We present a detailed analysis of two-band HST/ACS imaging of 21 ultra-compact dwarf (UCD) galaxies in the Virgo and Fornax Clusters. The aim of this work is to test two formation hypotheses for UCDs--whether they are bright globular clusters (GCs) or "threshed'' early-type dwarf galaxies--by comparison of UCD structural parameters and colors with GCs and galaxy nuclei. We find that the UCD surface brightness profiles can be described by a range of models and that the luminous UCDs can not be described by standard King models with tidal cutoffs as they have extended outer halos. This is not expected from traditional King models of GCs, but is consistent with recent results for massive GCs. The total luminosities, colors and sizes of the UCDs are consistent with them being either luminous GCs or threshed nuclei of both early-type and late-type galaxies (not just early-type dwarfs). For the most luminous UCDs we estimate color gradients over a limited range of radius. These are systematically positive in the sense of getting redder outwards: mean Delta(F606W-F814W)=0.14 mag per 100 pc with rms=0.06 mag per 100 pc. The positive gradients found in the bright UCDs are consistent with them being either bright GCs or threshed early-type dwarf galaxies (except VUCD3). In contrast to the above results we find a very significant difference in the sizes of UCDs and early-type galaxy nuclei: the effective radii of UCDs are 2.2 times larger than those of early-type galaxy nuclei at the same luminosity. This result suggests an important test can be made of the threshing hypothesis by simulating the process and predicting what size increase is expected.
We present the results of a search for clusters in dwarf irregular galaxies in the Virgo and Fornax Cluster using HST WFPC2 snapshot data. The galaxy sample includes 28 galaxies, 11 of which are confirmed members of the Virgo and Fornax clusters. In the 11 confirmed members, we detect 237 cluster candidates and determine their V magnitudes, V-I colors and core radii. After statistical subtraction of background galaxies and foreground stars, most of the cluster candidates have V-I colors of -0.2 and 1.4, V magnitudes lying between 20 and 25th magnitude and core radii between 0 and 6 pc. Using H…
We derive the relative distances to the Virgo, Fornax, and Coma clusters of galaxies by applying the Dn-sigma and the Fundamental Plane (FP) relations to the data of the homogeneous samples of early--type galaxies studied by Caon etal, Lucey etal, and Jorgensen etal. The two distance indicators give consistent results, the relative distance moduli to Fornax and Coma with respect to Virgo being Dmu(FV)=0.45+-0.15 and Dmu(CV)=3.55+-0.15) respectively. The formal error on D(m-M) may be as small as 0.07 mag (~3% in distance), provided that all the sources of bias are taken into account and a corre…
The Fornax Cluster is a conspicuous cluster of galaxies in the southern hemisphere and the second largest collection of early-type galaxies within <~ 20 Mpc after the Virgo Cluster. In this paper,we present a brief introduction to the ACS Fornax Cluster Survey - a program to image, in the F475W (g_475) and F850LP (z_850) bandpasses, 43 early-type galaxies in Fornax using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. Combined with a companion survey of Virgo, the ACS Virgo Cluster Survey, this represents the most comprehensive imaging survey to date of early-type galaxies…
We have discovered nine ultra-compact dwarf galaxies (UCDs) in the Virgo Cluster, extending samples of these objects outside the Fornax Cluster. Using the 2dF multi-fiber spectrograph on the Anglo-Australian Telescope, the new Virgo members were found among 1500 color-selected, star-like targets with 16.0 < b_j < 20.2 in a two-degree diameter field centered on M87 (NGC4486). The newly-found UCDs are comparable to the UCDs in the Fornax Cluster, with sizes <~ 100 pc, -12.9 < M_B < -10.7, and exhibiting red, absorption-line spectra, indicative of an older stellar population. The properties of th…
The influence of broken structural homology, and the implied broken dynamical homology, is examined for the Fundamental Plane (FP). A bisector method of linear regression was applied, in 3-dimensions, to derive the best FP and a bootstrapping procedure has been used to estimate the associated uncertainties. For 25 E and S0 Virgo galaxies, the `standard' FP, constructed using R^{1/4} model parameters for the effective radii (R_{e,4}) and the mean surface brightness within this radius (Sigma_{e,4}) and using central velocity dispersion measurements (sigma_0), gave a relation described by R_{e,4}…
