5 Classification and analysis of discrete sources in common to the radio and IR surveys

Out of the 130 sources common to the radio and IR surveys of the LMC (Sect. 3), 76 (58%) have been previously classified (see Table 1, Col. 8). Most are Hii regions (49) and SNRs (21, including nine SNR candidates). Only six sources towards the LMC from the radio surveys are listed as background objects.

Similarly, from 38 sources common to the radio and IR surveys of the SMC (Sect. 4), 26 (68%) have been classified in previous investigations (see Table 2, Col. 8). Again, most of these sources are intrinsic to the SMC (12 Hii regions and nine SNRs embedded in Hii regions). Five radio/IR sources towards the SMC are listed as background.

5.1 Source classifications

Most of the MCs Hii regions (and SNRs embedded in Hii regions) have been detected in IR surveys. Some 95% of Hii regions in the LMC (49 out of 52) and 86% in the SMC (12 out of 14) appear as IR sources. This is not surprising as IR emission is caused by emission from the dusty surroundings of the MC sources. In Filipovic et al. (1998b), we found very tight correlation between radio and H$\alpha$ source catalogues. Also, the similarity of broad- scale structure between radio, IR and H$\alpha$ emission from the MCs has been reported by Xu et al. (1992).

The comparison between radio and IR source spectral index (colour-colour diagram) did not show any correlation for different types of sources towards the MCs. Therefore this criterion is not useful in classifying sources.

From the relative number of radio sources seen in the IR frequencies that are background, compared to those that are intrinsic to the MCs, the conclusion is that the rest of the unclassified sources (54 in the LMC and 12 in the SMC) are more likely to be also intrinsic i.e. Hii regions. As additional criteria, we cross-checked these sources with existing H$\alpha$ catalogues (Filipovic et al. 1998b). However, some of these unclassified sources could be background objects.

Applying this criteria to the LMC, 40 out 54 previously unclassified (radio to IR) sources are suggested to be intrinsic (marked in Table 1, Col. 8 as "hii''). These sources are also detected in H$\alpha$ surveys such as Henize (1956), DEM (Davies et al. 1976) and Kennicutt & Hodge (1986). Two sources (LMC B0433-7139 and LMC B0603-7102) are more likely to be background objects because they are well away from the LMC field defined in Paper VI and cannot be seen at any H$\alpha$ surveys. The other 12 sources common to radio and IR surveys remain ambiguous.

Similarly, from 12 unclassified radio and IR sources in the SMC, 10 are suggested to be Hii region candidates (or SNR candidates), one is probably a background source (SMC B0018-7338) and source SMC B0100-7240 remains ambiguous (marked in Table 2, Col. 8 as "?'').