Journal Article

Properties of warm absorbers in active galaxies: a systematic stability curve analysis

Susmita Chakravorty, Ajit K. Kembhavi, Martin Elvis and Gary Ferland

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 393, issue 1, pages 83-98
Published in print February 2009 | ISSN: 0035-8711
Published online January 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.14249.x
Properties of warm absorbers in active galaxies: a systematic stability curve analysis

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Signatures of warm absorbers are seen in soft X-ray spectra of about half of all type 1 Seyfert galaxies observed and in some quasars and blazars. We use the thermal equilibrium curve to study the influence of the shape of the ionizing continuum, density and the chemical composition of the absorbing gas on the existence and nature of the warm absorbers. We describe circumstances in which a stable warm absorber can exist as a multiphase medium or one with continuous variation in pressure. In particular, we find the following results: (i) the warm absorber exists only if the spectral index of the X-ray power-law ionizing continuum α > 0.2 and has a multiphase nature if α∼ 0.8, which interestingly is the spectral index for most of the observed type 1 Seyfert galaxies; (ii) thermal and ionization states of highly dense warm absorbers are sensitive to their density if the ionizing continuum is sufficiently soft, i.e. dominated by the ultraviolet; (iii) absorbing gas with super-solar metallicity is more likely to have a multiphase nature and (iv) the nature of the warm absorber is significantly influenced by the absence of iron and associated elements which are produced in the later stages of star formation history in Type Ia supernovae.

Keywords: ISM: abundances; galaxies: active; quasars: absorption lines; galaxies: Seyfert; X-rays: ISM

Journal Article.  13744 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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