We present new imaging and spectroscopic observations of six ultra-compact dwarf (UCD) galaxies in the Virgo Cluster, along with re-analysed data for five Fornax Cluster UCDs. These are the most luminous UCDs: -14<Mv<-12 mag. Our HST imaging shows that most of the UCDs have shallow or steep cusps in their cores; only one UCD has a flat ``King'' core. None of the UCDs show tidal cutoffs down to our limiting surface brightness. Spectroscopic analysis shows that Virgo UCDs are older than 8 Gyr and have metallicities in the range [Z/H]=-1.35...+0.35 dex. Five Virgo UCDs have super-solar alpha/Fe a…
We have extended the search for luminous (M_{b_J} <= -10.5) compact stellar systems (CSSs) in the Virgo and Fornax galaxy clusters by targeting with the recently commissioned AAOmega spectrograph three cluster environments -- the cluster cores around M87 and NGC 1399, intracluster space, and a major galaxy merger site (NGC 1316). We have significantly increased the number of redshift-confirmed CSSs in the Virgo cluster core and located three Virgo intracluster globular clusters (IGCs) at a large distance from M87 (154-173 arcmin or ~750-850 kpc) -- the first isolated IGCs to be redshift-confir…
Using published photometry and spectroscopy, we construct the fundamental plane and D_n-Sigma relations in Leo I, Virgo and Fornax. The published Cepheid P-L relations to spirals in these clusters fixes the relation between angular size and metric distance for both the fundamental plane and D_n-Sigma relations. Using the locally calibrated fundamental plane, we infer distances to a sample of clusters with a mean redshift of cz \approx 6000 \kms, and derive a value of H_0=78+- 5+- 9 km/s/Mpc (random, systematic) for the local expansion rate. This value includes a correction for depth effects in…
The planetary nebula luminosity function (PNLF) technique for determining distances to galaxies now has been applied to 34 galaxies, including 6 in the Virgo cluster and 3 in the Fornax cluster. Of these, 16 galaxies are late-type or spirals and presumably contain Cepheid variables useful for verifying the PNLF method. For 7 of these galaxies, Cepheid distances exist; the PNLF distances agree with the Cepheid distances within the dispersion of 8% and within a zero-point offset of 1%. In addition, 3 small groups were studied (NGC 1023, Leo I, and Coma I) where both spiral and elliptical distanc…
We present the internal velocity dispersions and spectral line indices for six Virgo ultra-compact dwarf (UCD) galaxies obtained from spectroscopy with the Keck II 10-m telescope. We use these results: 1) to compare the Virgo UCDs with the Fornax UCD population; 2) to compare UCDs with globular clusters (GCs) to determine if UCDs and the most luminous GCs are the same or distinct systems; 3) to further test the nucleated dwarf elliptical (dE,N) stripping hypothesis for UCD formation.
We present photometric and kinematic evidence for the presence of stellar disks, seen practically edge-on, in two Fornax dwarf galaxies, FCC204 (dS0(6)) and FCC288 (dS0(7)). This is the first time such structures have been identified in Fornax dwarfs. FCC2088 has only a small bulge and a bright flaring and slightly warped disk that can be traced out to 23" from the center (2.05 kpc for H_0=75 km/s/Mpc). FCC204's disk can be traced out to 20" (1.78 kpc). This galaxy possesses a large bulge. These results can be compared to the findings of Jerjen et al. (2000) and Barazza et al. (2002) who disco…
Ultra-compact dwarf galaxies (UCDs) are a new type of galaxy we have discovered in the central region of the Fornax and Virgo clusters. Unresolved in ground-based imaging, UCDs have spectra typical of old stellar systems. Ninety-two have been found in Fornax, making them the most numerous galaxy type in the cluster. Here we present multicolour (u'g'r'i'z') imaging of the central region of the Fornax Cluster using the CTIO 4m Mosaic Telescope. The colour-magnitude relation for bright UCDs is qualitatively consistent with UCDs being the stripped nuclei of dE,Ns. However at faint magnitudes, GCs …
