Measurement of Galaxy Clustering at z~7.2 and the Evolution of Galaxy Bias from 3.8<z<8 in the XDF, GOODS-S AND GOODS-N

R. L. Barone-Nugent; M. Trenti; J. S. B. Wyithe; R. J. Bouwens; P. A. Oesch; G. D. Illingworth; C. M. Carollo; J. Su; M. Stiavelli; I. Labbe; P. G. van Dokkum

doi:10.1088/0004-637X/793/1/17

paper

Measurement of Galaxy Clustering at z~7.2 and the Evolution of Galaxy Bias from 3.8<z<8 in the XDF, GOODS-S AND GOODS-N

arXiv:1407.7316 · doi:10.1088/0004-637X/793/1/17

Abstract

Lyman-Break Galaxy (LBG) samples observed during reionization ( $z ≳ 6$ ) with Hubble Space Telescope's Wide Field Camera 3 are reaching sizes sufficient to characterize their clustering properties. Using a combined catalog from the Hubble eXtreme Deep Field and CANDELS surveys, containing $N = 743$ LBG candidates at z>6.5 at a mean redshift of $z = 7.2$ , we detect a clear clustering signal in the angular correlation function (ACF) at $\sim 4 σ$ , corresponding to a real-space correlation length $r_{0} = 6. 7_{- 1.0}^{+ 0.9} h^{- 1}$ cMpc. The derived galaxy bias $b = 8. 6_{- 1.0}^{+ 0.9}$ is that of dark-matter halos of $M = 1 0^{11. 1_{- 0.3}^{+ 0.2}}$ M $_{⊙}$ at $z = 7.2$ , and highlights that galaxies below the current detection limit ( $M_{A B} \sim - 17.7$ ) are expected in lower-mass halos ( $M \sim 1 0^{8} - 1 0^{10.5}$ M $_{⊙}$ ). We compute the ACF of LBGs at $z \sim 3.8 - z \sim 5.9$ in the same surveys. A trend of increasing bias is found from $z = 3.8$ ( $b \sim 3.0$ ) to $z = 7.2$ ( $b \sim 8.6$ ), broadly consistent with galaxies at fixed luminosity being hosted in dark-matter halos of similar mass at $4 < z < 6$ , followed by a slight rise in halo masses at $z \sim 7$ ( $\sim 2 σ$ confidence). Separating the data at the median luminosity of the $z = 7.2$ sample ( $M_{U V} = - 19.4$ ) shows higher clustering at $z = 5.9$ for bright galaxies ( $r_{0} = 5. 5_{- 1.5}^{+ 1.4} h^{- 1}$ cMpc, $b = 6. 2_{- 1.5}^{+ 1.2}$ ) compared to faint galaxies ( $r_{0} = 1. 9_{- 1.0}^{+ 1.1} h^{- 1}$ cMpc, $b = 2.7 \pm 1.2$ ) implying a constant mass-to-light ratio $\frac{d l o g M}{d l o g L} \sim 1. 2_{- 0.8}^{+ 1.8}$ . A similar trend is present in the $z = 7.2$ sample with larger uncertainty. Finally, our bias measurements allow us to investigate the fraction of dark-matter halos hosting UV-bright galaxies (the duty-cycle, $ε_{D C}$ ). At $z = 7.2$ values near unity are preferred, which may be explained by the shortened halo assembly time at high-redshift.

arXiv comment7 pages, 2 tables, 5 figures, accepted for publication in The Astrophysical Journal

Measurement of Galaxy Clustering at z~7.2 and the Evolution of Galaxy Bias from 3.8<z<8 in the XDF, GOODS-S AND GOODS-N

Abstract

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