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The nearby group centered on its bright central galaxy NGC 1407 has beensuggested to be an unusually dark system from previous kinematic studies. It isalso known for hosting a bright galaxy, NGC 1400, with a large radial velocity(1200 km s$^{-1}$) with respect to the group center. Previous ROSAT X-rayobservations revealed an extended region of enhanced surface brightness justeastward of NGC 1400. We investigate the NGC 1407/1400 complex with XMM-Newtonand Chandra observations. We find that the temperature and metallicity of theenhanced region are different (cooler and more metal rich) than those of thesurrounding group gas, but consistent with those of the ISM in NGC 1400. Therelative velocity of NGC 1400 is large enough that much of its ISM could havebeen ram pressure stripped while plunging through the group atmosphere. Weconclude that the enhanced region is likely to be hot gas stripped from the ISMof NGC 1400. We constrain the motion of NGC 1400 using the the pressure jump atits associated stagnation front and the total mass profile of the NGC 1407group. We conclude that NGC 1400 is moving within ~$30^{\circ}$ of theline-of-sight with Mach number $\mathcal{M}\lesssim3$. We do not detect anyobvious shock features in this complex, perhaps due to the highly line-of-sightmotion of NGC 1400. With an {\sl XMM-Newton} pointing on the relatively relaxedeastern side of NGC 1407, we derive a hydrostatic mass for this group of~$\times 10^{13}$ $M_\odot$ within 100 kpc. The total mass extrapolated to thevirial radius (681 kpc) is 3.8$\times 10^{13}$ $M_\odot$, which puts an upperlimit of ~300 $M_\odot/L_{B_\odot}$ on the mass-to-light ratio of this group.This suggests that the NGC 1407 group is not an unusually dark group.

Joint XMM-Newton and Chandra Observations of the NGC 1407/1400 Complex: a Tail of an Early-Type Galaxy and a Tale of a Nearby Merging Group