Nonisothermal X-Ray--emitting Gas in Clusters of Galaxies

Abstract

view Abstract Citations (20) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Nonisothermal X-Ray--emitting Gas in Clusters of Galaxies Henriksen, Mark J. ; White, Raymond E., III Abstract We have analyzed X-ray spectra from six galaxy clusters which contain cooling flows: A85, A478, A1795, A2142, A2147, and A2199. The X-ray spectra were taken with the HEAO 1 A-2 Medium and High Energy Detectors and the Einstein Solid State Spectrometer. For each cluster, we simultaneously fit the spectra from these three detectors with models incorporating one or more emission components comprised of either thermal or cooling flow models. Five of the clusters (all but A2142) are better fitted by a multicomponent model (a cooling flow plus one or two thermal components or a two thermal component model) than by isothermal models. In four of the clusters (A85, A1795, A2147, and A2199), we find evidence for cool gas outside of the canonical cooling flow region. These latter four clusters can be characterized by three temperature components: a temperature inversion in the central region, a hotter region with an emission-weighted temperature which is higher than that of an isothermal model fitted to the entire cluster, and a cooler region with an emission- weighted temperature of ~1 keV. The cool component outside the cooling flow region has a large minimum emission measure which we attribute, in part, to diffuse cool gas in the outer cluster atmosphere. If at least some of the cool exterior gas is virialized, this would imply a radially decreasing temperature profile. Together with the density profiles we have found, this leads to a baryon fraction in gas which increases with radius and is larger than that for an isothermal cluster atmosphere. Consequently, if clusters of galaxies trace the mass distribution in the universe, the gas mass fraction we have calculated for an isothermal gas (which is ~15%) together with the nominal galaxy contribution (~5%) gives a baryon fraction of ~20%. Using the upper limit to the baryon density derived from big bang nucleosynthesis gives a firm upper limit for {OMEGA} (~0.5). The isothermal gas baryon fractions calculated here are lower than earlier estimates due to our utilizing a three-component model together with data sets which allow us to remove the influence of the cooling flow on the integrated spectrum, as well as possible contaminating emission from unvirialized gas or discrete sources. Publication: The Astrophysical Journal Pub Date: July 1996 DOI: 10.1086/177437 arXiv: arXiv:astro-ph/9604018 Bibcode: 1996ApJ...465..515H Keywords: COSMOLOGY: DARK MATTER; GALAXIES: CLUSTERS: GENERAL; GALAXIES: COOLING FLOWS; X-RAYS: GALAXIES; Astrophysics E-Print: gzipped tar file of 26 PostScript pages, including 2 figures, 7 tables. Also available at http://www.astr.ua.edu/preprints/white/INDEX_READ_ME_1st.html full text sources arXiv | ADS | data products SIMBAD (9) NED (6)