Vol. 566
In section 4. Extragalactic astronomy

An ALMA Early Science survey of molecular absorption lines toward PKS1830-211. Analysis of the absorption profiles

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Detection of chloronium and measurement of the 35Cl/37Cl isotopic ratio at z=0.89 toward PKS 1830-211

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Gravitational lensing has made various "gifts to humanity" and one of these is illustrated in the two papers by Muller et al. highlighted in this issue. These authors have used ALMA to make a molecular spectral scan of absorption lines in a foreground galaxy (the lensing galaxy) at z=0.89 against the background of the blazar PKS 1830-211. This allows them to examine the composition of "normal" molecular gas at high red shift. Interestingly, the abundance distribution is similar to what is seen in Milky Way clouds which is somewhat surprising given the expected variation in metallicity, dust properties, etc. A byproduct of this research was the detection of both the 35Cl and 37Cl forms of chloronium (protonated HCl or H2CL+) with an isotope ratio similar to the one in Milky Way clouds .