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The Iron Discrepancy in Elliptical Galaxies afterASCA
Author(s) -
N. Arimoto,
Kyoko Matsushita,
Yuhri Ishimaru,
Takaya Ohashi,
A. Renzini
Publication year - 1997
Publication title -
the astrophysical journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.376
H-Index - 489
eISSN - 1538-4357
pISSN - 0004-637X
DOI - 10.1086/303684
Subject(s) - physics , astrophysics , supernova , galaxy , elliptical galaxy , chemical evolution , interstellar medium , spectral line , intracluster medium , observatory , astronomy , galaxy cluster
We present estimates for the iron content of the stellar and diffusedcomponents of elliptical galaxies, as derived respectively from integratedoptical spectra and from ASCA X-ray observations. A macroscopic discrepancyemerges between the expected iron abundances in the hot interstellar medium(ISM) and what is indicated by the X-ray observations, especially whenallowance is made for the current iron enrichment by Type Ia supernovae. Thisstrong discrepancy, that in some extreme instances may be as large as a factorof $\sim 20$, calls into question our current understanding of supernovaenrichment and chemical evolution of galaxies. We discuss several astrophysicalimplications of the inferred low iron abundances in the ISM, including thechemical evolution of galaxies and cluster of galaxies, the evolution of gasflows in ellipticals, and the heating of the intracluster medium. Some of theconsequences appear hard to accept, and in the attempt to avoid some of thesedifficulties we explore ways of hiding or diluting iron in the ISM ofellipticals. None of these possibilities appears astrophysically plausible, andwe alternatively rise the question of the reliability of iron-L linediagonostic tools. Various thin plasma emission models are shown to give ironabundances that may differ significantly, especially at low temperatures ($kT\lsim 1$ keV). From a collection of ASCA and other X-ray observatory data, itis shown that current thin plasma codes tend to give very low iron abundanceswhen the temperature of the objects is below $\sim 1$ keV. We conclude that --besides rethinking the chemical evolution of galaxies -- one should alsoconsider the possibility that existing thin plasma models may incorporateinaccurate atomic physics for the ions responsible for the iron-L complex.Comment: 39 pages, TeX file, 5 figures, Accepted for publication in the Ap

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