2021A&A...649L..11T

In this study, we investigate the X-ray properties of WISE J090924.01+000211.1 (WISEJ0909+0002), an extremely luminous infrared (IR) galaxy (ELIRG) at z_spec=1.871 in the eROSITA Final Equatorial-Depth Survey. WISEJ0909+0002 is a WISE 22µm source, located in the GAMA-09 field, which was detected by eROSITA during the performance and verification phase. The corresponding optical spectrum indicates that this object is a type-1 active galactic nucleus (AGN). Observations from eROSITA combined with Chandra and XMM-Newton archival data indicate a very luminous (L(2-10 keV)=(2.1±0.2)x10⁴⁵erg/s) unobscured AGN with a power-law photon index of Γ=1.73_–0.15^+0.16 and an absorption hydrogen column density of log (N_H/cm^–2)<21.0. The IR luminosity was estimated to be L_IR=(1.79±0.09)x10¹⁴L_☉ from spectral energy distribution modeling based on 22 photometric data points (X-ray to far-IR) with X-CIGALE, which confirmed that WISEJ0909+0002 is an ELIRG. A remarkably high L_IR despite very low N_H would indicate that we are witnessing a short-lived phase in which hydrogen gas along the line of sight is blown outward, whereas warm and hot dust heated by AGNs still exists. As a consequence of the eROSITA All-Sky Survey, 6.8_–5.6⁺¹⁶x10² such X-ray-bright ELIRGs are expected to be discovered in the entire extragalactic sky (|b|>10°). This can potentially be the key population to constrain the bright end of IR luminosity functions.