We present a new set of deep HI observations of member galaxies of the Fornax cluster. We detected 35 cluster galaxies in HI. The resulting sample, the most comprehensive to date, is used to investigate the distribution of HI in the cluster galaxies. We compare the HI content of the detected cluster galaxies with that of field galaxies by measuring HI mass-to-light ratios and the HI deficiency parameter of Solanes et al. (1996). The mean HI mass-to-light ratio of the cluster galaxies is 0.68+/-0.15, significantly lower than for a sample of HI-selected field galaxies (1.15+/-0.10), although not…
We have used the 2dF spectrograph on the Anglo-Australian Telescope to obtain a complete spectroscopic sample of all objects in the magnitude range, Bj= 16.5 to 19.8, regardless of morphology, in an area centred on the Fornax Cluster of galaxies. Among the unresolved targets are five objects which are members of the Fornax Cluster. They are extremely compact stellar systems with scale lengths less than 40 parsecs. These ultra-compact dwarfs are unlike any known type of stellar system, being more compact and significantly less luminous than other compact dwarf galaxies, yet much brighter than a…
Our VLT (FLAMES) observations near NGC1399 investigate the connection between ultra-compact dwarf galaxies (UCDs), NGC1399 globular clusters and intra-cluster globulars. We have uncovered 30 faint compact stellar systems in the Fornax galaxy cluster, adding to 62 bright UCDs previously reported. The magnitude limit of these stellar systems extends down to the globular cluster domain. We detect a filament of UCDs and globular clusters stretching across NGC1399 and find weak evidence for its rotation. These compact stellar systems not only congregate around several cluster galaxies but are also …
We review the progress of research on intracluster planetary nebulae (IPN). In the past five years, hundreds of IPN candidates have been detected in the Virgo and Fornax galaxy clusters and searches are also underway in poorer galaxy groups. From the observations to date, and applying the known properties of extragalactic planetary nebulae, the intracluster light in Virgo and Fornax: 1) is significant, at least 20% of the total cluster stellar luminosity, 2) is elongated in Virgo along our line of sight, and 3) may derive from lower-luminosity galaxies, consistent with some models of intraclus…
We report the results of a survey for novae in and between the galaxies of the Fornax cluster. Our survey provides strong evidence that intracluster novae exist and that they provide a useful, independent measure of the intracluster light in Fornax. We discovered six strong nova candidates in six distinct epochs spanning eleven years from 1993 to 2004. The data were taken with the 4m and the 1.5m telescopes at CTIO. The spatial distribution of the nova candidates is consistent with $\sim$16-41% of the total light in the cluster being in the intracluster light, based on the ratio of the number …
We present studies of the Extreme Ultraviolet (EUV) emission in the Fornax cluster of galaxies; a relatively nearby well-studied cluster with X-ray emitting cluster gas and a very large radio source. We examine both the large-scale (~size of the X-ray emitting cluster gas), and the small-scale (<arcmin) emission. We find that this cluster has large-scale diffuse EUV emission. However, at the sensitivity level of the existing EUVE data, this emission is due entirely to the low energy tail of the X-ray emitting gas. We have also examined small-scale structures in raw EUVE images of this cluster.…
This paper investigates the possibility that UCD galaxies in the Fornax cluster are formed by the threshing of nucleated, early-type dwarf galaxies (hereafter dwarf galaxies). Similar to the results of Cote et al. (2006) for the Virgo cluster, we show that the Fornax Cluster observations are consistent with a single population in which all dwarfs are nucleated, with a ratio of nuclear to total magnitude that varies slowly with magnitude. Importantly, the magnitude distribution of the UCD population is similar to that of the dwarf nuclei in the Fornax cluster. The joint population of UCDs and t…
The relation between the Ultra Compact Objects (UCOs) recently discovered in the Fornax cluster (Drinkwater et al. 2000, Hilker et al. 1999) and the brightest globular clusters associated with the central galaxy NGC 1399 has been investigated. The question was adressed whether the UCOs constitute a distinct population of objects not linked to globular clusters or whether there is a smooth transition between both populations. Therefore, a spectroscopic survey on compact objects in the central region of the Fornax cluster was carried out with the 2.5m du Pont telescope (LCO). UCOs and the bright…
