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The ACS Virgo Cluster Survey. VIII. The Nuclei of Early-Type Galaxies
The ACS Virgo Cluster Survey is a Hubble Space Telescope program toobtain high-resolution imaging in widely separated bandpasses (F475W~gand F850LP~z) for 100 early-type members of the Virgo Cluster, spanninga range of ~460 in blue luminosity. We use this large, homogenous dataset to examine the innermost structure of these galaxies and tocharacterize the properties of their compact central nuclei. We presenta sharp upward revision in the frequency of nucleation in early-typegalaxies brighter than MB~-15 (66%<~fn<~82%)and show that ground-based surveys underestimated the number of nucleidue to surface brightness selection effects, limited sensitivity andpoor spatial resolution. We speculate that previously reported claimsthat nucleated dwarfs are more concentrated toward the center of Virgothan their nonnucleated counterparts may be an artifact of theseselection effects. There is no clear evidence from the properties of thenuclei, or from the overall incidence of nucleation, for a change atMB~-17.6, the traditional dividing point between dwarf andgiant galaxies. There does, however, appear to be a fundamentaltransition at MB~-20.5, in the sense that the brighter,``core-Sérsic'' galaxies lack resolved (stellar) nuclei. A searchfor nuclei that may be offset from the photocenters of their hostgalaxies reveals only five candidates with displacements of more than0.5", all of which are in dwarf galaxies. In each case, however, theevidence suggests that these ``nuclei'' are, in fact, globular clustersprojected close to the galaxy photocenter. Working from a sample of 51galaxies with prominent nuclei, we find a median half-light radius of=4.2 pc, with the sizes of individual nucleiranging from 62 pc down to <=2 pc (i.e., unresolved in our images) inabout a half-dozen cases. Excluding these unresolved objects, the nucleisizes are found to depend on nuclear luminosity according to therelation rh L0.50+/-0.03. Because the largemajority of nuclei are resolved, we can rule out low-level AGNs as anexplanation for the central luminosity excess in almost all cases. Onaverage, the nuclei are ~3.5 mag brighter than a typical globularcluster. Based on their broadband colors, the nuclei appear to have oldto intermediate age stellar populations. The colors of the nuclei ingalaxies fainter than MB~-17.6 are tightly correlated withtheir luminosities, and less so with the luminosities of their hostgalaxies, suggesting that their chemical enrichment histories weregoverned by local or internal factors. Comparing the nuclei to the``nuclear clusters'' found in late-type spiral galaxies reveals a closematch in terms of size, luminosity, and overall frequency. A formationmechanism that is rather insensitive to the detailed properties of thehost galaxy properties is required to explain this ubiquity andhomogeneity. The mean of the frequency function for thenucleus-to-galaxy luminosity ratio in our nucleated galaxies,=-2.49+/-0.09 dex (σ=0.59+/-0.10), isindistinguishable from that of the SBH-to-bulge mass ratio,=-2.61+/-0.07dex (σ=0.45+/-0.09), calculated in 23 early-type galaxies withdetected supermassive black holes (SBHs). We argue that the compactstellar nuclei found in many of our program galaxies are the low-masscounterparts of the SBHs detected in the bright galaxies. If thisinterpretation is correct, then one should think in terms of ``centralmassive objects''-either SBHs or compact stellar nuclei-that accompanythe formation of almost all early-type galaxies and contain a meanfraction ~0.3% of the total bulge mass. In this view, SBHs would be thedominant formation mode above MB~-20.5.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555.
