New constraints on the 1.4 GHz source number counts and luminosity functions in the Lockman Hole field

TL;DR

This study analyzes 1173 radio sources in the Lockman Hole, classifies them into different populations, and provides new constraints on their number counts and luminosity functions across various redshifts, confirming previous models and evolutionary trends.

Contribution

It offers the first detailed classification and redshift estimation for a large sample of faint radio sources, refining models of their counts and evolution.

Findings

SFGs and RQ AGNs surpass RL AGNs below 300 μJy.

Confirmed evolution patterns of RQ AGNs and SFGs.

Results align with existing models and previous surveys.

Abstract

We present a study of the 1173 sources brighter than $S_{1.4\,\rm GHz}= 120\,\mu$Jy detected over an area of $\simeq 1.4\,\hbox{deg}^{2}$ in the Lockman Hole field. Exploiting the multi-band information available in this field for $\sim$79% of the sample, sources have been classified into radio loud (RL) active galactic nuclei (AGNs), star forming galaxies (SFGs) and radio quiet (RQ) AGNs, using a variety of diagnostics available in the literature. Exploiting the observed tight anti-correlations between IRAC band 1 or band 2 and the source redshift we could assign a redshift to 177 sources missing a spectroscopic measurement or a reliable photometric estimate. A Monte Carlo approach was used to take into account the spread around the mean relation. The derived differential number counts and luminosity functions at several redshifts of each population show a good consistency with models and with earlier estimates made using data from different surveys and applying different approaches. Our results confirm that below $\sim300\,\mu$Jy SFGs$+$RQ AGNs overtake RL AGNs that dominate at brighter flux densities. We also confirm earlier indications of a similar evolution of RQ AGNs and SFGs. Finally, we discuss the angular correlation function of our sources and highlight its sensitivity to the criteria used for the classification.