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Globular cluster systems in low-luminosity early-type galaxies near the Fornax cluster centre
We present a photometric study of the globular cluster systems (GCSs) ofthe Fornax cluster galaxies NGC1374, NGC1379 and NGC1387. The dataconsist of images from the wide-field MOSAIC imager of the Cerro TololoInter-American Observatory (CTIO) 4-m telescope, obtained withWashington C and Kron-Cousins R filters. The images cover a field of 36× 36arcmin2, corresponding to 200 ×200kpc2 at the Fornax distance. Two of the galaxies, NGC1374and NGC1379, are low-luminosity ellipticals while NGC1387 is alow-luminosity lenticular. Their cluster systems are still embedded inthe cluster system of NGC1399. Therefore, the use of a large field iscrucial and some differences to previous work can be explained by this.The colour distributions of all GCSs are bimodal. NGC1387 presents aparticularly distinct separation between red and blue clusters and anoverproportionally large population of red clusters. The radialdistribution is different for blue and red clusters, red clusters beingmore concentrated towards the respective galaxies. The different colourand radial distributions point to the existence of two globular clustersubpopulations in these galaxies. Specific frequencies are in the rangeSN= 1.4-2.4, smaller than the typical values for ellipticalgalaxies. These galaxies might have suffered tidal stripping of blueglobular clusters by NGC1399.
| The Look-Back Time Evolution of the UV Upturn Phenomenon
In order to investigate the origin of the far-UV (FUV) flux fromearly-type galaxies, Galaxy Evolution Explorer (GALEX) is collecting theUV data for the elliptical-rich clusters at moderate redshifts (z <0.25) where the dominant FUV source is predicted to be hothorizontal-branch (HB) stars and their post-HB progeny. The earlyresults show that the FUV flux of quiescent early-type galaxies doesevolve substantially during the last 1--2 Gyr of look-back time, and theobserved UV fading is consistent with the variation predicted by thepopulation synthesis models where the mean temperature of HB starsdeclines rapidly with increasing look-back time.
| A Chandra Survey of Early-Type Galaxies. I. Metal Enrichment in the Interstellar Medium
We present a Chandra study of the emission-weighted metal abundances in28 early-type galaxies, spanning ~3 orders of magnitude in X-rayluminosity (LX). We report constraints for Fe, O, Ne, Mg, Si,S, and Ni. We find no evidence of the very subsolar Fe abundance(ZFe) historically reported, confirming a trend in recentobservations of bright galaxies and groups, nor do we find anycorrelation between ZFe and luminosity. Excepting one case,the ISM is single-phase, indicating that multitemperature fits foundwith ASCA reflected temperature gradients that we resolve with Chandra.We find no evidence that ZFe (ISM) is substantially lowerthan the stellar metallicity estimated from simple stellar populationmodels. In general, these quantities are similar, which is inconsistentwith galactic wind models and recent hierarchical chemical enrichmentsimulations. Our abundance ratio constraints imply that 66%+/-11% of theISM Fe was produced in SNe Ia, similar to the solar neighborhood,indicating similar enrichment histories for elliptical galaxies and theMilky Way. Although these values are sensitive to the considerablesystematic uncertainty in the supernova yields, they are in agreementwith observations of more massive systems. This indicates considerablehomology in the enrichment process operating from cluster scales tolow-to-intermediate-LX galaxies. The data uniformly exhibitlow ZO/ZMg ratios, which have been reported insome clusters, groups, and galaxies. This is inconsistent with standardSN II metal yield calculations and may indicate an additional source ofenrichment, such as Population III hypernovae.
| Large-scale study of the NGC 1399 globular cluster system in Fornax
We present a Washington C and Kron-Cousins R photometric study of theglobular cluster system of NGC 1399, the central galaxy of the Fornaxcluster. A large areal coverage of 1 square degree around NGC 1399 isachieved with three adjoining fields of the MOSAIC II Imager at the CTIO4-m telescope. Working on such a large field, we can perform the firstindicative determination of the total size of the NGC 1399 globularcluster system. The estimated angular extent, measured from the NGC 1399centre and up to a limiting radius where the areal density of blueglobular clusters falls to 30 per cent of the background level, is 45± 5 arcmin, which corresponds to 220-275 kpc at the Fornaxdistance. The bimodal colour distribution of this globular clustersystem, as well as the different radial distribution of blue and redclusters, up to these large distances from the parent galaxy, areconfirmed. The azimuthal globular cluster distribution exhibitsasymmetries that might be understood in terms of tidal stripping ofglobulars from NGC 1387, a nearby galaxy. The good agreement between theareal density profile of blue clusters and a projected dark-matter NFWdensity profile is emphasized.