The Virgo and Fornax clusters of galaxies play central roles in determining the Hubble constant H_0. A powerful and direct way of establishing distances for elliptical galaxies is to use the luminosities of the brightest red-giant stars (the TRGB luminosity, at M_I = -4.2). Here we report the direct observation of the TRGB stars in a dwarf elliptical galaxy in the Virgo cluster. We find its distance to be 15.7 +- 1.5 Megaparsecs, from which we estimate a Hubble constant of H_0 = 77 +- 8 km/s/Mpc. Under the assumption of a low-density Universe with the simplest cosmology, the age of the Univers…
We analyse HST surface brightness profiles for 143 early-type galaxies in the Virgo and Fornax Clusters. Sersic models provide accurate descriptions of the global profiles with a notable exception: the observed profiles deviate systematically inside a characteristic "break" radius of R_b ~ 0.02R_e where R_e is the effective radius of the galaxy. The sense of the deviation is such that bright galaxies (M_B < -20) typically show central light deficits with respect to the inward extrapolation of the Sersic model, while the great majority of low- and intermediate-luminosity galaxies (-19.5 < M_B <…
The results of the Fornax Compact Object Survey (FCOS) are presented. The FCOS aims at investigating the nature of the Ultra Compact Dwarf galaxies (UCDs) recently discovered in the center of the Fornax cluster (Drinkwater et al. 2000). 280 unresolved objects in the magnitude space covering UCDs and bright globular clusters (18<V<21 mag) were observed spectroscopically. 54 new Fornax members were discovered, plus five of the seven already known UCDs. Their distribution in radial velocity, colour, magnitude and space was investigated. It is found that bright compact objects (V<20 or M_V<-11.4 m…
We present a photometric search for UCD candidates in the nearby galaxy group NGC 1023 (d=11 Mpc) -- the poorest environment searched for UCDs yet --, based on wide field imaging with CFHT. After photometric and morphological selection, we obtain a sample of 21 UCD candidates with -12<M_V<-11 mag, if located at NGC 1023's distance. From spectroscopy taken at Calar Alto observatory, we identify the UCD candidate in closest projection to NGC 1023 as an emission line background galaxy. Our photometric data show that in the NGC 1023 group, the mass spectrum of analogs to Fornax/Virgo UCD is restri…
By utilising the large multi-plexing advantage of the 2dF spectrograph on the Anglo-Australian Telescope, we have been able to obtain a complete spectroscopic sample of all objects in a predefined magnitude range, 16.5<Bj<19.7, regardless of morphology, in an area towards the centre of the Fornax Cluster of galaxies. Among the unresolved or marginally resolved targets we have found five objects which are actually at the redshift of the Fornax Cluster, i.e. they are extremely compact dwarf galaxies or extremely large star clusters. All five have absorption line spectra. With intrinsic sizes les…
I review the progress in research on Intracluster Planetary Nebulae (IPN). Hundreds of IPN candidates have now been found in the Virgo and Fornax galaxy clusters, and searches of two nearby galaxy groups have made. From the results thus far, approximately 10 - 20% of all stars in Virgo and Fornax are in an intracluster component, but there are few such stars in galaxy groups. From the spatial distribution of IPN, it appears that the intracluster stars are clustered, in agreement with tidal-stripping scenarios. In Virgo, the IPN have a large line-of-sight depth, which implies that the bulk of i…
We have discovered a new type of galaxy in the Fornax Cluster: ``ultra-compact'' dwarfs (UCDs). The UCDs are unresolved in ground-based imaging and have spectra typical of old stellar systems. Although the UCDs resemble overgrown globular clusters, based on VLT UVES echelle spectroscopy, they appear to be dynamically distinct systems with higher internal velocity dispersions and M/L ratios for a given luminosity than Milky Way or M31 globulars. Our preferred explanation for their origin is that they are the remnant nuclei of dwarf elliptical galaxies which have been tidally stripped, or ``thre…
