Globular Clusters in Dense Clusters of Galaxies

Deep imaging data from the Keck II telescope are employed to study the globular cluster (GC) populations in the cores of six rich Abell clusters. The sample includes A754, A1644, A2124, A2147, A2151, and A2152, and spans the redshift range z = 0.035-0.066. The clusters also range in morphology from spiral-rich, irregular systems to centrally concentrated cD clusters rich in early-type galaxies. Globular cluster specific frequencies S_N and luminosity function dispersions are measured for a total of 9 galaxies in six central fields. The measured values of S_N for the six brightest cluster galaxies (BCGs) are all higher than typical values for giant ellipticals, in accord with the known S_N-density correlations. The three non-BCGs analyzed also have elevated values of S_N, confirming that central location is a primary factor. The number of GCs per unit mass for these fields are consistent with those found in an earlier sample, giving further evidence that GC number scales with mass and that the S_N variations are due to a deficit of halo light, i.e., S_N reflects mass-to-light ratio. The discussion builds on an earlier suggestion that the GCs (both metal rich and metal poor) around the central cluster galaxies were assembled at early times, and that star formation halted prematurely in the central galaxies at the epoch of cluster collapse. This is consistent with recent simulations of BCG/cluster formation. The subsequent addition of luminous material through cluster dynamical evolution can cause S_N to decrease, and we may be seeing the first evidence of this. Finally, the GC luminosity function measurements are used to constrain the relative distances of the three clusters that make up the Hercules supercluster.Comment: Uses emulateapj.sty (included); 17 pages with 9 included PostScript figures. Figures 1-6 are separate GIF images (so 15 figures total) available from http://astro.caltech.edu/~jpb/clusters -- the full PostScript version of the paper (20 pages; 2.2 Mb compressed) incorporating Figures 1-6 can also be grabbed from this URL. Accepted for publication in A

The Properties of Poor Groups of Galaxies: III. The Galaxy Luminosity Function

We obtain R-band photometry for galaxies in six nearby poor groups for which we have spectroscopic data, including 328 new galaxy velocities. For the five groups with luminous X-ray halos, the composite group galaxy luminosity function (GLF) is fit adequately by a Schechter function with Mstar = -21.6 +/- 0.4 + 5log h and alpha = -1.3 +/- 0.1. We also find that (1) the ratio of dwarfs to giants is significantly larger for the five groups with luminous X-ray halos than for the one marginally X-ray detected group, (2) the composite GLF for the luminous X-ray groups is consistent in shape with that for rich clusters, (3) the composite group GLF rises more steeply at the faint end than that of the field, (4) the shape difference between the field and composite group GLF's results mostly from the population of non-emission line galaxies, whose dwarf-to-giant ratio is larger in the denser group environment than in the field, and (5) the non-emission line dwarfs are more concentrated about the group center than the non-emission line giants. This last result indicates that the dwarfs and giants occupy different orbits (i.e., have not mixed completely) and suggests that the populations formed at a different times. Our results show that the shape of the GLF varies with environment and that this variation is due primarily to an increase in the dwarf-to-giant ratio of quiescent galaxies in higher density regions, at least up to the densities characteristic of X-ray luminous poor groups. This behavior suggests that, in some environments, dwarfs are more biased than giants with respect to dark matter. This trend conflicts with the prediction of standard biased galaxy formation models. (Abridged)Comment: 36 pages, AASLaTeX with 8 figures. Table 1 also available at http://atropos.as.arizona.edu/aiz/papers/all_grp_lf_ascii.dat.final . To appear in Ap

Deep near-infrared luminosity function of a cluster of galaxies at z=0.3

The deep near-infrared luminosity function of AC118, a cluster of galaxies at z=0.3, is presented. AC118 is a bimodal cluster, as evidenced both by our near-infrared images of lensed galaxies, by public X-ray Rosat images and by the spatial distribution of bright galaxies. Taking advantage of the extension and depth of our data, which sample an almost unexplored region in the depth vs. observed area diagram, we derive the luminosity function (LF), down to the dwarf regime (M*+5), computed in several cluster portions. The overall LF, computed on a 2.66 Mpc2 areas (H_0=50 km/s/Mpc), has an intermediate slope (alpha=-1.2). However, the LF parameters depend on the surveyed cluster region: the central concentration has 2.6^{+5.1}_{-1.7} times more bright galaxies and 5.3^{+7.2}_{-2.3} times less dwarfs per typical galaxy than the outer region, which includes galaxies at an average projected distance of ~580 kpc (errors are quoted at the 99.9 % confidence level). The LF in the secondary AC118 clump is intermediate between the central and outer one. In other words, the near-infrared AC118 LF steepens going from high to low density regions. At an average clustercentric distance of ~580 kpc, the AC118 LF is statistically indistinguishable from the LF of field galaxies at similar redshift, thus suggesting that the hostile cluster environment plays a minor role in shaping the LF at large clustercentric distances, while it strongly affects the LF at higher galaxy density.Comment: ApJ, in press. The whole paper with all high resolution images is available at http://www.na.astro.it/~andreon/listapub.htm

