Modeling Lyman-α Forest Cross-Correlations with LyMAS

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 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 $(100h^{-1}\mathrm{Mpc}{)}^3$ comoving volume. We apply this calibration to a $(1h^{-1}\mathrm{Gpc}{)}^3$ 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 $M_h/10^{12}{h}^{-1}{M}_{\odot }=2.19_{-0.15}^{+0.16}$ and $0.69_{-0.14}^{+0.16}$ 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.

Accepted by MNRAS, 23 pages, 20 figures. For a short video summarizing this paper, please visit: https://youtu.be/9ghGNtF16JA

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• Non-linearities in the Lyman-$\alpha$ forest and in its cross-correlation with dark matter halos
• UV Background Fluctuations and Three-Point Correlations in the Large Scale Clustering of the Lyman-alpha Forest
• Testing Galaxy Formation Simulations with Damped Lyman-$\alpha$ Abundance and Metallicity Evolution
• LyMAS reloaded: improving the predictions of the large-scale Lyman-α forest statistics from dark matter density and velocity fields
• Lyman-alpha power spectrum as a probe of modified gravity