Herschel observations of the Centaurus cluster - the dynamics of cold
  gas in a cool core
  Brightest cluster galaxies (BCGs) in the cores of galaxy clusters have
distinctly different properties from other low redshift massive ellipticals.
The majority of the BCGs in cool-core clusters show signs of active star
formation. We present observations of NGC 4696, the BCG of the Centaurus galaxy
cluster, at far-infrared (FIR) wavelengths with the Herschel space telescope.
Using the PACS spectrometer, we detect the two strongest coolants of the
interstellar medium, CII at 157.74 micron and OI at 63.18 micron, and in
addition NII at 121.90 micron. The CII emission is extended over a region of 7
kpc with a similar spatial morphology and kinematics to the optical H-alpha
emission. This has the profound implication that the optical hydrogen
recombination line, H-alpha, the optical forbidden lines, NII 6583 Angstrom,
the soft X-ray filaments and the far-infrared CII line all have the same energy
source. We also detect dust emission using the PACS and SPIRE photometers at
all six wavebands. We perform a detailed spectral energy distribution fitting
using a two-component modified black-body function and find a cold 19 K dust
component with mass 1.6x10^6 solar mass and a warm 46 K dust component with
mass 4.0x10^3 solar mass. The total FIR luminosity between 8 micron and 1000
micron is 7.5x10^8 solar luminosity, which using Kennicutt relation yields a
low star formation rate of 0.13 solar mass per yr. This value is consistent
with values derived from other tracers, such as ultraviolet emission. Combining
the spectroscopic and photometric results together with optical H-alpha, we
model emitting clouds consisting of photodissociation regions (PDRs) adjacent
to ionized regions. We show that in addition to old and young stellar
populations, there is another source of energy, such as cosmic rays, shocks or
reconnection diffusion, required to excite the H-alpha and CII filaments.
