A radio Search for high redshift HI absorption

Ground based optical observations have yielded considerable information on the statistics of damped-lyman alpha systems. In particular these systems are known to be the dominant repository of the observed neutral gas at high redshift. However, particularly at high redshift, there is the possibility that optical observations could be biased due to the exclusion of damped-lyman alpha systems that contain moderate to significant amounts of dust. Independent observational constraints on the neutral hydrogen content at high redshifts and the amount of dust in high redshift systems can be obtained from a radio search against the bright lobes of distant radio galaxies (which is less affected by the presence of dust in foreground damped-lyman alpha systems). We describe here a pilot radio survey along the line of sight to a small sample of high redshift radio galaxies, and also present some preliminary results. The survey uses a novel observing mode at the WSRT which enables one to make sensitive searches of a large redshift interval in a modest amount of telescope time.Comment: A version with figures is available at http://www.nfra.nl/~chengalu/ To appear in "Cold Gas at High Redshift", Eds. M.Bremer et al. (Kluwer, Dordrecht

Optical and radio survey of Southern Compact Groups of galaxies. I. Pilot study of six groups

Multi-wavelength observations of Hickson's Compact Groups (HCGs) have shown that many of these groups are physical bound structures and are in different stage of evolution, from spiral-dominated systems to almost merged objects. Very few studies have analysed the Southern Compact Groups (SCGs) sample, which is though to be younger that HCGs, due to an on average higher number of spiral galaxies. We present here the first results from optical and radio observations on a pilot sample of SCGs.Comment: accepted on A&A on July 19, 2007. Figures 1 and 3-12 will be available only in electronic for

Populating a cluster of galaxies - I. Results at z=0

We simulate the assembly of a massive rich cluster and the formation of its constituent galaxies in a flat, low-density universe. Our most accurate model follows the collapse, the star-formation history and the orbital motion of all galaxies more luminous than the Fornax dwarf spheroidal, while dark halo structure is tracked consistently throughout the cluster for all galaxies more luminous than the SMC. Within its virial radius this model contains about 2.0e7 dark matter particles and almost 5000 distinct dynamically resolved galaxies. Simulations of this same cluster at a variety of resolutions allow us to check explicitly for numerical convergence both of the dark matter structures produced by our new parallel N-body and substructure identification codes, and of the galaxy populations produced by the phenomenological models we use to follow cooling, star formation, feedback and stellar aging. This baryonic modelling is tuned so that our simulations reproduce the observed properties of isolated spirals outside clusters. Without further parameter adjustment our simulations then produce a luminosity function, a mass-to-light ratio, luminosity, number and velocity dispersion profiles, and a morphology-radius relation which are similar to those observed in real clusters. In particular, since our simulations follow galaxy merging explicitly, we can demonstrate that it accounts quantitatively for the observed cluster population of bulges and elliptical galaxies.Comment: 28 pages, submitted to MNRA

The evolution of substructure II: linking dynamics to environment

We present results from a series of high-resolution N-body simulations that focus on the formation and evolution of eight dark matter halos, each of order a million particles within the virial radius. We follow the time evolution of hundreds of satellite galaxies with unprecedented time resolution, relating their physical properties to the differing halo environmental conditions. The self-consistent cosmological framework in which our analysis was undertaken allows us to explore satellite disruption within live host potentials, a natural complement to earlier work conducted within static potentials. Our host halos were chosen to sample a variety of formation histories, ages, and triaxialities; despite their obvious differences, we find striking similarities within the associated substructure populations. Namely, all satellite orbits follow nearly the same eccentricity distribution with a correlation between eccentricity and pericentre. We also find that the destruction rate of the substructure population is nearly independent of the mass, age, and triaxiality of the host halo. There are, however, subtle differences in the velocity anisotropy of the satellite distribution. We find that the local velocity bias at all radii is greater than unity for all halos and this increases as we move closer to the halo centre, where it varies from 1.1 to 1.4. For the global velocity bias we find a small but slightly positive bias, although when we restrict the global velocity bias calculation to satellites that have had at least one orbit, the bias is essentially removed.Comment: 14 pages, 14 figures, MNRAS in pres

Mass profiles and galaxy orbits in nearby galaxy clusters from the analysis of the projected phase-space

