The eROSITA Final Equatorial-Depth Survey (eFEDS). A multiwavelength view of WISE mid-infrared galaxies/active galactic nuclei

Abstract

Aims. We investigate the physical properties—such as the stellar mass (M∗), star-formation rate (SFR), infrared (IR) luminosity (LIR), X-ray luminosity (LX), and hydrogen column density (NH)—of mid-IR (MIR) galaxies and active galactic nuclei (AGN) at z < 4 in the 140 deg2 field observed by SRG/eROSITA using the Performance-and-Verification-Phase program named the eROSITA Final Equatorial Depth Survey (eFEDS). Methods. By cross-matching the WISE 22 μm (W4)-detected sample and the eFEDS X-ray point-source catalog, we find that 692 extragalactic objects are detected by eROSITA. We have compiled a multiwavelength dataset extending from X-ray to far-IR wavelengths. We have also performed (i) an X-ray spectral analysis, (ii) spectral-energy-distribution (SED) fitting using X-CIGALE, (iii) 2D image-decomposition analysis using Subaru Hyper Suprime-Cam (HSC) images, and (iv) optical spectral fitting with QSFit to investigate the AGN and host-galaxy properties. For 7,088 WISE 22 μm objects that are undetected by eROSITA, we have performed an X-ray stacking analysis to examine the typical physical properties of these X-ray faint and/or probably obscured objects. Results. We find that (i) 82% of the eFEDS–W4 sources are classified as X-ray AGN with log LX > 42 erg s−1; (ii) 67% and 24% of the objects have log (LIR/L ) > 12 and 13, respectively; (iii) the relationship between LX and the 6 μm luminosity is consistent with that reported in previous works; and (iv) the relationship between the Eddington ratio and NH for the eFEDS–W4 sample and a comparison with a model prediction from a galaxy-merger simulation indicates that approximately 5.0% of the eFEDS–W4 sources in our sample are likely to be in an AGN-feedback phase, in which strong radiation pressure from the AGN blows out the surrounding material from the nuclear region. Conclusions. Thanks to the wide area coverage of eFEDS, we have been able to constrain the ranges of the physical properties of the WISE 22 μm-selected sample of AGNs at z < 4, providing a benchmark for forthcoming studies on a complete census of MIR galaxies selected from the full-depth eROSITA all-sky survey.