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

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, LX, 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 LX (LX, 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 LX to test previous, tentative results. At LX, 2−10 keV > 1044.2 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 SFRnorm–LX relation up to LX, 2−10 keV ∼ 1044.5 erg s−1, with SFR similar to that of star-forming galaxies. However, at higher LX (LX, 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.