| The Chandra Fornax Survey. I. The Cluster Environment
We present the first results of a deep Chandra survey of the inner~1° of the Fornax cluster of galaxies. Ten 50 ks pointings wereobtained in a mosaic centered on the giant elliptical galaxy NGC 1399 atthe nominal cluster center. Emission and temperature maps of Fornax arepresented, and an initial study of more than 700 detected X-ray pointsources is made. Regions as small as 100 pc are resolved. Theintracluster gas in Fornax exhibits a highly asymmetric morphology andtemperature structure, dominated by a 180 kpc extended ``plume'' of lowsurface brightness, cool (<=1 keV) gas to the northeast of NGC 1399with a sharper edge to the southwest. The elliptical galaxy NGC 1404also exhibits a cool halo of X-ray gas within the cluster, with a highlysharpened leading edge as it presumably falls into the cluster and acomet-like tail. We estimate that some ~200-400 point sources arephysically associated with Fornax. Confirming earlier works, we findthat the globular cluster population in NGC 1399 is highly X-ray active,extending to globular clusters that may in fact be intracluster systems.We have also found a remarkable correlation between the location ofgiant and dwarf cluster galaxies and the presence of X-ray counterparts,such that systems inhabiting regions of low gas density are more likelyto show X-ray activity. Not only does this correlate with the asymmetryof the intracluster gas, but it also correlates with the axis joiningthe center of Fornax to an infalling group 1 Mpc to the southwest. Wesuggest that Fornax may be experiencing either an intergalactic``headwind'' due to motion relative to the surrounding large-scalestructure or that the intracluster medium has been disturbed relative tothe overall cluster gravitational potential by previous activity.
| The Vertical Stellar Kinematics in Face-On Barred Galaxies: Estimating the Ages of Bars
In order to perform a detailed study of the stellar kinematics in thevertical axis of bars, we obtained high signal-to-noise spectra alongthe major and minor axes of the bars in a sample of 14 face-on galaxiesand used them to determine the line-of-sight stellar velocitydistribution, parameterized as a Gauss-Hermite series. With these data,we developed a diagnostic tool that allows one to distinguish betweenrecently formed and evolved bars, as well as to estimate their ages,assuming that bars form in vertically thin disks that are recognizableby low values for the vertical velocity dispersion σz.Through N-body realizations of bar unstable disk galaxies we were alsoable to check the timescales involved in the processes that give bars animportant vertical structure. We show that σz inevolved bars is roughly 100 km s-1, which translates to aheight scale of about 1.4 kpc, giving support to scenarios in whichbulges form through disk material. Furthermore, the bars in ournumerical simulations have values for σz generallysmaller than 50 km s-1, even after evolving for 2 Gyr,suggesting that a slow process is responsible for making bars asvertically thick as we observe. We verify theoretically that theSpitzer-Schwarzschild mechanism is quantitatively able to explain theseobservations if we assume that giant molecular clouds are twice asconcentrated along the bar as in the rest of the disk.
| The Look-back Time Evolution of Far-Ultraviolet Flux from Elliptical Galaxies: The Fornax Cluster and A2670
In order to investigate the origin of the far-UV (FUV) flux from theearly-type galaxies, the Galaxy Evolution Explorer is collecting the UVdata for the elliptical-rich clusters at moderate redshifts (z<0.2)where the dominant FUV source is predicted to be hot horizontal-branch(HB) stars and their post-HB progeny. Here we present our first resultfor the early-type galaxies in A2670 at z=0.076. Compared to NGC 1399, anearby giant elliptical galaxy in the Fornax Cluster, it appears thatthe rest-frame FUV-V color of the giant elliptical galaxies gets redderby ~0.7 mag at the distance of A2670 (z=0.076; look-back time~1.0 Gyr).Although a detailed comparison with the models is postponed until morecluster data are accumulated, it is interesting to note that this valueis consistent with the variation predicted by the population synthesismodels where the mean temperature of HB stars declines rapidly withincreasing look-back time.