We analyze kinematic data of 41 nearby (z<0.1) relaxed galaxy clusters in terms of the projected phase-space density using a phenomenological, fully anisotropic model of the distribution function. We apply the Markov Chain Monte Carlo approach to place constraints on total mass distribution approximated by the universal NFW profile and the profile of the anisotropy of galaxy orbits. We find the normalization of the mean mass-concentration relation is c=6.9_{-0.7}^{+0.6} at the virial mass M_v=5x10^{14}M_sun. Assuming a one-to-one correspondence between sigma_8 and the normalization of the mass-concentration relation in the framework of the concordance model we estimate the normalization of the linear power spectrum to be sigma_8=0.91_{-0.08}^{+0.07}. Our constraints on the parameters of the mass profile are compared with estimates from other methods. We show that galaxy orbits are isotropic at the cluster centres (with the mean ratio of the radial-to-tangential velocity dispersions sigma_r/sigma_theta=0.97+/-0.04) and radially anisotropic at the virial sphere (with the mean ratio sigma_r/sigma_theta=1.75^{+0.23}_{-0.19}). Although the value of the central anisotropy appears to be universal, the anisotropy at the virial radius differs between clusters within the range 1<(sigma_r/sigma_theta)<2. Utilizing the Bautz-Morgan morphological classification and information on the prominence of a cool core we select two subsamples of galaxy clusters corresponding to less and more advanced evolutionary states. It is demonstrated that less evolved clusters have shallower mass profiles and their galaxy orbits are more radially biased at the virial sphere. This property is consistent with the expected evolution of the mass profiles as well as with the observed orbital segregation of late and early type galaxies.Comment: 16 pages, 12 figures, accepted for publication in MNRA

Intragroup diffuse light in compact groups of galaxies II. HCG 15, 35 and 51

This continuing study of intragroup light in compact groups of galaxies aims to establish new constraints to models of formation and evolution of galaxy groups, specially of compact groups, which are a key part in the evolution of larger structures, such as clusters. In this paper we present three additional groups (HCG 15, 35 and 51) using deep wide field $B$ and $R$ band images observed with the LAICA camera at the 3.5m telescope at the Calar Alto observatory (CAHA). This instrument provides us with very stable flatfielding, a mandatory condition for reliably measuring intragroup diffuse light. The images were analyzed with the OV\_WAV package, a wavelet technique that allows us to uncover the intragroup component in an unprecedented way. We have detected that 19, 15 and 26% of the total light of HCG 15, 35 and 51, respectively, is in the diffuse component, with colours that are compatible with old stellar populations and with mean surface brightness that can be as low as $28.4 {\rm B mag arcsec^{-2}}$. Dynamical masses, crossing times and mass to light ratios were recalculated using the new group parameters. Also tidal features were analyzed using the wavelet technique.Comment: 12 pages, 5 figures. Accepted for publication in MNRAS. See http://www.eso.org/~cdarocha/publications/DaRochaetal2008_IGL_HCG.pdf for full resolution version. Complementary reference adde

Modified Virial Formulae and the Theory of Mass Estimators

We show how to estimate the enclosed mass from the observed motions of an ensemble of test particles. Traditionally, this problem has been attacked through virial or projected mass estimators. Here, we examine and extend these systematically, and show how to construct an optimal estimator for any given assumption as to the potential. The estimators do not explicitly depend on any properties of the density of the test objects, which is desirable as in practice such information is dominated by selection effects. As particular examples, we also develop estimators tailored for the problem of estimating the mass of the Hernquist or NFW dark matter haloes from the projected positions and velocities of stars.Comment: 9 pages, MNRAS, in pres

Measuring the escape velocity and mass profiles of galaxy clusters beyond their virial radius

The caustic technique uses galaxy redshifts alone to measure the escape velocity and mass profiles of galaxy clusters to clustrocentric distances well beyond the virial radius, where dynamical equilibrium does not necessarily hold. We provide a detailed description of this technique and analyse its possible systematic errors. We apply the caustic technique to clusters with mass M_200>=10^{14}h^{-1} M_sun extracted from a cosmological hydrodynamic simulation of a LambdaCDM universe. With a few tens of redshifts per squared comoving megaparsec within the cluster, the caustic technique, on average, recovers the profile of the escape velocity from the cluster with better than 10 percent accuracy up to r~4 r_200. The caustic technique also recovers the mass profile with better than 10 percent accuracy in the range (0.6-4) r_200, but it overestimates the mass up to 70 percent at smaller radii. This overestimate is a consequence of neglecting the radial dependence of the filling function F_beta(r). The 1-sigma uncertainty on individual escape velocity profiles increases from ~20 to ~50 percent when the radius increases from r~0.1 r_200 to ~4 r_200. Individual mass profiles have 1-sigma uncertainty between 40 and 80 percent within the radial range (0.6-4) r_200. We show that the amplitude of these uncertainties is completely due to the assumption of spherical symmetry, which is difficult to drop. Alternatively, we can apply the technique to synthetic clusters obtained by stacking individual clusters: in this case, the 1-sigma uncertainty on the escape velocity profile is smaller than 20 percent out to 4 r_200. The caustic technique thus provides reliable average profiles which extend to regions difficult or impossible to probe with other techniques.Comment: MNRAS accepted, 20 page

DRI-Grass: a new experimental platform for addressing grassland ecosystem responses to future precipitation scenarios in south-east Australia

and contrasting levels of root herbivor