The evolution of the radio luminosity function of group galaxies in COSMOS
arxiv(2022)
摘要
[Abridged] To understand the role of the galaxy group environment on galaxy
evolution, we present a study of radio luminosity functions (RLFs) of group
galaxies based on the VLA-COSMOS 3 GHz Large Project. The radio-selected sample
of 7826 COSMOS galaxies with robust optical/near-infrared counterparts,
excellent photometric coverage, and the COSMOS X-ray galaxy groups (M_200c >
10^13.5 M_sun) enables us to construct the RLF of group galaxies (GGs) and
their contribution to the total RLF since z 2.3. Using the Markov chain Monte
Carlo algorithm, we fit a redshift-dependent pure luminosity evolution model
and a linear and power-law model to the luminosity functions. We compare it
with past RLF studies from VLA-COSMOS on individual populations of
radio-selected star-forming galaxies (SFGs) and galaxies hosting active
galactic nuclei (AGN). These populations are classified based on the presence
or absence of a radio excess concerning the star-formation rates derived from
the infrared emission. We find that the RLF of radio group galaxies is low
compared to the field up to z 1.25, followed by a sharp increase at z 1 by
a factor of 6, and then a smooth decline towards low redshifts. This is due to
the low abundance of massive groups at high-z and the AGN occupying lower halo
mass groups. Additionally, the slope of the GG RLF is flatter compared to the
field, with excess at high radio luminosities. The evolution in the GG RLF is
driven mainly by satellite galaxies in groups. In summary, our results show a
drop in occurrence of AGN in groups at high redshifts by a factor of 6,
suggesting that AGN feedback is lower by a factor of 6 at high-z. This
indicates that the bulk of high-z log10(M_200c/M_sun) > 13.5 groups must have
been forming recently, and so the cooling has not been established as yet.
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