Accretion History of AGN: Estimating the Host Galaxy Properties in X-ray Luminous AGN from z=0-3

TL;DR

This study investigates the host galaxy properties of X-ray luminous AGN across redshifts 0-3 by stacking Herschel far-IR data, revealing high star formation rates and gas depletion timescales similar to dusty star-forming galaxies.

Contribution

It introduces a stacking method to estimate IR emission and host galaxy properties of undetected AGN in large surveys, extending understanding of AGN host galaxy evolution.

Findings

AGN host galaxies have high star formation rates.

Gas depletion timescales are comparable to dusty star-forming galaxies.

X-ray selection does not determine galaxy position on the main sequence.

Abstract

We aim to determine the intrinsic far-Infrared (far-IR) emission of X-ray-luminous quasars over cosmic time. Using a 16 deg^2 region of the Stripe 82 field surveyed by XMM-Newton and Herschel Space Observatory, we identify 2905 X-ray luminous (LX > 10^42 erg/s) Active Galactic Nuclei (AGN) in the range z ~ 0-3. The IR is necessary to constrain host galaxy properties such as star formation rate (SFR) and gas mass. However, only 10% of our AGN are detected both in the X-ray and IR. Because 90% of the sample is undetected in the far-IR by Herschel, we explore the mean IR emission of these undetected sources by stacking their Herschel/SPIRE images in bins of X-ray luminosity and redshift. We create stacked spectral energy distributions from the optical to the far-IR, and estimate the median star formation rate, dust mass, stellar mass, and infrared luminosity using a fitting routine. We find that the stacked sources on average have similar SFR/L_bol ratios as IR detected sources. The majority of our sources fall on or above the main sequence line suggesting that X-ray selection alone does not predict the location of a galaxy on the main sequence. We also find that the gas depletion timescales of our AGN are similar to those of dusty star forming galaxies. This suggests that X-ray selected AGN host high star formation and that there are no signs of declining star formation.