Star Formation from DLA Gas in the Outskirts of Lyman Break Galaxies at z~3

TL;DR

This study investigates star formation in the outskirts of Lyman break galaxies at z~3, linking extended FUV emission to atomic hydrogen gas and revealing lower star formation efficiency than local expectations, with implications for DLA metallicities.

Contribution

It introduces a theoretical framework connecting DLA gas to star formation in LBG outskirts, showing reduced efficiency and addressing the 'Missing Metals' problem.

Findings

Star formation efficiency in atomic gas at z~3 is 10-50 times lower than local predictions.

The total star formation rate density in outskirts is about 10% of that in galaxy cores.

Metallicity from in situ star formation matches DLA observations, suggesting a solution to the 'Missing Metals' problem.

Abstract

We present evidence for spatially extended low surface brightness emission around Lyman break galaxies (LBGs) in the V band image of the Hubble Ultra Deep Field, corresponding to the z~3 rest-frame FUV light, which is a sensitive measure of star formation rates (SFRs). We find that the covering fraction of molecular gas at z~3 is not adequate to explain the emission in the outskirts of LBGs, while the covering fraction of neutral atomic-dominated hydrogen gas at high redshift is sufficient. We develop a theoretical framework to connect this emission around LBGs to the expected emission from neutral H I gas i.e., damped Lyman alpha systems (DLAs), using the Kennicutt-Schmidt (KS) relation. Working under the hypothesis that the observed FUV emission in the outskirts of LBGs is from in situ star formation in atomic-dominated hydrogen gas, the results suggest that the SFR efficiency in such gas at z~3 is between factors of 10 and 50 lower than predictions based on the local KS relation. The total SFR density in atomic-dominated gas at z~3 is constrained to be ~10% of that observed from the inner regions of LBGs. In addition, the metals produced by in situ star formation in the outskirts of LBGs yield metallicities comparable to those of DLAs, which is a possible solution to the "Missing Metals" problem for DLAs. Finally, the atomic-dominated gas in the outskirts of galaxies at both high and low redshifts has similar reduced SFR efficiencies and is consistent with the same power law.