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 compare 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 LyMAS using Horizon-AGN hydrodynamical cosmological simulations of a ( 100 h ^ { -1 } Mpc ) ^ { 3 } comoving volume .
We apply this calibration to a ( 1 h ^ { -1 } Gpc ) ^ { 3 } simulation realized with 2048 ^ { 3 } dark matter particles .
In the 100 h ^ { -1 } Mpc box , LyMAS reproduces the halo-flux correlations computed from the full hydrodynamic gas distribution very well .
In the 1 h ^ { -1 } Gpc box , the amplitude of the large scale cross-correlation tracks the halo bias b _ { h } as expected .
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 .
Fitting the BOSS measurements requires inclusion of random velocity errors ; we find best-fit RMS velocity errors of 399 km s ^ { -1 } and 252 km s ^ { -1 } for quasars and DLAs , respectively .
We infer bias-weighted mean halo masses of M _ { h } / 10 ^ { 12 } h ^ { -1 } M _ { \odot } = 2.19 ^ { +0.16 } _ { -0.15 } and 0.69 ^ { +0.16 } _ { -0.14 } for the host halos of quasars and DLAs , with \sim 0.2 dex systematic uncertainty associated with redshift evolution , IGM parameters , and selection of data fitting range .