Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Observational Mass Function of Loose Galaxy Groups   We analyze the three catalogs of nearby loose groups identified by Garcia
(1993). She used a percolation and a hierarchical method, and proposed a third
group catalog defined as a combination of the two. Each catalog contains almost
500 groups. In agreement with previous works on earlier catalogs, we find that
groups can be described as collapsing systems. Their sampled size is much
larger than their expected virialized region. We compute the virial masses and
correct them by taking into account the young dynamical status. We estimate
group masses, M, for two cosmological models, a flat one with Omega_0=1 and an
open one with Omega_0=0.2. For each of the three catalogs we calculate the mass
function, MF. The number density of groups with M>9x10^{12}\msun, which is the
adopted limit of sample completeness, ranges within 1.3-1.9x10^{-3}h^3/Mpc^3
for Omega_0=1, and it is about a factor of 15% lower for Omega_0=0.2. The MFs
of the hierarchical and combined catalogs have essentially the same shape,
while the MF of the percolation catalog shows a flattening towards large
masses. However, the difference decreases if we do not consider the most
massive groups, for which reliable results come from galaxy cluster studies.
After having estimated the mass contained within the central, presumably
virialized, regions of groups by adopting a reduction in mass of 30-40%, we do
a comparison with the results coming from the virial analysis of nearby rich
clusters (Girardi et al. 1998). All three group MFs turn out to be a smooth
extrapolation of the cluster MF at M<4x10^{14}\msun, which is the completeness
limit of the cluster sample. The resulting optical virial MF of galaxy systems,
which extends over two orders of magnitude, is fitted to a Schechter expression
with a slope of about -1.5 and a characteristic mass of about 3x10^{14}\msun.

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The categories of this paper are: cond-mat
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The categories of this paper are: hep-lat
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The categories of this paper are: adap-org
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The categories of this paper are: dg-ga
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The categories of this paper are: econ
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The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
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The categories of this paper are: chem-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: cs
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The categories of this paper are: quant-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-ph
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The categories of this paper are: math-ph
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The categories of this paper are: stat
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The categories of this paper are: nucl-ex