| Spitzer IRS spectra of Virgo Early-Type Galaxies: Detection of Stellar Silicate Emission
We present high signal-to-noise ratio Spitzer Infrared Spectrographobservations of 17 Virgo early-type galaxies. The galaxies were selectedfrom those that define the color-magnitude relation of the cluster, withthe aim of detecting the silicate emission of their dusty, mass-losingevolved stars. To flux calibrate these extended sources, we have deviseda new procedure that allows us to obtain the intrinsic spectral energydistribution and to disentangle resolved and unresolved emission withinthe same object. We have found that 13 objects of the sample (76%) arepassively evolving galaxies with a pronounced broad silicate featurethat is spatially extended and likely of stellar origin, in agreementwith model predictions. The other four objects (24%) are characterizedby different levels of activity. In NGC 4486 (M87), the line emissionand the broad silicate emission are evidently unresolved, and, givenalso the typical shape of the continuum, they likely originate in thenuclear torus. NGC 4636 shows emission lines superposed on extended(i.e., stellar) silicate emission, thus pushing the percentage ofgalaxies with silicate emission to 82%. Finally, NGC 4550 and NGC 4435are characterized by polycyclic aromatic hydrocarbon (PAH) and lineemission, arising from a central unresolved region. A more detailedanalysis of our sample, with updated models, will be presented in aforthcoming paper.
| The ACS Virgo Cluster Survey. XI. The Nature of Diffuse Star Clusters in Early-Type Galaxies
We use HST ACS imaging of 100 early-type galaxies in the ACS VirgoCluster Survey to investigate the nature of diffuse star clusters(DSCs). Compared to globular clusters (GCs), these star clusters havelow luminosities (MV>-8) and a broad distribution of sizes(320 magarcsec-2). The median colors of diffuse star cluster systems(1.1
| The ACS Virgo Cluster Survey. IX. The Color Distributions of Globular Cluster Systems in Early-Type Galaxies
We present the color distributions of globular cluster (GC) systems for100 early-type galaxies observed in the ACS Virgo Cluster Survey, thedeepest and most homogeneous survey of this kind to date. On average,galaxies at all luminosities in our study (-22
| On the nature of bulges in general and of box/peanut bulges in particular: input from N-body simulations
Objects designated as bulges in disc galaxies do not form a homogeneousclass. I distinguish three types: the classical bulges, the propertiesof which are similar to those of ellipticals and which form by collapseor merging; boxy and peanut bulges, which are seen in near-edge-ongalaxies and which are in fact just a part of the bar seen edge-on; and,finally, disc-like bulges, which result from the inflow of (mainly) gasto the centre-most parts, and subsequent star formation. I make adetailed comparison of the properties of boxy and peanut bulges withthose of N-body bars seen edge-on, and answer previously voicedobjections about the links between the two. I also present and analysesimulations where a boxy/peanut feature is present at the same time as aclassical spheroidal bulge, and compare them with observations. Finally,I propose a nomenclature that can help to distinguish between the threetypes of bulges and avoid considerable confusion.
| The ACS Virgo Cluster Survey. X. Half-Light Radii of Globular Clusters in Early-Type Galaxies: Environmental Dependencies and a Standard Ruler for Distance Estimation
We have measured half-light radii, rh, for thousands ofglobular clusters (GCs) belonging to the 100 early-type galaxiesobserved in the ACS Virgo Cluster Survey and the elliptical galaxy NGC4697. An analysis of the dependencies of the measured half-light radiion both the properties of the GCs themselves and their host galaxiesreveals that, in analogy with GCs in the Galaxy but in a milder fashion,the average half-light radius increases with increasing galactocentricdistance or, alternatively, with decreasing galaxy surface brightness.For the first time, we find that the average half-light radius decreaseswith the host galaxy color. We also show that there is no evidence for avariation of rh with the luminosity of the GCs. Finally, wefind in agreement with previous observations that the averagerh depends on the color of GCs, with red GCs being ~17%smaller than their blue counterparts. We show that this difference isprobably a consequence of an intrinsic mechanism, rather than projectioneffects, and