Radio continuum sources behind the Large Magellanic Cloud

Abstract

We present a comprehensive multi-frequency catalogue of radio sources behind the Large Magellanic Cloud(LMC) between 0.2 and 20 GHz, gathered from a combination of new and legacy radio continuum surveys. This catalogue covers an area of ∼144 deg2 at angular resolutions from 45 arcsec to ∼3 arcmin. We find 6434 discrete radio sources in total, of which 3789 are detected at two or more radio frequencies. We estimate the median spectral index (α; where Sv ∼ να) of α =-0.89 and mean of -0.88 ±0.48 for 3636 sources detected exclusively at two frequencies (0.843 and 1.384 GHz) with similar resolution (Full Width at Half-Maximum (FWHM) ∼40–45 arcsec). The large frequency range of the surveys makes it an effective tool to investigate Gigahertz Peak Spectrum (GPS), Compact Steep Spectrum (CSS) and Infrared Faint Radio sources populations within our sample. We find 10 GPS candidates with peak frequencies near 5 GHz, from which we estimate their linear size. 1 866 sources from our catalogue are CSS candidates with α < −0.8. We found six candidates for High Frequency Peaker (HFP) sources, whose radio fluxes peak above 5 GHz and no sources with unconstrained peaks and α > 0.5. We found optical counterparts for 343 of the radio continuum sources, of which 128 have a redshift measurement. Finally, we investigate the population of 123 Infrared Faint Radio Sources (IFRSs) found in this study.

The role of thermal and non-thermal processes in the ISM of the Magellanic Clouds

“…Otherwise, these pixels reduce the integrated flux density of the observed radio continuum emission by at most 30-35 per cent at 0.166 GHz in both the LMC and the SMC and at 1.4 GHz in the SMC, resulting in an artificial increase in the thermal fraction by about 15 per cent (see Section 4.3). For comparison, the integrated flux densities are reported before and after subtracting the background radio sources presented by Filipovi ć et al ( 2021 ) and Payne et al ( 2004 ). These sources account for 53 per cent, 14 per cent, and 4 per cent of the total RC flux at 0.166, 1.4, and 4.8 GHz, respectively, in the LMC, indicating that they are mostly steep radio sources ( α < −1.1).…”

A radio continuum study of NGC 2082

“…NGC 2082 has been observed in the ASKAP-EMU 888-MHz radio continuum survey of the Large Magellanic Cloud (LMC; Pennock et al 2021;Filipović et al 2022), as well as in the ATCA 20-cm mosaic survey (Filipović et al 2021). We have also made new observations from Parkes radio telescope, and obtained new and archival data from ATCA (pre-CABB) and the HST.…”

New ASKAP Radio Supernova Remnants and Candidates in the Large Magellanic Cloud

“…We find that J0506-6815 ([HP99] 635) is a circular source in our ASKAP radio image (see Figs. 2 (top left panel) and 3) with an estimated flux densities of 𝑆 888 MHz =78±2 mJy and 𝑆 1377 MHz =64±4 mJy (from Filipović et al (2021)) produce a spectral index 𝛼 = −0.45 ± 0.24. Together with a prominent central soft X-ray emission in the XMM-Newton survey and [S ]/H𝛼>0.9, we now safely confirm MCSNR J0506-6815 as a bona fide SNR.…”

“…In this paper, we make use of new radio continuum data taken by the ASKAP telescope (Pennock et al 2021;Filipović et al 2021) to add 14 new candidates to the LMC SNR sample, creating the most complete SNR sample of any galaxy (see Fig. 1).…”