Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...422..459d&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 422, no. 2, p. 459-466
Astronomy and Astrophysics
Astrophysics
14
Cooling Flows (Astrophysics), Coronas, Emission Spectra, Galactic Clusters, Iron, Line Spectra, Elliptical Galaxies, Gas Dynamics, Gas Flow, X Ray Spectra, X Ray Telescopes
Scientific paper
We report one marginal detection (PKS 0745-191) and four nondetections (A2199, 2A0335+096, A2597, and A1795) of the coronal emission line (Fe X) 6374 A radiated by approximately 106 K gas in the central regions of massive cooling flow clusters (mass cooling rates of (M dot) greater than or equal to 100 solar mass/yr). Except for the nondetection of (Fe X) in A1795, these observations are consistent with and more sensitive than previous upper limits for these and similar clusters of galaxies. We discuss in detail the specific difficulties in detecting this emission line against the starlight and the approximately 104 K emission-line region of the central cD galaxy. The (Fe X) emission directly probes the radiative behavior of cooling gas in the central 10 kpc of the cluster, which X-ray telescopes cannot yet spatially resolve. The (Fe X) detection in PKS 0745-191 cannot be explained by any plausible photoionization or gas heating model for cluster gas, except for the standard cooling gas picture. The (Fe X) luminosity measures (1) the cooling rate of gas in the centers of these clusters, and (2) the amount of photoionizing UV radiation that is generated by cooling gas. Such UV radiation can photoionize and heat the luminous, cool (approximately 104 K) filaments. The level of the detection and upper limits reported here suggest that a fraction (approximately less than or equal to 30%) of the rate of mass cooling observed by X-ray telescopes over extents of 100 kpc occurs in the central 10 kpc, and thus within the central cD galaxy itself. In addition, the (Fe X) strength is consistent with models for photoionizing the 104 K nebular filaments by cooling hot gas (e.g., self-ionized cooling filaments, turbulent mixing layers, or stripped interstellar medium photoionized by cooling gas), although upper limits a few times more sensitive than the limits presented here would challenge the simplest of these models.
Donahue Megan
Stocke John T.
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