The energy source of the filaments around the giant galaxy NGC1275
  The brightest galaxy in the nearby Perseus cluster, NGC1275, is surrounded by
a network of filaments. These were first observed through their Halpha emission
but are now known to have a large molecular component with a total mass
approaching 10^11Msun of gas. The filaments are embedded in hot intracluster
gas and stretch over 80 kpc. They have an unusual low excitation spectrum which
is well modelled by collisional heating and ionization by secondary electrons.
Here we note that the surface radiative flux from the outer filaments is close
to the energy flux impacting on them from particles in the hot gas. We propose
that the secondary electrons within the cold filaments, which excite the
observed submillimetre through UV emission, are due to the hot surrounding gas
efficiently penetrating the cold gas through reconnection diffusion. Some of
the soft X-ray emission seen from the filaments is then due to charge exchange,
although this is insufficient to account for all the observed X-ray flux. The
filaments are complex with multiphase gas. Interpenetration of hot and cold gas
leads to the filaments growing in mass, at a rate of up to 100Msunpyr. The lack
of soft X-ray cooling emission in cool core clusters is then due to the
non-radiative cooling of hot gas on mixing with cold gas around and within the
central galaxy.
