Velocity dispersion estimates of APM galaxy clusters

We present 83 new galaxy radial velocities in the field of 18 APM clusters with redshifts between 0.06 and 0.13. The clusters have Abell identifications and the galaxies were selected within 0.75 h$^{-1}$Mpc in projection from their centers. We derive new cluster velocity dispersions for 13 clusters using our data and published radial velocities. We analyze correlations between cluster velocity dispersions and cluster richness counts as defined in Abell and APM catalogs. The correlations show a statistically significant trend although with a large scatter suggesting that richness is a poor estimator of cluster mass irrespectively of cluster selection criteria and richness definition. We find systematically lower velocity dispersions in the sample of Abell clusters that do not fulfill APM cluster selection criteria suggesting artificially higher Abell richness counts due to contamination by projection effects in this subsample.Comment: Accepted for publication in MNRA

Extinction Effects in Spiral Galaxy Rotation Curves

Observations show that the slope of the inner part of the H$\alpha$/[NII] rotation curves of disk galaxies is depressed by extinction: at fixed luminosity, the observed slope is in fact seen to depend on the disk inclination to the line of sight. Using a simple extinction model, we are able to reproduce well the observed trends. The model assumes an exponential distribution, both in the radial and $z$ directions, identical for star--forming regions and dust. Fits to the data are optimized by varying the scale height and scale length of absorbers, as well as the disk's central optical depth $\tau_\circ$, as seen face--on. The observations indicate that disk central opacity increases with total luminosity. Model fits for the most luminous galaxies (brighter than $M-5\log h=-21.4$ in the I band) yield $\tau_\circ \simeq 3.5^{+4.0}_{-2.0}$, near $\lambda=0.66$ $\mu$m. The large uncertainty on the inferred value of $\tau_\circ$ is due to the poorly known characteristics of the distribution of absorbers in the disk, as well as to the likelihood of strong departures from an exponential radial distribution near the galaxy centers.Comment: 19 pages, 5 figures, accepted for publication in A

Cluster-Galaxy Correlations in CDM Models

We study the ability of COBE-normalized CDM models to reproduce observed properties of the distribution of galaxies and clusters using N-body numerical simulations. We analyze the galaxy-galaxy and cluster-galaxy two-point correlation functions, $\xi_{gg}$ and $\xi_{cg}$, in open ($\Omega_{0}=0.4, \Omega_{\Lambda}=0, \sigma_8=0.75$), and flat ($\Omega_{0}=0.3, \Omega_{\Lambda}=0.7, \sigma_8=1.05$) CDM models which both reproduce the observed abundances of rich clusters of galaxies. To compare models with observations we compute projected cross-correlation functions $\omega_{gg}$ and $\omega_{cg}$ to derive the corresponding $\xi_{gg}$ and $\xi_{cg}$. We use target galaxies selected from Las Campanas Redshift Survey, target clusters selected from the APM Cluster Survey and tracer galaxies from the Edinburgh Durham Sky Survey catalog.Comment: 13 pages, 6 figures, to appear in: The Astrophysical Journa

Low X-Ray Luminosity Galaxy Clusters. II. Optical properties and morphological content at 0.18 < z < 0.70

This is the second of a series of papers on low X-ray luminosity galaxy clusters, in which we present the $r^\prime$, $g^\prime$ and $i^\prime$ photometry obtained with GMOS-IMAGE at Gemini North and South telescopes for seven systems in the redshift range of 0.18 to 0.70. Optical magnitudes, colours and morphological parameters, namely, concentration index, ellipticity and visual morphological classification, are also given. At lower redshifts, the presence of a well-defined red cluster sequence extending by more than 4 magnitudes showed that these intermediate-mass clusters had reached a relaxed stage. This was confirmed by the small fraction of blue galaxy members observed in the central regions of $\sim$ 0.75 Mpc. In contrast, galaxy clusters at higher redshifts had a less important red cluster sequence. We also found that the galaxy radial density profiles in these clusters were well fitted by a single power law. At 0.18 $<$ z $<$ 0.70, we observed an increasing fraction of blue galaxies and a decreasing fraction of lenticulars, with the early-type fraction remaining almost constant. Overall, the results of these intermediate-mass clusters are in agreement with those for high mass clusters.Comment: 16 pages, 13 figures, 5 tables. Accepted for publication in MNRA

