The eROSITA view of the Abell 3391/95 field: The Northern Clump. The
  largest infalling structure in the longest known gas filament observed with
  eROSITA, XMM-Newton, and Chandra
  SRG/eROSITA PV observations revealed the A3391/95 cluster system and the
Northern Clump (MCXC J0621.7-5242 galaxy cluster) are aligning along a cosmic
filament in soft X-rays, similarly to what has been seen in simulations before.
We aim to understand the dynamical state of the Northern Clump as it enters the
atmosphere ($3\times R_{200}$) of A3391. We analyzed joint eROSITA, XMM-Newton,
and Chandra observations to probe the morphological, thermal, and chemical
properties of the Northern Clump from its center out to a radius of 988 kpc
($R_{200}$). We utilized the ASKAP/EMU radio data, DECam optical image, and
Planck y-map to study the influence of the WAT radio source on the Northern
Clump central ICM. From the Magneticum simulation, we identified an analog of
the A3391/95 system along with an infalling group resembling the Northern
Clump. The Northern Clump is a WCC cluster centered on a WAT radio galaxy. The
gas temperature over $0.2-0.5R_{500}$ is $k_BT_{500}=1.99\pm0.04$ keV. We
employed the $M-T$ scaling relation and obtained a mass estimate of
$M_{500}=(7.68\pm0.43)\times10^{13}M_{\odot}$ and $R_{500}=(636\pm12)$ kpc. Its
atmosphere has a boxy shape and deviates from spherical symmetry. We identify a
southern surface brightness edge, likely caused by subsonic motion relative to
the filament gas. At $\sim\! R_{500}$, the southern atmosphere appears to be
42% hotter than its northern atmosphere. We detect a downstream tail pointing
toward the north with a projected length of $\sim318$ kpc, plausibly the result
of ram pressure stripping. The analog group in the Magneticum simulation is
experiencing changes in its gas properties and a shift between the position of
the halo center and that of the bound gas while approaching the main cluster
pair.
