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Register a new userStringent constraints on fundamental constant evolution using conjugate 18 cm satellite OH lines
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We have used the Arecibo Telescope to carry out one of the deepest-ever integrations in radio astronomy, targetting the redshifted conjugate satellite OH 18 cm lines at $z approx 0.247$ towards PKS1413+135. The satellite OH 1720 and 1612 MHz lines are respectively in emission and absorption, with exactly the same line shapes due to population inversion in the OH ground state levels. Since the 1720 and 1612 MHz line rest frequencies have different dependences on the fine structure constant $alpha$ and the proton-electron mass ratio $mu$, a comparison between their measured redshifts allows one to probe changes in $alpha$ and $mu$ with cosmological time. In the case of conjugate satellite OH 18 cm lines, the predicted perfect cancellation of the sum of the line optical depths provides a strong test for the presence of systematic effects that might limit their use in probing fundamental constant evolution. A non-parametric analysis of our new Arecibo data yields $left[Delta X/X right] = (+0.97 pm 1.52) times 10^{-6}$, where $X equiv mu alpha^2$. Combining this with our earlier results from the Arecibo Telescope and the Westerbork Synthesis Radio Telescope, we obtain $left[Delta X/X right] = (-1.0 pm 1.3) times 10^{-6}$, consistent with no changes in the quantity $mu alpha^2$ over the last 2.9~Gyr. This is the most stringent present constraint on fractional changes in $mu alpha^2$ from astronomical spectroscopy, and with no evidence for systematic effects.
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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.
We report the results of a full-Stokes survey of all four 18 cm OH lines in 77 OH megamasers (OHMs) using the Arecibo Observatory. This is the first survey of OHMs that included observations of the OH satellite lines; only 4 of the 77 OHMs have existing satellite line observations in the literature. In 5 sources, satellite line emission is detected, with 3 of the 5 sources re-detections of previously published sources. The 2 sources with new detections of satellite line emission are IRAS F10173+0829, which was detected at 1720 MHz, and IRAS F15107+0724, for which both the 1612 MHz and 1720 MHz lines were detected. In IRAS F15107+0724, the satellite lines are partially conjugate, as 1720 MHz absorption and 1612 MHz emission have the same structure at some velocities within the source, along with additional broader 1612 MHz emission. This is the first observed example of conjugate satellite lines in an OHM. In the remaining sources, no satellite line emission is observed. The detections and upper limits are generally consistent with models of OHM emission in which all of the 18 cm OH lines have the same excitation temperature. There is no evidence for a significant population of strong satellite line emitters among OHMs.
We present the serendipitous detection of the two main OH maser lines at 1667 and 1665 MHz associated with IRAS 10597+5926 at z = 0.19612 in the untargeted Apertif Wide-area Extragalactic Survey (AWES), and the subsequent measurement of the OH 1612 MHz satellite line in the same source. With a total OH luminosity of log(L/L_Sun) = 3.90 +/- 0.03, IRAS 10597+5926 is the fourth brightest OH megamaser (OHM) known. We measure a lower limit for the 1667/1612 ratio of R_1612 > 45.9 which is the highest limiting ratio measured for the 1612 MHz OH satellite line to date. OH satellite line measurements provide a potentially valuable constraint by which to compare detailed models of OH maser pumping mechanisms. Optical imaging shows the galaxy is likely a late-stage merger. Based on published infrared and far ultraviolet fluxes, we find that the galaxy is an ultra luminous infrared galaxy (ULIRG) with log(L_TIR/L_Sun) = 12.24, undergoing a star burst with an estimated star formation rate of 179 +/- 40 M_Sun/yr. These host galaxy properties are consistent with the physical conditions responsible for very bright OHM emission. Finally, we provide an update on the predicted number of OH masers that may be found in AWES, and estimate the total number of OH masers that will be detected in each of the individual main and satellite OH 18 cm lines.
We have detected the two 18cm OH satellite lines from the $z sim 0.247$ source PKS1413+135, the 1720 MHz line in emission and the 1612 MHz line in absorption. The 1720 MHz luminosity is $L_{rm OH} sim 354 L_odot$, more than an order of magnitude larger than that of any other known 1720 MHz maser. The profiles of the two satellite lines are conjugate, implying that they arise in the same gas. This allows us to test for any changes in the values of fundamental constants, without being affected by systematic uncertainties arising from relative motions between the gas clouds in which the different lines arise. Our data constrain changes in $G equiv g_p [alpha^2/y]^{1.849}$, where $ y equiv m_e/m_p$; we find $Delta G/G = 2.2 pm 3.8 times 10^{-5}$, consistent with no changes in $alpha$, $g_p$ and $y$.
We have detected narrow HI 21cm and CI absorption at $z sim 1.4 - 1.6$ towards Q0458$-$020 and Q2337$-$011, and use these lines to test for possible changes in the fine structure constant $alpha$, the proton-electron mass ratio $mu$, and the proton gyromagnetic 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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