Galaxy Peculiar Velocities and Infall onto Groups

We perform statistical analyses to study the infall of galaxies onto groups and clusters in the nearby Universe. The study is based on the UZC and SSRS2 group catalogs and peculiar velocity samples. We find a clear signature of infall of galaxies onto groups over a wide range of scales 5 h^{-1} Mpc<r<30 h^{-1} Mpc, with an infall amplitude on the order of a few hundred kilometers per second. We obtain a significant increase in the infall amplitude with group virial mass (M_{V}) and luminosity of group member galaxies (L_{g}). Groups with M_{V}<10^{13} M_{\odot} show infall velocities V_{infall} \simeq 150 km s^{-1} whereas for M_{V}>10^{13} M_{\odot} a larger infall is observed, V_{infall} \simeq 200 km s^{-1}. Similarly, we find that galaxies surrounding groups with L_{g}<10^{15} L_{\odot} have V_{infall} \simeq 100 km s^{-1}, whereas for L_{g}>10^{15} L_{\odot} groups, the amplitude of the galaxy infall can be as large as V_{infall} \simeq 250 km s^{-1}. The observational results are compared with the results obtained from mock group and galaxy samples constructed from numerical simulations, which include galaxy formation through semianalytical models. We obtain a general agreement between the results from the mock catalogs and the observations. The infall of galaxies onto groups is suitably reproduced in the simulations and, as in the observations, larger virial mass and luminosity groups exhibit the largest galaxy infall amplitudes. We derive estimates of the integrated mass overdensities associated with groups by applying linear theory to the infall velocities after correcting for the effects of distance uncertainties obtained using the mock catalogs. The resulting overdensities are consistent with a power law with \delta \sim 1 at r \sim 10 h^{-1}Mpc.Comment: 25 pages, 10 figure

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

The V-band luminosity function of galaxies in A2151

We present a wide field $V$-band imaging survey of approximately 1 deg$^2$ ($\sim7.2 h^{-2}_{75}$ Mpc$^{2}$) in the direction of the nearby cluster of galaxies Abell 2151 (the Hercules Cluster). The data are used to construct the luminosity function (LF) down to $M_V \approx -14.85$, thus allowing us to study the dwarf galaxy population in A2151 for the first time. The obtained global LF is well described by a Schechter function with best-fit parameters $\alpha = -1.29^{+0.09}_{-0.08}$ and $M_V^* = -21.41^{+0.44}_{-0.41}$. The radial dependence of the LF was investigated, with the faint-end slope tending to be slightly steeper in the outermost regions and farther away than the virial radius. Given the presence of significant substructure within the cluster, we also analysed the LFs in three different regions. We find that the dwarf to giant ratio increases from the northern to the southern subcluster, and from low to high local density environments, although these variations are marginally significant (less than 2$\sigma$).Comment: Accepted for publication in A&

The luminosity function of field galaxies

Schmidt's method for construction of luminosity function of galaxies is generalized by taking into account the dependence of density of galaxies from the distance in the near Universe. The logarithmical luminosity function (LLF) of field galaxies depending on morphological type is constructed. We show that the LLF for all galaxies, and also separately for elliptical and lenticular galaxies can be presented by Schechter function in narrow area of absolute magnitudes. The LLF of spiral galaxies was presented by Schechter function for enough wide area of absolute magnitudes: . Spiral galaxies differ slightly by parameter . At transition from early spirals to the late spirals parameter in Schechter function is reduced. The reduction of mean luminosity of galaxies is observed at transition from elliptical galaxies to lenticular galaxies, to early spiral galaxies, and further, to late spiral galaxies, in a bright end, . The completeness and the average density of samples of galaxies of different morphological types are estimated. In the range the mean number density of all galaxies is equal 0.127 Mpc-3.Comment: 14 page, 8 figures, to appear in Astrophysic

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

Gemini Observations of Galaxies in Rich Early Environments (GOGREEN) I : survey description.

