Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Merger and Ring Galaxy Formation Rates at z<=2   We compare the observed merger rate of galaxies over cosmic time and the
frequency of collisional ring galaxies (CRGs), with analytic models and halo
merger and collision rates from a large cosmological simulation. In the Lambda
cold dark matter (LCDM) model we find that the cosmic {\it merger fraction}
does not evolve strongly between 0.2<z<2, implying that the observed decrease
of the cosmic star formation rate since z~1 might not be tied to a disappearing
population of major mergers. Halos hosting massive galaxies undergo on average
~2 mergers from z~2 up to present day, reflecting the late assembly time for
the massive systems and the related downsizing problem. The cosmic {\it merger
rate} declines with redshift: at the present time it is a factor of 10 lower
than at z~2, in reasonable agreement with the current available data. The rate
of CRG formation derived from the interactions between halo progenitors up to
z=2 is found to be a good tracer of the cosmic merger rate. In the LCDM model
the rate of CRGs as well as the merger rate do not scale as (1+z)^m, as
suggested by previous models. Our predictions of cosmic merger and CRG rates
may be applied to forthcoming surveys such as GOODS and zCOSMOS.

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The categories of this paper are: q-alg
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
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The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex