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2018 Cold Science Colloquia

The Cosmic-ray Flux in z~2 Galaxies Inferred from Molecular Abundances

Presented by: Nick Indriolo (STScI)
Category: Science Colloquia   Duration: 30 minutes   Broadcast date: January 17, 2018
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Nick Indriolo (STScI) – The Cosmic-ray Flux in z~2 Galaxies Inferred from Molecular Abundances Interstellar gas-phase chemistry is primarily driven by fast ion-molecule reactions, and cosmic rays are the dominant mechanism for ionizing hydrogen in shielded regions of the ISM. The formation of molecular ions such as OH+ and H2O+ begins with ionization of atomic hydrogen, and their abundances are useful in constraining the cosmic-ray ionization rate. Observations of these molecules in the nuclear regions of starburst galaxies suggest ionization rates more than 1000 times greater than inferred in the Milky Way disk. As cosmic rays are accelerated in shocks associated with star formation (e.g., supernova remnants and stellar wind bubbles), this is not unexpected. Using ALMA, we have observed transitions of OH+ and H2O+ in a small sample of lensed, submm galaxies at z~2 for the purpose of constraining the cosmic-ray ionization rate at a time when the star formation rate per unit volume is at its highest. I will discuss our analysis of these observations and the preliminary results of our study.

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Nick Indriolo's slides PowerPoint (.ppt)