Article

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

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.23). 03/2011; 413. DOI: 10.1111/j.1745-3933.2011.01038.x
Source: arXiv

ABSTRACT We present a study of 9 galaxy groups with evidence for non-Gaussianity in
their velocity distributions out to 4R200. This sample is taken from 57 groups
selected from the 2PIGG catalog of galaxy groups. Statistical analysis
indicates that non-Gaussian groups have masses significantly higher than
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 distribution of such
units are similar to that of 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.

0 Bookmarks
 · 
91 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We introduce a new method to study the velocity distribution of galaxy systems, the Hellinger Distance (HD) - designed for detecting departures from a Gaussian velocity distribution. We define a relaxed galactic system as the one with unimodal velocity distribution and a normality deviation below a critical value (HD<0.05). In this work, we study the gaussian nature of the velocity distribution of the Berlind group sample, and of the FoF groups from the Millennium simulation. For the Berlind group sample (z<0.1), 67% of the systems are classified as relaxed, while for the Millennium sample we find 63% (z=0). We verify that in multimodal groups the average mass of modes in high multiplicity (N >= 20) systems are significantly larger than in low multiplicity ones (N<20), suggesting that groups experience a mass growth at an increasing virialization rate towards z=0, with larger systems accreting more massive subunits. We also investigate the connection between galaxy properties ([Fe/H], Age, eClass, g-r, R_petro and ) and the gaussianity of the velocity distribution of the groups. Bright galaxies (M_r <=-20.7) residing in the inner and outer regions of groups, do not show significant differences in the listed quantities regardless if the group has a Gaussian (G) or a Non-Gaussian (NG) velocity distribution. However, the situation is significantly different when we examine the faint galaxies (-20.7<M_r<=-17.9). In G groups, there is a remarkable difference between the galaxy properties of the inner and outer galaxy populations, testifying how the environment is affecting the galaxies. Instead, in NG groups there is no segregation between the properties of galaxies in the inner and outer regions, showing that the properties of these galaxies still reflect the physical processes prevailing in the environment where they were found earlier.
    Monthly Notices of the Royal Astronomical Society 06/2013; 434(1). · 5.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We investigate relations between the color and luminosity distributions of cluster galaxies and the evolutionary state of their host clusters. Our aim is to explore some aspects of cluster galaxy evolution and the dynamical state of clusters as two sides of the same process. We used 10,721 member galaxies of 183 clusters extracted from the Sloan Digital Sky Survey using a list of NoSOCS and CIRS targets. First, we classified the clusters into two categories, Gaussian and non-Gaussian, according to their velocity distribution measurements, which we used as an indicator of their dynamical state. We then used objective criteria to split up galaxies according to their luminosities, colors, and photometric mean stellar age. This information was then used to evaluate how galaxies evolve in their host clusters. Meaningful color gradients, i.e., the fraction of red galaxies as a function of radius from the center, are observed for both the Gaussian velocity distribution and the non-Gaussian velocity distribution cluster subsamples, which suggests that member galaxy colors change on a shorter timescale than the time needed for the cluster to reach dynamical equilibrium. We also found that larger portions of fainter red galaxies are found, on average, in smaller radii. The luminosity function in Gaussian clusters has a brighter characteristic absolute magnitude and a steeper faint-end slope than it does in the non-Gaussian velocity distribution clusters. Our findings suggest that cluster galaxies experience intense color evolution before virialization, while the formation of faint galaxies through dynamical interactions probably takes place on a longer timescale, possibly longer than the virialization time.
    Astronomy and Astrophysics 06/2013; · 4.48 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We study 416 galaxy systems with more than 7 members selected from the 2MASS catalog. We applied five well known normality tests to the velocity distributions of these systems to distinguish Gaussian and non-Gaussian clusters. Using controlled samples, we estimated type I and II errors for each test. We verified that individual tests minimize the chances of classifying a Gaussian system as non-Gaussian, while the Fisher’s meta-analysis method, a procedure to combine p-values from several statistical tests, minimizes the chances of classifying a non-Gaussian system as Gaussian. Taking the positive elements of each method and also including a modality analysis of the velocity distribution, we defined objective criteria to split up the sample into Gaussian and non-Gaussian clusters. Our analysis indicates that 50–58% of groups have Gaussian distribution, a lower fraction than that we found using individual normality tests, 71–87%. We also found that some properties of galaxy clusters are significantly different between Gaussian and non-Gaussian systems. For instance, non-Gaussian clusters have larger radii and contain more galaxies than Gaussian clusters. Finally, we discussed the importance of choosing the adequate methodology to classify galaxy systems from their velocity distributions and also the dependence of the results on the criteria used to identify clusters in galaxy surveys.
    New Astronomy 02/2014; 27:41–55. · 1.24 Impact Factor

Full-text (2 Sources)

Download
67 Downloads
Available from
May 26, 2014