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arXiv · 1804.09654

New places and phases of CO-poor/CI-rich molecular gas in the Universe

Padelis P. Papadopoulos·Thomas G. Bisbas·Zhiyu Zhang
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Abstract

In this work we extend the work on the recently discovered role of Cosmic Rays (CRs) in regulating the average CO/$\rm H_2$ abundance ratio in molecular clouds (and thus their CO line visibility) in starburst galaxies, and find that it can lead to a CO-poor/CI-rich $\rm H_2 $ gas phase even in environments with Galactic or in only modestly enhanced CR backgrounds expected in ordinary star-forming galaxies. Furthermore, the same CR-driven astro-chemistry raises the possibility of a widespread phase transition of molecular gas towards a CO-poor/CI-rich phase in: a) molecular gas outflows found in star-forming galaxies, b) active galactic nuclei (AGNs), and c) near synchrotron-emitting radio jets and the radio-loud cores of powerful radio galaxies. For main sequence galaxies we find that CRs can render some of their molecular gas mass CO-invisible, compounding the effects of low metallicities. Imaging the two fine structure lines of atomic carbon with resolution high enough to search beyond the CI/CO-bright line regions associated with central starbursts can reveal such a CO-poor/CI-rich molecular gas phase, provided that relative brightness sensitivity levels of $T_b$(CI $1-0$)/$T_b$(CO $J=1-0$)$\sim $0.15 are reached. The capability to search for such gas in the Galaxy is now at hand with the new high-frequency survey telescope HEAT deployed in Antarctica and future ones to be deployed in Dome A. ALMA can search for such gas in star-forming spiral disks, galactic molecular gas outflows and the CR-intense galactic and circumgalactic gas-rich environments of radio-loud objects.

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Padelis P. Papadopoulos, Thomas G. Bisbas, Zhiyu Zhang. 2018-04-26. New places and phases of CO-poor/CI-rich molecular gas in the Universe. https://doi.org/10.1093/mnras%2Fsty1077

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