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The Epochs of Early-Type Galaxy Formation as a Function of Environment
The aim of this paper is to set constraints on the epochs of early-typegalaxy formation through the ``archaeology'' of the stellar populationsin local galaxies. Using our models of absorption-line indices thataccount for variable abundance ratios, we derive ages, totalmetallicities, and element ratios of 124 early-type galaxies in high-and low-density environments. The data are analyzed by comparison withmock galaxy samples created through Monte Carlo simulations taking thetypical average observational errors into account, in order to eliminateartifacts caused by correlated errors. We find that all threeparameters, age, metallicity, and α/Fe ratio, are correlated withvelocity dispersion. We show that these results are robust againstrecent revisions of the local abundance pattern at high metallicities.To recover the observed scatter we need to assume an intrinsic scatterof about 20% in age, 0.08 dex in [Z/H], and 0.05 dex in [α/Fe].All low-mass objects withM*<~1010Msolar (σ<~130kms-1) show evidence for the presence of intermediate-agestellar populations with low α/Fe ratios. About 20% of theintermediate-mass objects with1010<~M*/Msolar<~1011[110<~σ/(kms-1)<~230 both elliptical andlenticular galaxies] must have either a young subpopulation or a bluehorizontal branch. On the basis of the above relationships, valid forthe bulk of the sample, we show that the Mg-σ relation is mainlydriven by metallicity, with similar contributions from the α/Feratio (23%) and age (17%). We further find evidence for an influence ofthe environment on the stellar population properties. Massive early-typegalaxies in low-density environments seem on average ~2 Gyr younger andslightly (~0.05-0.1 dex) more metal-rich than their counterparts inhigh-density environments. No offsets in the α/Fe ratios areinstead detected. With the aid of a simple chemical evolution model, wetranslate the derived ages and α/Fe ratios into star formationhistories. We show that most star formation activity in early-typegalaxies is expected to have happened between redshifts ~3 and 5 inhigh-density environments and between redshifts 1 and 2 in low-densityenvironments. We conclude that at least 50% of the total stellar massdensity must have already formed at z~1, in good agreement withobservational estimates of the total stellar mass density as a functionof redshift. Our results suggest that significant mass growth in theearly-type galaxy population below z~1 must be restricted to lessmassive objects, and a significant increase of the stellar mass densitybetween redshifts 1 and 2 should be present, caused mainly by the fieldgalaxy population. The results of this paper further imply the presenceof vigorous star formation episodes in massive objects at z~2-5 andevolved elliptical galaxies around z~1, both observationally identifiedas SCUBA galaxies and extremely red objects, respectively.
| Study of the Structure of the Coma Cluster Based on a Hierarchical Force Clustering Method
Six subclusters in the Coma cluster have been selected on the basis of ahierarchical clustering method that takes the gravitational interactionamong galaxies into account. Of these, 3 central subclusters around thegalaxies NGC 4889, NGC 4874, and NGC 4839 have been singled out. We haveused the objective statistical criterion applied by Vennik and Anosovain studies of close groups of galaxies to evaluate each member includedin a subcluster with a high probability. Galaxies with a significantdeficit of hydrogen HI, including objects from the Bravo-Alfaro list,have been identified with members of the subclusters, with the greatestnumber of them in the subclusters around NGC 4874 and NGC 4839. Aquantitative estimate of the hydrogen deficit using the HI index in theRCG3 catalog reveals a statistically significant excess value for thosegalaxies that are members of the subclusters compared to galaxies with ahydrogen deficit in the overall Coma cluster field. A substantial numberof the spiral galaxies with a hydrogen deficit in the subclusters turnedout to be radio galaxies as well.
