122 research outputs found

    Constraining the variation of fundamental constants using 18cm OH lines

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    We describe a new technique to estimate variations in the fundamental constants using 18cm OH absorption lines. This has the advantage that all lines arise in the same species, allowing a clean comparison between the measured redshifts. In conjunction with one additional transition (for example, an HCO+^+ line), it is possible to simultaneously measure changes in α\alpha, gpg_p and y≡me/mpy \equiv m_e/m_p. At present, only the 1665 MHz and 1667 MHz lines have been detected at cosmological distances; we use these line redshifts in conjunction with those of HI 21cm and mm-wave molecular absorption in a gravitational lens at z∼0.68z\sim 0.68 to constrain changes in the above three parameters over the redshift range 0<z≲0.680 < z \lesssim 0.68. While the constraints are relatively weak (≲\lesssim 1 part in 10310^3), this is the first simultaneous constraint on the variation of all three parameters. We also demonstrate that either one (or more) of α\alpha, gpg_p and yy must vary with cosmological time or there must be systematic velocity offsets between the OH, HCO+^+ and HI absorbing clouds.Comment: 5 pages, no figures. Accepted for publication in Phys. Rev. Let

    Molecular gas at intermediate redshifts

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    We present Giant Metrewave Radio Telescope (GMRT) observations of OH absorption in B3~1504+377 (z∼0.673z \sim 0.673) and PKS 1413+135 (z∼0.247z \sim 0.247). OH has now been detected in absorption towards four intermediate redshift systems, viz. the lensing galaxies towards B~0218+357 (z∼0.685z \sim 0.685; Kanekar et al. 2001) and 1830-211 (z∼0.886z \sim 0.886; Chengalur et al. 1999), in addition to the two systems listed above. All four systems also give rise to well studied millimetre wavelength molecular line absorption from a host of molecules, including HCO+^+. Comparing our OH data with these millimetre line transitions, we find that the linear correlation between NOHN_{\rm OH} and NHCO+N_{\rm HCO^+} found in molecular clouds in the Milky Way (Liszt & Lucas 1996) persists out to z∼1z \sim 1. It has been suggested (Liszt & Lucas 1999) that OH is a good tracer of H2{\rm H_2}, with NH2/NOH≈107N_{\rm H_2}/N_{\rm OH} \approx 10^7 under a variety of physical conditions. We use this relationship to estimate NH2N_{\rm H_2} in these absorbers. The estimated NH2N_{\rm H_2} is \ga 10^{22} in all four cases and substantially different from estimates based on CO observations.Comment: 4 pages, 3 figures. Accepted for publication in Astronomy and Astrophysics Letter

    Conjugate 18cm OH Satellite Lines at a Cosmological Distance

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    We have detected the two 18cm OH satellite lines from the z∼0.247z \sim 0.247 source PKS1413+135, the 1720 MHz line in emission and the 1612 MHz line in absorption. The 1720 MHz luminosity is LOH∼354L⊙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≡gp[α2/y]1.849G \equiv g_p [\alpha^2/y]^{1.849}, where y≡me/mp y \equiv m_e/m_p; we find ΔG/G=2.2±3.8×10−5\Delta G/G = 2.2 \pm 3.8 \times 10^{-5}, consistent with no changes in α\alpha, gpg_p and yy.Comment: 5 pages, 1 figure. Minor changes to match published versio

    The use of OH "main" lines to constrain the variation of fundamental constants

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    We describe a new technique to measure variations in the fundamental parameters α\alpha and y≡me/mpy \equiv m_e/m_p, using the sum of the frequencies of cm-wave OH ``main'' lines. The technique is ∼\sim three orders of magnitude more sensitive than that of Chengalur & Kanekar (2003), which utilised only the four 18cm OH lines. The increase in sensitivity stems from the use of OH ``main'' lines arising from different rotational states, instead of the frequency difference between lines from the same state. We also show that redshifts of the main OH 18cm and 6cm lines can be combined with the redshift of an HCO+^+ transition to measure any evolution in α\alpha and yy. Both 18cm main lines and a number of HCO+^+ lines have already been detected in absorption in four cosmologically distant systems; the detection of the main 6cm OH line in any of these systems would thus be sufficient to simultaneously constrain changes in α\alpha and yy between the absorption redshift and today.Comment: 5 pages, no figures. MNRAS (Letters), in pres

    FLAGCAL:A flagging and calibration package for radio interferometric data

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    We describe a flagging and calibration pipeline intended for making quick look images from GMRT data. The package identifies and flags corrupted visibilities, computes calibration solutions and interpolates these onto the target source. These flagged calibrated visibilities can be directly imaged using any standard imaging package. The pipeline is written in "C" with the most compute intensive algorithms being parallelized using OpenMP.Comment: 15 Pages, 6 figures, 2 Tables, Accepted for publication in the Experimental Astronomy Journa

    A search for HI 21cm absorption in strong MgII absorbers in the redshift desert

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    We report results from a deep search for redshifted HI 21cm absorption in 55 strong MgIIλ\lambda2796 absorbers (having W(MgII)>0.5A˚W (MgII) > 0.5 \AA) at intermediate redshifts, 0.58<zabs<1.700.58 < z_{\rm abs} < 1.70, with the Green Bank Telescope (GBT) and the Giant Metrewave Radio Telescope (GMRT). Nine detections of HI 21cm absorption were obtained, all at 1.17<zabs<1.681.17 < z_{\rm abs} < 1.68, including three systems reported earlier by Gupta et al. (2007). Absorption was not detected at >3σ> 3\sigma significance in 32 other MgII absorbers, with 26 of these providing strong upper limits to the HI 21cm optical depth, τ3σ<0.013\tau_{3\sigma} < 0.013 per ∼10\sim 10 km/s. For the latter 26 systems, the spin temperature TsT_s of the absorber must be >[800×f]> [800 \times f] K (where ff is the covering factor), if the HI column density is ≥2×1020\ge 2 \times 10^{20} cm−2^{-2}, i.e. if the absorber is a damped Lyman-α\alpha system (DLA). Data on the remaining 13 systems of the sample were affected by radio frequency interference and were hence not useful. Excluding "associated" systems (within 3000 km/s of the quasar redshift), the detection rate of HI 21cm absorption in strong MgII absorbers is x21,MgII(zˉ=1.1)=25−8+11x_{\rm 21,MgII} ({\bar z} = 1.1) = 25^{+11}_{-8}%, at a 3σ3\sigma optical depth sensitivity of ∼0.013\sim 0.013 per 10 km/s. Comparing the detection rates of HI 21cm and damped Lyman-α\alpha absorption in strong MgII absorber samples yields a detection rate of HI 21cm absorption in DLAs of x21,DLA(zˉ=1.1)=(73±27)x_{\rm 21,DLA} ({\bar z} = 1.1) = (73 \pm 27)%, consistent with the detection rate of HI 21cm absorption in low-zz DLAs. Since HI 21cm absorption arises in cold neutral gas, this indicates that most gas-rich galaxies contain significant fractions of cold HI by z∼1z \sim 1. (abridged)Comment: 18 pages, 56 figures, MNRAS (in press
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