spectra and produced more accuratemeasurements of the weak Brγ feature. We concentrate on thevelocity-resolved ratio of Paβ/Brγ and its implication fordust within the central active galactic nucleus (AGN). For our Seyfert1s, the line ratios of Paβ/Brγ are not only comparable inboth broad- and narrow-line regions but also consistent with case Brecombination, confirming that the ratio Paβ/Brγ is lessaffected by collisional effects than optical lines and is a goodindicator of dust extinction up to Av~10 in AGN. Using thesame diagnostic the Seyfert 1.9 galaxy, NGC 2992, has an extinction ofAv=4.03+/-0.20 to the broad-line region while the narrow-lineregion is unobscured. Assuming that Seyfert 1.9 galaxy has the samebroad-line region that Seyfert 1 galaxies have, we conclude that theobscuring dust is located between the broad-line regions and thenarrow-line regions, consistent with the AGN unification model. TheSeyfert 2 galaxy, NGC 5929, consistent with dust being present on largerscales, shows significant obscuration to the narrow-line region. Thesedata are part of a larger program to measure many spectral properties ofSeyfert galaxies.
| The Cold and Hot Gas Content of Fine-Structure E and S0 Galaxies
We investigate trends of the cold and hot gas content of early-typegalaxies with the presence of optical morphological peculiarities, asmeasured by the fine-structure index Σ. H I mapping observationsfrom the literature are used to track the cold gas content, and archivalROSAT Position Sensitive Proportional Counter data are used to quantifythe hot gas content. We find that E and S0 galaxies with a highincidence of optical peculiarities are exclusively X-ray underluminousand, therefore, deficient in hot gas. In contrast, more relaxed galaxieswith little or no signs of optical peculiarities span a wide range ofX-ray luminosities. That is, the X-ray excess anticorrelates withΣ. There appears to be no similar trend of cold gas content witheither fine-structure index or X-ray content. The fact that onlyapparently relaxed E and S0 galaxies are strong X-ray emitters isconsistent with the hypothesis that after strong disturbances, such as amerger, hot gas halos build up over a timescale of several gigayears.This is consistent with the expected mass loss from stars.
| A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening
Accurate maps of Galactic reddening are important for a number ofapplications, such as mapping the peculiar velocity field in the nearbyuniverse. Of particular concern are systematic errors which vary slowlyas a function of position on the sky, as these would induce spuriousbulk flow. We have compared the reddenings of Burstein & Heiles (BH)and those of Schlegel, Finkbeiner, & Davis (SFD) to independentestimates of the reddening, for Galactic latitudes |b|>10^deg. Ourprimary source of Galactic reddening estimates comes from comparing thedifference between the observed B-V colors of early-type galaxies, andthe predicted B-V color determined from the B-V-Mg_2 relation. We havefitted a dipole to the residuals in order to look for large-scalesystematic deviations. There is marginal evidence for a dipolar residualin the comparison between the SFD maps and the observed early-typegalaxy reddenings. If this is due to an error in the SFD maps, then itcan be corrected with a small (13%) multiplicative dipole term. Weargue, however, that this difference is more likely to be due to a small(0.01 mag) systematic error in the measured B-V colors of the early-typegalaxies. This interpretation is supported by a smaller, independentdata set (globular cluster and RR Lyrae stars), which yields a resultinconsistent with the early-type galaxy residual dipole. BH reddeningsare found to have no significant systematic residuals, apart from theknown problem in the region 230^deg
| On the relationship between age and dynamics in elliptical galaxies
Galaxy age estimates (mostly from spectroscopy of the central regions)are now available for many early-type galaxies. In a previous paper weshowed that the offset of galaxies from the fundamental plane depends ongalaxy age. Here, using the same sample of 88 galaxies, we examine thescatter about the Faber-Jackson (FJ) relation, and find that theposition of a galaxy relative to this relation depends on its age. Inparticular, younger ellipticals are systematically brighter inMB and/or have a lower central velocitydispersion (σ0). The mean relation corresponds togalaxies that are ~10Gyr old. We attempt to reproduce the observed trendof the FJ residuals with age using two simple models. The first assumesthat galaxy age is tracing the last major star formation event in anelliptical galaxy. We assume that this starburst was instantaneous,centrally located and involved 10per cent of the galaxy by mass. Thefading of this burst changes the MBcomponent of the FJ residuals, with time. Such a model was verysuccessful at reproducing the B-V and Mg2 evolution reportedin our previous paper, but is unable to reproduce the strength of the FJtrend. A second model is required to describe age-correlated changes ingalaxy dynamics. Following expectations from cosmological simulations,we assume that σ0, for a galaxy of a given mass, scaleswith the epoch of galaxy formation, i.e. with the mean density of theUniverse. Hence recently formed ellipticals have systematically lowervelocity dispersions than do old ellipticals. We find that a combinationof these two models provides a good match to the change in FJ residualswith galaxy age. This suggests that young ellipticals will have subtlydifferent dynamical properties from old ellipticals. We also find thatthere is not a strong relationship between the age of a galaxy and itsluminosity for our sample. This suggests that the tilt of thefundamental plane is not totally driven by age.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| Central Mg_2 indices for early-type galaxies
We present 210 new measurements of the central absorption line-strength{Mg_2} index for 87 early-type galaxies drawn from the \cite[Prugniel& Simien (1996)]{PS96} sample. 28 galaxies were not observed before.The results are compared to measurements published previously asavailable in HYPERCAT, and rescaled to the Lick system. The meanindividual internal error on these measurements is 0.009m+/-0.003m andthe mean external error is 0.012m+/-0.002m for this series ofmeasurements. Based on observations collected at the Observatoire deHaute-Provence. Tables 1, 3 and 4 are available in electronic form fromthe CDS, Strasbourg (via anonymous ftp to 130.79.128.5). Tables 1 and 3are available from CDS only.
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