Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-11-06
Astronomy and Astrophysics
Astrophysics
12 pages (emulateapj5) with 10 figures; accepted by The Astrophysical Journal
Scientific paper
10.1086/338425
X-ray observations of M87 in the Virgo cluster and NGC 4874 in Coma reveal that the gas temperature beyond about 50 kpc from these cD galaxies is comparable to the virial temperature of the cluster, 3 or 9 keV respectively, but within the optical galaxy the temperature drops to the galactic virial temperature, about 1 keV. We show that these steep thermal (and density) gradients follow naturally from the usual cooling inflow assumptions without recourse to thermal conductivity. To avoid unobserved central mass concentrations, most of the gas must radiatively cool (``dropout'') before it flows to the galactic core, i.e. the gas must be multiphase. Recent XMM spectra of M87 indicate single phase flow at every radius with no apparent radiative cooling to low temperatures. However, the X-ray spectral evidence for multiphase cooling beginning at lower temperatures near 1 keV (within about 10 kpc) may be less apparent and may have escaped detection. Finally, we show that the standard decomposition method used by X-ray observers to determine the mass flow dM/dt(r) may fail rather badly due to small deviations from perfectly steady state flow. When applied to our slightly non-steady computed flows, this decomposition (incorrectly) gives the usual result, dM/dt proportional to r, and overestimates the mass dropout dM/dt(r) at large radii.
Brighenti Fabrizio
Mathews William G.
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