Low X-Ray Luminosity Galaxy Clusters. IV. SDSS galaxy clusters at z < 0.2

This is the fourth of a series of papers on low X-ray luminosity galaxy clusters. The sample comprises 45 galaxy clusters with X-ray luminosities fainter than 0.7 × 1044 erg s.1 at redshifts lower than 0.2 in the regions of the Sloan Digital Sky Survey. The sample of spectroscopic members of the galaxy clusters was obtained with the criteria: Rp ≤ 1Mpc and δV ≤ σ using our σ estimates containing 21 galaxy clusters with more than six spectroscopic members. We have also defined a sample of photometric members with galaxies that satisfy rp ≤ 1Mpc, and δV ≤ 6000 km s -1 including 45 galaxy clusters with more than six cluster members.We have divided the redshift range in three bins: Z ≤ 0.065; 0.065 z 0.10; and z ≤ 0.10. We have stacked the galaxy clusters using the spectroscopic sub-sample and we have computed the best RS linear fit within 1 σ dispersion.With the photometric sub-sample we have added more data to the RS obtaining the photometric 1σ dispersion relative to the spectroscopic RS fit. We have computed the luminosity function using the 1/Vmax method fitting it with a Schechter function. The obtained parameters for these galaxy clusters with low X-ray luminosities are remarkably similar to those for groups and poor galaxy clusters at these lower redshifts.Fil: O'Mill, Ana Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Alonso, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Valotto, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Nilo Castellón, Jos Luis. Universidad de La Serena; Chil

Grupos de galaxias: dependencia de las propiedades de sus galaxias miembros con la emisión en radio

We present a study of the observational properties of Galaxies in Groups and its AGN host galaxies. We analyze the characteristics of the emision from the host AGN galaxies, both in the optical region as in the radio frecuencies, and its relation with their environment. In order to make these studies, the information from AGN associated with galaxy clusters has been correlated to the FIRST radio survey. In this correlation we analyze the parameters of these galaxies: luminosity, morphology, stellar mass, stellar age, etc.Fil: Nieto, L.. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Coldwell Lloveras, Georgina Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Valotto, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentin

Quasar-galaxy and AGN-galaxy cross-correlations

We compute quasar-galaxy and AGN-galaxy cross-correlation functions for samples taken from the \cite{VCV98} catalog of quasars and active galaxies, using tracer galaxies taken from the Edinburgh/Durham Southern Catalog. The sample of active galaxy targets shows positive correlation at projected separations $r_p < 6 h^{-1} Mpc$ consistent with the usual power-law. On the other hand, we do not find a statistically significant positive quasar-galaxy correlation signal except in the range $3 h^{-1} Mpc < r_p < 6 h^{-1} Mpc$ where we find similar AGN-galaxy and quasar-galaxy correlation amplitudes. At separations $r_p<3 h^{-1} Mpc$ a strong decline of quasar-galaxy correlations is observed, suggesting a significant local influence of quasars in galaxy formation. In an attempt to reproduce the observed cross-correlation between quasars and galaxies, we have performed CDM cosmological hydrodynamical simulations and tested the viability of a scenario based on the model developed by \cite{silkrees98}. In this scheme a fraction of the energy released by quasars is considered to be transferred into the baryonic component of the intergalactic medium in the form of winds. The results of the simulations suggest that the shape of the observed quasar-galaxy cross-correlation function could be understood in a scenario where a substantial amount of energy is transferred to the medium at the redshift of maximum quasar activity.Comment: 11 pages, 9 figures. Accepted for publication in Ap