A Fully-Identified Sample of AEGIS20 Microjansky Radio Sources

TL;DR

This study presents a nearly complete identification of faint radio sources in the AEGIS20 sample using infrared imaging, providing insights into their redshifts, stellar masses, and classifications as starbursts or AGNs.

Contribution

It is the first deep radio sample with nearly 100% optical/infrared identification, enabling detailed analysis of source properties and redshift distribution.

Findings

Almost all sources with bright 3.6 micron magnitudes have z < 1.1.

Fainter sources mostly have photometric redshifts between 1 and 3.

Stellar masses vary by more than a factor of 10 at z ~ 1.

Abstract

Infrared 3.6 to 8 micron images of the Extended Groth Strip yield plausible counterpart identifications for all but one of 510 radio sources in the AEGIS20 S(1.4 GHz) > 50 micro-Jy sample. This is the first such deep sample that has been effectively 100% identified. Achieving the same identification rate at R-band would require observations reaching R_AB > 27. Spectroscopic redshifts are available for 46% of the sample and photometric redshifts for an additional 47%. Almost all of the sources with 3.6 micron AB magnitudes brighter than 19 have spectroscopic redshifts z < 1.1, while fainter objects predominantly have photometric redshifts with 1 \lapprox z \lapprox 3. Unlike more powerful radio sources that are hosted by galaxies having large stellar masses within a relatively narrow range, the AEGIS20 counterparts have stellar masses spanning more than a factor of 10 at z \sim 1. The sources are roughly 10--15% starbursts at z \lapprox 0.5 and 20--25% AGNs mostly at z > 1 with the remainder of uncertain nature.