| Spatially resolved spectroscopy of Coma cluster early-type galaxies. III. The stellar population gradients
Based on Paper I of this series (Mehlert et al. \cite{Mehlert00}), wederive central values and logarithmic gradients for the Hβ, Mg andFe indices of 35 early-type galaxies in the Coma cluster. We find thatpure elliptical galaxies have on average slightly higher velocitydispersions, lower Hβ, and higher metallic line-strengths thangalaxies with disks (S0). The latter form two families, one comparableto the ellipticals and a second one with significantly higher Hβ,and weaker metallic lines. Our measured logarithmic gradients within theeffective radius are ~ -0.037, ~ -0.029, ~ +0.017 and ~ -0.063. The gradients strongly correlate with the gradientsof sigma , but only weakly with the central index values and galaxyvelocity dispersion. Using stellar population models with variableelement abundance ratios from Thomas et al. (\cite{Thomas03a}) we deriveaverage ages, metallicities and [α/Fe] ratios in the center and atthe effective radius. We find that the α/Fe ratio correlates withvelocity dispersion and drives 30% of the Mg-sigma relation, theremaining 70% being caused by metallicity variations. We confirmprevious findings that part of the lenticular galaxies in the Comacluster host very young ( ~ 2 Gyr) stellar populations, hence must haveexperienced relatively recent star formation episodes. Again inaccordance with previous work we derive negative metallicity gradients (~ -0.16 dex per decade) that are significantly flatter than what isexpected from gaseous monolithic collapse models, pointing to theimportance of mergers in the galaxy formation history. Moreover, themetallicity gradients correlate with the velocity dispersion gradients,confirming empirically earlier suggestions that the metallicity gradientin ellipticals is produced by the local potential well. The gradients inage are negligible, implying that no significant residual star formationhas occurred either in the center or in the outer parts of the galaxies,and that the stellar populations at different radii must have formed ata common epoch. For the first time we derive the gradients of theα/Fe ratio and find them very small on average. Hence, α/Feenhancement is not restricted to galaxy centers but it is a globalphenomenon. Our results imply that the Mg-sigma local relation inside agalaxy, unlike the global Mg-sigma relation, must be primarily drivenby metallicity variations alone. Finally we note that none of thestellar population parameters or their gradients depend on the densityprofile of the Coma cluster, even though it spans 3 dex in density.Appendix A (Tables A.1-A.3) is only available in electronic form athttp://www.edpsciences.org
| Stellar populations in early-type Coma cluster galaxies - I. The data
We present a homogeneous and high signal-to-noise ratio data set (meanS/N ratio of ~60 Å-1) of Lick/IDS stellar populationline indices and central velocity dispersions for a sample of 132 bright(bj<= 18.0) galaxies within the central 1°(≡1.26h-1 Mpc) of the nearby rich Coma cluster (A1656). Ourobservations include 73 per cent (100 out of 137) of the totalearly-type galaxy population (bj<= 18.0). Observationswere made with the William Herschel 4.2-m telescope and theAUTOFIB2/WYFFOS multi-object spectroscopy instrument (resolution of~2.2-Å FWHM) using 2.7-arcsec diameter fibres (≡0.94h-1 kpc). The data in this paper have well-characterizederrors, calculated in a rigorous and statistical way. Data are comparedwith previous studies and are demonstrated to be of high quality andwell calibrated on to the Lick/IDS system. Our data have median errorsof ~0.1 Å for atomic line indices, ~0.008 mag for molecular lineindices and 0.015 dex for velocity dispersions. This work provides awell-defined, high-quality baseline at z~ 0 for studies of medium- tohigh-redshift clusters. Subsequent papers will use this data set toprobe the stellar populations (which act as fossil records of galaxyformation and evolution) and the spectrophotometric relations of thebright early-type galaxies within the core of the Coma cluster.
| A catalogue and analysis of local galaxy ages and metallicities
We have assembled a catalogue of relative ages, metallicities andabundance ratios for about 150 local galaxies in field, group andcluster environments. The galaxies span morphological types from cD andellipticals, to late-type spirals. Ages and metallicities were estimatedfrom high-quality published spectral line indices using Worthey &Ottaviani (1997) single stellar population evolutionary models. Theidentification of galaxy age as a fourth parameter in the fundamentalplane (Forbes, Ponman & Brown 1998) is confirmed by our largersample of ages. We investigate trends between age and metallicity, andwith other physical parameters of the galaxies, such as ellipticity,luminosity and kinematic anisotropy. We demonstrate the existence of agalaxy age-metallicity relation similar to that seen for local galacticdisc stars, whereby young galaxies have high metallicity, while oldgalaxies span a large range in metallicities. We also investigate theinfluence of environment and morphology on the galaxy age andmetallicity, especially the predictions made by semi-analytichierarchical clustering models (HCM). We confirm that non-clusterellipticals are indeed younger on average than cluster ellipticals aspredicted by the HCM models. However we also find a trend for the moreluminous galaxies to have a higher [Mg/Fe] ratio than the lowerluminosity galaxies, which is opposite to the expectation from HCMmodels.
