The Lockman Hole Project: new constraints on the sub-mJy source counts from a wide-area 1.4 GHz mosaic

Abstract

This paper is part of a series discussing the results obtained in the framework of a wide international collaboration - the Lockman Hole Project - aimed at improving the extensive multiband coverage available in the Lockman Hole region, through novel deep, wide-area, multifrequency (60, 150, 350 MHz, and 1.4 GHz) radio surveys. This multifrequency, multiband information will be exploited to get a comprehensive view of star formation and active galactic nucleus activities in the high-redshift Universe from a radio perspective. In this paper, we present novel 1.4 GHz mosaic observations obtained with the Westerbork Synthesis Radio Telescope. With an area coverage of 6.6 deg<SUP>2</SUP>, this is the largest survey reaching an rms noise of 11 μJy beam<SUP>-1</SUP>. In this paper, we present the source catalogue (∼6000 sources with flux densities S ≳ 55 μJy (5σ), and we discuss the 1.4 GHz source counts derived from it. Our source counts provide very robust statistics in the flux range 0.1< S< 1 mJy, and are in excellent agreement with other robust determinations obtained at lower and higher flux densities. A clear excess is found with respect to the counts predicted by the semi-empirical radio sky simulations developed in the framework of the Square Kilometre Array Simulated Skies project. A preliminary analysis of the identified (and classified) sources suggests this excess is to be ascribed to star-forming galaxies, which seem to show a steeper evolution than predicted.