Henkel, C. and Menten, K. M. and Murphy, M. T. and Jethava, N. and Flambaum, V. V. and Braatz, J. A. and Muller, S. and Ott, J. and Mao, R. Q. (2009) The density, the cosmic microwave background and the proton-to-electron mass ratio in a cloud at redshift 0.9. Astronomy and Astrophysics, 500 (2). pp. 725-734. ISSN 0004-6361 http://resolver.caltech.edu/CaltechAUTHORS:20090828-142109514
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Based on measurements with the Effelsberg 100-m telescope, a multi-line study of molecular species is presented toward the gravitational lens system PKS 1830–211, which is by far the best known target to study dense cool gas in absorption at intermediate redshift. Determining average radial velocities and performing Large Velocity Gradient radiative transfer calculations, the aims of this study are (1) to determine the density of the gas, (2) to constrain the temperature of the cosmic microwave background (CMB), and (3) to evaluate the proton-to-electron mass ratio at redshift z ∼ 0.89. Analyzing data from six rotational HC_3N transitions (this includes the J = 7 ← 6 line, which is likely detected for the first time in the interstellar medium) we obtain n(H_2) ∼ 2600 cm^(−3) for the gas density of the south-western absorption component, assuming a background source covering factor, which is independent of frequency. With a possibly more realistic frequency dependence proportional to ν^(0.5) (the maximal exponent permitted by observational boundary conditions), n(H2) ∼ 1700 cm^(−3). Again toward the south-western source, excitation temperatures of molecular species with optically thin lines and higher rotational constants are, on average, consistent with the expected temperature of the cosmic microwave background, T^(CMB) = 5.14 K. However, individually, there is a surprisingly large scatter which far surpasses expected uncertainties. A comparison of CS J = 1 ← 0 and 4 ← 3 optical depths toward the weaker north-western absorption component results in T_(ex) = 11 K and a 1-σ error of 3 K. For the main component, a comparison of velocities determined from ten optically thin NH_3 inversion lines with those from five optically thin rotational transitions of HC_3N, observed at similar frequencies, constrains potential variations of the proton-to-electron mass ratio μ to Δμ/μ < 1.4 × 10^(−6) with 3-σ confidence. Also including optically thin rotational lines from other molecular species, it is emphasized that systematic errors are ΔV < 1 kms^(−1), corresponding to Δμ/μ < 1.0 × 10^(−6).
|Additional Information:||© ESO 2009. Received 4 December 2008. Accepted 26 March 2009. It is a pleasure to thank J. N. Chengalur, S. Thorwirth, and C. M. Walmsley for useful discussions and critical reading of the manuscript. M. T. M. thanks the Australian Research Council for a QEII Fellowship (DP0877998). We used NASA’s Astrophysical Data System (ADS), the Cologne Database for Molecular Spectroscopy (CDMS; seeMüller et al. 2001, 2005), the JPL Catalog (http://spec.jpl.nasa.gov/ftp/pub/catalog/catform. html), and the line lists of Lovas (1992) and Coudert & Roueff (2006).|
|Subject Keywords:||galaxies: abundances galaxies: ISM galaxies: individual: PKS 1830-211 gravitational lensing radio lines: galaxies elementary particles|
|Official Citation:||The density, the cosmic microwave background, and the proton-to-electron mass ratio in a cloud at redshift 0.9 C. Henkel, K. M. Menten, M. T. Murphy, N. Jethava, V. V. Flambaum, J. A. Braatz, S. Muller, J. Ott and R. Q. Mao A&A 500 (2) 725-734 (2009) DOI: 10.1051/0004-6361/200811475|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||03 Sep 2009 18:09|
|Last Modified:||26 Dec 2012 11:16|
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