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

Lyman-break galaxy (LBG) samples observed during reionization (z ≳ 6) with the 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 , we detect a clear clustering signal in the angular correlation function (ACF) at ≳ 4σ, corresponding to a real-space correlation length cMpc. The derived galaxy bias is that of dark matter halos of at z = 7.2, and highlights that galaxies below the current detection limit (MAB∼ -17.7) are expected in lower-mass halos (M ∼ 108-1010.5). We compute the ACF of LBGs at z ∼ 3.8-z ∼ 5.9 in the same surveys. A trend of increasing bias is found from (b ∼ 3.0) to (b ∼ 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 ≳ 7 (∼2σ confidence). Separating the data at the median luminosity of the sample (M UV= -19.4) shows higher clustering at for bright galaxies (cMpc, ) compared to faint galaxies (cMpc, ) implying a constant mass-to-light ratio . A similar trend is present in the 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, εDC). At values near unity are preferred, which may be explained by the shortened halo assembly time at high redshift.