| 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.
| A Photometric and Spectroscopic Study of Dwarf and Giant Galaxies in the Coma Cluster. II. Spectroscopic Observations
This is the second paper in a series studying the photometric andspectroscopic properties of galaxies of different luminosities in theComa Cluster. We present the sample selection, spectroscopicobservations, and completeness functions. To study the spectralproperties of galaxies as a function of their local environment, twofields were selected for spectroscopic observations to cover both thecore (Coma 1) and outskirts (i.e., southwest of the core and centered onNGC 4839; Coma 3) of the cluster. To maximize the efficiency ofspectroscopic observations, two subsamples were defined, consisting of``bright'' and ``faint'' galaxies, both drawn from magnitude-limitedparent samples. Medium-resolution spectroscopy (6-9 Å) was thencarried out for a total of 490 galaxies in both fields (302 in Coma 1and 188 in Coma 3), using the WYFFOS multifiber spectrograph on theWilliam Herschel Telescope. The galaxies cover a range of 122. The completeness functions for our sampleare calculated. These show that the bright sample is 65% complete atR<17 mag, becoming increasingly incomplete toward fainter magnitudes,while the faint sample follows a monotonically decreasing completenessfunction at R>19 mag. Based on observations made with the WilliamHerschel Telescope, operated on the island of La Palma by the IsaacNewton Group in the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofisica de Canarias.
| 1.65 μm (H-band) surface photometry of galaxies. III. observations of 558 galaxies with the TIRGO 1.5 m telescope
We present near-infrared H-band (1.65 μm ) surface photometry of 558galaxies in the Coma Supercluster and in the Virgo cluster. This dataset, obtained with the Arcetri NICMOS3 camera ARNICA mounted on theGornergrat Infrared Telescope, is aimed at complementing, withobservations of mostly early-type objects, our NIR survey of spiralgalaxies in these regions, presented in previous papers of this series.Magnitudes at the optical radius, total magnitudes, isophotal radii andlight concentration indices are derived. We confirm the existence of apositive correlation between the near-infrared concentration index andthe galaxy H-band luminosity Based on observations taken at TIRGO(Gornergrat, Switzerland). TIRGO is operated by CAISMI-CNR, Arcetri,Firenze, Italy. Tables 1 and 2 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Spatially resolved spectroscopy of Coma cluster early-type galaxies. I. The database
We present long slit spectra for a magnitude limited sample of 35 E andS0 galaxies of the Coma cluster. The high quality of the data allowed usto derive spatially resolved spectra for a substantial sample of Comagalaxies for the first time. From these spectra we obtained rotationcurves, the velocity dispersion profiles and the H_3 and H_4coefficients of the Hermite decomposition of the line of sight velocitydistribution. Moreover, we derive the radial line index profiles of Mg,Fe and Hβ line indices out to R~ 1 r_e - 3 r_e with highsignal-to-noise ratio. We describe the galaxy sample, the observationsand data reduction, and present the spectroscopic database. Ground-basedphotometry for a subsample of 8 galaxies is also presented. The Comacluster is one of the richest known clusters of galaxies, spanning about4 decades in density. Hence it is the ideal place to study the structureof galaxies as a function of environmental density in order to constrainthe theories of galaxy formation and evolution. Based on thespectroscopic database presented, we will discuss these issues in aseries of future papers. Tables 1 and 4 are also available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/Abstract.html Tables 5 to 82 are onlyavailable in electronic form at CDS.
