Scattering of emission lines in galaxy cluster cores: measuring electron temperature

Abstract

The central galaxies of some clusters can be strong emitters in the Lyα and Hα lines. This emission may arise either from the cool/warm gas located in the cool core of the cluster or from the bright AGN within the central galaxy. The luminosities of such lines can be as high as 10 42 − 10 44 erg/s. This emission originating from the core of the cluster will get Thomson scattered by hot electrons of the intra-cluster medium (ICM) with an optical depth ∼ 0.01 giving rise to very broad (∆λ/λ ∼ 15%) features in the scattered spectrum. We discuss the possibility of measuring the electron density and temperature using information on the flux and width of the highly broadened line features.

Discovery of a diffuse optical line emitting halo in the core of the Centaurus cluster of galaxies: line emission outside the protection of the filaments

“…Given the considerably lower flux in the diffuse regions this could be light which originated within the filaments. However, the electrons within the ICM will have thermal velocities of ∼10000 km s −1 (at 0.5 keV) which would broaden the scattered light to comparable line widths (Khedekar et al 2014) which would be undetectable in the spectrum and are far in excess of those measured. The possibility remains that line emission could be scattered by cooler gas or dust (e.g.…”

Revealing the Warm and Hot Halo Baryons via Thomson Scattering of Quasar Light

“…This effect has been explored in the early theoretical papers by Gilfanov et al (1987); Fabian (1989); Sarazin & Wise (1993) to discuss the beamed AGN radiation. Since the broadening is linearly proportional to the thermal velocity of the gas, Loeb (1998) and Khedekar et al (2014) showed that analysis of the line width can also be used to derive the electron temperature of the gas, which is a valuable complementary probe, together with the diffuse emission, to better constrain the properties of the warm and hot gas.…”