Bubbles In A Galaxy Atmosphere M84

The examples above have concentrated on the radio-X-ray connection around central galaxies in clusters and groups. These galaxies are clearly the brightest cluster members and lie at the cluster center, a special position in the cluster's gravitational potential. However, a notable example of the influence of radio plasma on the X-ray emitting gas in a more typical early-type galaxy is M84 (NGC4374, 3C272.1), an E1 galaxy, within the core of the Virgo cluster, but not at its center.

Finoguenov & Jones (2001) found very complex structure in the soft X-ray emitting gas around the Virgo galaxy M84 (NGC4374) whose appearance is completely explained by the morphology of the radio lobes. Fig. 4.10 shows the strong influence of radio bubbles on the X-ray emitting gas distribution. The X-ray emission appears ^-shaped, with a bar extending east-west and two filaments roughly perpendicular to this bar. The complex X-ray surface brightness distribution arises from the presence of two radio lobes (approximately north and south of the galaxy) that produce two low density cavities surrounded by higher density X-ray filaments. As with Perseus/NGC1275 and Hydra A, the filaments, defining the %-shaped emission, have gas temperatures comparable to the gas in the central and outer regions of the galaxy and hence argue against any strong shock heating of the galaxy atmosphere by the radio plasma.

From the gas density distribution surrounding the radio lobes and the observed Faraday rotation, Finoguenov & Jones (2001) determined the strength of the magnetic field. A simple model of the X-ray gas distribution gave an integrated electron density of ~ 0.04 cm-3 kpc. From the observed Faraday rotation, Finoguenov & Jones (2001) inferred a line-of-sight magnetic field of 0.8/u Gauss (below the equipartition value of 20 m Gauss; Laing & Bridle 1987).

In summary, the high resolution Chandra image of M84 shows the remarkable interaction between the radio plasma and the X-ray emitting interstellar medium (ISM). The radio lobes have created cavities in the ISM that are surrounded by higher density shells and, with some assumptions, the magnetic field overlying the radio bubbles can be calculated.

Figure 4-10. Left: ^-shaped X-ray emission from M84 image (0.5-2.0 keV band) as observed with Chandra. The X-ray emission shows an east-west bar and two filaments extending from each end. The galaxy nucleus lies in the bright region at the west end of the bar. Right: Radio emission overlayed on the smoothed Chandra image. (Finoguenov & Jones 2001) "explains" the unusual X-ray morphology - the radio plasma has displaced the hot X-ray emitting gas.

Figure 4-10. Left: ^-shaped X-ray emission from M84 image (0.5-2.0 keV band) as observed with Chandra. The X-ray emission shows an east-west bar and two filaments extending from each end. The galaxy nucleus lies in the bright region at the west end of the bar. Right: Radio emission overlayed on the smoothed Chandra image. (Finoguenov & Jones 2001) "explains" the unusual X-ray morphology - the radio plasma has displaced the hot X-ray emitting gas.

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