Boekbesprekingen

Lick optical spectra of quasar HS 1946+7658 at 10 kilometers per second resolution Lyman-alpha forest and metal absorption systems

“…The abundance ratios for C, O, Al and Si are all within a factor of two of solar, which suggests that there is not much depletion onto dust grains. We do not see an excess of O with respect to C, as was reported in a few absorption systems (Vogel & Reimers 1993).…”

“…First, we believe that the gas abundances which we measure are close to the total abundances, because the ratio of Aluminum to other elements is near cosmic, and Al is a refractory element which depletes very readily, like Chromium, in the interstellar medium. Second, we do not see the enhancement of O with respect to C of [O/C] ≃ 0.5 − 0.9 reported in three partial Lyman limit systems by Reimers et al 1992 andReimers 1993; we measure [O/C] = −0.06 for observed ions and [O/C] ≃ 0.2 after ionization corrections, which is consistent with solar abundances. We see C II * (λ1335) offset by 15 km s −1 with respect to C II(λ1334), presumably because the gas density varies from 2 -8 cm −3 with changing velocity in the DLA system.…”

“…In the ISM [Al/X] < −0.5 (Spitzer 1978;Jenkins 1987). In this DLA system we do not see the enhancement of O with respect to C claimed by Vogel & Reimers (1993); we measure [O/C]=-0.06 for observed ions and [O/C]=0.2 after ionization correction.…”

“…Early work on LLSs abundances includes Steidel (1990), who found typical gas phase metal abundances in eight LLSs at z abs ≈ 3 of [M/H] ∼ −2.5, and Sargent et al (1990) who reported [M/H] ≤ −2.3 in one partial LLS at z abs =2.9676 toward QSO PKS 2126−158. In an important set of papers, Reimers et al (1992) and Vogel & Reimers (1993) showed that far UV lines allow easy estimation of the ionization and hence abundances in partial LLS. For three systems at 1.8 ≤ z abs ≤ 2.4 they find abundances [C/H] = −1.7, −1.9, −2.3, and they see that both O and N are over abundant with respect to C: [O/C] = 0.6, 0.8, 0.9, and [N/C] = 0.4, 0.8, 0.8.…”