Aims. We determine masses and mass-to-light ratios of five ultra-compact dwarf galaxies and one dwarf elliptical nucleus in the Fornax cluster from high resolution spectroscopy. Methods. Velocity dispersions were derived from selected wavelength regions using a direct-fitting method. To estimate the masses of the UCDs a new modelling program has been developed that allows a choice of different representations of the surface brightness profile (i.e. Nuker, Sersic or King laws) and corrects the observed velocity dispersions for observational parameters (i.e. seeing, slit size). Results. The obse…
A recent all-object spectroscopic survey centred on the Fornax cluster of galaxies, has discovered a population of sub-luminous and extremely compact members, called ``ultra-compact dwarf'' (UCD) galaxies. In order to clarify the origin of these objects, we have used self-consistent numerical simulations to study the dynamical evolution a nucleated dwarf galaxy would undergo if orbiting the center of the Fornax cluster and suffering from its strong tidal gravitational field. We find that the outer stellar components of a nucleated dwarf are removed by the strong tidal field of the cluster, whe…
The application of the I band Tully--Fisher relation towards determining the Hubble constant is reviewed, with particular attention to the impact of scatter and bias corrections in the relation. A template relation is derived from galaxies in 24 clusters. A subset of 14 clusters with cz ~ 4000 to 9000 km/s is used as an inertial frame to define the velocity zero point of the relation. Twelve galaxies with Cepheid distances are used to establish the absolute magnitude scale of the Tully--Fisher relation, and thus to determine a value of H_not = 70\pm5 km/s/Mpc. Estimates of the peculiar velocit…
Aim: To extend the investigations of ultra-compact dwarf galaxies (UCDs) beyond the well studied Fornax and Virgo clusters. Methods: We measured spectroscopic redshifts of about 400 compact object candidates with 19.2 < V < 22.4 mag in the central region of the Centaurus galaxy cluster (d=43Mpc), using VIMOS@VLT. The luminosity range of the candidates covers that of bright globular clusters (GCs) and of UCDs in Fornax and Virgo. Results: We confirm the cluster membership of 27 compact objects, covering an absolute magnitude range -12.2 < M_V < -10.9 mag. We do not find counterparts to the two …
Using the Hubble Space Telescope (HST) 37 long-period Cepheid variables have been discovered in the Fornax Cluster spiral galaxy NGC 1365. The resulting V and I period-luminosity relations yield a true distance modulus of 31.35 +/- 0.07 mag, which corresponds to a distance of 18.6 +/- 0.6 Mpc. This measurement provides several routes for estimating the Hubble Constant. (1) Assuming this distance for the Fornax Cluster as a whole yields a local Hubble Constant of 70 +/-18_{random} [+/-7]_{systematic} km/s/Mpc. (2) Nine Cepheid-based distances to groups of galaxies out to and including the Forna…
We present the $V$-band globular cluster luminosity functions (GCLFs) of the Fornax Cluster galaxies NGC 1344, NGC 1380, NGC 1399, and NGC 1404. Our observations reach to $V = 24.8$, roughly one magnitude beyond the GCLF turnover $m^0_V$, with $\sim90\%$ completeness. From the amplitude of the galaxy surface brightness fluctuations, we also estimate the number of globular clusters fainter than this cutoff magnitude. The GCLFs of these galaxies are well fitted by Gaussians; the weighted means of their turnover magnitudes and dispersions are $\langle m^0_V\rangle = 23.88 \pm 0.10$ mag and $\lang…
Various formation channels for the puzzling ultra-compact dwarf galaxies (UCDs) have been proposed in the last few years. To better judge on some of the competing scenarios, we present spectroscopic [Fe/H] estimates for a sample of 26 compact objects in the central region of the Fornax cluster, covering the magnitude range of UCDs and bright globular clusters. We find a break in the metallicity distribution of compact objects at M_V ~ -11 mag (~3*10^6 M_sun): for M_V<-11 mag the mean metallicity is [Fe/H]=-0.62 +/- 0.05 dex, 0.56 +/- 0.15 dex higher than for M_V>-11 mag. This metallicity break…
We review some properties of ultracompact dwarf galaxies (UCDs) in Fornax and of their brighter counterparts in Abell 1689, among which are two M32 twins, and discuss various possible UCD formation scenarios. We note that it is indispensable to carefully take into account the bright end of the globular cluster luminosity function when estimating the number density of UCDs. It is suggested that the search for more luminous UCDs in dense and rich galaxy clusters is the best way towards establishing UCDs as a new class of galaxies.