Surface photometry of new nearby dwarf galaxies

We present CCD surface photometry of 16 nearby dwarf galaxies, many of which were only recently discovered. Our sample comprises both isolated galaxies and galaxies that are members of nearby galaxy groups. The observations were obtained in the Johnson B and V bands (and in some cases in Kron-Cousins I). We derive surface brightness profiles, total magnitudes, and integrated colors. For the 11 galaxies in our sample with distance estimates the absolute B magnitudes lie in the range of -10>Mb>-13. The central surface brightness ranges from 22.5 to 27.0 mag/sq.arcsec. Most of the dwarf galaxies show exponential light profiles with or without a central light depression. Integrated radial color gradients, where present, appear to indicate a more centrally concentrated younger population and a more extended older population.Comment: accepted by A&

Iron and s-elements abundance variations in NGC5286: comparison with anomalous globular clusters and Milky Way satellites

We present a high resolution spectroscopic analysis of 62 red giants in the Milky Way globular cluster NGC5286. We have determined abundances of representative light proton-capture, alpha, Fe-peak and neutron-capture element groups, and combined them with photometry of multiple sequences observed along the colour-magnitude diagram. Our principal results are: (i) a broad, bimodal distribution in s-process element abundance ratios, with two main groups, the s-poor and s-rich groups; (ii) substantial star-to-star Fe variations, with the s-rich stars having higher Fe, e.g. _s-rich - _s-poor ~ 0.2~dex; and (iii) the presence of O-Na-Al (anti-)correlations in both stellar groups. We have defined a new photometric index, c_{BVI}=(B-V)-(V-I), to maximise the separation in the colour-magnitude diagram between the two stellar groups with different Fe and s-element content, and this index is not significantly affected by variations in light elements (such as the O-Na anticorrelation). The variations in the overall metallicity present in NGC5286 add this object to the class of "anomalous" GCs. Furthermore, the chemical abundance pattern of NGC5286 resembles that observed in some of the anomalous GCs, e.g. M22, NGC1851, M2, and the more extreme Omega Centauri, that also show internal variations in s-elements, and in light elements within stars with different Fe and s-elements content. In view of the common variations in s-elements, we propose the term s-Fe-anomalous GCs to describe this sub-class of objects. The similarities in chemical abundance ratios between these objects strongly suggest similar formation and evolution histories, possibly associated with an origin in tidally disrupted dwarf satellites.Comment: 28 pages, 21 figures, accepted for publication in MNRA

Accretion and nuclear activity of quiescent supermassive black holes. I: X-ray study

We have studied the nuclear activity in a sample of six quiescent early-type galaxies, with new Chandra data and archival HST optical images. Their nuclear sources have X-ray luminosities ~ 10^{38} - 10^{39} erg/s (L_X/L_Edd ~ 10^{-8} - 10^{-7}), and colors or spectra consistent with accreting supermassive black holes (SMBHs)--except for the nucleus of NGC 4486B, which is softer than typical AGN spectra. In a few cases, the X-ray morphology of the nuclear sources shows hints of marginally extended structures, in addition to the surrounding diffuse thermal emission from hot gas, which is detectable on scales >~ 1 kpc. In one case (NGC 5845), a dusty disk may partially obstruct our direct view of the SMBH. We have estimated the temperature and density of the hot interstellar medium, which is one major source of fuel for the accreting SMBH; typical central densities are n_e ~ (0.02 +/- 0.01) cm^{-3}. Assuming that the hot gas is captured by the SMBH at the Bondi rate, we show that the observed X-ray luminosities are too faint to be consistent with standard disk accretion, but brighter than predicted by radiatively-inefficient solutions (eg, ADAF). In total, there are ~ 20 galaxies for which SMBH mass, hot gas density, and nuclear X-ray luminosity are simultaneously known. In some cases, the nuclear sources are brighter than predicted by the ADAF model; in other cases, they are consistent or fainter. We discuss the apparent lack of correlations between Bondi rate and X-ray luminosity, and suggest that, in order to understand the observed distribution, we need to know two additional parameters: the amount of gas supplied by the stellar population inside the accretion radius, and the fraction (possibly << 1) of the total gas available that is accreted by the SMBH. We shall discuss these issues in our Paper II.Comment: 18 pages, accepted by ApJ. This is Paper I; Paper II will be on astro-ph next Monda

