Oral Presentation

The cosmic-ray flux in sub-millimeter bright galaxies at z>2

Author(s): Nick Indriolo (NAOJ) Ted Bergin (U. Michigan) Edith Falgarone (Ecole Normale Superieure) Benjamin Godard (Ecole Normale Superieure) Martin Zwaan (ESO) David Neufeld (Johns Hopkins U.) Mark Wolfire (U. Maryland) Thomas Bisbas (U. Köln)

Presenter: Nick Indriolo (NAOJ)

Interstellar chemistry is driven by fast ion-molecule reactions, and in molecular clouds the chemical reaction network is initiated primarily by the ionization of H and H2 by cosmic rays. Particles are accelerated in shocks associated with supernova remnants and stellar wind bubbles, so it is expected that the cosmic-ray ionization rate in a galaxy scales with its star formation rate. Molecules such as OH+ and H2O+, with abundances highly dependent on the ionization rate, have been used extensively in the Milky Way to infer interstellar cosmic-ray ionization rates. We have used ALMA to observe OH+ and H2O+ absorption in a sample of 12 galaxies with a range of star formation rate surface densities from 10 to 1000 solar masses per year per square kiloparsec at 2 < z < 6. In concert with chemical models, these observations are used to infer average cosmic-ray ionization rates in the target galaxies. Here, I will present our preliminary findings on cosmic-ray ionization rates in sub-millimeter bright galaxies and the relation with star formation rate.