Point sources in the fields

Tables 6.1 to 6.5 presents a list of point source flux densities at 327 MHz from the GMRT observations and 1420-MHz flux densities from the NVSS images. Reliable flux densities for point sources in the field of G001.4$+$0.0 were not available at either of these frequencies because of higher noise and poor image quality due to proximity to the Galactic centre. Also, no compact sources was detected in the field of G004.2$-$0.0. Data from IRAS and other RRL surveys have been used by Becker et al. (1994) to classify the compact sources as HII regions, UC H II regions and Planetary Nebula. These surveys, however, are confined to $\vert b\vert<0{^\circ}.4$ and only two fields used in this dissertation, namely G003.7$-$0.2 and G001.4$-$0.1, overlap with these surveys. For these fields, additional data at 5 GHz from the Galactic plane surveys by Becker et al. (1994); Helfand et al. (1992) was also used.

The barrel-type SNR G003.7$-$0.2 (field of Table 6.1) was mapped by Gaensler (1999) at L-band using the VLA (CnB and DnC configurations with the smallest spacing of $\sim0.12k\lambda$). This image was available from Astronomy Digital Image Library (ADIL)^9.1. After correcting for the primary beam attenuation, it was used to obtain the 1420-MHz flux densities of compact sources in this field. The flux densities of compact sources measured from this image are listed in Table 6.1.

Most of the compact sources detected at 327 MHz show a negative spectral index, indicative of non-thermal nature of emission from these sources. A few compact sources detected at 1420 MHz are not detected at 327 MHz to a limit of $10-30$ mJy (the RMS noise in the images). These could be Galactic thermal sources or extragalactic sources with absorption due to the intervening Galactic ISM. Most of these sources are also weak and even if they have a flat spectrum till 327 MHz, they are below the detection limit of the 327 MHz observations.