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

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 (H 2 ) 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 ∼10 5 –10 6 cm -3 in both IRS 2 East and IRS 2 West from [Fe III] line ratios. In both regions, observed H 2 line ratios indicate that the excitation of H 2 is dominated by fluorescence rather than by shocks.