Cosmos: Stochastic Bias from Measurements of Weak Lensing and Galaxy Clustering (original) (raw)
2012, The Astrophysical Journal
In the theory of structure formation, galaxies are biased tracers of the underlying matter density field. The statistical relation between galaxy and matter density field is commonly referred as galaxy bias. In this paper, we test the linear bias model with weak-lensing and galaxy clustering measurements in the 2 square degrees COSMOS field ). We estimate the bias of galaxies between redshifts z = 0.2 and z = 1, and over correlation scales between R = 0.2 h −1 Mpc and R = 15 h −1 Mpc. We focus on three galaxy samples, selected in flux (simultaneous cuts I 814W < 26.5 and K s < 24), and in stellar-mass (10 9 < M * < 10 10 h −2 M ⊙ and 10 10 < M * < 10 11 h −2 M ⊙ ). At scales R > 2 h −1 Mpc, our measurements support a model of bias increasing with redshift. The fitting function provides a good fit to the data. We find the best fit mass of the galaxy halos to be log(M 200 /h −1 M ⊙ ) = 11.7 +0.6 −1.3 and log(M 200 /h −1 M ⊙ ) = 12.4 +0.2 −2.9 respectively for the low and high stellar-mass samples. In the halo model framework, bias is scale-dependent with a change of slope at the transition scale between the one and the two halo terms. We detect a scale-dependence of bias with a turn-down at scale R = 2.3 ± 1.5h −1 Mpc, in agreement with previous galaxy clustering studies. We find no significant amount of stochasticity, suggesting that a linear bias model is sufficient to describe our data. We use N-body simulations to quantify both the amount of cosmic variance and systematic errors in the measurement. mate of stochasticity and non-linearity. In the zCOS-MOS redshift survey found non-linearity to contribute less than ∼ 0.2% to the bias relation for luminosity-selected galaxies (M B < −20 − z). Therefore in the following, we will assume that the correlation coefficient r mostly quantifies bias stochasticity. With respect to the bias parameter b, found the bias relation to be scale-independent between scales R = 8 h −1 Mpc and R = 10 h −1 Mpc, and redshift-dependent between redshifts z = 0.4 and z = 1.
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