Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-12-07
Astronomy and Astrophysics
Astrophysics
11 pages, 6 figures, accepted 7/12/07 MNRAS
Scientific paper
10.1111/j.1365-2966.2007.12829.x
We discuss the effects of energy injection into the intra-group medium of the group of galaxies associated with NGC 741. The X-ray emission reveals a large bubble, which in the absence of a currently bright central radio source, may have been inflated by a previous cycle of nuclear activity . If the bubble is filled with a light, relativistic fluid we calculate that in expanding, it has done more than sufficient work to counteract the energy lost from the intra-group medium via radiative cooling; the bubble can provide this energy as it expands and rises. Using upper limits on the flux density of the plasma filling the bubble at 330 MHz and 1.4 GHz, we derive constraints on its electron energy distribution and magnetic field strength. We show that the data require the high-energy cut-off of the electron spectrum to be very low compared to the cut-offs seen in more typical radio sources if the fluid filling the bubble is a conventional relativistic plasma. This suggests that the fluid filling the bubble may not have evolved by expansion or synchrotron losses consistent with a dead radio source, leaving a puzzle as to what the origin of the bubble may be.
Babul Arif
Hardcastle Martin J.
Jetha Nazirah N.
O'Sullivan Ewan
Ponman Trevor J.
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