We present a study of the old globular cluster (GC) population of the dwarf irregular galaxy NGC 1427A using multi-wavelength VLT observations in U, B, V, I, H_alpha, J, H, and Ks bands under excellent observing conditions. We applied color and size selection criteria to select old GC candidates and made use of archival ACS images taken with the Hubble Space Telescope to reject contaminating background sources and blended objects from the GC candidates' list. The H_alpha observations were used to check for contamination due to compact, highly reddened young star clusters whose colors and sizes…
We present HI 21cm line observations, obtained with the Australia Telescope Compact Array, of two dwarf elliptical galaxies (dEs) in the Fornax cluster: FCC032 and FCC336. The optical positions and velocities of these galaxies place them well within the Fornax cluster. FCC032 was detected at the 3sigma significance level with a total HI flux density of 0.66+-0.22 Jy km s^-1 or an HI mass of 5.0+-1.7 10^7 h_75^-2 M_sun. Based on our deep Halpha+[NII] narrow-band images, obtained with FORS2 mounted on the VLT, this dE was already known to contain 600-1800 h_75^-2 M_sun of ionised Hydrogen (depen…
We examine the luminosity and B-I color distribution of globular clusters for three early-type galaxies in the Fornax cluster using imaging data from the Wide Field/Planetary Camera 2 on the Hubble Space Telescope. The luminosity functions we derive are in most cases better than 50% complete down to B = 26.6. We find that the color distributions of globular clusters in the central region of NGC 1399 and its nearby neighbor NGC 1404 are bimodal and statistically indistinguishable. The metallicity spread, as inferred from the color distributions in these two galaxies, is very similar to that of …
Top of the wish list of any astronomer who wants to understand galaxy formation and evolution is to resolve the stellar populations of a sample of giant elliptical galaxies: to take spectra of the stars and make Colour-Magnitude Diagrams going down to the oldest main sequence turn-offs. It is only by measuring the relative numbers of stars on Main Sequence Turnoffs at ages ranging back to the time of the earliest star formation in the Universe that we can obtain unambiguous star formation histories. Understanding star formation histories of individual galaxies underpins all our theories of gal…
We have obtained high-resolution spectra of 23 ultra-compact dwarf galaxies (UCDs) in the Fornax cluster with -10.4>M_V>-13.5 mag (10^6<M/M_*<10^8), using FLAMES/Giraffe at the VLT. This is the largest homogeneous data set of UCD internal dynamics assembled to date. We derive dynamical M/L ratios for 15 UCDs covered by HST imaging. In the M_V-sigma plane, UCDs with M_V<-12 mag are consistent with the extrapolated Faber-Jackson relation for luminous ellipticals, while fainter UCDs are closer to the extrapolated globular cluster (GC) relation. At a given metallicity, Fornax UCDs have on average …
Using imaging from the Hubble Space Telescope, we derive surface brightness profiles for ultra-compact dwarfs in the Fornax cluster and for the nuclei of dwarf elliptical galaxies in the Virgo cluster. Ultra-compact dwarfs are more extended and have higher surface brightnesses than typical dwarf nuclei, while the luminosities, colors, and sizes of the nuclei are closer to those of Galactic globular clusters. This calls into question the production of ultra-compact dwarfs via ``threshing'' whereby the lower surface brightness envelope of a dwarf elliptical is removed by tidal processes, leaving…
We find that the bright part (M_B<-18.5 mag) of luminosity function of each Hubble type has the same shape in three poor clusters (Virgo, Fornax and Centaurus) and in two rich clusters (Coma and Cl0939+4713). The fact that these type-dependent luminosity functions are invariant in shape from poor to rich environments gives support to the hypothesis that they may be universal. We also present in tabular form improved type-dependent luminosity functions, based on a much larger sample than previous works.
