First measurement of Mg isotope abundances at high redshifts and accurate estimate of Δα/α
Abstract
Aims: Abundances of the Mg isotopes 24Mg, 25Mg, and 26Mg can be used to test models of chemical enrichment of interstellar/intergalactic gas clouds. Additionally, because the position of the Mg ii λλ2796,2803 Å lines is often taken as a reference in computations of possible changes of the fine-structure constant α, it should be clarified to which extent these lines are affected by isotopic shifts.
Methods: We use a high-resolution spectrum (pixel size ≈ 1.3 km s-1) of the quasar
Results: In the system at zabs = 0.45, which is probably a fragment of the outflow caused by SN Ia explosion of high-metallicity white dwarf(s), we measured velocity shifts of Mg ii and Mg i lines with respect to other lines (Fe i, Fe ii, Ca i, Ca ii): ΔVMg II = -0.44 ± 0.05 km s-1, and ΔVMg I = -0.17 ± 0.17 km s-1. This translates into the isotopic ratio 24Mg:25Mg:26Mg = (19 ± 11):(22 ± 13):(59 ± 6) with a strong relative overabundance of heavy Mg isotopes, (25Mg+26Mg)/24Mg = 4, as compared to the solar ratio 24Mg:25Mg:26Mg = 79:10:11, and (25Mg+26Mg)/24Mg = 0.3. In the systems at zabs = 1.58 and zabs = 1.65 enriched by AGB-stars we find only upper limits on the content of heavy Mg isotopes (25Mg+ 26Mg)/24Mg ≲ 0.7 and (25Mg+ 26Mg)/24Mg ≲ 2.6, respectively. At zabs = 1.58, we also put a strong constraint on a putative variation of α: Δα/α = (-1.5 ± 2.6) × 10-6, which is one of the most stringent limits obtained from optical spectra of QSOs. We reveal that the wavelength calibration in the range above 7500 Å is subject to systematic wavelength-dependent drifts.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- May 2011
- DOI:
- 10.1051/0004-6361/201016194
- arXiv:
- arXiv:1102.2967
- Bibcode:
- 2011A&A...529A..28A
- Keywords:
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- line: profiles;
- methods: data analysis;
- galaxies: abundances;
- quasars: absorption lines;
- quasars: individual:HE0001-2340;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 20 pages, 13 figures, 7 tables. Accepted for publication in Astronomy and Astrophysics