B,V,I - photometry of 20 dwarf irregular galaxies within 10 Mpc

CCD - photometry is presented for 20 dIrr galaxies situated in the nearby complexes CenA/M83, and CVnI as well as in the general field of the Local Volume. We present integrated magnitudes of the galaxies in B,V,I - bands and also surface brightness profiles to a median isophote mu_B ~ 28 mag /sq.arcsec. The popular Sersic parameterization of surface brightness profiles generally does a poor job of simultaneously fitting the inner cores and outer exponential surface brightness fall-offs observed in many of our targets. The observed sample is a part of a general project to image about 500 nearby (D < 10 Mpc) dwarf galaxies in multiple bands.Comment: 3 figures, accepted to the MNRA

Local galaxy flows within 5 Mpc

We present Hubble Space Telescope/WFPC2 images of sixteen dwarf galaxies as part of our snapshot survey of nearby galaxy candidates. We derive their distances from the luminosity of the tip of the red giant branch stars with a typical accuracy of ~12%. The resulting distances are 4.26 Mpc (KKH 5), 4.74 Mpc (KK 16), 4.72 Mpc (KK 17), 4.66 Mpc (ESO 115-021), 4.43 Mpc (KKH 18), 3.98 Mpc (KK 27), 4.61 Mpc (KKH 34), 4.99 Mpc (KK 54), 4.23 Mpc (ESO 490-017), 4.90 Mpc (FG 202), 5.22 Mpc (UGC 3755), 5.18 Mpc (UGC 3974), 4.51 Mpc (KK 65), 5.49 Mpc (UGC 4115), 3.78 Mpc (NGC 2915), and 5.27 Mpc (NGC 6503). Based on distances and radial velocities of 156 nearby galaxies, we plot the local velocity-distance relation, which has a slope of H_0 = 73 km/(c * Mpc) and a radial velocity dispersion of 85 km/s. When members of the M81 and CenA groups are removed, and distance errors are taken into account, the radial velocity dispersion drops to sigma_v=41 km/s. The local Hubble flow within 5 Mpc exibits a significant anisotropy, with two infall peculiar velocity regions directed towards the Supergalactic poles. However, two observed regions of outflow peculiar velocity, situated on the Supergalactic equator, are far away (~50 degr.) from the Virgo/anti-Virgo direction, which disagrees with a spherically symmetric Virgo-centric flow. About 63% of galaxies within 5 Mpc belong to known compact and loose groups. Apart from them, we found six new probable groups, consisting entirely of dwarf galaxies.Comment: 22 pages, 7 figures. A&A Accepted. High resolution Figures 1 and 2 (9616k) are available at http://www.sao.ru/~sme/figs.tar.g

Infrared luminosities of galaxies in the Local Volume

Near-infrared properties of 451 galaxies with distances D \leq 10 Mpc are considered basing on the all-sky two micron survey (2MASS). A luminosity function of the galaxies in the K-band is derived within [-25,-11] mag. The local (D < 8 Mpc) luminosity density is estimated to be 6.8*10^8 L_sun/Mpc^3 that exceeds (1.5+-0.1) times the global cosmic density in the K-band. Virial mass-to-K-luminosity ratios are determined for nearby groups and clusters. In the luminosity range of (5*10^{10} - 2*10^{13})L_sun, the groups and clusters follow the relation \lg(M/L_K) propto (0.27+-0.03) lg(L_K) with a scatter of \~0.1 comparable to errors of the observables. The mean ratio ~= (20-25) M_sun/L_sun for the galaxy systems turns out to be significantly lower than the global ratio, (80-90)M_sun/L_sun, expected in the standard cosmological model with the matter density of Omega_m =0.27. This discrepancy can be resolved if most of dark matter in the universe is not associated with galaxies and their systems.Comment: 15 pages, 7 figures. Astronomy Letters, submitte