that it is in good agreement with the mechanism proposed byJordán. We discuss these findings in light of two simple picturesfor the origin of the rh of GCs and show that both lead to abehavior in rough agreement with the observations. After accounting forthe dependencies on galaxy color, galactocentric radius, and underlyingsurface brightness, we show that the average GC half-light radii can be successfully used as a standard ruler fordistance estimation. We outline the methodology, provide a calibrationfor its use, and discuss the prospects for this distance estimator withfuture observing facilities. We find =2.7+/-0.35 pcfor GCs with (g-z)=1.2 mag in a galaxy with color(g-z)gal=1.5 mag and at an underlying surface z-bandbrightness of μz=21 mag arcsec-2. Using thistechnique, we place an upper limit of 3.4 Mpc on the 1 σline-of-sight depth of the Virgo Cluster. Finally, we examine the formof the rh distribution for our sample galaxies and provide ananalytic expression that successfully describes this distribution.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| The Kinematic Signature of Face-On Peanut-shaped Bulges
We present a kinematic diagnostic for peanut-shaped bulges in nearlyface-on galaxies. The face-on view provides a novel perspective onpeanuts that would allow study of their relation to bars and disks ingreater detail than hitherto possible. The diagnostic is based on thefact that peanut shapes are associated with a flat density distributionin the vertical direction. We show that the kinematic signaturecorresponding to such a distribution is a minimum in the fourth-orderGauss-Hermite moment s4. We demonstrate our method on N-bodysimulations of varying peanut strength, showing that strong peanuts canbe recognized to inclinations i~=30deg, regardless of thestrength of the bar. We also consider compound systems in which a bulgeis present in the initial conditions, as may happen if bulges form athigh redshift through mergers. We show that in this case, because thevertical structure of the bulge is not derived from that of the disk,the signature of a peanut in s4 is weakened. Thus the samekinematic signature of peanuts can be used to explore bulge formationmechanisms. The observational requirements for identifying peanuts withthis method are challenging, but feasible.
| Radio sources in low-luminosity active galactic nuclei. IV. Radio luminosity function, importance of jet power, and radio properties of the complete Palomar sample
We present the completed results of a high resolution radio imagingsurvey of all ( 200) low-luminosity active galactic nuclei (LLAGNs) andAGNs in the Palomar Spectroscopic Sample of all ( 488) bright northerngalaxies. The high incidences of pc-scale radio nuclei, with impliedbrightness temperatures ≳107 K, and sub-parsec jetsargue for accreting black holes in ≳50% of all LINERs andlow-luminosity Seyferts; there is no evidence against all LLAGNs beingmini-AGNs. The detected parsec-scale radio nuclei are preferentiallyfound in massive ellipticals and in type 1 nuclei (i.e. nuclei withbroad Hα emission). The radio luminosity function (RLF) of PalomarSample LLAGNs and AGNs extends three orders of magnitude below, and iscontinuous with, that of “classical” AGNs. We find marginalevidence for a low-luminosity turnover in the RLF; nevertheless LLAGNsare responsible for a significant fraction of present day massaccretion. Adopting a model of a relativistic jet from Falcke &Biermann, we show that the accretion power output in LLAGNs is dominatedby the kinetic power in the observed jets rather than the radiatedbolometric luminosity. The Palomar LLAGNs and AGNs follow the samescaling between jet kinetic power and narrow line region (NLR)luminosity as the parsec to kilo-parsec jets in powerful radio galaxies.Eddington ratios {l_Edd} (=L_Emitted/L_Eddington) of≤10-1{-}10-5 are implied in jet models of theradio emission. We find evidence that, in analogy to Galactic black holecandidates, LINERs are in a “low/hard” state (gas poornuclei, low Eddington ratio, ability to launch collimated jets) whilelow-luminosity Seyferts are in a “high” state (gas richnuclei, higher Eddington ratio, less likely to launch collimated jets).In addition to dominating the radiated bolometric luminosity of thenucleus, the radio jets are energetically more significant thansupernovae in the host galaxies, and are potentially able to depositsufficient energy into the innermost parsecs to significantly slow thegas supply to the accretion disk.
