A Galactic Supernova Remnant Candidate at l = 25 . ° 8, b = +0 . ° 2 Revealed by Near-infrared Imaging and Spectroscopy

Abstract We present high-resolution near-infrared spectroscopic observations of the newly identified supernova remnant candidate G25.8+0.2 obtained with the Immersion Grating Infrared Spectrograph on the Harlan J. Smith Telescope. The source was originally discovered in the UKIRT Wide-field Infrared Survey for Fe + . Our spectra reveal multiple kinematic components in [Fe II ] 1.644 μ m emission. The high-velocity components exhibit elevated [Fe II ]/Br γ 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 ( ∼ 1 5 ′ × 3 0 ′ , corresponding to ∼28 pc × 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 μ m/Br γ line ratios.