Non-thermal pressure in M87 and NGC 1399 gas: X-ray vs. optical potential profiles
Abstract
We compare the gravitational potential profiles of the elliptical galaxies NGC 4486 (M87) and NGC 1399 (the central galaxy in the Fornax cluster) derived from X-ray and optical data. This comparison suggests that the combined contribution of cosmic rays, magnetic fields and micro-turbulence to the pressure is at the level of 7-15% of the gas thermal pressure in the cores of NGC 1399 and M87 respectively, although the uncertainties in our model assumptions (e.g., spherical symmetry) are sufficiently large that the contribution could be consistent with zero. We show that these results are consistent with the current paradigm of cool cluster cores, based on the assumption that AGN activity regulates the thermal state of the gas by injecting energy into the intra-cluster medium. In the absence of any other form of non-thermal pressure support, these upper bounds translate into upper limits on the magnetic field of $\sim$8 and $\sim$20 $\mu$G respectively (evaluated at a distance of 1' in NGC1399 and 2' in M87). The limit of $\sim$10-20% on the energy density in the form of relativistic protons, applies not only to the current state of the gas, but essentially to the entire history of the intra-cluster medium, provided that cosmic ray protons evolve adiabatically and that their spatial diffusion is suppressed.Keywords
All Related Versions
This publication has 0 references indexed in Scilit: