The X-ray invisible Universe. A look into the halos undetected by eROSITA

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The paper presents the analysis of optically selected GAMA groups and clusters in the SRG/eROSITA X-ray map of eFEDS (eROSITA Final Equatorial Depth Survey), in the halo mass range $10^{13}-5{\times}10^{14}$ $M_{\odot}$ and at $z < 0.2$.

• All X-ray detections have a clear GAMA counterpart, but most of the GAMA groups in the halo mass range $10^{13}-10^{14}$ $M_{\odot}$ remain undetected.
• We compare the X-ray surface brightness profiles of the eROSITA detected groups with the mean stacked profile of the undetected low-mass halos at fixed halo mass.
• Overall, we find that the undetected groups exhibit less concentrated X-ray surface brightness, dark matter, and galaxy distributions with respect to the X-ray detected halos.