SIMBAD references

Molecular hydrogen (H₂) absorption in the damped Lyman α system at z_abs = 2.34 towards quasar SDSS J123437.55+075843.3 is analysed in order to derive'a constraint on a possible temporal variation of the proton-to-electron mass ratio, µ, over cosmological time-scales. Some 106 H₂ and deuterated molecular hydrogen (HD) transitions, covering the range 3290-3726 Å, are analysed with a comprehensive fitting technique, allowing for the inclusion of overlapping lines associated with hydrogen molecules, the atomic hydrogen lines in the Lyman α forest as well as metal lines. The absorption model, based on the most recent and accurate rest wavelength for H₂ and HD transitions, delivers a value of Δµ/µ = (19 ± 9_stat ± 5_syst) x 10^–6. An attempt to correct the spectrum for possible long-range wavelength distortions is made, and the uncertainty on the distortion correction is included in the total systematic uncertainty. The present result is an order of magnitude more stringent than a previous measurement from the analysis of this absorption system, based on a line-by-line comparison of only 12 prominent and isolated H₂ absorption lines. This is consistent with other measurements of Δµ/µ from 11 other absorption systems in showing a null variation of the proton-to-electron mass ratio over a look-back time of 11 Gyr.