The Zabs approximately Zem 2 QSO absorption line systems: evidence for abundances in excess of solar

Details The Zabs approximately Zem 2 QSO absorption line systems: evidence for abundances in excess of solar The Zabs approximately Zem 2 QSO absorption line systems: evidence for abundances in excess of solar

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...291...29p&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 291, no. 1, p. 29-56

Astronomy and Astrophysics

Astrophysics

110

Absorption Spectra, Abundance, Emission Spectra, Interstellar Matter, Metallicity, Quasars, Carbon, Photoionization, Red Shift, Spectral Resolution

Scientific paper

We present high spectral resolution (R approximately 15000) and high signal to noise ratio (20-50) of two Zem approximately 2 quasars PKS 0424-131 and Q 0450-131 in the wavelength range 370-510 nm. We detect in total 16 C IV systems with C IV lambda 1548 rest equivalent width 0.03 less than wr less than 10.6 A. The number of such systems per unit redshift is N approximately 7.7 for z in the range 1.4-2, out of which 3.1 have wr greater than 0.15 A. This suggest that the number of C IV systems is dominated by weak lines (wr less than 0.15 A) and is comparable to the number of Ly alpha clouds with N(HI) greater than 1016/sq cm. Two intervening systems are of particular interest. The strong zabs approximately 1.5615 CIV system in Q 0450-131 splits into components spread over 1030 km/s. The system is a member of the distinct population of CIV systems exhibiting large velocity spread and small equilvalent width, it is of high excitation with weak Si II absorption detected only in one component and no associated Al III absorption. The Zabs = 2.033 system in PKS 0424-131 has a strong Si III and neither Si IV nor C IV absorption. We argue that the line of sight passes through a H II region of low carbon (0.04 solar abundance) but enhanced oxygen (by a factor of five) abundances and ionized by a black body type spectrum with temperature 35,000 K. We are able to derive abundances in six Z(abs) approximately Zem systems since for each of them well detached and weak components are observed in which column densities of H I, O I, C II, C IV, N V, S II, S III and Si IV can be evaluated. The systems are highly ionized and have N(H I) less than 1015.4/sq. cm. Using detailed photoionization models we find in all of these systems abundances close to or in excess of solar values. This is in sharp contrast with the abundances found in intervening Lyman limit (0.01-0.1 solar abundance) or damped (approximately 0.1 solar abundance with large scatter) systems. The overabundances are found in systems with velocity separation relative to the emission redshift of the quasar as large as 13,000 km/s.

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