| The ACS Virgo Cluster Survey. II. Data Reduction Procedures
The ACS Virgo Cluster Survey is a large program to carry out multicolorimaging of 100 early-type members of the Virgo Cluster using theAdvanced Camera for Surveys (ACS) on the Hubble Space Telescope. DeepF475W and F850LP images (~SDSS g and z) are being used to study thecentral regions of the program galaxies, their globular cluster systems,and the three-dimensional structure of Virgo itself. In this paper, wedescribe in detail the data reduction procedures used for the survey,including image registration, drizzling strategies, the computation ofweight images, object detection, the identification of globular clustercandidates, and the measurement of their photometric and structuralparameters.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| The ACS Virgo Cluster Survey. I. Introduction to the Survey
The Virgo Cluster is the dominant mass concentration in the LocalSupercluster and the largest collection of elliptical and lenticulargalaxies in the nearby universe. In this paper, we present anintroduction to the ACS Virgo Cluster Survey: a program to image, in theF475W and F850LP bandpasses (~Sloan g and z), 100 early-type galaxies inthe Virgo Cluster using the Advanced Camera for Surveys on the HubbleSpace Telescope. We describe the selection of the program galaxies andtheir ensemble properties, the choice of filters, the field placementand orientation, the limiting magnitudes of the survey, coordinatedparallel observations of 100 ``intergalactic'' fields with WFPC2, andsupporting ground-based spectroscopic observations of the programgalaxies. In terms of depth, spatial resolution, sample size, andhomogeneity, this represents the most comprehensive imaging survey todate of early-type galaxies in a cluster environment. We brieflydescribe the main scientific goals of the survey, which include themeasurement of luminosities, metallicities, ages, and structuralparameters for the many thousands of globular clusters associated withthese galaxies, a high-resolution isophotal analysis of galaxiesspanning a factor of ~450 in luminosity and sharing a commonenvironment, the measurement of accurate distances for the full sampleof galaxies using the method of surface brightness fluctuations, and adetermination of the three-dimensional structure of Virgo itself.ID="FN1"> 1Based on observations with the NASA/ESA Hubble SpaceTelescope obtained at the Space Telescope Science Institute, which isoperated by the association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
| Morphology and kinematics in thick box-peanut bulge galaxies
Both, observational and theoretical results support the close connectionbetween bars and box/peanut-shaped bulges in spiral galaxies. However,for the sub-class of thick box/peanut-shaped bulges, an environmentalprocess instead of an internal mechanism is suggested to account for theprominence of the box/peanut component. In this paper a multi-wavelengthstudy of the morphology and the kinematics of a sample of thickbox/peanut-shaped bulges is presented. The results suggest a scenario inwhich interaction events play a significant role in the history of thickbox/peanut-shaped bulge galaxies. Most likely these sources haveexperienced a mass infall.
| A New Nonparametric Approach to Galaxy Morphological Classification
We present two new nonparametric methods for quantifying galaxymorphology: the relative distribution of the galaxy pixel flux values(the Gini coefficient or G) and the second-order moment of the brightest20% of the galaxy's flux (M20). We test the robustness of Gand M20 to decreasing signal-to-noise ratio (S/N) and spatialresolution and find that both measures are reliable to within 10% forimages with average S/N per pixel greater than 2 and resolutions betterthan 1000 and 500 pc, respectively. We have measured G andM20, as well as concentration (C), asymmetry (A), andclumpiness (S) in the rest-frame near-ultraviolet/optical wavelengthsfor 148 bright local ``normal'' Hubble-type galaxies (E-Sd) galaxies, 22dwarf irregulars, and 73 0.05
| Spectrophotometry of galaxies in the Virgo cluster. II. The data
Drift-scan mode (3600-6800 Å) spectra with 500
| The Relationship between Stellar Light Distributions of Galaxies and Their Formation Histories
A major problem in extragalactic astronomy is the inability todistinguish in a robust, physical, and model-independent way how galaxypopulations are physically related to each other and to their formationhistories. A similar, but distinct, and also long-standing question iswhether the structural appearances of galaxies, as seen through theirstellar light distributions, contain enough physical information tooffer this classification. We argue through the use of 240 images ofnearby galaxies that three model-independent parameters measured on asingle galaxy image reveal its major ongoing and past formation modesand can be used as a robust classification system. These parametersquantitatively measure: the concentration (C), asymmetry (A), andclumpiness (S) of a galaxy's stellar light distribution. When combinedinto a three-dimensional ``CAS'' volume all major classes of galaxies invarious phases of evolution are cleanly distinguished. We argue thatthese three parameters correlate with important modes of galaxyevolution: star formation and major merging activity. This is arguedthrough the strong correlation of Hα equivalent width andbroadband colors with the clumpiness parameter S, the uniquely largeasymmetries of 66 galaxies undergoing mergers, and the correlation ofbulge to total light ratios, and stellar masses, with the concentrationindex. As an obvious goal is to use this system at high redshifts totrace evolution, we demonstrate that these parameters can be measured,within a reasonable and quantifiable uncertainty with available data outto z~3 using the Hubble Space Telescope GOODS ACS and Hubble Deep Fieldimages.
