CHANDRAAND VERY LARGE ARRAY OBSERVATIONS OF THE NEARBY Sd GALAXY NGC 45

Abstract

We present an analysis of high angular resolution observations made in the X-ray and the radio with the Chandra X-ray Observatory and the Karl Jansky Very Large Array (VLA), respectively, of the nearby spiral galaxy NGC 45. This galaxy is the third that we have considered in a study of the supernova remnant (SNR) populations of nearby spiral galaxies and the present work represents the first detailed analysis of the discrete X-ray and radio source populations of this galaxy. We analyzed data sets from the three pointed observations made of this galaxy with Chandra along with a merged data set obtained from combining these data sets: the total effective exposure time of the merged data set is 63515 s. A total of 25 discrete X-ray sources are found in the entire field of view of the ACIS-S3 chip, with 16 sources found within the visual extent of the galaxy. We estimate that as many as half of the sources detected in the entire field of view of the ACIS-S3 chip and seven of the sources detected in the optical extent of NGC 45 may be background sources. We analyzed the spectral properties of the discrete X-ray sources within the galaxy and conclude that the majority of these sources are X-ray binaries. We have searched for counterparts at different wavelengths to the discrete X-ray sources and we find two associations: one with a star cluster and the other with a background galaxy. We have found one source that is clearly variable within one observation and seven that are seen to vary from one observation to another. We also conduct a photometric analysis to determine the near-infrared fluxes of the discrete X-ray sources in Spitzer Infrared Array Camera channels. We constructed a cumulative luminosity function of the discrete X-ray sources seen toward NGC 45: taking into account simultaneously the luminosity function of background sources, the fitted slope of the cumulative luminosity function Γ = -1.3 1.6 0.7 -+ (all error bounds correspond to 90% confidence intervals). The VLA observations reveal seven discrete radio sources: we find no overlaps between these sources and the X-ray detected sources. Based on their measured spectral indices and their locations with respect to the visible extent of NGC 45, we classify one source as a candidate radio SNR associated with the galaxy and the others as likely background galaxies seen in projection toward NGC 45. Finally, we discuss the properties of a background cluster of galaxies (denoted as CXOU J001354.2-231254.7) seen in projection toward NGC 45 and detected by the Chandra observations. The fit parameters to the extracted Chandra spectra of this cluster are a column density N H = 0.07 (<0.14) × 10 22 cm −2 , a temperature kT = 4.22 1.42 2.08 -+ keV, an abundance Z = 0.30(<0.75) relative to solar and a redshift z = 0.28 ± 0.14. From the fit parameters we derive an electron number density n e = 4(±1) × 10 −3 cm −3 , an unabsorbed X-ray luminosity L 0.5 7.0 keV-8.77(±0.96) × 10 43 erg s −1 for the cluster and an X-ray emitting mass M = 2.32(±1.75) × 10 12 M  .

The supernova remnant population of the Small Magellanic Cloud

“…Despite larger distances, external galaxies are therefore better suited to SNR population studies. The SNRs of several galaxies in the Local Group (M31, M33, Sasaki et al 2012;Long et al 2010;Galvin & Filipovic 2014;Garofali et al 2017) and beyond (Payne et al 2004a;Chomiuk & Wilcots 2009;Leonidaki et al 2010;Millar et al 2011;Pannuti et al 2011;Millar et al 2012;O'Brien et al 2013;Long et al 2014;Pannuti et al 2015;Yew et al 2018) have been studied at various wavelengths. Closer to us, our Galactic neighbours the Large and Small Magellanic Clouds (LMC, SMC) provide excellent benchmarks for the study of star-forming galaxies.…”

The Supernova Remnant Populations of the galaxies NGC 45, NGC 55, NGC 1313, NGC 7793: Luminosity and Excitation Functions

“…Following, we discuss in more detail these comparisons. In NGC 45, we find that none of the optically detected SNRs has any counterpart in radio or X-ray wavelengths (Pannuti et al 2015). In NGC 55, only source 1 from the possible candidate SNRs has also emission in X-rays (source 131 in Binder et al 2015, or source 85 in Stobbart, Roberts, & Warwick 2006.…”

“…Dodorico, Dopita, & Benvenuti (1980) looked for optical SNRs in NGC 45 but without any success. However, a candidate SNR in radio with no X-ray counterpart and a candidate one in X-rays are reported in the work of Pannuti et al (2015). NGC 55 has given 6 radio candidate SNRs that are reported to have also X-ray emission (O'Brien et al 2013).…”

The Core Starbursts of the Galaxy NGC 3628: Radio Very Long Baseline Interferometry and X-Ray Studies

“…Through high-resolution radio observations (Carral et al 1990;Cole & Mundell 1998, Very Large Array (VLA) A-array 15 GHz and MERLIN 1.4 GHz, respectively), a list of compact radio sources were identified as star-forming products. Therefore, combining radio and X-ray observations may help to confirm the nature of starforming galaxies (Wik et al 2014;Pannuti et al 2015). Unfortunately, previous radio observations were unable to resolve the central radio sources, so a higher resolution is necessary to determine their sizes and structures.…”