Comparative analysis of the SFR of AGN and non-AGN galaxies, as a function of stellar mass, AGN power, cosmic time, and obscuration

Instituto de Fisica de Cantabria (CSIC-Universidad de Cantabria), Avenida de los Castros, 39005 Santander, Spain
e-mail: gmountrichas@gmail.com

Received: 14 December 2023
Accepted: 15 January 2024

Abstract

This study involves a comparative analysis of the star formation rates (SFRs) of active galactic nucleus (AGN) galaxies and non-AGN galaxies and of the SFRs of type 1 and 2 AGNs. To carry out this investigation, we assembled a dataset consisting of 2677 X-ray AGNs detected by the XMM-Newton observatory and a control sample of 64 556 galaxies devoid of AGNs. We generated spectral energy distributions (SEDs) for these objects using photometric data from the DES, VHS, and AllWISE surveys, and we harnessed the CIGALE code to extract measurements for the (host) galaxy properties. Our dataset encompasses a diverse parameter space, with objects spanning a range of stellar masses from 9.5 < log [M_*(M_⊙)] < 12.0, intrinsic X-ray luminosities within 42 < log[L_{X,2−10 keV}(erg s⁻¹)] < 45.5, and redshifts between 0.3 < z < 2.5. To compare SFRs, we calculated the SFR_norm parameter, which signifies the ratio of the SFR of an AGN galaxy to the SFR of non-AGN galaxies sharing similar M_* and redshift. Our analysis reveals that systems hosting an AGN tend to exhibit elevated SFRs compared to non-AGN galaxies, particularly beyond a certain threshold in L_X. Notably, this threshold increases as we move toward more massive galaxies. Additionally, for AGN systems with the same L_X, the magnitude of the SFR_norm decreases as we consider more massive galaxies. This suggests that in galaxies with an AGN, the increase in SFR as a function of stellar mass is not as prominent as in galaxies without an AGN. This interpretation finds support in the shallower slope that we identify in the X-ray star-forming main sequence in contrast to the galaxy main sequence. Employing CIGALE’s measurements, we classified AGNs into type 1 and type 2. In our investigation, we focused on a subset of 652 type 1 AGNs and 293 type 2 AGNs within the stellar mass range of 10.5 < log[M (M_⊙)] < 11.5. Based on our results, type 1 AGNs display higher SFRs than type 2 AGNs, at redshifts below z < 1. However, at higher redshifts, the SFRs of the two AGN populations tend to be similar. At redshifts z < 1, type 1 AGNs show augmented SFRs in comparison to non-AGN galaxies. In contrast, type 2 AGNs exhibit lower SFRs when compared to galaxies that do not host an AGN, at least up to log[L_{X,2−10 keV}(erg s⁻¹)] < 45.