The VLA-VIRMOS Deep Field I. Radio observations probing the microJy source population

TL;DR

This paper presents a deep 1.4 GHz radio survey of a 1 square degree field, cataloging over 1000 sources, analyzing their properties, and revealing a significant change in the source count slope at sub-mJy levels.

Contribution

It provides a detailed methodology for data reduction, bias correction, and source cataloging in deep radio surveys, and offers new insights into the source count distribution at faint flux levels.

Findings

Radio counts agree with previous surveys at higher fluxes.

Counts are 50% higher than in the HDF.

Clear change in slope observed in sub-mJy source counts.

Abstract

We have conducted a deep survey (r.m.s noise 17 microJy) with the Very Large Array (VLA) at 1.4 GHz, with a resolution of 6 arcsec, of a 1 square degree region included in the VIRMOS VLT Deep Survey. In the same field we already have multiband photometry down to I(AB)=25, and spectroscopic observations will be obtained during the VIRMOS VLT survey. The homogeneous sensitivity over the whole field has allowed to derive a complete sample of 1054 radio sources (5 sigma limit). We give a detailed description of the data reduction and of the analysis of the radio observations, with particular care to the effects of clean bias and bandwidth smearing, and of the methods used to obtain the catalogue of radio sources. To estimate the effect of the resolution bias on our observations we have modelled the effective angular-size distribution of the sources in our sample and we have used this distribution to simulate a sample of radio sources. Finally we present the radio count distribution down to 0.08 mJy derived from the catalogue. Our counts are in good agreement with the best fit derived from earlier surveys, and are about 50 % higher than the counts in the HDF. The radio count distribution clearly shows, with extremely good statistics, the change in the slope for the sub-mJy radio sources.