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تسجيل مستخدم جديدProbing fundamental constant evolution with redshifted conjugate-satellite OH lines
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Nissim Kanekar
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We report Westerbork Synthesis Radio Telescope and Arecibo Telescope observations of the redshifted satellite OH-18cm lines at $z sim 0.247$ towards PKS1413+135. The conjugate nature of these lines, with one line in emission and the other in absorption, but with the same shape, implies that the lines arise in the same gas. The satellite OH-18cm line frequencies also have different dependences on the fine structure constant $alpha$, the proton-electron mass ratio $mu = m_p/m_e$, and the proton gyromagnetic ratio $g_p$. Comparisons between the satellite line redshifts in conjugate systems can hence be used to probe changes in $alpha$, $mu$, and $g_p$, with few systematic effects. The technique yields the expected null result when applied to Cen.A, a nearby conjugate satellite system. For the $z sim 0.247$ system towards PKS1413+135, we find, on combining results from the two telescopes, that $[Delta G/G] = (-1.18 pm 0.46) times 10^{-5}$ (weighted mean), where $G = g_p [mu alpha^2]^{1.85}$; this is tentative evidence (with $2.6 sigma$ significance, or at 99.1% confidence) for a smaller value of $alpha$, $mu$, and/or $g_p$ at z~0.247, i.e. at a lookback time of ~2.9 Gyrs. If we assume that the dominant change is in $alpha$, this implies $[Delta alpha /alpha ] = (-3.1 pm 1.2) times 10^{-6}$. We find no evidence that the observed offset might be produced by systematic effects, either due to observational or analysis procedures, or local conditions in the molecular cloud.
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yromagnetic ratio $g_p$. A comparison between the HI 21cm and CI line redshifts yields $Delta X/X = [+6.8 pm 1.0] times 10^{-6}$ over $0 < <z> le 1.46$, where $X = g_p alpha^2/mu$, and the errors are purely statistical, from the gaussian fits. The simple line profiles and the high sensitivity of the spectra imply that statistical errors in this comparison are an order of magnitude lower than in previous studies. Further, the CI lines arise in cold neutral gas that also gives rise to HI 21cm absorption, and both background quasars are core-dominated, reducing the likelihood of systematic errors due to local velocity offsets between the hyperfine and resonance lines. The dominant source of systematic error lies in the absolute wavelength calibration of the optical spectra, which appears uncertain to $sim 2$ km/s, yielding a maximum error in $Delta X/X$ of $sim 6.7 times 10^{-6}$. Including this, we obtain $Delta X/X = [+6.8 pm 1.0 (statistical) pm 6.7 (max. systematic)] times 10^{-6}$ over $0 < <z> le 1.46$. Using literature constraints on $Delta mu/mu$, this is inconsistent with claims of a smaller value of $alpha$ from the many-multiplet method, unless fractional changes in $g_p$ are larger than those in $alpha$ and $mu$.
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