DUST OBSCURATION IN LYMAN BREAK GALAXIES AT z ∼ 4

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 mu m to determine the intrinsic SFRs of rest-frame UV-selected galaxies, but the results suffered from the low sensitivity and poor resolution (similar to 15 ''). Here, we use ultradeep Very Large Array 1.4 GHz images with similar to 1 ''-2 '' resolutions to measure the intrinsic SFRs. We perform stacking analyses in the radio images centered on similar to 3500 Lyman break galaxies (LBGs) at z similar to 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 mu Jy, implying a mean SFR of 6 +/- 11 M-circle dot yr(-1). This is comparable to the uncorrected mean UV SFRs of similar to 5 M-circle dot yr(-1), implying that the z similar to 4 LBGs have little dust extinction. The low SFR and dust extinction support the previous results that z similar to 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 similar to 22 kpc from the LBGs.