Dust Obscuration in Lyman Break Galaxies at z ~ 4

Abstract

Measuring star formation rates (SFRs) in high-z galaxies with their rest-frame ultraviolet (UV) continuum can be uncertain because of dust obscuration. Prior studies had used the submillimeter emission at 850 μm to determine the intrinsic SFRs of rest-frame UV-selected galaxies, but the results suffered from the low sensitivity and poor resolution (~15''). Here, we use ultradeep Very Large Array 1.4 GHz images with ~1''-2'' resolutions to measure the intrinsic SFRs. We perform stacking analyses in the radio images centered on ~3500 Lyman break galaxies (LBGs) at z ~ 4 in the Great Observatories Origins Deep Survey-North and South fields selected with Hubble Space Telescope/Advanced Camera for Surveys data. The stacked radio flux is very low, 0.08 ± 0.15 μJy, implying a mean SFR of 6 ± 11 {{M_{⊙} yr^{-1}}}. This is comparable to the uncorrected mean UV SFRs of ∼ 5 {{M_{⊙} {yr^{-1}}}}, implying that the z ~ 4 LBGs have little dust extinction. The low SFR and dust extinction support the previous results that z ~ 4 LBGs are in general not submillimeter galaxies. We further show that there is no statistically significant excess of dust-hidden star-forming components within ~22 kpc from the LBGs.