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
  The nearby group centered on its bright central galaxy NGC 1407 has been
suggested to be an unusually dark system from previous kinematic studies. It is
also 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-ray
observations revealed an extended region of enhanced surface brightness just
eastward of NGC 1400. We investigate the NGC 1407/1400 complex with XMM-Newton
and Chandra observations. We find that the temperature and metallicity of the
enhanced region are different (cooler and more metal rich) than those of the
surrounding group gas, but consistent with those of the ISM in NGC 1400. The
relative velocity of NGC 1400 is large enough that much of its ISM could have
been ram pressure stripped while plunging through the group atmosphere. We
conclude that the enhanced region is likely to be hot gas stripped from the ISM
of NGC 1400. We constrain the motion of NGC 1400 using the the pressure jump at
its associated stagnation front and the total mass profile of the NGC 1407
group. We conclude that NGC 1400 is moving within ~$30^{\circ}$ of the
line-of-sight with Mach number $\mathcal{M}\lesssim3$. We do not detect any
obvious shock features in this complex, perhaps due to the highly line-of-sight
motion of NGC 1400. With an {\sl XMM-Newton} pointing on the relatively relaxed
eastern 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 the
virial radius (681 kpc) is 3.8$\times 10^{13}$ $M_\odot$, which puts an upper
limit 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.