Six independent methods yield a Virgo cluster modulus of (m-M)=31.66+/- 0.08. This inserted into the Hubble diagram of clusters, whose relative distances to the Virgo cluster are known, gives H_0=54+/-4. The result is independent of any observed or inferred velocity of the Virgo cluster and holds out 10 000 km/s. An analogous use of the Fornax cluster is not yet possible because of its unknown structure in space and its poorly understood distance relative to other clusters. Field galaxies, corrected for Malmquist bias, give H_0=53+/-3. The results of purely physical distance determinations clu…
Surface brightness fluctuations (SBFs) are much brighter in the IR than they are at optical wavelengths, making it possible to measure greater distances using IR SBFs. We report new K' (2.1 micron) SBF measurements of 9 galaxies in the Fornax and Eridanus clusters using a 1024^2-pixel HgCdTe array. We used improved analysis techniques to remove contributions from globular clusters and background galaxies, and we assess the relative importance of other sources of residual variance. We applied the improved methodology to Fornax and Eridanus images and to previously published Virgo cluster data. …
We have employed FORS1/2+VLT to acquire deep B and R CCD images of 16 dwarf elliptical galaxies in the direction of the Virgo cluster. For each dwarf we measure the R-band surface brightness fluctuation (SBF) magnitude \bar{m}_R and the (B-R) colour in a number of fields at different galactocentric distances. From the field-to-field variation of the two quantities we determine the SBF distance by means of the (B-R)-\bar{M}_R relation. The derived distances of the dwarfs are ranging from 14.9-21.3Mpc, with a mean 1sigma uncertainty of 1.4Mpc, confirming that there is considerable depth in the d…
We have used deep HST/WFPC2 images in V (F606W) and I (F814W) to measure the luminosity distribution of the globular clusters in NGC 4874, the central cD galaxy of the Coma cluster. We find the ``turnover'' point of the globular cluster luminosity function (GCLF) to lie at V = 27.88 +/- 0.12, while the overall GCLF shape matches the standard Gaussian-like form with dispersion SIGMA_V = 1.49 +/- 0.12. We use the GCLF as a standard candle by matching the turnover points in NGC 4874 and another Coma elliptical, IC 4051, with those of the giant ellipticals in the Virgo cluster (M87 and five others…
We acquired radial velocities of a significant number of globular clusters (GCs) on wide fields between galaxies in the nearby Fornax cluster of galaxies, in order to derive their velocity dispersion radial profile and to probe the dynamics of the cluster. We used FLAMES on the VLT to obtain accurate velocities for 149 GCs, within a ~500x150 kpc strip centered on NGC 1399, the Fornax central galaxy. These objects are at the very bright tail (M_V < -9.5) of the GC luminosity function, overlapping the so-called ``ultra-compact dwarfs'' magnitude range. Eight of the brightest FLAMES-confirmed mem…
We present BVI photometry of 190 galaxies in the central region of the Fornax Cluster observed with the Michigan Curtis Schmidt Telescope. The cluster members exhibit a strong surface brightness-magnitude relation in our data: both giant and dwarf ellipticals decrease in surface brightness as luminosity decreases. However the surface brightness-magnitude relation is no longer a reliable method for determining cluster membership at surface brightnesses fainter than 22 mag/sq.arcsec. The newly discovered ultra-compact dwarf galaxies (UCDs) lie well off the normal surface brightness-magnitude rel…
Our 2dF Fornax Cluster Spectroscopic Survey (FCSS) and follow-up work in the Virgo Cluster have shown that the cores of both galaxy clusters contain a previously-unknown class of object, ultra-compact dwarf (UCD) galaxies. We present high resolution spectroscopy and deep multicolour imaging to show that these enigmatic objects are dynamically distinct from both globular clusters (GCs) and nucleated dwarf galaxies (dE,Ns). Our hypothesis for their origin may explain the observed high ``specific frequency'' of GCs in central cluster galaxies.
Recent observations have revealed that velocity dispersions of ``ultra-compact dwarf'' (UCD) galaxies are significantly smaller than those of other galaxy populations in the Fornax and the Virgo clusters of galaxies. In order to understand the origin of the observed lower velocity dispersions of UCDs, we numerically investigate line-of-sight velocity dispersion (sigma_los) of galaxy populations with variously different orbits in clusters of galaxies with the total masses of M_cl. We particularly investigate radial velocity dispersion profiles (sigma_los(R)) and velocity dispersions within the …
The Fornax Cluster Spectroscopic Survey (FCSS) project utilises the 2dF multi-object spectrograph on the AAT. Its aim is to obtain spectra for a complete sample of all 14000 objects with 16.5<bj<19.7 irrespective of their morphology in a 12 sq deg area centred on the Fornax Cluster. A sample of 24 Fornax Cluster members has been identified from the first 2dF field (3.1 sq deg in area) to be completed. This is the first complete smaple of cluster objects of known distance with well defined selection limits. 19 of the galaxies (with -15.8<M_B<-12.7) appear to be conventional dwarf elliptical or …
We present narrow band data on dwarf ellipticals in nearby (Virgo, Fornax) and intermediate redshift clusters (A2125, A2218) in order to study their mean age and metallicities. In all four clusters, nucleated dwarf ellipticals display colors that place them on the high metallicity end of the Milky Way globular cluster sequence. Normal dwarf ellipticals display colors, and resulting metallicities and ages, that align them with bright ellipticals. This suggests that dE,N's may be the ancestors to the red GC population found around many elliptical galaxies.
