On the temperature structure of M87

We revisit the XMM-Newton observation of M87, focusing our attention on the temperature structure. We find that spectra for most regions of M87 can be adequately fitted by single-temperature models. Only in a few regions, which are cospatial with the east and southwest radio arms, do we find evidence of a second temperature. The cooler component (kT similar to 0.8-1 keV). fills a small volume compared to the hotter component (kT similar to 1.6-2.5 keV); it is confined to the radio arms, rather than being associated with the potential well of the central cD galaxy; and it is probably structured in blobs with typical sizes smaller than a few 100 pc. Thermal conduction must be suppressed for the cool blobs to survive in the hotter ambient gas. Since the cool gas is observed only in those regions of M87 where we have evidence of radio halos, our results favor models in which magnetic fields play a role in suppressing heat conduction. The entropy of the cool blobs is, in general, smaller than that of the hot-phase gas; thus, cool blobs cannot originate from adiabatic evolution of hot-phase gas entrained by buoyant radio bubbles, as suggested by Churazov et al. An exploration of alternative origins for the cool gas leads to unsatisfactory results.