An ACA 1mm survey of HzRGs in the ELAIS-S1: survey description and first results

TL;DR

This survey used the ACA at 1.3 mm to identify and analyze high-redshift radio AGN candidates in the ELAIS-S1 field, revealing non-thermal emissions, spatial offsets, and jet-like structures, advancing understanding of early galaxy evolution.

Contribution

First millimeter survey of high-redshift radio AGN candidates in ELAIS-S1, demonstrating effective selection criteria and revealing detailed emission properties and structures.

Findings

16 out of 36 sources detected at mm wavelengths

8 detections have non-thermal emission origin

Serendipitous line detections reveal jet-like structures

Abstract

Radio-emitting jets might be one of the main ingredients shaping the evolution of massive galaxies in the Universe since early cosmic times. However, identifying early radio active galactic nuclei (AGN) and confirming this scenario has been hard to accomplish, with studies of samples of radio AGN hosts at z>2 becoming routinely possible only recently. With the above in mind, we have carried out a survey with the Atacama Compact Array (ACA, or Morita Array) at 1.3 mm (rms=0.15 mJy) of 36 high-redshift radio AGN candidates found within 3.9deg2 in the ELAIS-S1 field. The work presented here describes the survey and showcases a preliminary set of results. The selection of the sample was based on three criteria making use of infrared (IR) and radio fluxes only. The criterion providing the highest selection rate of high-redshift sources (86% at z>0.8) is one combining an IR colour cut and radio flux cut (S(5.8um)/S(3.6um)>1.3 and S(1.4GHz)>1mJy). Among the sample of 36 sources, 16 show a millimetre (mm) detection. In eight of these cases, the emission has a non-thermal origin. A zsp=1.58 object, with a mm detection of non-thermal origin, shows a clear spatial offset between the jet-dominated mm continuum emission and that of the host's molecular gas, as traced by serendipitously detected CO(5-4) emission. Among the objects with serendipitous line detections there is a source with a narrow jet-like region, as revealed by CS(6-5) emission stretching 20kpc out of the host galaxy.