325-MHz observations of the ELAIS-N1 field using the Giant Metrewave Radio Telescope

TL;DR

This paper presents deep 325 MHz GMRT observations of the ELAIS-N1 field, detecting over 1200 sources, analyzing their spectral properties, and exploring implications for galaxy evolution and source populations.

Contribution

It provides the lowest rms noise at 325 MHz for ELAIS-N1, combines multi-frequency data to analyze spectral indices, and investigates source counts and spectral types of radio sources.

Findings

Detected 1286 sources above 270 μJy flux density.

Identified potential relic, high-redshift, and Giga-Hertz Peaked Spectrum sources.

Observed flattening in source counts at low flux densities.

Abstract

We present observations of the European Large-Area {\it ISO} Survey-North 1 (ELAIS-N1) at 325 MHz using the Giant Metrewave Radio Telescope (GMRT), with the ultimate objective of identifying active galactic nuclei and starburst galaxies and examining their evolution with cosmic epoch. After combining the data from two different days we have achieved a median rms noise of $\approx40 \mu$Jy beam$^{-1}$, which is the lowest that has been achieved at this frequency. We detect 1286 sources with a total flux density above $\approx270 \mu$Jy. In this paper, we use our deep radio image to examine the spectral indices of these sources by comparing our flux density estimates with those of Garn et al. at 610 MHz with the GMRT, and surveys with the Very Large Array at 1400 MHz. We attempt to identify very steep spectrum sources which are likely to be either relic sources or high-redshift objects as well as inverted-spectra objects which could be Giga-Hertz Peaked Spectrum objects. We present the source counts, and report the possibility of a flattening in the normalized differential counts at low flux densities which has so far been reported at higher radio frequencies.