We describe a new Large Program in progress on the Gemini North and South telescopes: Gemini Observations of Galaxies in Rich Early Environments (GOGREEN). This is an imaging and deep spectroscopic survey of 21 galaxy systems at 1 10 in halo mass. The scientific objectives include measuring the role of environment in the evolution of low-mass galaxies, and measuring the dynamics and stellar contents of their host haloes. The targets are selected from the SpARCS, SPT, COSMOS, and SXDS surveys, to be the evolutionary counterparts of today's clusters and groups. The new red-sensitive Hamamatsu detectors on GMOS, coupled with the nod-and-shuffle sky subtraction, allow simultaneous wavelength coverage over λ ∼ 0.6–1.05 μm, and this enables a homogeneous and statistically complete redshift survey of galaxies of all types. The spectroscopic sample targets galaxies with AB magnitudes z΄ < 24.25 and [3.6] μm < 22.5, and is therefore statistically complete for stellar masses M* ≳ 1010.3 M⊙, for all galaxy types and over the entire redshift range. Deep, multiwavelength imaging has been acquired over larger fields for most systems, spanning u through K, in addition to deep IRAC imaging at 3.6 μm. The spectroscopy is ∼50 per cent complete as of semester 17A, and we anticipate a final sample of ∼500 new cluster members. Combined with existing spectroscopy on the brighter galaxies from GCLASS, SPT, and other sources, GOGREEN will be a large legacy cluster and field galaxy sample at this redshift that spectroscopically covers a wide range in stellar mass, halo mass, and clustercentric radius

Estudio sobre los efectos del medio sobre propiedades de galaxias

Hemos realizado un estudio estadístico en los catálogos CfA y SRC 2 sobre la dependencia de la morfología de las galaxias y sus velocidades circulares con el medio. El índice morfológico resulta una función decreciente de la densidad numérica de galaxias. Para un determinado valor de la densidad en una capa interna encontramos que el índice morfológico del objeto central es más negativo cuando la densidad de galaxias en capas externas es mayor. Este efecto está presente sólo cuando los tip tempranos y tardíos están simultáneamente presentes en la estadística y no cuando los tipos tempranos y los tipos tardíos son considerados por separado. Este resultado puede ser explicado en términos de una mayor tasa de "mergers" de galaxias espirales que dan origen a objetos tempranos en regiones 'globalmente densas (cúmulos). Por otro lado, tanto la relación disk-bulge de tipos tardíos como las elipticidades de tipos tempranos dependen sólo localmente de la densidad. Encontramos que la velocidad circular media de las galaxias tiene aproximadamente un incremento lineal con la densidad como es esperado en el régimen lineal de un escenario de agregación jerárquica como el modelo CDM. Mediante una técnica de análisis similar a la utilizada con los tipos morfológicos se encuentra que las velocidades circulares son un 10% menores para aquellas galaxias en regiones globalmente densas (cúmulos). Este resultado es evidencia estadística del "stripping" del material de los halos causado por encuentros.Asociación Argentina de Astronomí

The faint-end of the galaxy luminosity function in groups

We compute the galaxy luminosity function in spectroscopically selected nearby groups and clusters. Our sample comprises 728 systems extracted from the third release of the Sloan Digital Sky Survey in the redshift range $0.03 < z < 0.06$ with virial mass range $10^{11}M_\odot < M_{vir} < 2\times 10^{14}M_\odot$. In order to compute the galaxy luminosity function, we apply a statistical background subtraction method following usually adopted techniques. In the $r$ band, the composite galaxy luminosity function shows a slope $\alpha=-1.3$ in the bright--end, and an upturn of the slope in the faint--end, M_r\ga -18+5log(h), to slopes $-1.9<\alpha<-1.6$. We find that this feature is present also in the $i,g$ and $z$ bands, and for all explored group subsamples, irrespective of the group mass, number of members, integrated color or the presence of a hot intra-cluster gas associated to X-ray emission.Comment: 8 pages, 10 figures, Submitted to Astronomy and Astrophysic

Acondicionamiento de un radiotelescopio utilizando Software Defined Radio (SDR)

En este reporte, presentamos el desarrollo de una antena para la detección de ondas de radio. El sistema receptor consiste de un dipolo de media onda para 610 MHz acoplado a un reflector semi-parabólico de parrilla, un amplificador de bajo ruido y, como detector, un Software Defined Radio RTL-SDR conectado a una computadora. El objetivo principal del trabajo es la calibración del sistema por el método del factor-Y, utilizando al Sol como fuente. Nuestros resultados preliminares indican que la primer implementación del sistema no produjo las medidas necesarias para llevar a cabo la calibración. Concluimos que las causas más probables de esto son la inestabilidad a lo largo del tiempo del receptor y la forma en que se tomaron las mediciones. Discutimos los próximos pasos para solucionar el problema y concluir con la calibración proyectada.We present the development of a radio antenna using a Software Defined Radio (RTL-SDR). The receiver system consists of a half-wave dipole for a frequency of 610 MHz, a low noise amplifier and the RTL-SDR receiver connected to a computer. The main goal of this work is the calibration of the system by means of the Y-factor method, using the Sun as the source. Our first results show that we could not obtain the necessary measurements to carry out the calibration. We conclude that the main issue is the time-instability of the system. We discuss the following steps required to complete the calibration.Asociación Argentina de Astronomí