We present the results of a 7 mm spectral survey of molecular absorption lines originating in the disk of a z = 0.89 spiral galaxy located in front of the quasar PKS 1830−211. Our survey was performed with the Australia Telescope Compact Array and covers the frequency interval 30-50 GHz, corresponding to the rest-frame frequency interval 57-94 GHz. A total of 28 different species, plus 8 isotopic variants, were detected toward the south-west absorption region, located about 2 kpc from the center of the z = 0.89 galaxy, which therefore has the largest number of detected molecular species of any extragalactic object so far. The results of our rotation diagram analysis show that the rotation temperatures are close to the cosmic microwave background temperature of 5.14 K that we expect to measure at z = 0.89, whereas the kinetic temperature is one order of magnitude higher, indicating that the gas is subthermally excited. The molecular fractional abundances are found to be in-between those in typical Galactic diffuse and translucent clouds, and clearly deviate from those observed in the dark cloud TMC 1 or in the Galactic center giant molecular cloud Sgr B2. The isotopic ratios of carbon, nitrogen, oxygen, and silicon deviate significantly from the solar values, which can be linked to the young age of the z = 0.89 galaxy and a release of nucleosynthesis products dominated by massive stars. Toward the north-east absorption region, where the extinction and column density of gas is roughly one order of magnitude lower than toward the SW absorption region, only a handful of molecules are detected. Their relative abundances are comparable to those in Galactic diffuse clouds. We also report the discovery of several new absorption components, with velocities spanning between −300 and +170 km s −1 . Finally, the line centroids of several species (e.g., CH 3 OH, NH 3 ) are found to be significantly offset from the average velocity. If caused by a variation in the proton-to-electron mass ratio μ with redshift, these offsets yield an upper limit | Δμ μ | < 4×10 −6 , which takes into account the kinematical noise produced by the velocity dispersion measured from a large number of molecular species.

Context. According to the Big Bang theory and as a consequence of adiabatic expansion of the Universe, the temperature of the cosmic microwave background (CMB) increases linearly with redshift. This relation is, however, poorly explored, and detection of any deviation would directly lead to (astro-)physics beyond the standard model. Aims. We aim to measure the temperature of the CMB with an accuracy of a few percent at z = 0.89 toward the molecular absorber in the galaxy lensing the quasar PKS 1830−211. Methods. We adopted a Monte-Carlo Markov chain approach, coupled with predictions from the non-LTE radiative transfer code RADEX, to solve the excitation conditions of a set of various molecular species directly from their spectra. Results. We determine T CMB = 5.08 ± 0.10 K at 68% confidence level. Our measurement is consistent with the value T CMB = 5.14 K predicted by the standard cosmological model with adiabatic expansion of the Universe. This is the most precise determination of T CMB at z > 0 to date.

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We investigate the practice of assigning high spin temperatures to damped Lyman α absorption systems (DLAs) not detected in H I 21-cm absorption. In particular, Kanekar & Chengalur have attributed the mix of 21-cm detections and non-detections in low-redshift (z abs 2.04) DLAs to a mix of spin temperatures, while the non-detections at high redshift were attributed to high spin temperatures. Below z abs = 0.9, where some of the DLA host galaxy morphologies are known, we find that 21-cm absorption is normally detected towards large radio sources when the absorber is known to be associated with a large intermediate (spiral) galaxy. Furthermore, at these redshifts, only one of the six 21-cm non-detections has an optical identification and these DLAs tend to lie along the sight-lines to the largest background radio continuum sources. For these and many of the high-redshift DLAs occulting large radio continua, we therefore expect covering factors of less than the assumed/estimated value of unity. This would have the effect of introducing a range of spin temperatures considerably narrower than the current range of T s 9000 K, while still supporting the hypothesis that the high-redshift DLA sample comprises a larger proportion of compact galaxies than the low-redshift sample.

In a recent study of z ≥ 0.1 active galactic nuclei (AGN), we found that 21-cm absorption has never been detected in objects in which the ultra-violet luminosity exceeds L UV ∼ 10 23 W Hz −1 . In this paper, we further explore the implications that this has for the currently popular consensus that it is the orientation of the circumnuclear obscuring torus, invoked by unified schemes of AGN, which determines whether absorption is present along our sight-line. The fact that at L UV < ∼ 10 23 W Hz −1 , both type-1 and type-2 objects exhibit a 50% probability of detection, suggests that this is not the case and that the bias against detection of H i absorption in type-1 objects is due purely to the inclusion of the L UV 10 23 W Hz −1 sources. Similarly, the ultra-violet luminosities can also explain why the presence of 21-cm absorption shows a preference for radio galaxies over quasars and the higher detection rate in compact sources, such as CSS or GPS sources, may also be biased by the inclusion of high-luminosity sources. Being comprised of all 21-cm searched sources at z ≥ 0.1, this is a necessarily heterogeneous sample, the constituents of which have been observed by various instruments. By this same token, however, the dependence on the UV luminosity may be an all encompassing effect, superseding the unified schemes model, although there is the possibility that the exclusive 21-cm non-detections at high UV luminosities could be caused by a bias towards gas-poor ellipticals. Additionally, the high UV fluxes could be sufficiently exciting/ionising the H i above 21-cm detection thresholds, although the extent to which this is related to the neutral gas deficit in ellipticals is currently unclear.Examining the moderate UV luminosity (L UV < ∼ 10 23 W Hz −1 ) sample further, from the profile widths and offsets from the systemic velocities, we find no discernible differences between the two AGN types. This may suggest that the bulk of the absorption generally occurs in the galactic disk, which must therefore be randomly orientated with respect to the circumnuclear torus. Furthermore, we see no difference in the reddening between the two AGN types, indicating, like the 21-cm absorption, that the orientation of the torus has little bearing on this. We also find a correlation between 21-cm line strength and the optical-near-infrared colour, which suggests that the reddening is caused by dust located in the large-scale, H i absorbing disk which intervenes the sight-line to the AGN.