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21-07-2014
The Nature of Filamentary Cold Gas in the Core of the Virgo Cluster
| Submitter: | Raymond Oonk |
| Description: | A study led by N. Werner (Stanford University) and J.B.R. Oonk (ASTRON) discovered for the first time the cold gas component of the filamentary H-alpha web surrounding M87. These gas webs surrounding the cD galaxy are common in cool-core clusters. The cool H-alpha gas is so luminous that it requires constant reheating by a still unknown source (i.e. part of the cooling flow problem). In order to determine the origin and excitation of these filaments we need to understand their local mass and energy budget. M87 is the nearest cool-core cluster and therefore important. Attempts at characterizing its filamentary web have been difficult as the low temperature phase of this gas (HI, CO) is not detected. This is primarily due to the strong continuum source affecting the spectral baseline. Now, with Herschel, we have succeeded in detecting and spatially resolving the [CII] (157 micron) emission along the south-eastern filaments. The upperlimit on the [OI] to [CII] FIR line ratio indicates a large optical depth in the FIR lines. In combination with the absorption inferred from optical lines and X-rays this indicates the presence of a significant reservoir of cold atomic and molecular gas distributed in filaments with small volume filling fraction, but large area covering factor. We find good correspondence, in both intensity and kinematics, between the cool (T~1e4 K) and cold (T~100 K) gas. A multi-wavelength study shows that the cool gas (T<1e4 K) is likely uplifted by the AGN. The thermal pressure of the H-alpha gas is significantly lower than that of the surrounding medium, thus indicating the need for additional pressure due to turbulence and/or magnetic fields. Invoking cosmic rays in combination with X-ray photoionzation we are able to explain the observed excitation of the cool gas surrounding M87 (Werner, Oonk et al. 2013, ApJ, 767, 153: http://adsabs.harvard.edu/abs/2013ApJ...767..153W). Figure caption: The multi-phase structure of the South-eastern filaments surrounding M87. The top panels show the Far-infrared CII-157 micron structure of the cold (100 K) gas in intensity and dynamics. The middle panels show the corresponding optical H-alpha, Far-ultraviolet and X-ray emission. The bottom panels show the emission measure of the hot X-ray emiting gas at three different temperatures from cool (left) to very hot (right). |
| Copyright: | N. Werner (Stanford University) |
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