The Star-forming Interstellar Medium of Lyman Break Galaxy Analogs

Abstract

We present Very Large Telescope SINFONI near-infrared (NIR) integral field spectroscopy of six z  ∼ 0.2 Lyman break galaxy “analogs” (LBAs) from which we detect H i , He i , and [Fe ii ] recombination lines and multiple H 2 rovibrational lines in emission. The Pa α kinematics reveal high velocity dispersions and low rotational velocities relative to random motions ( ). Matched-aperture comparisons of H β , H α , and Pa α reveal that the nebular color excesses are lower relative to the continuum color excesses than is the case for typical local star-forming systems. We compare observed He i /H i recombination line ratios to photoionization models to gauge the effective temperatures ( T eff ) of massive ionizing stars, finding that the properties of at least one LBA are consistent with extra heating from an active galactic nucleus (AGN) and/or an overabundance of massive stars. We use H 2  1−0 S(·) rovibrational spectra to determine a rotational excitation temperature T ex  ∼ 2000 K for warm molecular gas, which we attribute to UV heating in dense photon-dominated regions. Spatially resolved NIR line ratios favor excitation by massive young stars, rather than supernova or AGN feedback. Our results suggest that the local analogs of Lyman break galaxies are primarily subject to strong feedback from recent star formation, with evidence for AGNs and outflows in some cases.