| A Search for ``Dwarf'' Seyfert Nuclei. VI. Properties of Emission-Line Nuclei in Nearby Galaxies
We use the database from Paper III to quantify the global and nuclearproperties of emission-line nuclei in the Palomar spectroscopic surveyof nearby galaxies. We show that the host galaxies of Seyferts, LINERs,and transition objects share remarkably similar large-scale propertiesand local environments. The distinguishing traits emerge on nuclearscales. Compared with LINERs, Seyfert nuclei are an order of magnitudemore luminous and exhibit higher electron densities and internalextinction. We suggest that Seyfert galaxies possess characteristicallymore gas-rich circumnuclear regions and hence a more abundant fuelreservoir and plausibly higher accretion rates. The differences betweenthe ionization states of the narrow emission-line regions of Seyfertsand LINERs can be partly explained by the differences in their nebularproperties. Transition-type objects are consistent with being composite(LINER/H II) systems. With very few exceptions, the stellar populationwithin the central few hundred parsecs of the host galaxies is uniformlyold, a finding that presents a serious challenge to starburst orpost-starburst models for these objects. Seyferts and LINERs havevirtually indistinguishable velocity fields as inferred from their linewidths and line asymmetries. Transition nuclei tend to have narrowerlines and more ambiguous evidence for line asymmetries. All threeclasses of objects obey a strong correlation between line width and lineluminosity. We argue that the angular momentum content of circumnucleargas may be an important factor in determining whether a nucleus becomesactive. Finally, we discuss some possible complications for theunification model of Seyfert galaxies posed by our observations.
| The Tully-Fisher Relation in Coma and Virgo Cluster S0 Galaxies
We use the Tully-Fisher relation (TFR) to compare the behavior of S0 andlate-type spiral galaxies. We determine circular velocities based onstellar kinematics derived from stellar absorption line spectroscopy for10 S0's in the Coma Cluster and eight S0's in the Virgo Cluster. Wecombine these results with similar measurements of 13 Coma S0 galaxiesobtained previously. We find that there is only a small offset,ΔmH~0.2, in the H-band luminosity at a given circularvelocity, vc~200 km s-1, between S0 and late-typespirals. This result implies a similar total H-band mass-to-light ratio(within an effective radius) among disk galaxies of different Hubbletypes. As the older stellar population in S0's is dimmer, this suggestsa somewhat larger fraction of stellar mass in these S0's than inlate-type spirals. We also find that the relation between (I- andH-band) luminosity and vc for the S0 galaxies is at bestpoorly defined and has a scatter of ~1 mag, significantly larger thanthe TFR for late-type spirals, where the observed I- and H-band scatteris σ~0.3-0.5 mag. This substantial scatter confirms the originalfindings of Dressler & Sandage and is similar to that found in astudy by Neistein and coworkers of 18 nearby S0 galaxies in the fieldwhere σI~0.7 mag, but differs from the small scatterfound by Mathieu and coworkers, σI~0.3 mag, for sixnearby S0's. Our results suggest that differing formation histories canlead to S0's with diverse properties and that S0's are more likely to bethe outcomes of minor mergers or some ``preprocessing'' in groups ofgalaxies falling into clusters, rather than simply late-type spiralsthat have been stripped of their gas but are kinematically preserved. Wesuggest that it is likely that many mechanisms, such as slow encounters,tidal interactions, and gas stripping, may have occurred in thelifetimes of the galaxies and produced the heterogeneous class of S0'sthat are observed today.
