Abstract
We use the Ly-$\alpha$ Mass Association Scheme (LyMAS; Peirani et al. 2014)
to predict cross-correlations at z = 2.5 between dark matter halos and
transmitted flux in the Ly-$\alpha$ forest, and we compare these predictions to
cross-correlations measured for quasars and damped Ly-$\alpha$ systems (DLAs)
from the Baryon Oscillation Spectroscopic Survey (BOSS) by Font-Ribera et al.
(2012, 2013). We calibrate and test LyMAS using Horizon-AGN hydrodynamical
cosmological simulations of a $(100\ h^-1\ Mpc)^3$ comoving volume with
and without AGN feedback. We apply this calibration to a $(1\ h^-1\
Gpc)^3$ simulation realized with $2048^3$ dark matter particles for our
primary predictions. In the $100\ h^-1\ Mpc$ box, LyMAS reproduces the
halo-flux correlations computed from the full hydrodynamic gas distribution
essentially perfectly. In the $1\ h^-1\ Gpc$ box, the amplitude of the
cross-correlation tracks the halo bias as expected, and the correlation for a
halo sample with a distribution of masses scales linearly with the
number-weighted mean bias. We provide empirical fitting functions that describe
our numerical results. In the transverse separation bins used for the BOSS
analyses, LyMAS cross-correlation predictions follow linear theory accurately
down to small scales, though the quadrupole departs from linear theory on
scales below $\sim15\ h^-1\ Mpc$. Fitting the BOSS measurements requires
inclusion of random velocity errors; we find best-fit RMS velocity errors of
399 km/s and 252 km/s for quasars and DLAs, respectively. We infer
bias-weighted mean halo masses of $M_h/10^12\ h^-1\ M_=
2.19^+0.16_-0.15$ and $0.69^+0.16_-0.14$ for the host halos of quasars
and DLAs, with ~ 0.2 dex systematic uncertainty associated with redshift
evolution, IGM parameters, and selection of data fitting range.
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