出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We present a detailed analysis of chemical abundances in a damped Lyman
absorber at zabs =
2.618 toward the quasar Q0913+072 (zem = 2.785) using public UVES/VLT high resolution data.
The total hydrogen column density is logN(HI)=20.39. We find a very low overall metallicity
where the detected species include HI, OI, C II, Fe II, Al II, and Si II. Upper limits can be given for
Fe III, Si III, Al III, Mg II, S II, S III, NI, NII, NIII, CIV, Si IV, and molecular hydrogen. The system
is very deficient in carbon ([C/H]=−2.91), nitrogen ([N/H] −3.69) and oxygen ([O/H]=−2.47),
representing one of the few DLA systems where the CNO-elements can be measured accurately.
Direct measurements of OI and upper limits for NI, as well as NII and NIII, imply [N/O]. −1.22.
Thus, we are looking at a chemically juvenile DLA system, possibly only enriched by the first
generation of stars. Plotting the [N/Si] versus [N/H] ratios supports the idea of a common nitrogen
ground floor for DLAs at [N/Si] −1.5, indicating a primary nitrogen production by Pop III stars,
due to the explosion as Type II Supernovae.
