ASTRONOMY & ASTROPHYSICS JUNE II 1998, PAGE 421 SUPPLEMENT SERIES Astron. Astrophys. Suppl. Ser. 130, 421–440 (1998) A radio continuum study of the Magellanic Clouds VII. Discrete radio sources in the Magellanic Clouds? M.D. Filipovi´c1,2,3,R.F.Haynes3,1,G.L.White1, and P.A. Jones1 1 University of Western Sydney, Nepean, P.O. Box 10, Kingswood, NSW 2747, Australia e-mail: [email protected]; [email protected]; [email protected] 2 Max-Planck-Institut f¨ur extraterrestrische Physik, Giessenbachstraße, D-85740 Garching, Germany 3 Australia Telescope National Facility, CSIRO, P.O. Box 76, Epping, NSW 2121, Australia e-mail: mfi[email protected]; [email protected] Received November 28; accepted December 24, 1997 Abstract. We present a study of discrete radio sources in 1. Radio-continuum surveys of the Magellanic Clouds the Magellanic Clouds (MCs) using the latest large-scale radio surveys made with the Parkes radio telescope be- During the last few decades, the Magellanic Clouds (MCs) tween 1.4 and 8.55 GHz. These surveys achieved higher have been investigated over almost all of the electro- sensitivity then previous surveys done with the Parkes magnetic spectrum. Radio-continuum investigations of the telescope and so the number of discrete radio sources de- MCs started with the detection by Mills & Little (1953). tected towards the MCs has increased by factor of five. Since that time, numerous radio surveys have been un- Also, we have obtained improved positions, flux densities dertaken. These include: Mills (1955) at 85.5 MHz; Mills and radio spectral indices for all of these sources. & Little (1959) at 96.8 MHz and 158 MHz; Shain (1959) at 19.7 MHz; Mathewson & Healey (1964a) at 1400 MHz; A total of 483 sources towards the Large Magellanic Alvarez et al. (1987) at 45 MHz; and Mountfort et al. Cloud (LMC) and 224 towards the Small Magellanic (1987) at 2300 MHz. The low-resolution observations Cloud (SMC) have been detected at at least one radio helped to determine the large-scale structure and the total frequency. Most of the MC’s sources have been classi- radio spectrum of the MCs (Mills & Little 1959; Haynes ii fied in one of three groups: SNRs, H regions or back- et al. 1991; Klein et al. 1991) whereas high-resolution stud- ground sources according to classification criteria estab- ies concentrated on discrete sources in the Clouds. lished here. In total, 209 discrete radio sources in the LMC and the 37 sources in the SMC are classified here to be either H ii regions or SNRs. We investigate their lu- 1.1. High-frequency radio continuum surveys of discrete minosity functions as well as the statistics of background sources in the Magellanic Clouds sources behind the MCs. Also, we examine the distribu- tion of SNRs and H ii regions in the MCs. The first high-frequency radio-continuum detection of dis- crete sources in the MCs was made by Mathewson & Healey (1964b) at 1.4 GHz. In the past 30 years, numer- Key words: galaxies: Magellanic Clouds — radio ous radio observations of many discrete sources in the MCs continuum: galaxies — ISM: H ii regions — ISM: have been undertaken. supernova remnants (SNRs) — galaxies: ISM In 1972, McGee et al. (1972a) made detailed obser- vations of the LMC at 5.00 GHz with the Parkes radio telescope (See Table 1 for a summary of the radio-source surveys of the LMC) and established the first catalogue of discrete radio sources in the LMC, known as the MC cata- logue. Later, McGee et al. (1976) presented a list of sources towards the Small Magellanic Cloud (SMC) at 5.00 GHz Send offprint requests to: M.D. Filipovi´c (See Table 2 for a summary of the radio-source surveys ? Tables 5 and 6 are only available electronically at of the SMC). McGee et al. (1972b) and Bolton & Butler the CDS via ftp 130.79.128.5 or via http://cdsweb.u- (1975) observed the MCs at 2.70 GHz which became part strasbg.fr/Abstract.html of the PKSCAT-90 catalogue (Otrupcek & Wright 1991). 