2003ApJ...586..850P

We present an X-ray investigation of the elliptical galaxy NGC 507 in the Pisces cluster. We make use of archival ROSAT HRI and Chandra data, and of previously published PSPC data, to connect the large-scale structure of the halo to the core morphology. Our analysis, based on a bidimensional double beta model of the halo surface brightness, shows that the halo core (r<2-3r_e) and the external halo (r>3r_e) are characterized by different dynamical properties and suggests a different origin of the two components. The halo core has a complex morphology with a main X-ray emission peak, coincident with the center of the optical galaxy, and several secondary peaks. The spatial and spectral analysis of the central peak shows that this feature is produced by denser hot gas in the galaxy core. While both homogeneous and inhomogeneous cooling flow models predict a deposited mass exceeding the observed amount, our data support the scenario in which the gas is kinetically heated by stellar mass losses. Comparison with previously published studies suggests that the core of an X-ray extended galaxy is associated with the stellar distribution and has properties similar to the X-ray halos of compact galaxies. The secondary peaks are due instead to interactions between the radio-emitting plasma and the surrounding ISM, producing density fluctuations in the hot gas. We find that the energy input by the central radio source in the ISM is large enough to prevent gas cooling and may explain the failure of the cooling flow models. The total mass profile derived from the bidimensional model shows that a significant amount of dark matter is present at large radii. The dark halo extends on cluster scales and is likely associated with the whole cluster rather than with NGC 507. This structure is typical of many X-ray-bright early-type galaxies and may explain the spatial and spectral differences with X-ray compact galaxies largely debated in the literature. The large-scale surface brightness distribution is irregular and more extended in the northeast direction. The displacement of the cluster halo from the optical galaxy and the filamentary structures observed in the halo core further suggest that the galaxy may be slowly moving within the group potential. Finally, we found that ∼20% of the sources detected by Kim & Fabbiano in the NGC 507 halo are due to point sources, while the nature of the remaining population is not clear. If associated with NGC 507, they could be either accreting binaries hosting a massive black hole or density clumps of the X-ray halo.