演講資訊

摘要：

Isotopic ratios provide valuable probes of the enrichment history of the Universe, and molecular absorbers provide the perfect sources to study intermediate redshift gas. As these galaxies are seen in absorption against a distant quasar, the observed line strengths are not affected by distance and even rare isotopologues can be studied. Two of the most well studied molecular absorbers are at redshift z=0.89 towards PKS1830-211 and at redshift 0.68 towards B0218+357. A wide range of molecules and their isotopologues have been detected in these galaxies. I will focus on the chlorine-bearing molecules HCl and H2Cl+, and their isotopologues. Comparing the 35/37 Cl ratio at intermediate redshift and in the Milky Way, along with other previously measured isotopic ratios, constrains the chemical evolution of galaxies. The two molecules also trace different gas densities, and constrain the physical conditions in two galaxies at half the current age of the Universe.