| Tramp Novae between Galaxies in the Fornax Cluster: Tracers of Intracluster Light
We report the results of a survey for novae in and between the galaxiesof the Fornax Cluster. Our survey provides strong evidence thatintracluster novae exist and that they provide a useful, independentmeasure of the intracluster light in Fornax. We discovered six strongnova candidates in six distinct epochs spanning 11 yr from 1993 to 2004.The data were taken with the 4 m and the 1.5 m telescopes at CerroTololo Inter-American Observatory. The spatial distribution of the novacandidates is consistent with ~16%-41% of the total light in the clusterbeing in the intracluster light, based on the ratio of the number ofnovae we discovered in intracluster space over the total number of novaediscovered plus a simple completeness correction factor. This estimateis consistent with independent measures of intracluster light in Fornaxand Virgo using intracluster planetary nebulae. The accuracy of theintracluster light measurement improves with each survey epoch as morenovae are discovered.
| A sample of X-ray emitting normal galaxies from the BMW-HRI Catalogue
We obtained a sample of 143 normal galaxies with X-ray luminosity in therange 1038{-}1043 erg s-1 from thecross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW-HRI)Catalogue with the Lyon-Meudon Extragalactic Database (LEDA). We findthat the average X-ray properties of this sample are in good agreementwith those of other samples of galaxies in the literature. We selected acomplete flux limited serendipitous sample of 32 galaxies from which wederived the log N-log S distribution of normal galaxies in the fluxrange 1.1{-} 110 × 10-14 erg cm-2s-1. The resulting distribution is consistent with theEuclidean -1.5 slope. Comparisons with other samples, such as theExtended Medium Sensitivity Survey, the ROSAT All Sky Survey, theXMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate thatthe log N -log S distribution of normal galaxies is consistent with aEuclidean slope over a flux range of about 6 decades.
| Dynamical evolution of globular cluster systems in clusters of galaxies - I. The case of NGC 1404 in the Fornax cluster
We investigate, via numerical simulations, the tidal stripping andaccretion of globular clusters (GCs). In particular, we focus oncreating models that simulate the situation for the GC systems of NGC1404 and 1399 in the Fornax cluster, which have poor (specific frequencySN~ 2) and rich (SN~ 10) GC systems, respectively.We initially assign NGC 1404 in our simulation a typical SN(~5) for cluster ellipticals, and find that its GC system can only bereduced through stripping to the presently observed value, if its orbitis highly eccentric (with orbital eccentricity of >0.5) and if theinitial scalelength of the GCs system is about twice as large as theeffective radius of NGC 1404 itself. These stripped GCs can be said tohave formed a `tidal stream' of intracluster globular clusters (ICGCs)orbiting the centre of the Fornax cluster (many of which would beassigned to NGC 1399 in an imaging study). The physical properties ofthese GCs (e.g. number, radial distribution and kinematics) depend onthe orbit and initial distribution of GCs in NGC 1404. Our simulationsalso predict a trend for SN to rise with increasingclustercentric distance - a trend for which there is some observationalsupport in the Fornax cluster. We demonstrate that, because thekinematical properties of ICGCs formed by tidal stripping in the clustertidal field depend strongly on the orbits of their previous hostgalaxies, observations of ICGC kinematics provides a new method forprobing galaxy dynamics in a cluster.
| The surface brightness and colour-magnitude relations for Fornax cluster galaxies
We present BVI photometry of 190 galaxies in the central 4 ×3deg2 region of the Fornax cluster observed with the MichiganCurtis Schmidt Telescope. Results from the Fornax Cluster SpectroscopicSurvey (FCSS) and the Flair-II Fornax Surveys have been used to confirmthe membership status of galaxies in the Fornax Cluster Catalogue (FCC).In our catalogue of 213 member galaxies, 92 (43 per cent) have confirmedradial velocities.In this paper, we investigate the surface brightness-magnitude relationfor Fornax cluster galaxies. Particular attention is given to the sampleof cluster dwarfs and the newly discovered ultracompact dwarf galaxies(UCDs) from the FCSS. We examine the reliability of the surfacebrightness-magnitude relation as a method for determining clustermembership and find that at surface brightnesses fainter than 22 magarcsec-2, it fails in its ability to distinguish betweencluster members and barely resolved background galaxies. Cluster membersexhibit a strong surface brightness-magnitude relation. Both elliptical(E) galaxies and dwarf elliptical (dE) galaxies increase in surfacebrightness as luminosity decreases. The UCDs lie off the locus of therelation.B-V and V-I colours are determined for a sample of 113 cluster galaxiesand the colour-magnitude relation is explored for each morphologicaltype. The UCDs lie off the locus of the colour-magnitude relation. Theirmean V-I colours (~1.09) are similar to those of globular clustersassociated with NGC 1399. The location of the UCDs on both surfacebrightness and colour-magnitude plots supports the `galaxy threshing'model for infalling nucleated dwarf elliptical (dE, N) galaxies.
