The nature of filamentary cold gas in the core of the Virgo Cluster
  We present a multi-wavelength study of the emission-line nebulae located
southeast of the nucleus of M87, the central dominant galaxy of the Virgo
Cluster. We report the detection of far-infrared (FIR) [CII] line emission from
the nebulae using observations made with Herschel PACS. The infrared line
emission is extended and cospatial with optical H{\alpha}+[NII],
far-ultraviolet CIV lines, and soft X-ray emission. The filamentary nebulae
evidently contain multi-phase material spanning a temperature range of at least
5 orders of magnitude, from ~100 K to ~10^7 K. This material has most likely
been uplifted by the AGN from the center of M87. The thermal pressure of the
10^4 K phase appears to be significantly lower than that of the surrounding hot
intra-cluster medium (ICM) indicating the presence of additional turbulent and
magnetic pressure in the filaments. If the turbulence in the filaments is
subsonic then the magnetic field strength required to balance the pressure of
the surrounding ICM is B~30-70 {\mu}G. The spectral properties of the soft
X-ray emission from the filaments indicate that it is due to thermal plasma
with kT~0.5-1 keV, which is cooling by mixing with the cold gas and/or
radiatively. Charge exchange can be ruled out as a significant source of soft
X-rays. Both cooling and mixing scenarios predict gas with a range of
temperatures. This is at first glance inconsistent with the apparent lack of
X-ray emitting gas with kT<0.5 keV. However, we show that the missing very soft
X-ray emission could be absorbed by the cold gas in the filaments with an
integrated hydrogen column density of ~1.6x10^21 cm^-2, providing a natural
explanation for the apparent temperature floor to the X-ray emission at kT~0.5
keV. The FIR through ultra-violet line emission is most likely primarily
powered by the ICM particles penetrating the cold gas following a shearing
induced mixing process.
