#### Publication Date

2005

#### Journal or Book Title

ASTROPHYSICAL JOURNAL

#### Abstract

We test the reliability of a method to measure the mean halo mass of absorption-line systems such as damped Lyα absorbers (DLAs). The method is based on measuring the ratio of the cross-correlation between DLAs and galaxies to the autocorrelation of the galaxies themselves, which is (in linear theory) the ratio of their bias factor . We show that the ratio of the projected cross- and autocorrelation functions [*w*_{dg}(*r*_{θ})/*w*_{gg}(*r*_{θ})] is also the ratio of their bias factor, irrespective of the galaxy distribution, provided that one uses the same galaxies for *w*_{dg}(*r*_{θ}) and *w*_{gg}(*r*_{θ}). Thus, the method requires only multiband imaging of DLA fields and is applicable to all redshifts. Here, we focus on *z* = 3 DLAs. We demonstrate that the method robustly constrains the mean DLA halo mass using smoothed particle hydrodynamics (SPH) cosmological simulations that resolve DLAs and galaxies in halos of mass *M*_{h} 5.2 × 10^{10} *M*_{}. If we use the bias formalism of Mo & White with the DLA and galaxy mass distributions of these simulations, we predict an amplitude ratio *w*_{dg}/*w*_{gg} of 0.771. Direct measurement of these correlation functions from the simulations yields *w*_{dg}/*w*_{gg} = _{DLA}/_{gal} = 0.73 ± 0.08, in excellent agreement with that prediction. Equivalently, inverting the measured correlation ratio to infer the (logarithmically) averaged DLA halo mass yields log *M*_{DLA}(*M*_{}) = 11.13, in excellent agreement with the true value in the simulations: log *M*_{DLA}(*M*_{}) = 11.16 is the probability-weighted mean mass of the DLA host halos in the simulations. The cross-correlation method thus appears to yield a robust estimate of the average host halo mass, even though the DLAs and the galaxies occupy a broad mass spectrum of halos and massive halos contain multiple galaxies with DLAs. If we consider subsets of the simulated galaxies with high star formation rates (representing Lyman break galaxies [LBGs]), then both correlations are higher, but their ratio still implies the same DLA host mass, irrespective of the galaxy subsamples, i.e., the cross-correlation technique is also reliable. The inferred mean DLA halo mass, log *M*_{DLA} = 11.13, is an upper limit, since the simulations do not resolve halos less massive than ~10^{10.5} *M*_{}. Thus, our results imply that the correlation length between DLAs and LBGs is predicted to be at most ~2.85 *h*^{-1} Mpc, given that *z* = 3 LBGs have a correlation length of *r*_{0} 4 *h*^{-1} Mpc. While the small size of current observational samples does not allow strong conclusions, future measurements of this cross-correlation can definitively distinguish models in which many DLAs reside in low-mass halos from those in which DLAs are massive disks occupying only high-mass halos.

#### Volume

628

#### Pages

89-103

#### Issue

1

#### Recommended Citation

Bouche, N; Gardner, JP; Katz, N; Weinberg, DH; Dave, R; and Lowenthal, JD, "Measuring the halo mass of z similar to 3 damped Ly alpha absorbers from the absorber-galaxy cross-correlation" (2005). *ASTROPHYSICAL JOURNAL*. 327.

http://scholarworks.umass.edu/astro_faculty_pubs/327

## Comments

This is the pre-published version harvested from ArXiv. The published version is located at http://iopscience.iop.org/0004-637X/628/1/89/