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

Abstract

We report the detection of near-infrared (NIR) [Fe II] (1.644 µm) and H 2 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 H 2 -emitting SNRs, giving a detection rate of 24% for each. Eleven SNRs show both emission features. The detection rate of [Fe II] and H 2 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]-H 2 reversal," where H 2 emission features are found outside the SNR boundary in [Fe II] emission. Our NIR spectroscopy shows that the H 2 emission originates from collisionally excited H 2 gas. The brightest SNR in both [Fe II] and H 2 emissions is W49B, contributing more than 70% and 50% of the total [Fe II] 1.644 µm (2.0 × 10 4 L ) and H 2 2.122 µm (1.2 × 10 3 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.

High-resolution Near-infrared Spectroscopic Study of Galactic Supernova Remnants. I. Kinematic Distances

“…Another distance estimate for W49B is from CO observations. Toward W49B, there are three large MCs at different In Lee et al (2019), we found bright H 2 emission features in the eastern and western areas of the remnant.…”

“…Previous NIR H 2 narrowband imaging observations had detected two long H 2 filaments aligned along the north-south direction, leaving an interval of ∼ 1. 5 in the western region of the remnant (Lee et al 2009(Lee et al , 2019. The brighter filament is located near the western edge of the remnant, slightly outside the radio boundary of the SNR.…”

“…The observations had been carried out in 2014 May, 2015 June, and 2016 July. Among the 19 H 2 -emitting SNRs confirmed by Lee et al (2019), 16 were observed ( Figure 1). We carefully selected slit positions to obtain spectra of strong H 2 emission features at the border of the remnants.…”

“…In order to confirm their physical association, we investigate the excitation mechanism of the H 2 emission using H 2 line ratios. Previous NIR spectroscopic studies of several SNRs have shown that the H 2 lines excited by SNR shocks have thermal line ratios corresponding to T ∼ 2000-3000 K (IC 443, Burton et al 1988Burton et al , 1989Moorhouse et al 1991;RCW 103, Oliva et al 1990;Burton & Spyromilio 1993;Cygnus Loop, Graham et al 1991;G11.2−0.3, Koo et al 2007;Lee et al 2019;Kes 69, Lee et al 2019). In this paper, we use the flux ratios of 2-1 S(1)/1-0 S(1), 1-0 S(2)/1-0 S(0), and 1-0 S(1)/1-0 S(0) ( Table 1) to confirm the physical association between the observed H 2 lines and the SNRs.…”

“…It is, however, worthwhile to note that several H 2 emission features are beyond the SNR boundary in radio: G11.2−0.3-N, S, SE, and NE; Kes 73-W; W44-N; 3C 396-W1 and W2; and W49B-E1 and E2 ( Figure 1; see also Lee et al 2019). Most of them have some morphological connection with the SNRs, i.e., they are either connected to an SNR filament (W44) or parallel to the SNR boundary (Kes 73, 3C 396, and W49B).…”