Abstract
We present a measurement of the cross-correlation of MgII absorption and
massive galaxies, using the DR11 galaxy sample of the Baryon Oscillation
Spectroscopic Survey of SDSS-III, and the DR7 quasar spectra of SDSS-II. The
cross-correlation is measured by stacking quasar absorption spectra shifted to
the redshift of galaxies that are within a certain impact parameter bin of the
quasar, after dividing by a quasar continuum model. This results in an average
MgII equivalent width as a function of impact parameter from a galaxy, ranging
from 50 kpc to more than 10 Mpc in proper units, which includes all MgII
absorbers. We show that special care needs to be taken to use an unbiased
quasar continuum estimator, to avoid systematic errors in the measurement of
the mean stacked MgII equivalent width. The measured cross-correlation follows
the expected shape of the galaxy correlation function, although measurement
errors are large. We use the cross-correlation amplitude to derive the bias
factor of MgII absorbers, finding $b_MgII=1.500.19$, where the
error accounts only for the statistical uncertainty in measuring the mean
equivalent width. This result indicates that MgII absorbers at redshift
$z0.5$ are spatially distributed on large scales similarly to galaxies
with $L L_*$.
Keywords: galaxies: haloes, galaxies: formation, quasars: absorption lines,
large-scale structure of universe
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