A 12 year-long monitoring of the absorption caused by a z=0.89 spiral galaxy on the line of sight to the radio-loud gravitationally lensed quasar PKS 1830-211 reveals spectacular changes in the HCO+ and HCN (2-1) line profiles. The depth of the absor
ption toward the quasar NE image increased by a factor of ~3 in 1998-1999 and subsequently decreased by a factor >=6 between 2003 and 2006. These changes were echoed by similar variations in the absorption line wings toward the SW image. Most likely, these variations result from a motion of the quasar images with respect to the foreground galaxy, which could be due to a sporadic ejection of bright plasmons by the background quasar. VLBA observations have shown that the separation between the NE and SW images changed in 1997 by as much as 0.2 mas within a few months. Assuming that motions of similar amplitude occurred in 1999 and 2003, we argue that the clouds responsible for the NE absorption and the broad wings of the SW absorption should be sparse and have characteristic sizes of 0.5-1 pc.
The Standard Model of particle physics assumes that the so-called fundamental constants are universal and unchanging. Absorption lines arising in molecular clouds along quasar sightlines offer a precise test for variations in the proton-to-electron m
ass ratio, mu, over cosmological time and distance scales. The inversion transitions of ammonia are particularly sensitive to mu compared to molecular rotational transitions. Comparing the available ammonia spectra observed towards the quasar B0218+357 with new, high-quality rotational spectra, we present the first detailed measurement of mu with this technique, limiting relative deviations from the laboratory value to |dmu/mu| < 1.8x10^{-6} (95% confidence level) at approximately half the Universes current age - the strongest astrophysical constraint to date. Higher-quality ammonia observations will reduce both the statistical and systematic uncertainties in these measurements.
We report a search for the presence of dust in the intra-cluster medium based on the study of statistical reddening of background galaxies. Armed with the Red Sequence Cluster survey data, from which we extracted (i) a catalog of 458 clusters with z_
clust < 0.5 and (ii) a catalog of ~90,000 galaxies with photometric redshift 0.5 < z_ph < 0.8 and photometric redshift uncertainty delta z_ph / (1+z_ph) < 0.06, we have constructed several samples of galaxies according to their projected distances to the cluster centers. No significant color differences [<E(B-R_c)> = 0.005 pm 0.008, and <E(V-z)> = 0.000 pm 0.008] were found for galaxies background to the clusters, compared to the references. Assuming a Galactic extinction law, we derive an average visual extinction of <A_V> = 0.004 pm 0.010 towards the inner 1x R_200 of clusters.