| Extensive near-infrared (H-band) photometry in Coma
We present extensive and accurate photometry in the near-infrared H bandof a complete sample of objects in an area of about 400arcmin2 toward the Coma cluster of galaxies. The sample,including about 300 objects, is complete down to H ~ 17 mag, the exactvalue depending on the type of magnitude (isophotal, aperture, Kron) andthe particular region studied. This is six magnitudes below thecharacteristic magnitude of galaxies, well into the dwarfs' regime atthe distance of the Coma cluster. For each object (star or galaxy) weprovide aperture magnitudes computed within five different apertures,the magnitude within the 22 mag arcsec-2 isophote, the Kronmagnitude and radius, magnitude errors, as well as the coordinates, theisophotal area, and a stellarity index. Photometric errors are 0.2 magat the completness limit. This sample is meant to be the zero-redshiftreference for evolutionary studies of galaxies. Based on observationscollected with the Telescope Bernard Lyot, at the Pic du MidiObservatory, operated by INSU (CNRS).
| 1.65 μm (H-band) surface photometry of galaxies. V. Profile decomposition of 1157 galaxies
We present near-infrared H-band (1.65 μm) surface brightness profiledecomposition for 1157 galaxies in five nearby clusters of galaxies:Coma, A1367, Virgo, A262 and Cancer, and in the bridge between Coma andA1367 in the ``Great Wall". The optically selected (mpg≤16.0) sample is representative of all Hubble types, from E to Irr+BCD,except dE and of significantly different environments, spanning fromisolated regions to rich clusters of galaxies. We model the surfacebrightness profiles with a de Vaucouleurs r1/4 law (dV), withan exponential disk law (E), or with a combination of the two (B+D).From the fitted quantities we derive the H band effective surfacebrightness (μe) and radius (re) of each component, theasymptotic magnitude HT and the light concentration indexC31. We find that: i) Less than 50% of the Ellipticalgalaxies have pure dV profiles. The majority of E to Sb galaxies is bestrepresented by a B+D profile. All Scd to BCD galaxies have pureexponential profiles. ii) The type of decomposition is a strong functionof the total H band luminosity (mass), independent of the Hubbleclassification: the fraction of pure exponential decompositionsdecreases with increasing luminosity, that of B+D increases withluminosity. Pure dV profiles are absent in the low luminosity rangeLH<1010 L\odot and become dominantabove 1011 L\odot . Based on observations taken atTIRGO, Gornergrat, Switzerland (operated by CAISMI-CNR, Arcetri,Firenze, Italy) and at the Calar Alto Observatory (operated by theMax-Planck-Institut für Astronomie (Heidelberg) jointly with theSpanish National Commission for Astronomy). Table 2 and Figs. 2, 3, 4are available in their entirety only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| E and S0 galaxies in the central part of the Coma cluster: ages, metal abundances and dark matter
Mean ages and metal abundances are estimated for the stellar populationsin a sample of 115 E and S0 galaxies in the central 64 arcmin × 70arcmin of the Coma cluster. The estimates are based on the absorptionline indices Mg2, and HβG, and themass-to-light ratios (M/L). Single stellar population models fromVazdekis et al. were used to transform from the measured line indicesand M/L ratios to mean ages and mean metal abundances ([Mg/H] and[Fe/H]). The non-solar abundance ratios [Mg/Fe] were taken into accountby assuming that for a given age and iron abundance, a [Mg/Fe] differentfrom solar will affect the Mg2 index but not the M/L ratio orthe and HβG indices. The derived ages andabundances are the luminosity-weighted mean values for the stellarpopulations in the galaxies.By comparing the mean ages derived from theMg2-HβG diagram with those derived from theMg2-M/L diagram, we estimate the variations of the fractionof dark matter. Alternatively, the difference between the two estimatesof the mean age may be caused by variations in the initial mass functionor any non-homology of the galaxies.The distributions of the derived mean ages and abundances show thatthere are real variations in both the mean ages and the abundances. Wefind an intrinsic rms scatter of [Mg/H], [Fe/H] and [Mg/Fe] of 0.2 dex,and an intrinsic rms scatter of the derived ages of 0.17 dex. Themagnesium abundances [Mg/H] and the abundance ratios [Mg/Fe] are bothstrongly correlated with the central velocity dispersions of thegalaxies, while the iron abundances [Fe/H] are uncorrelated with thevelocity dispersions. Further, [Mg/H] and [Fe/H] are stronglyanticorrelated with the mean ages of the galaxies. This is not the casefor [Mg/Fe].We have tested whether the slopes of the scaling relations between theglobal parameters for the galaxies (the Mg2-σ relation,the -σ relation, the HβG-σrelation and the Fundamental Plane) are consistent with the relationbetween the ages, the abundances and the velocity dispersions. We findthat all the slopes, except the slope of the Fundamental Plane, can beexplained in a consistent way as resulting from a combination betweenvariations of the mean ages and the mean abundances as functions of thevelocity dispersions. The slope of the Fundamental Plane is `steeper'than predicted from the variations in the ages and abundances.Because of the correlation between the mean ages and the meanabundances, substantial variations in the ages and the abundances arepossible while maintaining a low scatter of all the scaling relations.When this correlation is taken into account, the observed scatter of thescaling relations is consistent with the rms scatter in the derived agesand abundances at a given velocity dispersion.