| Companions of Bright Barred Shapley-Ames Galaxies
Companion galaxy environment for a subset of 78 bright and nearby barredgalaxies from the Shapley-Ames Catalog is presented. Among the spiralbarred galaxies, there are Seyfert galaxies, galaxies with circumnuclearstructures, galaxies not associated with any large-scale galaxy cloudstructure, galaxies with peculiar disk morphology (crooked arms), andgalaxies with normal disk morphology; the list includes all Hubbletypes. The companion galaxy list includes the number of companiongalaxies within 20 diameters, their Hubble type, and projectedseparation distance. In addition, the companion environment was searchedfor four known active spiral galaxies, three of them are Seyfertgalaxies, namely, NGC 1068, NGC 1097, and NGC 5548, and one is astarburst galaxy, M82. Among the results obtained, it is noted that theonly spiral barred galaxy classified as Seyfert 1 in our list has nocompanions within a projected distance of 20 diameters; six out of 10Seyfert 2 bar galaxies have no companions within 10 diameters, six outof 10 Seyfert 2 galaxies have one or more companions at projectedseparation distances between 10 and 20 diameters; six out of 12 galaxieswith circumnuclear structures have two or more companions within 20diameters.
| Star Formation Histories of Early-Type Galaxies. I. Higher Order Balmer Lines as Age Indicators
We have obtained blue integrated spectra of 175 nearby early-typegalaxies, covering a wide range in galaxy velocity dispersion andemphasizing those with σ<100 km s-1. Galaxies havebeen observed both in the Virgo Cluster and in lower densityenvironments. The main goals are the evaluation of higher order Balmerlines as age indicators and differences in stellar populations as afunction of mass, environment, and morphology. In this first paper, ouremphasis is on presenting the methods used to characterize the behaviorof the Balmer lines through evolutionary population synthesis models.Lower σ galaxies exhibit a substantially greater intrinsicscatter, in a variety of line-strength indicators, than do higherσ galaxies, with the large intrinsic scatter setting in below aσ of 100 km s-1. Moreover, a greater contrast inscatter is present in the Balmer lines than in the lines of metalfeatures. Evolutionary synthesis modeling of the observed spectralindexes indicates that the strong Balmer lines found primarily among thelow-σ galaxies are caused by young age, rather than by lowmetallicity. Thus we find a trend between the population age and thecentral velocity dispersion, such that low-σ galaxies have youngerluminosity-weighted mean ages. We have repeated this analysis usingseveral different Balmer lines and find consistent results from onespectral indicator to another.