| Globular Clusters as Candidates for Gravitational Lenses to Explain Quasar-Galaxy Associations
We argue that globular clusters (GCs) are good candidates forgravitational lenses in explaining quasar-galaxy associations. Thecatalog of associations (Bukhmastova 2001) compiled from the LEDAcatalog of galaxies (Paturel 1997) and from the catalog of quasars(Veron-Cetty and Veron 1998) is used. Based on the new catalog, we showthat one might expect an increased number of GCs around irregulargalaxies of types 9 and 10 from the hypothesis that distant compactsources are gravitationally lensed by GCs in the halos of foregroundgalaxies. The King model is used to determine the central surfacedensities of 135 GCs in the Milky Way. The distribution of GCs incentral surface density was found to be lognormal.
| Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations
To empirically calibrate the IR surface brightness fluctuation (SBF)distance scale and probe the properties of unresolved stellarpopulations, we measured fluctuations in 65 galaxies using NICMOS on theHubble Space Telescope. The early-type galaxies in this sample includeelliptical and S0 galaxies and spiral bulges in a variety ofenvironments. Absolute fluctuation magnitudes in the F160W (1.6 μm)filter (MF160W) were derived for each galaxy using previouslymeasured I-band SBF and Cepheid variable star distances. F160W SBFs canbe used to measure distances to early-type galaxies with a relativeaccuracy of ~10%, provided that the galaxy color is known to ~0.035 magor better. Near-IR fluctuations can also reveal the properties of themost luminous stellar populations in galaxies. Comparison of F160Wfluctuation magnitudes and optical colors to stellar population modelpredictions suggests that bluer elliptical and S0 galaxies havesignificantly younger populations than redder ones and may also be moremetal-rich. There are no galaxies in this sample with fluctuationmagnitudes consistent with old, metal-poor (t>5 Gyr, [Fe/H]<-0.7)stellar population models. Composite stellar population models implythat bright fluctuations in the bluer galaxies may be the result of anepisode of recent star formation in a fraction of the total mass of agalaxy. Age estimates from the F160W fluctuation magnitudes areconsistent with those measured using the Hβ Balmer-line index. Thetwo types of measurements make use of completely different techniquesand are sensitive to stars in different evolutionary phases. Bothtechniques reveal the presence of intermediate-age stars in theearly-type galaxies of this sample.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by AURA,Inc., under NASA contract NAS 5-26555.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| The Globular Cluster System of NGC 1399. I. A Wide-Field Photometric Study
We present a photometric investigation of the globular clusterpopulation of NGC 1399, the central galaxy in the Fornax cluster, inWashington C and Kron R filters within a field of 36'×36',corresponding to about 200×200 kpc at the Fornax distance. This isthe largest area around this galaxy ever studied with CCD photometry.The cluster system of NGC 1399 is found to extend farther than 100 kpcaway from the galaxy. The color distribution exhibits a pronouncedbimodality. Within a radial distance of about 55 kpc, the red clustersare more strongly concentrated toward the center than the blue clusters.At larger radii, the surface density profiles of the clusters areindistinguishable and match well the distribution of the galaxy light.Over the entire radial distance range, the surface brightness profile ofNGC 1399 can be very well fitted by a power law with an exponent of-1.85 and a core radius of 3.3". No steepening of the luminosity profilecan be detected at large radii. We suggest that the power-law profile ofNGC 1399 results from the galaxy being embedded in a large dark matterhalo, which prevents the stellar density profile from steepeningoutward. The cluster system contains 6450+/-700 clusters and thespecific frequency is found to be 5.1+/-1.2 in the V band. While NGC1399 shows a pronounced color gradient the nearby comparison galaxy NGC1404 does not show such a gradient. Using simple assumptions about theunderlying population that formed during the same star formation eventas the globular clusters, we present a model in which we use radiallychanging local specific frequencies for the red and blue subpopulationsto fit the observations. We find that within 7' the required specificfrequency of the blue clusters alone is a factor of approximately 3larger than that of the red ones. Outside this radius, however, bothpopulations have the same high local specific frequency of around 8 and13 (blue and red clusters, respectively).Based partly on observations collected at the European SouthernObservatory, Cerro Paranal, Chile; ESO program 66.B-0393.
