Near-Infrared Spectroscopy of the Compact H [CSC]ii[/CSC] Region W51 IRS 2

Abstract

Medium-resolution (R ~ 460) spectra in the K window have been obtained for the compact H II regions W51 IRS 2 East and IRS 2 West. Brγ, He I, three lines of [Fe III], and seven lines of molecular hydrogen (H2) have been detected. The unidentified line at 2.288 μm was also detected with ~2% of the intensity of Brγ. We derive an electron density of ~105–106 cm-3 in both IRS 2 East and IRS 2 West from [Fe III] line ratios. In both regions, observed H2 line ratios indicate that the excitation of H2 is dominated by fluorescence rather than by shocks.