| 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.
| Fundamental plane distances to early-type field galaxies in the South Equatorial Strip. I. The spectroscopic data
Radial velocities and central velocity dispersions are derived for 238E/S0 galaxies from medium-resolution spectroscopy. New spectroscopicdata have been obtained as part of a study of the Fundamental Planedistances and peculiar motions of early-type galaxies in three selecteddirections of the South Equatorial Strip, undertaken in order toinvestigate the reality of large-scale streaming motion; results of thisstudy have been reported in Müller et al. (1998). The new APM SouthEquatorial Strip Catalog (-17fdg 5 < delta < +2fdg 5) was used toselect the sample of field galaxies in three directions: (1) 15h10 -16h10; (2) 20h30 - 21h50; (3) 00h10 - 01h30. The spectra obtained have amedian S/N per Å of 23, an instrumental resolution (FWHM) of ~ 4Å, and the spectrograph resolution (dispersion) is ~ 100 kms-1. The Fourier cross-correlation method was used to derivethe radial velocities and velocity dispersions. The velocity dispersionshave been corrected for the size of the aperture and for the galaxyeffective radius. Comparisons of the derived radial velocities with datafrom the literature show that our values are accurate to 40 kms-1. A comparison with results from Jo rgensen et al. (1995)shows that the derived central velocity dispersion have an rms scatterof 0.036 in log sigma . There is no offset relative to the velocitydispersions of Davies et al. (1987).
| The Universality of the Fundamental Plane of E and S0 Galaxies: Sample Definition and I-Band Photometric Data
As part of a project to compare the fundamental plane and Tully-Fisherdistance scales, we present here I-band CCD photometry for 636early-type galaxies in eight clusters and groups of galaxies. These arethe A262, A1367, Coma (A1656), A2634, Cancer and Pegasus Clusters, andthe NGC 383 and NGC 507 Groups. Sample selection, cluster properties,and cluster membership assignment criteria are discussed. We presentphotometric parameters that are used in the fundamental plane relation,the effective radius r_e, and the effective surface brightness mu_e, asderived from a r^1/4 fit to the observed radial photometric profile ofeach galaxy. A comparison with similar data found in the literature forthe Coma Cluster shows that large systematic uncertainties can beintroduced in the measurement of r_e and mu_e by the particular methodused to derive those parameters. However, the particular combination ofthese two parameters that enters in the fundamental plane relation is aquantity that can be measured with high accuracy.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| The distribution of the rotation axes of the disk galaxies in the Coma cluster: statistical samples.
