The MgII Cross-section of Luminous Red Galaxies
  We describe a search for MgII(2796,2803) absorption lines in Sloan Digital
Sky Survey (SDSS) spectra of QSOs whose lines of sight pass within impact
parameters of 200 kpc of galaxies with photometric redshifts of z=0.46-0.6 and
redshift errors Delta z~0.05. The galaxies selected have the same colors and
luminosities as the Luminous Red Galaxy (LRG) population previously selected
from the SDSS. A search for Mg II lines within a redshift interval of +/-0.1 of
a galaxy's photometric redshift shows that absorption by these galaxies is
rare: the covering fraction is ~ 10-15% between 20 and 100 kpc, for Mg II lines
with rest equivalent widths of Wr >= 0.6{\AA}, falling to zero at larger
separations. There is no evidence that Wr correlates with impact parameter or
galaxy luminosity. Our results are consistent with existing scenarios in which
cool Mg II-absorbing clouds may be absent near LRGs because of the environment
of the galaxies: if LRGs reside in high-mass groups and clusters, either their
halos are too hot to retain or accrete cool gas, or the galaxies themselves -
which have passively-evolving old stellar populations - do not produce the
rates of star formation and outflows of gas necessary to fill their halos with
Mg II absorbing clouds. In the rarer cases where Mg II is detected, however,
the origin of the absorption is less clear. Absorption may arise from the
little cool gas able to reach into cluster halos from the intergalactic medium,
or from the few star-forming and/or AGN-like LRGs that are known to exist.