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| 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
| The DEEP Groth Strip Survey. X. Number Density and Luminosity Function of Field E/S0 Galaxies at z < 1
We present the luminosity function and color-redshift relation of amagnitude-limited sample of 145 mostly red field E/S0 galaxies atz<~1 from the DEEP Groth Strip Survey (GSS). Using nearby galaxyimages as a training set, we develop a quantitative method to classifyE/S0 galaxies based on smoothness, symmetry, and bulge-to-total lightratio. Using this method, we identify 145 E/S0's at 16.5~1.5. We use the tightcorrelation between V-I and zspec for this red subset toestimate redshifts of the remaining E/S0's to an accuracy of ~10%, withthe exception of a small number (16%) of blue interlopers at lowredshift that are quantitatively classified as E/S0's but are notcontained within the red envelope. Constructing a luminosity function ofthe full sample of 145 E/S0's, we find that there is about 1.1-1.9 magbrightening in rest-frame B-band luminosity back to z~=0.8 from z=0,consistent with other studies. Together with the red colors, thisbrightening is consistent with models in which the bulk of stars in redfield E/S0's formed before zfor>~1.5 and have beenevolving rather quiescently, with few large starbursts since then.Evolution in the number density of field E/S0 galaxies is more difficultto measure, and uncertainties in the raw counts and their ratio to localsamples might amount to as much as a factor of 2. Within thatuncertainty, the number density of red E/S0's to z~=0.8 seems relativelystatic, being comparable to or perhaps moderately less than that oflocal E/S0's, depending on the assumed cosmology. A doubling of E/S0number density since z=1 can be ruled out with high confidence (97%) ifΩm=1. Taken together, our results are consistent withthe hypothesis that the majority of luminous field E/S0's were alreadyin place by z~1, that the bulk of their stars were already fairly old,and that their number density has not changed by large amounts sincethen.
| Identification and classification of galaxies using a biologically-inspired neutral network
Recognition/Classification of galaxies is an important issue in thelarge-scale study of the Universe; it is not a simple task. According toestimates computed from the Hubble Deep Field (HDF), astronomers predictthat the universe may potentially contain over 100 billion galaxies.Several techniques have been reported for the classification ofgalaxies. Parallel developments in the field of neural networks havecome to a stage that they can participate well in the recognition ofobjects. Recently, the Pulse-Coupled Neural Network (PCNN) has beenshown to be useful for image pre-processing. In this paper, we present anovel way to identify optical galaxies by presenting the images of thegalaxies to a hierarchical neural network involving two PCNNs. The imageis presented to the network to generate binary barcodes (one periteration) of the galaxies; the barcodes are unique to the inputgalactic image. In the current study, we exploit this property toidentify optical galaxies by comparing the signatures (binary barcode)from a corresponding database.
| 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.
| Growth of a Peanut-shaped Bulge via Resonant Trapping of Stellar Orbits in the Vertical Inner Lindblad Resonances
We present a simple resonant Hamiltonian model for the vertical responseof a stellar disk to the growth of a bar perturbation. As a barperturbation grows, stars become trapped in vertical inner Lindbladresonances and are lifted into higher amplitude orbits. The verticalstructure of a boxy and peanut-shaped bulge as a function of radius andazimuthal angle in the galaxy plane can be predicted from the strengthand speed of the bar perturbation and the derivatives of thegravitational potential. This model predicts that stars on the outerside of the resonance are lifted higher than stars on the inner side,offering an explanation for the sharp outer edge of the boxy/peanut.
| Redshift-Distance Survey of Early-Type Galaxies. I. The ENEARc Cluster Sample
This paper presents data on the ENEARc subsample of the larger ENEARsurvey of nearby early-type galaxies. The ENEARc galaxies belong toclusters and were specifically chosen to be used for the construction ofa Dn-σ template. The ENEARc sample includes newmeasurements of spectroscopic and photometric parameters (redshift,velocity dispersion, line index Mg2, and the angular diameterdn), as well as data from the literature. New spectroscopicdata are given for 229 cluster early-type galaxies, and new photometryis presented for 348 objects. Repeat and overlap observations withexternal data sets are used to construct a final merged catalogconsisting of 640 early-type galaxies in 28 clusters. Objectivecriteria, based on catalogs of groups of galaxies derived from completeredshift surveys of the nearby universe, are used to assign galaxies toclusters. In a companion paper, these data are used to construct thetemplate Dn-σ distance relation for early-typegalaxies, which has been used to estimate galaxy distances and derivepeculiar velocities for the ENEAR all-sky sample. Based on observationsat Complejo Astronomico El Leoncito, operated under agreement betweenthe Consejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; Cerro Tololo Inter-American Observatory,National Optical Astronomical Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation; the EuropeanSouthern Observatory (ESO), partially under the ESO-ON agreement; theFred Lawrence Whipple Observatory; the Observatório do Pico dosDias, operated by the Laboratório Nacional de Astrofísicaand the MDM Observatory at Kitt Peak.
