A Galactic Supernova Remnant Candidate at l =25.8, b=+0.2 Revealed by Near-Infrared Imaging and Spectroscopy

TL;DR

This study identifies and characterizes a new supernova remnant candidate G25.8+0.2 in the inner Galaxy using near-infrared spectroscopy, revealing shock-excited filaments and linking it to recent supernova activity within a star-forming complex.

Contribution

First near-infrared spectroscopic confirmation of G25.8+0.2 as a supernova remnant candidate, analyzing its shock and photoionized components and its association with a star-forming region.

Findings

Shock-excited [Fe II] filaments trace the radio shell morphology.

High-velocity components indicate recent supernova activity.

Extinction and ionizing star spectral types constrained.

Abstract

We present high-resolution near-infrared spectroscopic observations of the newly identified supernova remnant (SNR) candidate G25.8+0.2 obtained with the Immersion Grating Infrared Spectrograph (IGRINS) on the Harlan J. Smith Telescope. The source was originally discovered in the UKIRT Wide-field Infrared Survey for Fe+ (UWIFE; Lee et al. 2014). Our spectra reveal multiple kinematic components in the [Fe II] 1.644 um emission. The high-velocity components exhibit elevated [Fe II]/Br gamma ratios characteristic of shock excitation, while the low-velocity components are dominated by hydrogen and helium recombination lines and are consistent with photoionized gas, indicating an H II-region origin. G25.8+0.2 lies within the G26 complex, a large (~15'x 30', corresponding to ~28 pc x 57 pc at a distance of 6.5 kpc) star-forming region in the inner Galaxy. The shock-excited [Fe II] filaments closely trace the morphology of the bright radio shell that partially encloses centrally filled soft X-ray emission, strongly suggesting recent supernova activity in this region. We discuss the physical nature of G25.8+0.2 and its relationship to the surrounding G26 star-forming complex. In addition, we derive the extinction toward the source using Brackett-line ratios and constrain the spectral types of the dominant ionizing stars from the He I 2.058 um/Br gamma line ratios.