High-resolution Near-infrared Spectroscopic Study of Galactic Supernova Remnants. I. Kinematic Distances
Abstract
We have carried out high-resolution near-infrared spectroscopic observations toward 16 Galactic supernova remnants (SNRs) showing strong H2 emission features. A dozen bright H2 emission lines are clearly detected for individual SNRs, and we have measured their central velocities, line widths, and fluxes. For all SNRs except one (G9.9-0.8), the H2 line ratios are well consistent with that of thermal excitation at T2000 K, indicating that the H2 emission lines are most likely from shock-excited gas and therefore that they are physically associated with the remnants. The kinematic distances to the 15 SNRs are derived from the central velocities of the H2 lines using a Galactic rotation model. We derive for the first time the kinematic distances to four SNRs: G13.5+0.2, G16.0-0.5, G32.1-0.9, and G33.2-0.6. Among the remaining 11 SNRs, the central velocities of the H2 emission lines for six SNRs are well consistent (5 km s-1) with those obtained in previous radio observations, while for the other five SNRs (G18.1-0.1, G18.9-1.1, Kes 69, 3C 396, W49B) they are significantly different. We discuss the velocity discrepancies in these five SNRs. In G9.9-0.8, the H2 emission shows nonthermal line ratios and narrow line width ( 4 km s-1), and we discuss its origin.