| 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.
| Total Magnitudes of Virgo Galaxies. I. Construction of a Self-Consistent Reference Dataset Spanning 8th to 18th Magnitude
The main objectives of this series of papers are: (1) to demonstrate theexistence of serious mutual disagreements between established total (andother integrated) magnitude scales for Virgo galaxies; (2) to attempt toquantify both the systematic and random errors present within thesemagnitude scales; (3) to investigate the origins of any large erroruncovered; and thereby (4) to encourage the general adoption of rigoroustotal-magnitude measurement procedures by the astronomical community.The ramifications of the findings presented in this series of paperswill be discussed in detail at a later date. In this paper, the first inthe series, a self-consistent dataset of trustworthy total-magnitudemeasurements is compiled for a sample of Virgo galaxies spanning a rangeof 10 000 in apparent brightness, based on only the most reliablemeasurements and photometry currently available. This reference dataset,which includes luminosity profile shape information, will be used insubsequent papers as one of the bases for assessing existing magnitudescales for Virgo galaxies. As most published magnitudes are based onB-band observations, this series of papers will also focus primarily onB-band measurements.
| 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.
| Luminosity versus Phase-Space-Density Relation of Galaxies Revisited
We reexamined the correlation between the BTmagnitude and the phase-space-density parameterw=(D225vc)-1 of galaxies forthe Virgo, the Coma, the Fornax, and the Perseus clusters in an effortto better understand the physical underpinning of the fundamental plane.A tight correlation (BT=alog w+b) common to differentmorphological types of galaxies (E, S0, S) was found for the Virgo andthe Coma clusters, with a=1.87+/-0.10 and 1.33+/-0.11, respectively. Aninvestigation using only E galaxies was made for the four clusters. Theresults indicated that the empirical linear relation might be commonamong the Coma, the Fornax, and the Perseus clusters, with the VirgoCluster showing deviation. This relation, which is another way toproject the fundamental plane, has an expression insensitive to themorphology and may be suitable for treating galaxies of differentmorphological types collectively.
| The Asymmetry of Galaxies: Physical Morphology for Nearby and High-Redshift Galaxies
We present a detailed study of rotational asymmetry in galaxies for bothmorphological and physical diagnostic purposes. An unambiguous methodfor computing asymmetry is developed, which is robust for both distantand nearby galaxies. By degrading real galaxy images, we test thereliability of this asymmetry measure over a range of observationalconditions, e.g., spatial resolution and signal-to-noise ratio (S/N).Compared to previous methods, this new algorithm avoids the ambiguityassociated with choosing a center by using a minimization method andsuccessfully corrects for variations in S/N. There is, however, a strongrelationship between the rotational asymmetry and physical resolution(distance at fixed spatial resolution): objects become more symmetricwhen less well-resolved. We further investigate asymmetry as a functionof galactic radius and rotation. We find the asymmetry index has astrong radial dependence that differs vastly between Hubble types. As aresult, a meaningful asymmetry index must be specified within awell-defined radius representative of the physical galaxy scale. Weenumerate several viable alternatives, which exclude the use ofisophotes. Asymmetry as a function of angle (Aφ) is alsoa useful indicator of ellipticity and higher order azimuthal structure.In general, we show that the power of asymmetry as a morphologicalparameter lies in the strong correlation with B-V color for galaxiesundergoing normal star formation spanning all Hubble types fromellipticals to irregular galaxies. The few interacting galaxies in ourstudy do not fall on this asymmetry-color ``fiducial sequence,'' asthese galaxies are too asymmetric for their color. We suggest this factcan be used to distinguish between ``normal'' galaxies and galaxiesundergoing an interaction or merger.
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