| 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
| Surface brightness fluctuation distances for dwarf elliptical galaxies in the Fornax cluster
We have obtained deep B and R-band CCD images of eight dwarf elliptical(dE) galaxies in the Fornax cluster using the FORS1 instrument at theVLT in service mode under excellent atmospheric conditions. A total of92 fields distributed over the central regions of the galaxies have beenanalysed to measure local (B-R)0 colours and R-band surfacebrightness fluctuation (SBF) magnitudes /line{m}R. Within agalaxy the observed correlation of (B-R)0 with/line{m}R0 follows closely the predicted slope ofthe colour-fluctuation luminosity relation for composite single-burst,mainly old, metal-poor stellar populations. This allows to determine thedistances of the dEs from simple offset measurements to a typically 9%accuracy. The distance distribution of these genuine cluster dwarfscenters at a mean distance of (m-M)0=31.54+/-0.07 mag, or20.3 +/- 0.7 Mpc, a value that is in best agreement with previous SBFwork on Fornax early-type giants and thus represents a robust estimateof the distance to the Fornax cluster core. The application of thebootstrap resampling technique on the distance data further reveals acluster depth of sigmaint = 1.4{+0.5 atop -0.8} Mpc. We takethis preliminary result as a confirmation of the compact appearance ofFornax in the projection on the sky although the cluster might beslightly more elongated along the line of sight. Combining the newlyderived cluster distance with the cosmological velocity of Fornax of1324+/-41 km s-1 gives a Hubble constant of H0 =65 +/- 4 km s-1 Mpc-1. This value is consistent atthe 95% confidence level with both the most recent result from the teamthat favours a long distance scale and the final value adopted by theHST ``Key Project'' team in their work for the Hubble constant. Finally,we explore the possibility to determine rough metallicities of ourcluster dEs from their (B-R)0 colours via Worthey's stellarpopulation synthesis models. The median metallicities are found in therange from -1.5 to -1 with a concentration around [Fe/H] =-1. Acomparison with spectral line indices results available for threegalaxies shows good agreement. Moreover, the derived metallicities placethe bright Fornax dEs on the extension of the metallicity-luminosityrelation defined by the low luminous Local Group dEs which providesadditional support for the (B-R)0 colour as a usefulmetallicity estimator. The data further suggest an age range between 10and 12 Gyr for the Fornax dwarfs.Based on observations collected at the European Southern Observatory(ESO 68.A-0176).
| Early-type galaxies in low-density environments
We describe the construction and study of an objectively defined sampleof early-type galaxies in low-density environments. The sample galaxiesare selected from a recently completed redshift survey using uniform andreadily quantified isolation criteria, and are drawn from a sky area of~700 deg2, to a depth of 7000 km s-1 and anapparent magnitude limit of bJ<= 16.1. Their early-type(E/S0) morphologies are confirmed by subsequent CCD imaging. Five out ofthe nine sample galaxies show signs of morphological peculiarity such astidal debris or blue circumnuclear rings. We confirm that E/S0 galaxiesare rare in low-density regions, accounting for only ~8 per cent of thetotal galaxy population in such environments. We present spectroscopicobservations of nine galaxies in the sample, which are used, inconjunction with updated stellar population models, to investigate starformation histories. Our line-strength analysis is conducted at therelatively high spectral resolution of 4.1 Å. Environmentaleffects on early-type galaxy evolution are investigated by comparisonwith a sample of Fornax cluster E/S0s (identically analysed). Resultsfrom both samples are compared with predictions from semi-analyticgalaxy formation models. From the strength of [OII]λ3727 emissionwe infer only a low level of ongoing star formation (<0.15Msolar yr-1). Relative to the Fornax sample, alarger fraction of the galaxies exhibit [OIII]λ5007 nebularemission and, where present, these lines are slightly stronger thantypical for cluster E/S0s. The Mg-σ relation of E/S0s inlow-density regions is shown to be indistinguishable from that of theFornax sample. Luminosity-weighted stellar ages and metallicities aredetermined by considering various combinations of line-indices; inparticular the HγF versus Fe5015 diagram cleanlyresolves the age-metallicity degeneracy at the spectral resolution ofour analysis. At a given luminosity, the E/S0 galaxies in low-densityregions are younger than the E/S0s in clusters (by ~2-3 Gyr), and alsomore metal-rich (by ~0.2 dex). We infer that an anti-correlation of ageand metallicity effects is responsible for maintaining the zero-point ofthe Mg-σ relation. The youngest galaxies in our sample show clearmorphological signs of interaction. The lower mean age of our sample,relative to cluster samples, confirms, at least qualitatively, a robustprediction of hierarchical galaxy formation models. By contrast, theenhanced metallicity in the field is contrary to the predictions andhighlights shortcomings in the detailed treatment of star formationprocesses in current models. The [Mg/Fe] abundance ratio appears to spana similar, mostly super-solar, range both in low-density regions and inFornax cluster galaxies. This result is quite unexpected in simplehierarchical models.
