THE NATURE OF FILAMENTARY COLD GAS IN THE CORE OF THE VIRGO CLUSTER
- Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 452 Lomita Mall, Stanford, CA 94305-4085 (United States)
- ASTRON, Netherlands Institute for Radio Astronomy, P.O. Box 2, 7990 AA Dwingeloo (Netherlands)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Institute for Computational Cosmology, Department of Physics, Durham University, Durham DH1 3LE (United Kingdom)
- Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Department of Astronomy and the Maryland Astronomy Center for Theory and Computation, University of Maryland, College Park, MD 20742 (United States)
We present a multi-wavelength study of the emission-line nebulae located {approx}38'' (3 kpc in projection) southeast of the nucleus of M87, the central dominant galaxy of the Virgo Cluster. We report the detection of far-infrared (FIR) [C II] line emission at 158 {mu}m from the nebulae using observations made with the Herschel Photodetector Array Camera and Spectrometer (PACS). The infrared line emission is extended and co-spatial with optical H{alpha}+ [N II], far-ultraviolet C IV lines, and soft X-ray emission. The filamentary nebulae evidently contain multi-phase material spanning a temperature range of at least five orders of magnitude, from {approx}100 K to {approx}10{sup 7} K. This material has most likely been uplifted by the active galactic nucleus from the center of M87. The thermal pressure of the 10{sup 4} K phase appears to be significantly lower than that of the surrounding hot intracluster 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 {approx} 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 {approx} 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 N{sub H} {approx} 1.6 Multiplication-Sign 10{sup 21} cm{sup -2}, providing a natural explanation for the apparent temperature floor to the X-ray emission at kT {approx} 0.5 keV. The FIR through ultraviolet line emission is most likely primarily powered by the ICM particles penetrating the cold gas following a shearing induced mixing process. An additional source of energy may, in principle, be provided by X-ray photoionization from cooling X-ray emitting plasma. The relatively small line ratio of [O I]/[C II] <7.2 indicates a large optical depth in the FIR lines. The large optical depth in the FIR lines and the intrinsic absorption inferred from the X-ray and optical data imply significant reservoirs of cold atomic and molecular gas distributed in filaments with small volume filling fraction, but large area covering factor.
- OSTI ID:
- 22126870
- Journal Information:
- Astrophysical Journal, Vol. 767, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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