Spatially Resolved Stellar Populations of Eight GOODS-South AGN at z~1

TL;DR

This study investigates the stellar populations of eight AGN host galaxies at z~1 using high-resolution multi-band imaging, revealing correlations between younger stars and AGN activity, and differences in galaxy morphology and starburst activity between Type I and II AGN.

Contribution

First spatially resolved analysis of stellar populations in z~1 AGN hosts combining adaptive optics and HST imaging, linking starburst activity with AGN obscuration.

Findings

Younger stellar populations correlate with AGN luminosity.

Type II AGN are often disk or irregular galaxies with starburst activity.

Type I AGN tend to have elliptical or spheroidal morphologies.

Abstract

We present a pilot study of the stellar populations of 8 AGN hosts at z~1 and compare to (1) lower redshift samples and (2) a sample of nonactive galaxies of similar redshift. We utilize K' images in the GOODS South field obtained with the laser guide star adaptive optics (LGSAO) system at Keck Observatory. We combine this K' data with B, V, i, and z imaging from the ACS on HST to give multi-color photometry at a matched spatial resolution better than 100 mas in all bands. The hosts harbor AGN as inferred from their high X-ray luminosities (L_X > 10^42 ergs/s) or mid-IR colors. We find a correlation between the presence of younger stellar populations and the strength of the AGN, as measured with [OIII] line luminosity or X-ray (2-10 keV) luminosity. This finding is consistent with similar studies at lower redshift. Of the three Type II galaxies, two are disk galaxies and one is of irregular type, while in the Type I sample there only one disk-like source and four sources with smooth, elliptical/spheroidal morphologies. In addition, the mid-IR SEDs of the strong Type II AGN indicate that they are excited to LIRG (Luminous InfraRed Galaxy) status via galactic starbursting, while the strong Type I AGN are excited to LIRG status via hot dust surrounding the central AGN. This supports the notion that the obscured nature of Type II AGN at z~1 is connected with global starbursting and that they may be extincted by kpc-scale dusty features that are byproducts of this starbursting.