A wide-area GMRT 610-MHz survey of ELAIS N1 field

Abstract

ABSTRACT In this paper, we present a wide-area 610-MHz survey of the ELAIS N1 field with the GMRT, covering an area of 12.8 deg2 at a resolution of 6 arcsec and with an rms noise of ∼40 $\mu$Jy beam−1. This is equivalent to ∼20 $\mu$Jy beam−1 rms noise at 1.4 GHz for a spectral index of −0.75. The primary goal of the survey was to study the polarized sky at sub-mJy flux densities at < GHz frequencies, alongwith a range of other science goals such as investigations into the nature of the low-frequency $\mu$Jy source populations and alignments of radio jets. A total of 6400 sources were found in this region, the vast majority of them compact. The sample jointly detected by GMRT at 610 MHz and by VLA FIRST at 1.4 GHz has a median spectral index of −0.85 ± 0.05 and a median 610-MHz flux density of 4.5 mJy. This region has a wealth of ancillary data, which is useful to characterize the detected sources. The multiwavelength crossmatching resulted optical/IR counterparts to ∼90 per cent of the radio sources, with a significant fraction having at least photometric redshift. Due to the improved sensitivity of this survey over preceding ones, we have discovered six giant radio sources (GRSs), with three of them at z ∼ 1 or higher. This implies that the population of GRS may be more abundant and common than known to date and if true, this has implications for the luminosity function and the evolution of radio sources. We have also identified several candidate-extended relic sources.