Optical and X-ray observational search for the possible supernova remnant candidates in the nearby galaxy NGC 1569

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 ii]/Hα ≥ 0.4 standard criteria, the identification of 13 new SNR candidates for this galaxy is proposed for two different epochs. We found the [S ii]/Hα ratios ranging from 0.46-0.84 and Hα intensities ranging from (2.2-32) × 10 −15 erg cm −2 s −1 . [S ii]λλ6716/6731 average flux ratio is calculated from the optical spectra for only one possible SNR candidate. By using this ratio the electron density, N e , is estimated to be 121 ± 17 cm −3 and by using the [O iii]λ5007/Hβ ratio of the same spectrum, the shock wave velocity, V s , is estimated to be between 100 < Vs < 150 km s −1 . Using 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 × 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 < kT e < 1.36 keV.

A kinematical study of the dwarf irregular galaxy NGC 1569 and its supernova remnants

“…Regarding the expansion velocities, almost all SNRs present Vexp >100 ±1 km s −1 except SNRs 3, 7 and 8 with Vexp of 95 ±1, 90 ±1 and 87 ±1 km s −1 , respectively. The Vexp value of SNR5 (Vexp = 114 ±1 km s −1 ) is in agreement with the Vexp value reported by Ercan et al (2018).…”

“…Recently, Ercan et al (2018) showed evidence of 13 possible optical SNRs candidates in this galaxy with CCD imaging using the [S ii]/Hα ≥ 0.4 standard criteria. They identified the new SNRs candidates and computed the electron density (ne), of about 121±17 cm −3 for only one SNR candidate using the [S ii]λ6716/[S ii]λ6731 average flux ratio.…”

NGC 2366 : An optical search for possible supernova remnants

“…[49], Buat et al [4] together with Neutral Hydrogen column density relation from Predehl and Schmitt [48]. This is similar to the determinations reported for another nearby galaxy by Ercan et al [14].…”