Molecular Abundances in Galaxies

Astronomy and Astrophysics – Astronomy

Scientific paper

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Atomic, Molecular, Chemical, And Grain Processes, Starburst Galaxies And Infrared Excess Galaxies, Interstellar Dust Grains, Diffuse Emission, Infrared Cirrus, Molecular And Chemical Processes And Interactions

Scientific paper

Two topics are discussed here. The first is an observational study on molecular abundance in nearby (< 10 Mpc) gas-rich galaxies based on our ammonia survey and on data in literature. As a result, a systematically peculiar molecular abundance was found in a famous starburst galaxy M 82 regarding the formation mechanisms of molecules. We discussed possible reasons for this peculiarity. We think that formation of molecules on dust grain is not effective, and/or that evaporation of molecules from dust to gas-phase is not effective in M 82. The second topic is our recent trial to detect ammonia toward a more distant galaxy. We observed ammonia toward a prototypical ultraluminous infrared galaxy, Arp 220 (~ 77 Mpc), with the Nobeyama 45-m radio telescope. Extremely wide absorption lines were detected at the (1,1) and (3,3) transitions. The maximum total velocity width was ~ 1800 km s-1. Such wide molecular absorption lines were detected for the first time in galaxies. The absorption lines are formed only by foreground ammonia of the central compact continuum emission (~ 1''=370 pc). The present results clearly indicate the existence of extremely high-velocity gas in the central compact region. A possible origin of such motion is rapidly rotating gas, suggesting the existence of an active galactic nucleus, or outflowing or inflowing gas. The obtained column density 1.8 × 1017 cm-2 is the largest among galaxies where ammonia is already detected.

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