422 M.D. Filipovi´c et al.: A radio continuum study of the MCs. VII. Table 1. Summary of the previous high-frequency radio surveys 1.2. Other Surveys of discrete sources in the Magellanic of the LMC Clouds Instrument Frequency Beam Size No. of Reference (GHz) (arcmin) Sources Detected Numerous observations of the MCs in the optical, Hα, infrared (IR), far- infrared (FIR), and X-ray wavelengths Molonglo 0.408 2.62×2.86 227 Clarke et al. 1976 MOST 0.843 0.75 42 Mills et al. 1984a,b have been undertaken together with the multi-waveband Parkes 2.70 7.7 38 McGee et al. 1972b cross-correlation of the discrete sources. Parkes 4.85 4.9 390 Wright et al. 1994 Parkes 5.009 4.0 95 McGee et al. 1972a Optical observations of the MCs made by Henize Parkes 8.80 2.5 35 McGee et al. 1978 Parkes 14.70 2.2 33 Milne et al. 1980 (1956) resulted in the first catalogue of emission-line ob- jects. Hodge & Wright (1967) presented an optical atlas of the LMC and, 10 years later, of the SMC (Hodge & Wright Table 2. Summary of the previous high-frequency radio surveys 1977). Photographic Hα emission-line surveys by Henize of the SMC (1956; N catalogue) and by Davies et al. (1976; DEM cat- alogue) have provided identifications, positions and sizes Instrument Frequency Beam Size No. of Reference for several hundred sources in the two galaxies, ranging (GHz) (arcmin) Sources Detected in scale from unresolved compact emission regions to the giant 30 Doradus complex in the LMC. Subsequent pho- Molonglo 0.408 2.62×2.86 75 Clarke et al. 1976 MOST 0.843 0.75 ∼1500 Ye 1988, 1993 tometric surveys have provided quantitative information Parkes 1.40 15.0 21 McGee et al. 1976 on the resolved MCs sources (Caplan & Deharveng 1985; Parkes 2.70 7.7 25 PKSCAT-90 Parkes 4.85 4.9 194 Wright et al. 1994 Kennicutt & Hodge 1986; Bothun & Thompson 1988; Parkes 5.009 4.0 27 McGee et al. 1976 Copetti & Dottori 1989; le Coarer et al. 1993; Caplan et al. Parkes 8.80 2.5 13 McGee et al. 1976 1996). Also some [S ii]and[Oiii] line surveys for detection of specific sources in the MCs, such as SNRs, were made by Mathewson et al. (1983, 1984, 1985). A number of MC After Mills & Aller 1971 detected a few sources at objects appear in Sinnott’s (1988) NGC (IC) catalogue of 0.408 GHz, as a part of a whole sky survey, Clarke et al. nebulae. (1976) observed the MCs with the Molonglo radio tele- Lucke & Hodge (1970) published a list of 122 stellar scope and produced the MC4 catalogue of 227 sources associations in the LMC and Hodge (1985) a list of 70 towards the LMC and 75 towards the SMC. Also, some stellar associations in the SMC. Up to 60 star clusters have sources in the direction of the MCs (mainly background) been identified in the SMC and some 1600 in the LMC. appear in the MRC catalogue of Large et al. (1981). Sanduleak et al. (1978) and Sanduleak (1984) published a McGee et al. (1976) and McGee et al. (1978) inves- list of planetary nebulae (PN), and Morgan (1994, 1995) tigated the MCs with the Parkes telescope at 8.80 GHz. updated these lists with 265 and 62 PN in the LMC and The PKSCAT-90 compilation (Otrupcek & Wright 1991) SMC, respectively. contains a number of MC sources with fluxes at 1.40, 2.70, The X-ray surveys of the LMC have been presented in 5.00 and 8.40 GHz. Long et al. (1981; LHG catalogue) and in Wang et al. New techniques and equipment evolved in the early (1991; W catalogue). The SMC X-ray surveys can be 1980s, and with improved sensitivity, increased the inter- found in Seward & Mitchell (1981; 1E catalogue), Inoue est in discrete sources in the MCs, such as H ii regions et al. (1983; IKT Catalogue), Bruhweiler et al. (1987) and supernova remnants (SNRs). Milne et al. (1980) ob- and in Wang & Wu (1992). All these surveys are based served a number of interesting LMC sources at 14.70 GHz on observations made with the Einstein satellite. Almost to estimate their radio spectral index. Mills (1983), Mills half of the X-ray sources in the LMC field catalogued by et al. (1984a,b), Ye (1988) and Ye & Turtle (1993) ob- Wang et al. (1991) were confirmed as SNRs, H ii regions served selected fields in the MCs at 0.843 GHz with or X-ray binaries. The other half are foreground stars or the Molonglo Synthesis Telescope (MOST), and Sabalisck background objects (e.g. clusters of galaxies, radio galax- & Abraham (1991) observed the 30 Doradus region at ies, quasars). In the Wang & Wu (1992) survey, out of 22 GHz. Recently, Wright et al. (1994) surveyed the MCs 70 sources towards the SMC, 24 are intrinsic. Tr¨umper as part of the PMN southern sky survey at 4.85 GHz. et al. (1991), Pietsch & Kahabka (1993), Snowden & Petre Following the first radio classification of sources in the (1994), Kahabka & Pietsch (1993) and Schmidtke et al. LMC based on studies of the spectral index (McGee & (1994) also made X- ray observations of the MCs with Newton 1972), Milne et al. (1980) and Mathewson et al. the ROSAT satellite. In addition, X-ray ROSAT All Sky (1983,a, 1984, 1985) provided the first detailed analysis of Survey (RASS) results are available from Pietsch et al.