A multi-frequency investigation of discrete sources in the Magellanic Clouds

Abstract

This project involves a detailed study of discrete sources observed in the Magellanic Clouds (MCs) using large scale surveys at radio, infra-red, optical, ultra-violet and X-ray wavelengths. As a part of the study, this project resulted in a catalogue of discrete radio sources in the MCs with their positions, fluxes and spectral index. These new surveys were compared with previous results and showed great improvement. Firstly, in improving number of discrete radio sources towards the Magellanic Clouds and, secondly, in the positions and flux densities of these sources. Classification criteria were established and most of the MCs sources were classified in one of three groups: SNRs, HII regions or background sources. Specific source flux density comparison was undertaken and source distributions throughout the Clouds were studied. From observations with the Parkes radio telescope, I am presenting catalogues of radio sources in the Large Magellanic Cloud (LMC) at six frequencies: 1.40, 2.30, 2.45, 4.75, 4.85 and 8.55 GHz. A total of 483 sources have been detected at at least one of these frequencies, 143 of which are reported here for the first time as radio sources. Also, catalogues of radio sources in the Small Magellanic Cloud (SMC) were presented at the same radio frequencies and the total number of catalogued radio sources is 224. Some 60 of these 224 sources are reported here for the first time as radio sources. A comparison of Parkes radio surveys and the X-ray ROSAT All-Sky Survey (RASS) of the LMC has found 71 discrete sources of both radio and X-ray emission. A flux density comparison of the radio and X-ray sources shows very little correlation, but we note that the strongest SNRs at both radio and X-ray frequencies are young SNRs from Population I. Six new SNR candidates are proposed. From the brightness of the SNRs we have estimated the SNR birth rate to be one ever 100 (±20) years and the star formation rate (SFR) to be 0.7 (±0.2) Myr-1. The comparison with the IRAS IR surveys showed 130 sources in common to the LMC and 38 to the SMC. Most of these sources (~90%) are intrinsic to the MCs as HII regions and SNRs. Similar results comes from the HI±, VUV and CO comparison. Sources seen at these surveys are believed to be very likely intrinsic. Some 94 sources in the LMC and 12 sources in the SMC are classified on this basis as HII region candidates. In total, 209 radio discrete sources in the LMC and the 38 sources in the SMC are classified here to be either HII regions or SNRs. From the distribution of the LMC sources it can be seen spiral structure patterns with a centre somewhere in 30 Doradus. The SMC source distribution follows Mathewson (1985) prediction and is generally grouped into three regions; Mini-MC, the SMC Remnant and Eastern Wing of the SMC.

Date of Award	1996
Original language	English