Not Available
| Morphological classification and structural parameters of galaxies in the Coma and Perseus clusters
We present the results of an isophotal shape analysis of galaxies in theComa and Perseus clusters. These data, together with those of twoprevious papers, provide two complete samples of galaxies with reliableHubble types in rich clusters: 1) all galaxies brighter than m_b = 16.5falling within one degree (=2.3 Mpc) from the center of the Coma cluster(187 galaxies), 2) all galaxies brighter than m_Zwicky=15.7 in a regionof 5 degr 3' times 5 degr 27' around the center of the Perseus cluster(139 galaxies). These two complete samples cover 5 orders of magnitudein galaxy density and span areas of 91 and 17 Mpc^2, clustercentricradii up to 6.4 and 2.3 Mpc, for Perseus and Coma respectively. Theywill be used in subsequent papers to study the dependence of galaxytypes on cluster environment and as reference samples in comparisonswith distant clusters. Based on observations made with the 2-meterTelescope Bernard Lyot of Pic-du-Midi Observatory, operated by INSU(CNRS) and the Schmidt telescope at the Calern Observatory (OCA). Alltables are only available in electronic form at the CDS anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| Multicolour CCD surface photometry for E and S0 galaxies in 10 clusters
CCD surface photometry for 232 E and S0 galaxies is presented. Thegalaxies are observed in Gunn r and Johnson B, or Gunn r and g. For 48of the galaxies surface photometry in Johnson U is also presented.Aperture magnitudes in Gunn nu are derived for half of the galaxies.Galaxies in the following clusters have been observed: Abell 194, Abell539, Abell 3381, Abell 3574, Abell S639, Abell S753, HydraI (Abell1060), DC2345-28, Doradus and Grm15. The data are part of our ongoingstudy of the large-scale motions in the Universe and the physicalbackground for the fundamental plane. We use a full model fittingtechnique for analysing the CCD images. This gives radial profiles oflocal surface brightness, colour, ellipticity and position angle. Theresiduals relative to the elliptical isophotes are describedquantitatively by Fourier expansions. Effective radius, mean surfacebrightness and total magnitude are derived by fitting a de Vaucouleursr^¼ growth curve. We have derived a characteristic radius r_nsimilar to the diameter D_n introduced by Dressler et al. The derivationof the effective parameters and of r_n takes the seeing into account. Weconfirm the results by Saglia et al. that the effects of the seeing canbe substantial. Seeing-corrected values of the effective parameters andr_n are also presented for 147 E and S0 galaxies in the Coma cluster.Colours, colour gradients and geometrical parameters are derived. Thephotometry is internally consistent within 0.016 mag. Comparison withthe photoelectric aperture photometry from Burstein et al. shows a meanoffset of 0.010 mag with an rms scatter of 0.034 mag. The globalphotometric parameters are compared with data from Faber et al., Luceyet al. and Lucey & Carter. These comparisons imply that the typicalrms errors are as follows - log r_n:+/-0.015 log r_e:+/-0.045m_T:+/-0.09 mag; _e:+/-0.16 mag. The rms error on thecombination log r_e-0.35_e which enters the fundamental planeis +/-0.020. Also, comparisons with data from Saglia et al. arepresented. The accuracy of the absolute photometry, as well as thederived parameters, makes the data suitable for our investigations ofthe fundamental plane and of the large-scale motions in the Universe.
| Automated surface photometry for the Coma Cluster galaxies: The catalog
A homogeneous photometry catalog is presented for 450 galaxies withB25.5 less than or equal to 16 mag located in the 9.8 deg x9.8 deg region centered on the Coma Cluster. The catalog is based onphotographic photometry using an automated surface photometry softwarefor data reduction applied to B-band Schmidt plates. The catalogprovides accurate positions, isophotal and total magnitudes, major andminor axes, and a few other photometric parameters including rudimentarymorphology (early of late type).
| ROSAT observations of Coma Cluster galaxies
The approximately 86 ks ROSAT Position Sensitive Proportional Counter(PSPC) image of the Coma Cluster is deeper than any previous X-rayobservation of a galaxy cluster. We search for X-ray emission from 35individual galaxies in a magnitude-limited sample, all of which liewithin 20 arcmins of the optical axis in at least one of the four Comapointings. We detect seven galaxies in the 0.4-2.4 keV band at asignificance level exceeding 3 sigma, and a further four at above 2sigma. Although we can set only upper limits on the individual flux fromeach of the other galaxies, we are able to measure their mean flux bystacking the observations. The X-ray luminosities of the sevendetections range from 6.2 x 1040 to 1.5 x 1042ergs/s (0.4-2.4 keV for H0 = 50 km/s/Mpc). For galaxies witha blue absolute magnitude of about -21 we find a mean X-ray luminosityof 1.3 x 1040 ergs/s. The ratio of X-ray to opticalluminosity is substantially smaller for such subjects than for thebrightest galaxies in the cluster. The X-ray luminosities of the fourbrightest galaxies are ill-defined, however, because of ambiguity indistinguishing galaxy emission from cluster emission. Each objectappears to be related to significant structure in the diffuseintracluster medium. We also investigate emission in the softer 0.2-0.4keV band where detections are less significant because of the higherbackground, and we discuss the properties of a number of interestingindividual sources. The X-ray luminosities of the Coma galaxies aresimilar to those of galaxies in the Virgo Cluster and in other regionswith relatively low galaxy density. We conclude that large-scaleenvironmental effects do not significantly enhance or suppress theaverage X-ray emission from galaxies, but that individual objects varyin luminosity substantially in a way which may depend on the detailedhistory of their environment.
