Deep GMRT 610 MHz Observations of the ELAIS N1 Field : Catalogue and Source Counts

Abstract

This is the first of a series of papers based on sensitive 610 MHz observations of the ELAIS N1 field using the Giant Metrewave Radio Telescope. We describe the observations, processing and source catalogue extraction from a deep image with area of 1.86\,deg${}^2$ and minimum noise of $\sim$7.1\,$\mu$Jy/beam. We compile a catalogue of 4290 sources with flux densities in the range 28.9\,$\mu$Jy - 0.503\,Jy, and derive the Euclidean-normalized differential source counts for sources with flux densities brighter than $35.5\mu \mathrm{Jy}$. Our counts show a flattening at 610 MHz flux densities below 1 mJy. Below the break the counts are higher than previous observations at this frequency, but generally consistent with recent models of the low-frequency source population. The radio catalogue is cross-matched against multi-wavelength data leading to identifications for 92\% and reliable redshifts for 72\% of our sample, with 19\% of the redshifts based on spectroscopy. For the sources with redshifts we use radio and X-ray luminosity, optical spectroscopy and mid-infrared colours to search for evidence of the presence of an Active Galactic Nucleus (AGN). We compare our identifications to predictions of the flux density distributions of star forming galaxies (SFGs) and AGN, and find a good agreement assuming the majority of the sources without redshifts are SFGs. We derive spectral index distributions for a sub-sample. The majority of the sources are steep spectra, with a median spectral index that steepens with frequency; ${\alpha }_{610}^{325}=-0.80\pm 0.29$, ${\alpha }_{1400}^{610}=-0.83\pm 0.31$ and ${\alpha }_{5000}^{610}=-1.12\pm 0.15$.

21 pages, 18 figures, 7 tables, accepted for publication in MNRAS

References in corpus (26)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• EAZY: A Fast, Public Photometric Redshift Code
• Astrophysics Source Code Library
• Distant Radio Galaxies and their Environments
• The Radio-Loud Fraction of Quasars is a Strong Function of Redshift and Optical Luminosity
• The faint radio sky: radio astronomy becomes mainstream
• Photometric redshifts in the SWIRE Survey
• The Star Formation History of the Universe as Revealed by Deep Radio Observations
• Seyfert galaxies in the local Universe (z$\le$ 0.1): the average X-ray spectrum as seen by $BeppoSAX$
• Galaxy Evolution in the Radio Band: The Role of Starforming Galaxies and Active Galactic Nuclei
• The Hard X-Ray Luminosity Function of High-Redshift ($3<z\lesssim 5$) Active Galactic Nuclei
• The Lockman Hole project: LOFAR observations and spectral index properties of low-frequency radio sources
• The MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey
• On the origin of radio core emission in radio-quiet quasars
• The ATESP 5 GHz radio survey I. Source counts and spectral index properties of the faint radio population
• A 610-MHz survey of the ELAIS-N1 field with the Giant Metrewave Radio Telescope - Observations, data analysis and source catalogue
• Discovery of Radio Jets in z~2 ULIRGs with Deep 9.7um Silicate Absorption
• 325-MHz observations of the ELAIS-N1 field using the Giant Metrewave Radio Telescope
• Multiwavelength characterization of faint Ultra Steep Spectrum radio sources : A search for high-redshift radio galaxies
• Imaging and Spectroscopy of Ultra Steep Spectrum Radio Sources
• A search for faint high-redshift radio galaxy candidates at 150 MHz
• Deep observations of the Super-CLASS super-cluster at 325 MHz with the GMRT: the low-frequency source catalogue
• The radio spectral energy distribution of infrared-faint radio sources
• The radio properties of optically obscured Spitzer sources
• GMRT 610-MHz observations of the faint radio source population - and what these tell us about the higher-radio-frequency sky
• Probing the nature of compact ultra-steep spectrum radio sources with the e-EVN and e-MERLIN

Cited by in corpus (3)

• Cosmic evolution of star-forming galaxies to $z\simeq 1.8$ in the faint low-frequency radio source population
• A Wide-area GMRT 610~MHz survey of ELAIS N1 field
• J1615+5452: a remnant radio galaxy in the ELAIS-N1 field