Expected Emission from the Lithium-like $^{57}$Fe Hyperfine Radio Line in Cluster Cooling Flows

Previous abstract Next abstract

Session 53 -- Cluster Cooling Flows and Abundances
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[53.08] Expected Emission from the Lithium-like $^{57}$Fe Hyperfine Radio Line in Cluster Cooling Flows

N. D'Cruz, C.L. Sarazin (U. of Virginia)

The lithium-like ion Fe$^{+23}$ of the stable iron isotope $^{57}$Fe has a hyperfine line at a wavelength of 3.071~mm. In 1984, Sunyaev and Churazov suggested that it might be observable in clusters of galaxies. In particular, cluster cooling flows seem to be most promising because, firstly, they have cooler temperatures, so the ion Fe$^{+23}$ is more abundant. Secondly, they have large column densities and emission measures. The chemical history of the intracluster gas can also affect the detectability of the line. If the line can be detected, its strength can be compared to the strength of X-ray lines from the same element and ionization state, which come mainly from the more abundant isotope $^{56}$Fe. The comparison would help determine the nucleosynthetic source of the intracluster gas. If the line can be detected, the velocity structure of the gas can also be determined since spectral resolution in the radio region is much better than that of the current X-ray spectrometers.

We include the effects of electrons collisions, collisional ionization and recombination, proton collisions and the radiation field of the cosmic microwave background in our calculations. A few cooling flow clusters possess bright radio sources, hence the effect of a radio source is also included. A bright radio source in the cooling flow gas is important because if one tries to detect the line by looking along the line of sight of the radio source then it should appear in absorption, otherwise it should be in emission. We calculate integrated surface brightness profiles for homogenous and inhomogenous cooling flow models. Line profiles are also calculated for pure thermal and transonically turbulent broadening in both models. The luminosity of the line in both models is found to be of the order of 10$^{36}$ erg s$^{-1}$, and thermal line widths are of the order of a few hundred km s$^{-1}$.

Thursday program listing