Measuring the non-thermal pressure in early-type galaxy atmospheres: a comparison of X-ray and optical potential profiles in M87 and NGC 1399

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 microturbulence to the pressure is ∼10 per cent of the gas thermal pressure in the cores of NGC 1399 and M87, although the uncertainties in our model assumptions (e.g. spherical symmetry) are sufficiently large that the contribution could be consistent with zero. In the absence of any other form of non‐thermal pressure support, these upper bounds translate into upper limits on the magnetic field of ∼10–20 μG at a distance of 1–2 arcmin from the centers of NGC 1399 and M87. We show that these results are consistent with the current paradigm of cool cluster cores, based on the assumption that active galactic nuclei regulate the thermal state of the gas by injecting energy into the intracluster medium. The limit of ∼10–20 per cent on the energy density in the form of relativistic protons applies not only to the current state of the gas, but also essentially to the entire history of the intracluster medium, provided that cosmic ray protons evolve adiabatically and that their spatial diffusion is suppressed.

Searching for FUV line emission from 107 K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities

“…These values are physically plausible for the gas around 10 7 K in M87, and they also agree with Xray measurements. For example, Di Matteo et al (2003), Churazov et al (2008), and Russell et al (2015) all find deprojected electron density profiles which are fairly constant from 100 pc out to a few kpc, at values of 0.1-0.2 cm −3 . Additionally, the sightline is projected 1.9 kpc from the center of M87, so an effective path length of this order is a reasonable first-order assumption.…”

“…We also compute the corresponding average electron density (upper X-axis), electron column density (dotted lines), and path length (dashed lines) for the hot gas, assuming a constant total pressure of P = 1.91Pe = 4 × 10 6 cm −3 K in the sightline (Churazov et al 2008). [Fe xix] has a lower emissivity than [Fe xxi], so it does not yield as strong of a constraint.…”

“…The 90% upper limit on the pencil-beam emission measure nenpdl from the nuclear sightline towards M87 inferred from our limits on the measured [Fe xxi] flux. We also compute limits on the corresponding average electron density (upper Xaxis), electron column density (dotted lines), and path length (dashed lines) for the hot gas, assuming a constant total pressure of P = 1.91Pe = 4 × 10 6 cm −3 K in the sightline (Churazov et al 2008). This curve is sharply peaked at 10 7.05 K, and if the [Fe xxi]-emitting gas has this temperature the limits approach physically plausible parameters for the hot gas in the sightline.…”

Instability of supersonic cold streams feeding galaxies – I. Linear Kelvin–Helmholtz instability with body modes

“…(v) Magnetic Fields: While the intra-cluster medium is known to be mildly magnetized (Churazov et al 2008) little is known about the magnetization state of gas in galactic haloes. Dubois & Teyssier (2010) argued that initial magnetic fields in the ICM originate from winds outflowing from dwarf galaxies, whose IGM contain magnetic fields well below 1µG in amplitude.…”

A deepXMM–Newtonstudy of the hot gaseous halo around NGC 1961

“…We neglect magnetic support or other forms of non-thermal pressure. We interpolate between the points in our pressure and density profiles in order to calculate the gradient, and extrapolate to larger and smaller radii based on the distance-weighted slope of the nearest data points (for more details, see Appendix B of Churazov et al 2008). The effective circular velocity corresponding to this derived mass profile is shown in Figure 10.…”