We present far-UV spectroscopy of the giant elliptical galaxy NGC 1399, obtained with the Far Ultraviolet Spectroscopic Explorer. Of all quiescent ellipticals, NGC 1399 has the strongest known ``UV upturn'' -- a sharp spectral rise shortward of 2500 A. It is now well-established that this emission comes from hot horizontal branch (HB) stars and their progeny; however, the chemical composition of these stars has been the subject of a long-standing debate. For the first time in observations of any elliptical galaxy, our spectra clearly show photospheric metallic absorption lines within the UV up…
In recent years, increasing evidence for chemical complexity and multiple stellar populations in massive globular clusters (GCs) has emerged, including extreme horizontal branches (EHBs) and UV excess. Our goal is to improve our understanding of UV excess in the regime of both massive GCs and ultra-compact dwarf galaxies (UCDs). To this end, we use deep archival GALEX data of the central Fornax cluster to measure NUV and FUV magnitudes of UCDs and massive GCs. We obtain NUV photometry for a sample of 35 compact objects with -13.5<M_V<-10 mag. Of those, 21 objects also have FUV photometry. Roug…
We derive $I$ band luminosity functions for galaxies in Abell 426 (Perseus and Abell 539, two rich, low galactic latitude clusters at moderate redshift. Cluster members are selected via the color-magnitude relation for bright galaxies. We find $α=-1.56 \pm 0.07$ for Perseus over the range $-19.4 < M_I < -13.4$ ($15 < I < 21$) and $α=-1.42 \pm 0.14$ for $-18.5 < M_I < -14$ ($17 < I < 21.5$) for A539. These LF's are similar to those derived in Virgo and Fornax, weakly supporting claims for the existence of a universal luminosity function for galaxies in clusters.
We investigate the connection between globular clusters and ultra-compact dwarf galaxies (UCDs) by examining the properties of several compact objects associated with M87, all of which were previously classified as globular clusters. Combining imaging from the Hubble Space Telescope with ground-based Keck spectroscopy, we find two objects to have half-light radii, velocity dispersions and mass-to-light ratios that are consistent with the predictions of population synthesis models for old, metal-rich, luminous globular clusters. Three other objects are much larger, with half-light radii of appr…
Recent spectroscopic observations of galaxies in the Fornax-Cluster reveal nearly unresolved `star-like' objects with red-shifts appropriate to the Fornax-Cluster. These objects have intrinsic sizes of about 100 pc and absolute B-band magnitudes in the range -14 < M_B < -11.5 mag and lower limits for the central surface brightness mu_B > 23 mag/arcsec^2 (Phillipps et al. 2001), and so appear to constitute a new population of ultra-compact dwarf galaxies (UCDs). Such compact dwarfs were predicted to form from the amalgamation of stellar super-clusters (Kroupa 1998), which are rich aggregates of…
The flux excess of elliptical galaxies in the far-ultraviolet can be reproduced by population synthesis models when accounting for the population of old hot helium-burning subdwarf stars. This has been achieved by Han and coworkers through a quantitative model of binary stellar evolution. Here, we compare the resulting evolutionary population synthesis model to the GALEX far-near ultraviolet colors (FUV-NUV) of Virgo cluster early-type galaxies that were published by Boselli and coworkers. FUV-NUV is reddest at about the dividing luminosity of dwarf and giant galaxies, and becomes increasingly…
We present the first results of a project aimed to study the galaxy population of the Antlia cluster, the third nearest galaxy cluster after Virgo and Fornax. The observations for the Antlia project consist of Washington wide-field images taken with the MOSAIC camera mounted at the prime focus of the CTIO 4-m Blanco telescope. Our preliminary results correspond to the identification and classification of dwarf galaxies in the central cluster region, extending the list of Ferguson & Sandage (1990). The final aim of our project is to study the luminosity function, morphology and structural param…
The Pierre Auger Observatory reports that 20 of the 27 highest energy cosmic rays have arrival directions within 3.2 deg of a nearby galaxy in the Veron-Cetty & Veron Catalog of Quasars and Active Galactic Nuclei (12th Ed.), with ~5 of the correlations expected by chance. In this paper we examine the correlated galaxies to gain insight into the possible UHECR sources. We find that 14 of the 21 correlated VCV galaxies are AGNs and we determine their bolometric luminosities. The remaining 7 are primarily star-forming galaxies. The bolometric luminosities of the correlated AGNs are all greater th…
