Evidence of AGN feedback and sloshing in the X-ray luminous NGC 1550
  galaxy group
  We present results from GMRT and Chandra observations of the NGC 1550 galaxy
group. Although previously thought of as relaxed, we show evidence that gas
sloshing and active galactic nucleus (AGN) heating have affected the structure
of the system. The 610 and 235 MHz radio images show an asymmetric jet-lobe
structure with a total size of $\sim$33 kpc, with a sharp kink at the base of
the more extended western jet, and bending of the shorter eastern jet as it
enters the lobe. The 235$-$610 MHz spectral index map shows that both radio
lobes have steep spectral indices ($\alpha_{235}^{610}\geq-1.5$) indicating the
presence of an old electron population. The X-ray images reveal an asymmetric
structure in the hot gas correlated with the radio structure, as well as
potential cavities coincident with the radio lobes, with rims and arms of gas
that may have been uplifted by the cavity expansion. The X-ray residual map
reveals an arc shaped structure to the east that resembles a sloshing cold
front. Radio spectral analysis suggests a radiative age of about 33 Myr for the
source, comparable to the sloshing timescale and dynamical estimates of the age
of the lobes. An estimate of the mechanical energy required to inflate the
cavities suggests that the AGN of NGC 1550 is capable of balancing radiative
losses from the intragroup medium (IGM) and preventing excessive cooling,
providing that the AGN jets are efficiently coupled to the IGM gas. In
conclusion, we find evidence of sloshing motions from both radio and X-ray
structures, suggesting that NGC 1550 was perturbed by a minor merger or
infalling galaxy about 33 Myr ago.
