Optical and X-ray Observational Search for the Possible Supernova Remnant Candidates in the Nearby Galaxy NGC 1569

TL;DR

This study identifies 13 new supernova remnant candidates in galaxy NGC 1569 using optical and X-ray observations, providing detailed spectral analysis and physical parameters for these remnants.

Contribution

First comprehensive optical and X-ray search for SNR candidates in NGC 1569, including spectroscopic confirmation and physical property estimation.

Findings

Identified 13 new SNR candidates based on optical emission line ratios.

Confirmed 10 SNR candidates with X-ray counterparts.

Estimated physical parameters such as electron density and shock velocity for some candidates.

Abstract

We report the results of our investigation on the possible existence of supernova remnants (SNRs) in the nearby galaxy, NGC 1569, using the CCD imaging and spectroscopic observations from the RTT150 telescope of TUG-TUBITAK in Antalya, Turkey for two different observing periods. Using [S\,{\sc ii}]/H$\alpha$ $\geq$ 0.4 standard criteria, the identification of 13 new SNR candidates for this galaxy is proposed for two different epochs. We found the [S\,{\sc ii}]/H$\alpha$ ratios ranging from 0.46--0.84 and H$\alpha$ intensities ranging from (2.2--32) $\times$ 10$^{-15}$ erg cm$^{-2}$ s$^{-1}$. [S\,{\sc ii}]$\lambda\lambda$6716/6731 average flux ratio is calculated from the optical spectra for only one possible SNR candidate. By using this ratio the electron density, $N_{\rm e}$, is estimated to be 121 $\pm$ 17 cm$^{-3}$ and by using the [O\,{\sc iii}]$\lambda$5007/H$\beta$ ratio of the same spectrum, the shock wave velocity, $V_{\rm s}$, is estimated to be between 100 < Vs < 150 km s$^{-1}$. Using {\it Chandra} data, we find that out of 13 SNR candidates only 10 of them have yielded a spectrum with good statistics, confirming the existence of 10 SNR candidates with matched positions in X-ray region as well. We measure the 0.5--2 keV band flux down to 0.58 $\times$ 10$^{-15}$ erg cm$^{-2}$ s$^{-1}$ for 10 X-ray sources. Our spectral analysis revealed that spectra of the SNR candidates are best modelled with the Collisional Ionisation Equilibrium plasma with a temperature range of 0.84 keV < \textit{kT$_{e}$} < 1.36 keV.