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Title

The density, the cosmic microwave background, and the proton-to-electron mass ratio in a cloud at redshift 0.9

Author(s)

Henkel, Christian;  Menten, K. M.;  Murphy, M. T.;  Jethava, N.;  Flambaum, Victor V.;  Braatz, James A.;  Muller, Sebastien;  Ott, J.;  Mao, R. Q.

Abstract

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 HC3N transitions (this includes the J = 7 ← 6 line, which is likely detected for the first time in the interstellar medium) we obtain n(H2) ∼ 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 ν0.5 (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, TCMB = 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 Tex = 11 K and a 1-σ error of 3 K. For the main component, a comparison of velocities determined from ten optically thin NH3 inversion lines with those from five optically thin rotational transitions of HC3N, observed at similar frequencies, constrains potential variations of the proton-to-electron mass ratio μ to & 0916;μ/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.

Publication type

Journal article

Research centre

Swinburne University of Technology. Faculty of Information and Communication Technologies. Centre for Astrophysics and Supercomputing

Source

Astronomy & Astrophysics, Vol. 500, no. 2 (Jun 2009), pp. 725-734

Publication year

2009

FOR Code(s)

0201 Astronomical and Space Sciences

Keyword(s)

Einstein ring;  Fine-structure constant;  Galaxies radio lines;  Gravitational lens B0218+357;  Gravitational lensing;  ISM galaxies;  Molecular absorption;  Particles;  PKS 1830-211;  Radiation temperature

Publisher

EDP Sciences

ISSN

0004-6361

Publisher URL

http://dx.doi.org/10.1051/0004-6361/200811475

Copyright

Copyright © ESO 2009. Published version of the paper reproduced here in accordance with the copyright policy of the publisher.

Research Projects

Galaxy formation and femtosecond frequency combs, Australian Research Council grant number DP0877998

Full text

Peer reviewed