Comparison of the star formation in X-ray-selected AGN in eFEDS with that of star-forming galaxies

¹ Instituto de Fisica de Cantabria (CSIC-Universidad de Cantabria), Avenida de los Castros, 39005 Santander, Spain
e-mail: gmountrichas@gmail.com
² Aix Marseille Univ, CNRS, CNES, LAM Marseille, France
³ Institut Universitaire de France (IUF), Paris, France
⁴ Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
⁵ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
⁶ Centro de Astronomía (CITEVA), Universidad de Antofagasta, Avenida Angamos 601, Antofagasta, Chile
⁷ National Centre for Nuclear Research, ul. Pasteura 7, 02-093 Warszawa, Poland
⁸ Astronomy Centre, Department of Physics & Astronomy, University of Southampton, Southampton SO17 1BJ, UK
⁹ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

Received: 2 February 2022
Accepted: 3 May 2022

Abstract

We use approximately 1800 X-ray active galactic nuclei (AGN) in the eROSITA Final Equatorial-Depth Survey (eFEDS) that span over two orders of magnitude in X-ray luminosity, L_{X, 2−10 keV} ≈ 10⁴³⁻⁴⁵ erg s⁻¹, and compare their star-formation rate (SFR) to that of non-AGN star-forming systems, at 0.5 < z < 1.5. To this end, we compiled a reference galaxy catalogue of about 17 000 sources. Both samples have the same photometric coverage, from optical to far-infrared. We construct the spectral energy distributions (SEDs) of all sources and fit them using the CIGALE code, using the same templates and parametric grid for both samples, and accounting for the mass incompleteness and exclude quiescent systems from both datasets. This allows us to compare the SFR of the two populations in a uniform manner, minimising systematic effects. Based on our analysis, AGN at low and moderate L_X (L_{X, 2−10 keV} < 10⁴⁴ erg s⁻¹) have SFR that is lower than, or at most equal to, that of star-forming galaxies, in agreement with previous studies. The large number of luminous X-ray AGN available in the eFEDS dataset enable us to expand our investigations at higher L_X to test previous, tentative results. At L_{X, 2−10 keV} > 10^44.2 erg s⁻¹, the SFR of AGN appears enhanced by ∼30% compared to that of star-forming sources, for systems with stellar mass in the range of 10.5 < log [M_*(M_⊙)] < 11.5, confirming indications found in previous studies. The most massive sources, log [M_*(M_⊙)] > 11.5, present a flat SFR_norm–L_X relation up to L_{X, 2−10 keV} ∼ 10^44.5 erg s⁻¹, with SFR similar to that of star-forming galaxies. However, at higher L_X (L_{X, 2−10 keV} ∼ 10⁴⁵ erg s⁻¹), we find indications that the SFR of these massive AGN hosts may be enhanced compared to that of non-AGN systems.