| Galaxy Properties at the North Galactic Pole. I. Photometric Properties on Large Spatial Scales
A two-color study of the galaxies detected on POSS-I in a 289 squaredegree region centered on the North Galactic Pole is presented. We use avariety of mapping techniques to characterize the large-scale spatialdistribution of galaxies. The depth and sample size of this new surveyallows, for the first time, the isolation of large photometricsubsamples of galaxies in high- and low-density environments on thescale of superclusters. Our principal finding is a statisticallysignificant difference between the mean photometric properties of thesesubsamples in the sense that galaxies in the high-density Coma andfilament environments have redder colors and larger concentrationindices than galaxies drawn from low-density interfilament regions.These results are in accord with the known morphology-density relation.Thus, appropriately chosen photometric and morphological parameters, inconcert with a galaxy surface density map, can be used to selectstructures from the projected galaxy distribution which correspond toregions of high density. An illustration of this point is our discoveryof a concentration of blue galaxies identified in our maps near the coreof the Coma cluster. This feature is comprised of early-type galaxieswhich exhibit signs of current or recent star formation. These resultsare predicated on relations between morphological type and photometricparameters derived from APS scans of POSS-I. We therefore discuss theimage calibration procedures used to compile our catalog of physicallysignificant photometric parameters. We demonstrate the morphologicaltype dependence among quantities such as mean color and imageconcentration index, and the lack of such a dependence for mean surfacebrightness.
| The nature of E and S0 galaxies: A study of magnitude-limited sample of galaxies in the Coma Cluster
Differences and similarities of E and S0 galaxies have been investigatedon basis of new CCD surface photometry in Gunn r for 171 galaxies withinthe central square degree of the Coma Cluster; 146 of the galaxies areclassified as E or S0. The galaxies form a magnitude-limited sample withGunn r less than or equal to 15.3 mag. Together with the sample of Virgogalaxies compiled by Caon et al. (1993), this sample is one of the firstvolume-limited samples. The isophotal shapes of the galaxies have beenstudied in terms of ellipticity, c4 and c6. Thesample is deficit of apparently round S0 galaxies. The distribution ofthe apparent ellipticities for the S0 galaxies cannot be fittedsatisfactorily with any simple distribution of the intrinsicellipticities. This suggests that face-on S0 galaxies have beenclassified as ellipticals. It is shown that theellipticity-c4 diagram can be used for determination ofrelative disk luminosities, LD/Ltot. Thedistribution of LD/Ltot for galaxies fainter thanMB(sub T) = -22 mag is very broad (H0 = 50 km/(sMpc) is used). The distribution is best fitted by a model where 10% ofthe galaxies are diskless and 90% of the galaxies are drawn from adistribution which is uniform from zero to one. This model also predictsdistributions of apparent ellipticities, c4, and inclinationswhich are in agreement with the data. E galaxies brighter thanMB(sub T) = -22 mag do not show any evidence of disks and mayform another class. The sample contains no S0 galaxies brighter thanMB(sub T) = -22 mag. Our analysis implies that the E and S0galaxies fainter than MB(sub T) = -22 mag form one class ofgalaxies with a continuous change in LD/Ltot.Face-on members of this class are mostly classified as E galaxies whilemore edge-on members are classified as S0 galaxies. Further, it is foundthat only 12% of all the galaxies in the sample are truly disklesssystems. The diskless systems contribute approximately 30% to the totalluminosity of the sample, most of this originates from the six brightestgalaxies.
