First measurement of Mg isotope abundances at high redshifts and accurate estimate of Δα/α

Abstract

Aims. Abundances of the Mg isotopes 24 Mg, 25 Mg, and 26 Mg 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 HE0001-2340 observed with the UVES/VLT to measure Mg isotope abundances in the intervening absorption-line systems at high redshifts. Line profiles are prepared taking into account possible shifts between the individual exposures. In the line-fitting procedure, the lines of each ion are treated independently. Because of the unique composition of the selected systems -the presence of several transitions of the same ion -we can test the local accuracy of the wavelength scale calibration, which is the main source of errors in the sub-pixel line position measurements. Results. In the system at z abs = 0.45, which is probably a fragment of the outflow caused by SN Ia explosion of highmetallicity white dwarf(s), we measured velocity shifts of Mg ii and In the systems at z abs = 1.58 and z abs = 1.65 enriched by AGB-stars we find only upper limits on the content of heavy Mg isotopes ( 25 Mg+ 26 Mg)/ 24 Mg < ∼ 0.7 and ( 25 Mg+ 26 Mg)/ 24 Mg < ∼ 2.6, respectively. At z abs = 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.

The UVES Large Program for testing fundamental physics I. Bounds on a change inαtowards quasar HE 2217−2818

“…Three other studies of individual absorbers have claimed measurements with comparably small uncertainties. These are ∆α/α = −0.07 ± 1.8 ppm obtained from absorption at z abs = 1.15 towards the extremely bright quasar HE 0515−4414 (Molaro et al 2008b), ∆α/α = 5.4 ± 2.5 ppm from the system at z abs = 1.84 towards quasar Q 1101−264 (Levshakov et al 2006), and ∆α/α = −1.5 ± 2.6 ppm from the system at z abs = 1.58 towards HE 0001−2340 (Agafonova et al 2011). The first two were both obtained by comparing only Fe  lines with each other, while the last was derived through a comparison of Fe  and Si  transitions.…”

Molecules atz= 0.89

“…Interestingly, the magnesium isotopic ratios were derived from UV-spectroscopy for a z = 0.45 absorption line system (Agafonova et al 2011), and also suggest that there is a significant relative overabundance of heavy Mg isotopes. Silicon and sulfur (and magnesium) are both produced by massive stars.…”

An upper limit to the variation in the fundamental constants at redshiftz= 5.2

“…The lowest spectroscopic limits on α are |Δα/α| < 3 ppm at z = 0.77 obtained from radio observations (Kanekar et al 2012) and the same order of magnitude |Δα/α| < ∼ 3 ppm at z ∼ 2−3 derived from optical spectra of quasars (Agafonova et al 2011;Molaro et al 2008;Srianand et al 2007;Quast et al 2004). To complement these results, the measurements of Murphy et al (2003) claim detection of an α-variation in about 140 absorption systems from quasar spectra observed with the Keck telescope Δα/α = −5.4±1.2 ppm in the range 0.2 < z < 3.7.…”