The Environments of Local Luminous Infrared Galaxies: Star Formation
  Rates increase with Density
  This work studies the environments and star formation relationships of local
luminous infrared galaxies (LIRG) in comparison to other types of local and
distant (z~1) galaxies. The infrared (IR) galaxies are drawn from the IRAS
sample. The density of the environment is quantified using 6dF and Point Source
Catalogue redshift survey (PSCz) galaxies in a cylinder of 2h^-1 Mpc radius and
10h^-1 Mpc length. Our most important result shows the existence of a dramatic
density difference between local LIRGs and local non-LIRG IR galaxies. LIRGs
live in denser environments than non-LIRG IR galaxies implying that L_IR=10^11
h^-2 L_sun marks an important transition point among IR-selected local
galaxies. We also find that there is a strong correlation between the densities
around LIRGs and their L_IR luminosity, while the IR-activity of non-LIRG IR
galaxies does not show any dependence on environment. This trend is independent
of mass-bin selection. The SF-density trend in local LIRGs is similar to that
found in some studies of blue cloud galaxies at z~1 which show a correlation
between star formation and local density (the reversal of the relation seen for
local galaxies). This, together with the rapid decline of the number count of
LIRGs since z~1, could mean that local LIRGs are survivors of whatever process
transformed blue cloud galaxies at z~1 to the present day or local LIRGs came
into existence by similar process than high redshift LIRGs but at later stage.