| Surface Brightness Fluctuations of Fornax Cluster Galaxies: Calibration of Infrared Surface Brightness Fluctuations and Evidence for Recent Star Formation
We have measured KS-band (2.0-2.3 μm) surface brightnessfluctuations (SBFs) of 19 early-type galaxies in the Fornax Cluster.Fornax is ideally suited both for calibrating SBFs as distanceindicators and for using SBFs to probe the unresolved stellar content ofearly-type galaxies. Combining our results with published data for othernearby clusters, we calibrate KS-band SBFs using Hubble SpaceTelescope (HST) Cepheid cluster distances and I-band SBF distances toindividual galaxies. With the latter, the resulting calibrationisMKS=(-5.84+/-0.04)+(3.6+/-0.8)[(V-Ic)0-1.15],valid for1.05<(V-Ic)0<1.25 and not including anysystematic errors in the HST Cepheid distance scale. The fit accountsfor the covariance between V-Ic and MKSwhen calibrated in this fashion. The intrinsic cosmic scatter ofMKS appears to be larger than that of I-band SBFs.S0 galaxies may follow a different relation, although the data areinconclusive. The discovery of correlation between KS-bandfluctuation magnitudes and colors with V-Ic is a new clueinto the star formation histories of early-type galaxies. This relationnaturally accounts for galaxies previously claimed to have anomalouslybright K-band SBFs, namely, M32 and NGC 4489. Models indicate that thestellar populations dominating the SBF signal have a significant rangein age; some scatter in metallicity may also be present. The youngestages imply some galaxies have very luminous giant branches, akin tothose in intermediate-age (few Gyr) Magellanic Cloud clusters. Theinferred metallicities are roughly solar, although this depends on thechoice of theoretical models. A few Fornax galaxies have unusuallybright KS-band SBFs, perhaps originating from ahigh-metallicity burst of star formation in the last few Gyr. Theincreased spread and brightening of the KS-band SBFs withbluer V-Ic suggest that the lower mass cluster galaxies(<~0.1L*) may have had more extended and more heterogeneous starformation histories than those of the more massive galaxies.
| Research in Concepción on globular cluster systems and galaxy formation, and the extragalactic distance scale
Not Available
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| 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.
| The Infrared Surface Brightness Fluctuation Hubble Constant
We measured infrared surface brightness fluctuation (SBF) distances toan isotropically distributed sample of 16 distant galaxies withredshifts reaching 10,000 km s-1 using the near-IR camera andmultiobject spectrometer (NICMOS) on the Hubble Space Telescope (HST).The excellent spatial resolution, very low background, and brightness ofthe IR fluctuations yielded the most distant SBF measurements to date.Twelve nearby galaxies were also observed and used to calibrate theF160W (1.6 μm) SBF distance scale. Of these, three have Cepheidvariable star distances measured with HST and eleven have optical I-bandSBF distance measurements. A distance modulus of 18.5 mag to the LargeMagellanic Cloud was adopted for this calibration. We present the F160WSBF Hubble diagram and find a Hubble constant H0=76+/-1.3 (1σ statistical) +/-6 (systematic) km s-1Mpc-1. This result is insensitive to the velocity model usedto correct for local bulk motions. Restricting the fit to the six mostdistant galaxies yields the smallest value of H0=72+/-2.3 kms-1 Mpc-1 that is consistent with the data. This6% decrease in the Hubble constant is consistent with the hypothesisthat the Local Group inhabits an underdense region of the universe, butis also consistent with the best-fit value of H0=76 kms-1 Mpc-1 at the 1.5 σ level. Based onobservations with the NASA/ESA Hubble Space Telescope, obtained at theSpace Telescope Science Institute, which is operated by AURA, Inc.,under NASA contract NAS 5-26555.
