Sloshing cold fronts in galaxy groups and their perturbing disk
  galaxies: an X-ray, Optical and Radio Case Study
  We present a combined X-ray, optical, and radio analysis of the galaxy group
IC 1860 using the currently available Chandra and XMM data, literature
multi-object spectroscopy data and GMRT data. The Chandra and XMM imaging and
spectroscopy reveal two surface brightness discontinuities at 45 and 76 kpc
shown to be consistent with a pair of cold fronts. These features are
interpreted as due to sloshing of the central gas induced by an off-axis minor
merger with a perturber. This scenario is further supported by the presence of
a peculiar velocity of the central galaxy IC 1860 and the identification of a
possible perturber in the optically disturbed spiral galaxy IC 1859. The
identification of the perturber is consistent with the comparison with
numerical simulations of sloshing. The GMRT observation at 325 MHz shows faint,
extended radio emission contained within the inner cold front, as seen in some
galaxy clusters hosting diffuse radio mini-halos. However, unlike mini-halos,
no particle reacceleration is needed to explain the extended radio emission,
which is consistent with aged radio plasma redistributed by the sloshing. There
is strong analogy of the X-ray and optical phenomenology of the IC 1860 group
with two other groups, NGC 5044 and NGC 5846, showing cold fronts. The evidence
presented in this paper is among the strongest supporting the currently favored
model of cold-front formation in relaxed objects and establishes the group
scale as a chief environment to study this phenomenon.
