Varstrometry for Off-nucleus and Dual sub-Kpc AGN (VODKA): A Mix of Singles, Lenses, and True Duals at Cosmic Noon

TL;DR

This study uses multi-wavelength observations to identify and characterize dual AGNs at cosmic noon, revealing several high-redshift systems with diverse properties and confirming some as true dual SMBH systems.

Contribution

It provides one of the largest multi-wavelength follow-up campaigns at high redshift, confirming dual AGNs and refining methods to distinguish them from other phenomena.

Findings

Confirmed 4 dual AGN systems at z~2

Refuted gravitational lensing in most candidates

Found diverse radio and optical properties among AGNs

Abstract

Dual Active Galactic Nuclei (dual AGNs), a phase in some galaxy mergers during which both central supermassive black holes (SMBHs) are active, are expected to be a key observable stage leading up to SMBH mergers. Constraining the population of dual AGNs in both the nearby and high-z universe has proven to be elusive until very recently. We present a multi-wavelength follow-up campaign to confirm the nature of a sample of 20 candidate dual AGNs at cosmic noon (z~2) from the VODKA sample. Through a combination of Hubble Space Telescope (HST) and Very Large Array (VLA) imaging, we refute the possibility of gravitational lensing in all but one target. We find evidence of dual AGNs in four systems, while seven exhibit single AGN in galaxy pairs, either through strong radio emission or ancillary emission line data. The remaining systems are either confirmed as quasar-star superpositions (six) or non-lensed pairs (two) that require further investigations to establish AGN activity. Among the systems with radio detections, we find a variety of radio spectral slopes and UV/optical colors suggesting that our sample contains a range of AGN properties, from obscured radio-quiet objects to those with powerful synchrotron-emitting jets. This study presents one of the largest dedicated multi-wavelength follow-up campaigns to date searching for dual AGNs at high redshift. We confirm several of the highest-z systems at small physical separations, thus representing some of the most evolved dual AGN systems at the epoch of peak quasar activity known to date.