| Optical positions and 327 MHz flux-densities of UGC galaxies in selected Westerbork fields
The study presents accurate optical positions of 421 UGC galaxies whichare used to search for 30 92-cm WSRT fields observed for emission fromthese galaxies. Good 92-cm flux densities were obtained for 140galaxies, marginal flux densities for 71 galaxies, and upper limits for210 galaxies. For 35 galaxies, spectral indices in the decimeterwavelength range are determined. The mean spectral index for spiralgalaxies (0.72 +/- 0.03) is very similar to that of elliptical galaxies(0.64 +/- 0.10). The four multiple systems in the sample have a muchflatter spectral index (-0.21 +/- 0.07), from which the presence of asignificant thermal component in their total radio emission issuggested. Comparison with IRAS results show that about half of thegalaxies detected at radio wavelengths are detected in the FIR. It isproposed that some spiral galaxies are anomalously weak in the IR ascompared with their radio brightness.
| Upper limit on interstellar gas in Coma cluster ellipticals
X-ray emission from 45 early-type galaxies in Coma is explored usingdata from the IPC on the Einstein Observatory. Data for a cleansubsample of 27 observations of galaxies greater than 13 arcmin from thecluster center yield only upper limits, which are generally larger thanthose of field ellipticals with similar optical luminosities. The meangalaxy X-ray and blue luminosities for the subsample are less than 2.2 x10 exp 40 ergs/s and 4.4 x 10 exp 10 solar luminosities, respectively.It is concluded that environmental effects in rich clusters do notenhance the X-ray emission from individual elliptical galaxies. It isargued that the small-scale fluctuations in cluster X-ray surfacebrightness observed by Soltan and Fabricant (1990) and attributed to asmall number of sources with luminosities of about 4 x 10 exp 41 ergs/sare more likely due to AGN than to hot interstellar gas.
| Optical positions of miscellaneous galaxies
Not Available
| Associations between quasi-stellar objects and galaxies
A table is presented here listing all close pairs of QSOs and galaxiesthat were found in a computer-aided search of catalogs of QSOs andbright galaxies and an extensive search of the literature. There is alarge excess of pairs with separations of 2 arcmin lor less, or about 60kpc, over the numbers expected if the configurations were accidental.The angular separation for 392 pairs adds to the evidence for physicalassociation, and it is shown that selection effects are not important. Ageneral rule is stated that QSOs tend to lie in the vicinity of normalgalaxies much more often than is expected by chance whether or not thegalaxies and the QSOs have the same redshifts. It is emphasized thatthis rule cannot be explained in terms of gravitational microlensing,and it is concluded that some part of the redshift of all classes ofactive nuclei is not associated with the expansion of the universe.
| The manifold of early-type galaxies from IR photometry - The Coma cluster
Accurate IR JHK photometry was obtained for galaxies of variousmorphotogical types (38 elliptical, 48 lenticular, 18 spiral, and oneirregular), which are members of the Coma cluster, to determine if thereare systematic trends in the population and metallicity effectscorrelated with galaxy morphology and/or luminosity. Results show nodefinite trends in (J-H), (H-K), and (J-K) vs K(-0.3) diagrams. Theaperture-corrected (V-K)sub -0.3 vs K(-0.3) diagram revealed a weakrelationship between the color and the magnitude for the early-typegalaxies in the Coma cluster. The positive correlations between themetallicity index Mg2 and the luminosities L(B) and L(K) are confirmed;the metallicity effect was found to be steeper in the blue region thanin the IR.
| Groups of galaxies in the Center for Astrophysics redshift survey
By applying the Huchra and Geller (1982) objective group identificationalgorithm to the Center for Astrophysics' redshift survey, a catalog of128 groups with three or more members is extracted, and 92 of these areused as a statistical sample. A comparison of the distribution of groupcenters with the distribution of all galaxies in the survey indicatesqualitatively that groups trace the large-scale structure of the region.The physical properties of groups may be related to the details oflarge-scale structure, and it is concluded that differences among groupcatalogs may be due to the properties of large-scale structures andtheir location relative to the survey limits.
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