Near-infrared [Fe ii] and H2 Emission-line Study of Galactic Supernova Remnants in the First Quadrant

Abstract

Abstract We report the detection of near-infrared (NIR) [Fe ii] (1.644 μm) and H2 1–0 S(1) (2.122 μm) line features associated with Galactic supernova remnants (SNRs) in the first quadrant using two narrowband imaging surveys, UWIFE and UWISH2. Among the total of 79 SNRs fully covered by both surveys, we found 19 [Fe ii]-emitting and 19 H2-emitting SNRs, giving a detection rate of 24% for each. Eleven SNRs show both emission features. The detection rate of [Fe ii] and H2 peaks at the Galactic longitude (l) of 40°–50° and 30°–40°, respectively, and gradually decreases toward smaller/larger l. Five out of the eleven SNRs emitting both emission lines clearly show an “[Fe ii]–H2 reversal,” where H2 emission features are found outside the SNR boundary in [Fe ii] emission. Our NIR spectroscopy shows that the H2 emission originates from collisionally excited H2 gas. The brightest SNR in both [Fe ii] and H2 emissions is W49B, contributing more than 70% and 50% of the total [Fe ii] 1.644 μm (2.0 × 104 L ⊙ ) and H2 2.122 μm (1.2 × 103 L ⊙ ) luminosities of the detected SNRs. The total [Fe ii] 1.644 μm luminosity of our Galaxy is a few times smaller than that expected from the SN rate using the correlation found in nearby starburst galaxies. We discuss possible explanations for this.