| The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances
We report data for I-band surface brightness fluctuation (SBF)magnitudes, (V-I) colors, and distance moduli for 300 galaxies. Thesurvey contains E, S0, and early-type spiral galaxies in the proportionsof 49:42:9 and is essentially complete for E galaxies to Hubblevelocities of 2000 km s-1, with a substantial sampling of Egalaxies out to 4000 km s-1. The median error in distancemodulus is 0.22 mag. We also present two new results from the survey.(1) We compare the mean peculiar flow velocity (bulk flow) implied byour distances with predictions of typical cold dark matter transferfunctions as a function of scale, and we find very good agreement withcold, dark matter cosmologies if the transfer function scale parameterΓ and the power spectrum normalization σ8 arerelated by σ8Γ-0.5~2+/-0.5. Deriveddirectly from velocities, this result is independent of the distributionof galaxies or models for biasing. This modest bulk flow contradictsreports of large-scale, large-amplitude flows in the ~200 Mpc diametervolume surrounding our survey volume. (2) We present adistance-independent measure of absolute galaxy luminosity, N and showhow it correlates with galaxy properties such as color and velocitydispersion, demonstrating its utility for measuring galaxy distancesthrough large and unknown extinction. Observations in part from theMichigan-Dartmouth-MIT (MDM) Observatory.
| The neutral hydrogen content of Fornax cluster galaxies
We present a new set of deep H I observations of member galaxies of theFornax cluster. We detected 35 cluster galaxies in HI. The resulting sample, the most comprehensive to date, is used toinvestigate the distribution of neutral hydrogen in the clustergalaxies. We compare the H I content of the detected cluster galaxieswith that of field galaxies by measuring H I mass-to-light ratios andthe H I deficiency parameter of Solanes et al. (\cite{Sol96}). The meanH I mass-to-light ratio of the cluster galaxies is 0.68+/- 0.15,significantly lower than for a sample of H I-selected field galaxies(1.15+/- 0.10), although not as low as in the Virgocluster (0.45+/- 0.03). In addition, the H I content of twocluster galaxies (NGC 1316C and NGC1326B) appears to have been affected by interactions. The meanH I deficiency for the cluster is 0.38+/-0.09 (for galaxy types T=1-6),significantly greater than for the field sample (0.05+/-0.03). Boththese tests show that Fornax cluster galaxies are HI-deficient compared to field galaxies. The kinematics of the clustergalaxies suggests that the H I deficiency may be caused by ram-pressurestripping of galaxies on orbits that pass close to the cluster core. Wealso derive the most complete B-band Tully - Fisher relation of inclinedspiral galaxies in Fornax. A subcluster in theSouth-West of the main cluster contributes considerably to the scatter.The scatter for galaxies in the main cluster alone is 0.50 mag, which isslightly larger than the intrinsic scatter of 0.4 mag. We use the Tully- Fisher relation to derive a distance modulus ofFornax relative to the Virgocluster of -0.38+/- 0.14 mag. The galaxies in the subclusterare (1.0+/-0.5) mag brighter than the galaxies of the main cluster,indicating that they are situated in the foreground. With their meanvelocity 95 km s-1 higher than that of the main cluster weconclude that the subcluster is falling into the main Fornaxcluster.
| A Database of Cepheid Distance Moduli and Tip of the Red Giant Branch, Globular Cluster Luminosity Function, Planetary Nebula Luminosity Function, and Surface Brightness Fluctuation Data Useful for Distance Determinations
We present a compilation of Cepheid distance moduli and data for foursecondary distance indicators that employ stars in the old stellarpopulations: the planetary nebula luminosity function (PNLF), theglobular cluster luminosity function (GCLF), the tip of the red giantbranch (TRGB), and the surface brightness fluctuation (SBF) method. Thedatabase includes all data published as of 1999 July 15. The mainstrength of this compilation resides in the fact that all data are on aconsistent and homogeneous system: all Cepheid distances are derivedusing the same calibration of the period-luminosity relation, thetreatment of errors is consistent for all indicators, and measurementsthat are not considered reliable are excluded. As such, the database isideal for comparing any of the distance indicators considered, or forderiving a Cepheid calibration to any secondary distance indicator, suchas the Tully-Fisher relation, the Type Ia supernovae, or the fundamentalplane for elliptical galaxies. This task has already been undertaken byFerrarese et al., Sakai et al., Kelson et al., and Gibson et al.Specifically, the database includes (1) Cepheid distances, extinctions,and metallicities; (2) reddened apparent λ5007 Å magnitudesof the PNLF cutoff; (3) reddened apparent magnitudes and colors of theturnover of the GCLF (in both the V and B bands); (4) reddened apparentmagnitudes of the TRGB (in the I band) and V-I colors at 0.5 mag fainterthan the TRGB; and (5) reddened apparent surface brightness fluctuationmagnitudes measured in Kron-Cousin I, K', andKshort, and using the F814W filter with the Hubble SpaceTelescope (HST) WFPC2. In addition, for every galaxy in the database wegive reddening estimates from IRAS/DIRBE as well as H I maps, J2000coordinates, Hubble and T-type morphological classification, apparenttotal magnitude in B, and systemic velocity.
