Extremely high-velocity gas in the galaxy Arp 220, revealed with ammonia absorption lines

Abstract

We observed ammonia (J, K) = (1, 1), (2, 2), (3, 3), and (4, 4) transitions at a wavelength of 1.3 cm toward a prototypical ultraluminous infrared galaxy, Arp 220, with the Nobeyama 45-m radio telescope. We detected extremely wide absorption lines at the (1, 1) and (3, 3) transitions. The maximum total velocity width was ∼ 1800 kms-1. Such wide molecular absorption lines were detected for the first time in galaxies. The absorption lines are formed by ammonia only in front of the central compact continuum emission (∼ 1″ = 370 pc). The present results clearly indicate the existence of extremely high-velocity motion in the central compact region of Arp 220. A possible origin of such motion is rapidly rotating gas, suggesting the existence of an active galactic nucleus, or outflowing or inflowing gas. © 2005. Astronomical Society of Japan.