Cosmology

Abstract:

© 2016 The Authors. We use the Lya Mass Association Scheme (LyMAS) to predict cross-correlations at z = 2.5 between dark matter haloes and transmitted flux in the Lya forest, and compare to crosscorrelations measured for quasars and damped Lya systems (DLAs) from the Baryon Oscillation Spectroscopic Survey (BOSS) by Font-Ribera et al. 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-fitting rms velocity errors of 399 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⊙ = 2.19 +0.16 -0.15 and 0.69 +0.16 -0.14 for the host haloes of quasars and DLAs, with ~0.2 dex systematic uncertainty associated with redshift evolution, intergalactic medium parameters, and selection of data fitting range.