| 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.
| The QDOT all-sky IRAS galaxy redshift survey
We describe the construction of the QDOT survey, which is publiclyavailable from an anonymous FTP account. The catalogue consists ofinfrared properties and redshifts of an all-sky sample of 2387 IRASgalaxies brighter than the IRAS PSC 60-μm completeness limit(S_60>0.6Jy), sparsely sampled at a rate of one-in-six. At |b|>10deg, after removing a small number of Galactic sources, the redshiftcompleteness is better than 98per cent (2086/2127). New redshifts for1401 IRAS sources were obtained to complete the catalogue; themeasurement and reduction of these are described, and the new redshiftstabulated here. We also tabulate all sources at |b|>10 deg with noredshift so far, and sources with conflicting alternative redshiftseither from our own work, or from published velocities. A list of 95ultraluminous galaxies (i.e. with L_60μm>10^12 L_solar) is alsoprovided. Of these, ~20per cent are AGN of some kind; the broad-lineobjects typically show strong Feii emission. Since the publication ofthe first QDOT papers, there have been several hundred velocity changes:some velocities are new, some QDOT velocities have been replaced by moreaccurate values, and some errors have been corrected. We also present anew analysis of the accuracy and linearity of IRAS 60-μm fluxes. Wefind that the flux uncertainties are well described by a combination of0.05-Jy fixed size uncertainty and 8per cent fractional uncertainty.This is not enough to cause the large Malmquist-type errors in the rateof evolution postulated by Fisher et al. We do, however, find marginalevidence for non-linearity in the PSC 60-μm flux scale, in the sensethat faint sources may have fluxes overestimated by about 5per centcompared with bright sources. We update some of the previous scientificanalyses to assess the changes. The main new results are as follows. (1)The luminosity function is very well determined overall but is uncertainby a factor of several at the very highest luminosities(L_60μm>5x10^12L_solar), as this is where the remainingunidentified objects are almost certainly concentrated. (2) Thebest-fitting rate of evolution is somewhat lower than our previousestimate; expressed as pure density evolution with density varying as(1+z)^p, we find p=5.6+/-2.3. Making a rough correction for the possible(but very uncertain) non-linearity of fluxes, we find p=4.5+/-2.3. (3)The dipole amplitude decreases a little, and the implied value of thedensity parameter, assuming that IRAS galaxies trace the mass, isΩ=0.9(+0.45, -0.25). (4) Finally, the estimate of density varianceon large scales changes negligibly, still indicating a significantdiscrepancy from the predictions of simple cold dark matter cosmogonies.
| HST imaging of the globular clusters in the Fornax cluster - NGC 1399 and NGC 1404
The Fornax cluster galaxies NGC 1399 and NGC 1404 are ideal for studyingthe effects of a cluster environment on globular cluster systems. Herewe present new optical imaging of these two galaxies from both the HST'sWide Field and Planetary Camera 2 and the Cerro Tololo Inter-AmericanObservatory 1.5-m telescope. The combination of both data sets providesa unique insight on the spatial and color distribution of globularclusters. From B-I colors, we find that both galaxies have a broadglobular cluster metallicity distribution that is inconsistent with asingle population. Two Gaussians provide a reasonable representation ofthe metallicity distribution in each galaxy. The metal-richsubpopulation is more centrally concentrated than the metal-poor one. Weshow that the radial metallicity gradient can be explained by thechanging relative mix of the two globular cluster subpopulations. Wederive globular cluster surface density profiles, and find that they areflatter than the underlying starlight. The total number of globularclusters and specific frequency are calculated to be N = 5700 +/- 500,SN = 11.5 +/- 1.0 for NGC 1399, and N = 725 +/- 145, S(N) = 2.0 +/- 0.5for NGC 1404. Our results are compared with the expectations of globularcluster formation scenarios.
| NGC 1428: from the Discordant Redshift Caused by a Star, to the Determination of the Morphological Type
We summarise the main results of our study of NGC 1428, an early-type galaxy belonging to the Fornax cluster. By means of long-slit spectroscopic data we study it's kinematics and also solve the problems connected to a star superimposed on its nucleus - which have led to wrong measurements of its redshift in the past. The present analysis allows us to determine the morphological type of NGC 1428 as well as an accurate value of its redshift.
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