Star formation of X-ray AGN in COSMOS: The role of AGN activity and galaxy stellar mass

¹ Instituto de Fisica de Cantabria (CSIC-Universidad de Cantabria), Avenida de los Castros, 39005 Santander, Spain
e-mail: gmountrichas@gmail.com
² National Observatory of Athens, Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, Ioannou Metaxa and Vasileos Pavlou, 15236 Athens, Greece
³ Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
e-mail: veronique.buat@lam.fr
⁴ Institut Universitaire de France (IUF), 54124 Thessaloniki, Greece
⁵ Department of Astrophysics, Astronomy & Mechanics, School of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece

Received: 30 November 2021
Accepted: 9 March 2022

Abstract

We use approximately 1000 X-ray sources in the COSMOS-Legacy survey and study the position of the AGN relative to the star forming main sequence (MS). We also construct a galaxy (non-AGN) reference sample that includes about 90 000 sources. We apply the same photometric selection criteria to both datasets and construct their spectral energy distributions (SEDs) using optical to far-infrared photometry compiled by the HELP project. We perform SED fitting using the X-CIGALE algorithm and the same parametric grid for both datasets in order to measure the star formation rate (SFR) and stellar mass of the sources. The mass completeness of the data is calculated at different redshift intervals and is applied to both samples. We define our own MS based on the distributions of the specific SFR at different redshift ranges and exclude quiescent galaxies from our analysis. These allow us to compare the SFR of the two populations in a uniform manner, minimising systematic errors and selection effects. Our results show that at low to moderate X-ray luminosities, AGN tend to have lower or at most equal SFRs compared to non-AGN systems with similar stellar mass and redshift. At higher (L_{X, 2 − 10 keV} > 2 − 3 × 10⁴⁴ erg s⁻¹), we observe an increase in the SFR of AGN for systems that have 10.5 < log [M_*(M_⊙)] < 11.5.