Decomposing the kinematics of SNR G180.0-01.7 with medium-resolution spectra

ABSTRACT

The exceptionally large angular diameter and intrinsic optical faintness of the Galactic supernova remnant (SNR) G180.0-01.7 (S147) have historically hindered a comprehensive spectroscopic census of its filamentary structure. We present the first dedicated medium-resolution (R $\sim$ 7500) spectroscopic study of S147 using the LAMOST medium-resolution spectroscopic survey of Galactic Nebulae. By implementing multi-Gaussian decomposition on the ${\mathrm{H}\,\,\alpha }$, [N ii], and [S ii] emission complexes and applying combined spectroscopic and spatial criteria, we disentangle the shock-ionized filaments of the SNR from the pervasive foreground and background diffuse ionized gas (DIG). Our analysis reveals a distinct bimodal radial velocity distribution for the SNR: a low-velocity population tracing the decelerated forward shock at a dense cavity wall, and a high-velocity population (with absolute radial velocities of $\sim$70 $\pm$ 30 $\mathrm{km\, s^{-1}}$) corresponding to ejecta within a low-density cavity. The coexistence of these populations provides kinematic evidence for the ‘supernova-in-a-cavity’ scenario. Furthermore, we detect enhanced [S ii]/${\mathrm{H}\,\,\alpha }$ ratios in the DIG along the eastern and northern boundaries of the remnant, signaling shock compression of the ambient interstellar medium and highlighting remnant’s multifaceted feedback.