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

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 similar to 1800 km s(-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 (similar to 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.