The nature of the ghost cavity in the NGC 741 group - AstrophysicsReport as inadecuate

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Abstract: We discuss the effects of energy injection into the intra-group medium of thegroup of galaxies associated with NGC 741. The X-ray emission reveals a largebubble, which in the absence of a currently bright central radio source, mayhave been inflated by a previous cycle of nuclear activity . If the bubble isfilled with a light, relativistic fluid we calculate that in expanding, it hasdone more than sufficient work to counteract the energy lost from theintra-group medium via radiative cooling; the bubble can provide this energy asit expands and rises. Using upper limits on the flux density of the plasmafilling the bubble at 330 MHz and 1.4 GHz, we derive constraints on itselectron energy distribution and magnetic field strength. We show that the datarequire the high-energy cut-off of the electron spectrum to be very lowcompared to the cut-offs seen in more typical radio sources if the fluidfilling the bubble is a conventional relativistic plasma. This suggests thatthe fluid filling the bubble may not have evolved by expansion or synchrotronlosses consistent with a dead radio source, leaving a puzzle as to what theorigin of the bubble may be.

Author: Nazirah N. Jetha 1 and 2, Martin J. Hardcastle 3, Arif Babul 4, Ewan O'Sullivan 5, Trevor J. Ponman 2, Somak Raychaudhury 2,


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