Metallic Absorbers and the Evolution of Galaxy Haloes and the Metagalactic Ionizing Background
msra(1998)
摘要
An extremely careful separation of the weak metal-line systems relating to
the Lyman forest absorbers into individual ``single-phase ionization''
components with accurate parameters has yielded a large sample in the wide
redshift range 1.9 < z < 4.4. The systems typically span several hundred km/s
and within each the components show a strong coherence in their ionization
properties. No sudden evolution is found in the column density ratio N(Si
IV)/N(C IV), contrary to previous indication of a large change near z = 3,
although there is an apparent rise below z~2.2 and above z~3.8. A smooth not
sudden spectral evolution is reflected in the z distribution of N(N V)/N(C IV).
Comparisons of N(Si IV)/N(C IV) vs N(C II)/N(C IV) from the observations with
CLOUDY derived values using several model ionizing spectra show the general
dominance of a QSO ionizing background at the lower redshifts while an
additional strong and eventually dominating stellar contribution is required
progressively to higher redshifts.
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