Constraining the variation of fundamental constants at z ∼ 1.3 using 21-cm absorbers

Abstract

We present high‐resolution optical spectra obtained with the Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope and 21‐cm absorption spectra obtained with the Giant Metrewave Radio Telescope and the Green Bank Telescope of five quasars along the line of sight of which 21‐cm absorption systems at 1.17 < z < 1.56 have been detected previously. We also present milliarcsecond‐scale radio images of these quasars obtained with the Very Large Baseline Array. We use the data on four of these systems to constrain the time variation of x ≡ gpα2/μ, where gp is the proton gyromagnetic factor, α is the fine structure constant and μ is the proton‐to‐electron mass ratio. We carefully evaluate the systematic uncertainties in redshift measurements using cross‐correlation analysis and repeated Voigt profile fitting. In both cases, we also confirm our results by analysing optical spectra obtained with the Keck telescope. We find the weighted and the simple means of Δx/x to be, respectively, −(0.1 ± 1.3) × 10−6 and (0.0 ± 1.5) × 10−6 at the mean redshift of 〈z〉 = 1.36 corresponding to a look‐back time of ∼9 Gyr. This is the most stringent constraint ever obtained on Δx/x. If we only use the two systems towards quasars unresolved at milliarcsecond scales, we get the simple mean of Δx/x = +(0.2 ± 1.6) × 10−6. Assuming the constancy of other constants, we get Δα/α = (0.0 ± 0.8) × 10−6, which is a factor of 2 better than the best constraints obtained so far using the many‐multiplet method. On the other hand, assuming that α and gp have not varied we derive Δμ/μ = (0.0 ± 1.5) × 10−6 which is again the best limit ever obtained on the variation of μ over this redshift range. Using independent constraints on Δα/α at z < 1.8 and Δμ/μ at z ∼ 0.7 available in the literature, we get Δgp/gp ≤ 3.5 × 10−6(1σ).

Microwave and submillimeter molecular transitions and their dependence on fundamental constants

“…Less stringent constraints at a percent level have been obtained from the cosmic microwave background (CMB) at z ∼ 10 3 [16][17][18] and big bang nucleosynthesis (BBN) at z ∼ 10 10 [19,20]. We note that space and/or time dependence of α based on optical spectra of quasars and discussed in the literature [21, and references therein] is still controversial and probably caused by systematic effects since independent radio-astronomical observations, which are more sensitive, show only null results for both α/α and μ/μ [22,23]. Surprisingly, it looks as if the Einstein heuristic principle of local position invariance (LPI) -the outcome of any local non-gravitational experiment is independent of where and when in the universe it is performed -is valid all over the universe, i.e., at the level of ∼10 −6 neither α no μ deviate from their terrestrial values for the passed 10 10 yr.…”

“…This may seem strange as the fine structure is significantly reduced by the Renner-Teller mixing: the finestructure parameter is 29 cm −1 and the splitting between 1/2 and 3/2 is only 13.9 cm −1 . According to (22) the mixing reduces the splitting. However, this effect de- Table 3 and for parameters A eff and E defined by (22) and (29) respectively.…”

“…According to (22) the mixing reduces the splitting. However, this effect de- Table 3 and for parameters A eff and E defined by (22) and (29) respectively. Frequencies are in cm −1 .…”

Fundamental constants and high‐resolution spectroscopy

“…Alternatively one can place good constraints using 21-cm absorption in conjunction with metal lines and assuming all other constants have not changed. Rahmani et al (2012) have obtained ∆µ/µ= (0.0 ± 1.50) × 10 −6 using a well selected sample of four 21-cm absorbers at z abs ∼1.3. Srianand et al (2010) have obtained ∆µ/µ= (−1.7 ± 1.7) × 10 −6 at z ∼3.17 using the 21-cm absorber towards J1337+3152.…”

Molecular hydrogen in thezabs = 2.66 damped Lyman-αabsorber towards Q J 0643−5041

“…Bagdonaite et al (2013) obtained the strongest constraint till date of ∆µ/µ = (0.0 ± 1.0) × 10 −7 at z = 0.89 using methanol transitions. Tight constraints have been obtained using 21-cm absorption in conjunction with UV metal lines and assuming all other constants have not changed: Rahmani et al (2012) derived ∆µ/µ = (0.0 ± 1.50) × 10 −6 , using a sample of four 21 cm absorbers at z < 1.3, and Srianand et al (2010) measured ∆µ/µ = (1.7 ± 1.7) × 10 −6 at z = 3.17, using the 21-cm absorber towards J1337+3152.…”