Young AGN outburst running over older X-ray cavities
  Although the energetic feedback from active galactic nuclei (AGN) is believed
to have a profound effect on the evolution of galaxies and clusters of
galaxies, details of the AGN heating remain elusive. Here, we study NGC 193 - a
nearby lenticular galaxy - based on X-ray (Chandra) and radio (VLA and GMRT)
observations. These data reveal the complex AGN outburst history of the galaxy:
we detect a pair of inner X-ray cavities, an outer X-ray cavity, a shock front,
and radio lobes extending beyond the inner cavities. We suggest that the inner
cavities were produced ~78 Myr ago by a weaker AGN outburst, while the outer
cavity, the radio lobes, and the shock front are due to a younger (13-26 Myr)
and (4-8) times more powerful outburst. Combining this with the observed
morphology of NGC 193, we conclude that NGC 193 likely represents the first
example of a second, more powerful, AGN outburst overrunning an older, weaker
outburst. These results help to understand how the outburst energy is
dissipated uniformly in the core of galaxies, and therefore may play a crucial
role in resolving how AGN outbursts suppress the formation of large cooling
flows at cluster centers.
