The Compact Star-Forming Galaxies at $2<z<3$ in 3D-HST/CANDELS: AGN and Non-AGN Physical Properties

TL;DR

This study examines the physical, structural, and environmental differences between AGN-hosting and non-AGN massive compact star-forming galaxies at redshifts 2 to 3, revealing similarities in properties and suggesting internal processes trigger AGN activity.

Contribution

It provides the most complete AGN census for massive cSFGs at 2<z<3 and compares their properties, structural parameters, and environments, highlighting internal mechanisms as potential AGN triggers.

Findings

AGN-hosting and non-AGN cSFGs have similar stellar and structural properties.

Structural parameters of cSFGs become more concentrated at lower redshifts.

Environmentally, AGN activity appears driven by internal secular processes.

Abstract

We investigate the differences in the stellar population properties, the structure, and the environment between massive compact star-forming galaxies (cSFGs) with or without active galactic nucleus (AGN) at $2<z<3$ in the five 3D-HST/CANDELS fields. In a sample of 221 massive cSFGs, we constitute the most complete AGN census so far, identifying 66 AGNs by the X-ray detection, the mid-infrared color criterion, and/or the SED fitting, while the rest (155) are non-AGNs. Further dividing these cSFGs into two redshift bins, i.e., $2<z<2.5$ and $2.5 \leq z<3$, we find that in each redshift bin the cSFGs with AGNs have similar distributions of the stellar mass, the specific star formation rate, and the ratio of $L_{\rm IR}$ to $L_{\rm UV}$ to those without AGNs. After having performed a two-dimensional surface brightness modeling for those cSFGs with X-ray-detected AGNs (37) to correct for the influence of the central point-like X-ray AGN on measuring the structural parameters of its host galaxy, we find that in each redshift bin the cSFGs with AGNs have comparable distributions of all concerned structural parameters, i.e., the Sersic index, the 20\%-light radius, the Gini coefficient, and the concentration index, to those without AGNs. With a gradual consumption of available gas and dust, the structure of cSFGs, indicated by the above structural parameters, seem to be slightly more concentrated with decreasing redshift. At $2<z<3$, the similar environment between cSFGs with and without AGNs suggests that their AGN activities are potentially triggered by internal secular processes, such as gravitational instabilities or/and dynamical friction.