Non-Gaussian velocity distributions - The effect on virial mass estimates of galaxy groups

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 03/2011; 413(1). DOI: 10.1111/j.1745-3933.2011.01038.x
Source: arXiv


We present a study of nine galaxy groups with evidence for non-Gaussianity in their velocity distributions out to 4R200. This sample is taken from the 57 groups selected from the 2dF Percolation-Inferred Galaxy Groups (2PIGG) catalogue of galaxy
groups. Statistical analysis indicates that the non-Gaussian groups have masses significantly higher than that of the Gaussian
groups. We also have found that all non-Gaussian systems seem to be composed of multiple velocity modes. Besides, our results
indicate that multimodal groups should be considered as a set of individual units with their own properties. In particular,
we have found that the mass distributions of such units are similar to that of the Gaussian groups. Our results reinforce
the idea of non-Gaussian systems as complex structures in the phase space, likely corresponding to secondary infall aggregations
at a stage before virialization. The understanding of these objects is relevant for cosmological studies using groups and
clusters through the mass function evolution.

Download full-text


Available from: Marina Trevisan
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We analyse the dependence of the luminosity function (LF) of galaxies in groups on group dynamical state. We use the Gaussianity of the velocity distribution of galaxy members as a measurement of the dynamical equilibrium of groups identified in the Sloan Digital Sky Survey Data Release 7 by Zandivarez & Martínez. We apply the Anderson–Darling goodness-of-fit test to distinguish between groups according to whether they have Gaussian or non-Gaussian velocity distributions, i.e. whether they are relaxed or not. For these two subsamples, we compute the 0.1r-band LF as a function of group virial mass and group total luminosity. For massive groups, , we find statistically significant differences between the LF of the two subsamples: the LFs of groups that have Gaussian velocity distributions have a brighter characteristic absolute magnitude (∼0.3 mag) and a steeper faint-end slope (∼0.25). We detect a similar effect when comparing the LF of bright [ Gaussian and non-Gaussian groups. Our results indicate that, for massive/luminous groups, the dynamical state of the system is directly related to the luminosity of its galaxy members.
    Full-text · Article · Oct 2011 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We search for the presence of substructure, a non-Gaussian, asymmetrical velocity distribution of galaxies, and large peculiar velocities of the main galaxies in galaxy clusters with at least 50 member galaxies, drawn from the SDSS DR8. We employ a number of 3D, 2D, and 1D tests to analyse the distribution of galaxies in clusters: 3D normal mixture modelling, the Dressler-Shectman test, the Anderson-Darling and Shapiro-Wilk tests and others. We find the peculiar velocities of the main galaxies, and use principal component analysis to characterise our results. More than 80% of the clusters in our sample have substructure according to 3D normal mixture modelling, the Dressler-Shectman (DS) test shows substructure in about 70% of the clusters. The median value of the peculiar velocities of the main galaxies in clusters is 206 km/s (41% of the rms velocity). The velocities of galaxies in more than 20% of the clusters show significant non-Gaussianity. While multidimensional normal mixture modelling is more sensitive than the DS test in resolving substructure in the sky distribution of cluster galaxies, the DS test determines better substructure expressed as tails in the velocity distribution of galaxies. Richer, larger, and more luminous clusters have larger amount of substructure and larger (compared to the rms velocity) peculiar velocities of the main galaxies. Principal component analysis of both the substructure indicators and the physical parameters of clusters shows that galaxy clusters are complicated objects, the properties of which cannot be explained with a small number of parameters or delimited by one single test. The presence of substructure, the non-Gaussian velocity distributions, as well as the large peculiar velocities of the main galaxies, shows that most of the clusters in our sample are dynamically young.
    Full-text · Article · Feb 2012 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: [Abridged] We present an analysis of the relation between the masses of cluster- and group-sized halos, extracted from $\Lambda$CDM cosmological N-body and hydrodynamic simulations, and their velocity dispersions, at different redshifts from $z=2$ to $z=0$. The main aim of this analysis is to understand how the implementation of baryonic physics in simulations affects such relation, i.e. to what extent the use of the velocity dispersion as a proxy for cluster mass determination is hampered by the imperfect knowledge of the baryonic physics. In our analysis we use several sets of simulations with different physics implemented. Velocity dispersions are determined using three different tracers, DM particles, subhalos, and galaxies. We confirm that DM particles trace a relation that is fully consistent with the theoretical expectations based on the virial theorem and with previous results presented in the literature. On the other hand, subhalos and galaxies trace steeper relations, and with larger values of the normalization. Such relations imply that galaxies and subhalos have a $\sim10$ per cent velocity bias relative to the DM particles, which can be either positive or negative, depending on halo mass, redshift and physics implemented in the simulation. We explain these differences as due to dynamical processes, namely dynamical friction and tidal disruption, acting on substructures and galaxies, but not on DM particles. These processes appear to be more or less effective, depending on the halo masses and the importance of baryon cooling, and may create a non-trivial dependence of the velocity bias and the $\soneD$--$\Mtwo$ relation on the tracer, the halo mass and its redshift. These results are relevant in view of the application of velocity dispersion as a proxy for cluster masses in ongoing and future large redshift surveys.
    Preview · Article · Jan 2013 · Monthly Notices of the Royal Astronomical Society
Show more