Metal-Line Systems and the Intergalactic Ionizing Field

Details Metal-Line Systems and the Intergalactic Ionizing Field Metal-Line Systems and the Intergalactic Ionizing Field

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.3302g&link_type=abstract

American Astronomical Society, 181st AAS Meeting, #33.02; Bulletin of the American Astronomical Society, Vol. 24, p.1171

Astronomy and Astrophysics

Astronomy

Scientific paper

At high spectral resolution, strong quasar absorption-line systems break up into a multiplicity of velocity components. Examples are shown of echelle spectra at 20 km/s resolution, in which there are a few strong components with neutrals, first and some second ions reminiscent of galactic H II regions. High-velocity clouds in these systems can show strong high-ionization species, with weak or absent corresponding lower ions. A range of formally fitted thermal widths are found, with isolated components as cool as 6000 K. A scenario is proposed in which both the low and high ionization systems are ionized by local sources rather than by a diffuse intergalactic radiation field. The idea is based on the computed EUV flux from the Galactic disk escaping into the halo. Stellar remnants probably provide the dominant contribution, with hot subdwarfs being a major component. The emergent spectral shape is remarkably similar to that postulated for the diffuse UV background from quasars, but substantially exceeds in intensity the extragalactic contribution in the near halo and would dominate the ionization state of halo clouds in such a system. The evolution of the properties and number density of absorbing clouds seen on quasar sightlines would therefore depend on the evolution of star formation local to the clouds as well as their own dynamical history.

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