The density, the cosmic microwave background, and the proton-to-electron mass ratio in a cloud at redshift 0.9
Artikel i vetenskaplig tidskrift, 2009

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≤ftarrow6 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, T_CMB = 5.14 K. However, individually, there is a surprisingly large scatter which far surpasses expected uncertainties. A comparison of CS J =1 ≤ftarrow0 and 4≤ftarrow3 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 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 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 Δ V < 1 km s-1, corresponding to Δμ/μ< 1.0× 10-6.

galaxies: ISM

gravitational lensing

radio lines: galaxies

galaxies: abundances

elementary particles

galaxies: individual: PKS 1830-211


C. Henkel

Max Planck-institutet

K.M. Menten

Max Planck-institutet

M.T. Murphy

Swinburne University of Technology

N. Jethava

National Institute of Standards and Technology

V. V. Flambaum

University of New South Wales (UNSW) Australia

J. A. Braatz

National Radio Astronomy Observatory

Sebastien Muller

Chalmers, Institutionen för radio- och rymdvetenskap

J. Ott


National Radio Astronomy Observatory

R. Q. Mao

Purple Mountain Observatory Chinese Academy of Sciences

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 500 725-


Astronomi, astrofysik och kosmologi