NGC 2366 : An optical search for possible supernova remnants

TL;DR

This study conducted an optical search for supernova remnants in galaxy NGC 2366 using imaging and spectral data, identifying four candidates with spectral characteristics consistent with SNRs and confirming their locations with previous radio and X-ray observations.

Contribution

First spectral analysis of four SNR candidates in NGC 2366, providing new spectral parameters and confirming their optical and radio counterparts.

Findings

Four SNR candidates identified with [SII]/Hα ratios ≥ 0.4.

Spectral parameters obtained for the first time for these candidates.

One candidate aligns with an extended X-ray source from previous observations.

Abstract

The results of an optical search for supernova remnants (SNRs) in the nearby irregular galaxy NGC 2366 are presented. We took interference filter images and collected spectral data in three epochs with the f/7.7 1.5 m Russian Turkish Telescope (RTT150) at T\"{U}B\.{I}TAK National Observatory (TUG) located in Antalya, Turkey. The continuum-subtracted H$\alpha$ and continuum-subtracted [SII]$\lambda \lambda$6716, 6731 images and their ratios were used for the identification of SNRs. With [SII]/H$\alpha$ $\geq$ 0.4 criteria, four possible SNR candidates were identified in NGC 2366 with [SII]/H$\alpha$ ratios of $\sim$(0.68, 0.57, 0.55 and 0.75), H$\alpha$ intensities of $\sim$(2.10, 0.36, 0.14, 0.11)$\times 10^{-15}$ erg cm$^{-2}$ s$^{-1}$ [SII]$\lambda$6716/$\lambda$6731 average flux ratios of $\sim$(1.01 and 1.04), electron densities of $N_{\rm e}$ $\sim$(582 and 513) cm$^{-3}$ and [OIII] $\lambda$5007/H$\beta$ $\lambda$4861 $\sim$(3.6 and 2.6) line ratio values are obtained for two of the SNR candidates. A shock velocity $V_{\rm s}$ of 80 $\leq$ $V_{\rm s}$ $\leq$ 100 km s$^{-1}$ is reported. The spectral parameters are obtained for the first time for these possible SNR candidates. The locations of the four SNRs obtained here are found to be consistent with optical and radio results reported so far. One of the sources categorised earlier by XMM-Newton observations as an extended X-ray source position is found to be consistent with one of four possible SNR candidates reported here.