The Role of Cerenkov Radiation in the Pressure Balance of Cool Core Clusters of Galaxies

Despite the substantial progress made recently in understanding the role of AGN feedback and associated non-thermal effects, the precise mechanism that prevents the core of some clusters of galaxies from collapsing catastrophically by radiative cooling remains unidentified. In this Letter, we demons...

Full description

Saved in:
Bibliographic Details
Published in:Astrophysical journal. Letters 2017-03, Vol.838 (1), p.L5-L5
Main Author: Lieu, Richard
Format: Article
Language:English
Subjects:
ACCURACY
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Cerenkov radiation
CHERENKOV RADIATION
Clusters
Cooling
DISTRIBUTION
Emission
EQUILIBRIUM
EVOLUTION
FEEDBACK
Galactic clusters
GALAXIES
galaxies: clusters: general
GALAXY CLUSTERS
Gas heating
HYDROSTATICS
LOSSES
MAGNETIC FIELDS
MASS
PLASMA
RADIATIVE COOLING
RADIOWAVE RADIATION
RAYLEIGH-TAYLOR INSTABILITY
STIMULATED EMISSION
TEMPERATURE DEPENDENCE
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Despite the substantial progress made recently in understanding the role of AGN feedback and associated non-thermal effects, the precise mechanism that prevents the core of some clusters of galaxies from collapsing catastrophically by radiative cooling remains unidentified. In this Letter, we demonstrate that the evolution of a cluster's cooling core, in terms of its density, temperature, and magnetic field strength, inevitably enables the plasma electrons there to quickly become Cerenkov loss dominated, with emission at the radio frequency of 350 Hz, and with a rate considerably exceeding free-free continuum and line emission. However, the same does not apply to the plasmas at the cluster's outskirts, which lacks such radiation. Owing to its low frequency, the radiation cannot escape, but because over the relevant scale size of a Cerenkov wavelength the energy of an electron in the gas cannot follow the Boltzmann distribution to the requisite precision to ensure reabsorption always occurs faster than stimulated emission, the emitting gas cools before it reheats. This leaves behind the radiation itself, trapped by the overlying reflective plasma, yet providing enough pressure to maintain quasi-hydrostatic equilibrium. The mass condensation then happens by Rayleigh-Taylor instability, at a rate determined by the outermost radius where Cerenkov radiation can occur. In this way, it is possible to estimate the rate at 2 M year−1, consistent with observational inference. Thus, the process appears to provide a natural solution to the longstanding problem of "cooling flow" in clusters; at least it offers another line of defense against cooling and collapse should gas heating by AGN feedback be inadequate in some clusters.
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8213/aa6257