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

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 HC 3 N 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(H 2 ) ∼ 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 3 N, 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 km s −1 , corresponding to Δμ/μ < 1.0 × 10 −6 .

The ortho-to-para ratio of H2Cl+: Quasi-classical trajectory calculations and new simulations in light of new observations

“…For the SW absorption, the physical conditions were constrained by Henkel et al (2008Henkel et al ( , 2009) using NH 3 and HC 3 N and by Muller et al (2013) using multi-transition observations of a set of various molecular species (CH 3 CN, SO, c−C 3 H 2 , HC 3 N, H 13 CO + , H 13 CN, HC 15 N, HNCO, and SiO). The absorbing gas has properties similar to Galactic diffuse to translucent clouds, with a kinetic temperature of ∼ 80 K and an H 2 volume density of the order of 10 3 cm −3 .…”

Fundamental constants and high‐resolution spectroscopy

“…The best reported constraints based on a single system being ∆µ/µ = +(0.3 ± 3.7) × 10 −6 reported by King et al (2011) towards Q 0528−250. Among the developments in the field since then we must signal a number of high precision measurements of ∆µ/µ both using UV lines (Malec et al 2010;van Weerdenburg et al 2011;Wendt & Molaro 2011b At z ≤ 1.0 a stringent constraint on ∆µ/µ is obtained using inversion transitions of NH 3 and rotational molecular transitions (Henkel et al 2009;Kanekar 2011;Murphy et al 2008). The best reported limit using this technique is ∆µ/µ = −(3.5 ± 1.2) × 10 −7 (Kanekar 2011).…”

Searching for chameleon-like scalar fields with the ammonia method

“…The measurements of μ rely on the same H 2 systems observed with VLT/UVES and claim a variability of Δμ/μ = 24 ± 6 ppm (Reinhold et al 2006) or no variability with −15 ppm < Δμ/μ < 57 ppm (Levshakov et al 2002), |Δμ/μ| ≤ 49 ppm (Wendt & Reimers 2008), Δμ/μ = 2.6 ± 3.0 ppm (King et al 2008), and Δμ/μ = −7 ± 8 ppm (Thompson et al 2009). Radio astronomical observations place constraints on μ-variations of |Δμ/μ| < 1.8 ppm at redshift z = 0.68 (Murphy et al 2008b), and |Δμ/μ| < 0.6 ppm at z = 0.89 (Henkel et al 2009). …”