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

作者：Papadopoulos Padelis P^*; Bi**as Thomas G^*; Zhang Zhi Yu

来源：Monthly Notices of the Royal Astronomical Society, 2018, 478(2): 1716-1725.

DOI：10.1093/mnras/sty1077

• astrochemistry
• radiative transfer
• methods: numerical
• cosmic rays
• photodissociation region (PDR)
• galaxies: ISM

In this work, we extend the work on the recently discovered role of Cosmic Rays (CRs) in regulating the average CO/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/C I-rich 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 a 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/C I-rich molecular gas phase, provided that relative brightness sensitivity levels of T-b(C I 1-0)/T-b(CO J= 1-0) similar to 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 discs, galactic molecular gas outflows, and the CR-intense galactic and circumgalactic gas-rich environments of radio-loud objects.

• 出版日期2018-8