We present results of new optical narrow-band imaging and long-slit spectroscopy of a superwind-driven nebula around an archetypical ultraluminous infrared galaxy, Arp 220. Although the nebula is known to show a simple "figure-8" shaped morphology and is often recognized as a pair of twin bubbles, we find that the nebula has rather complex properties than expected from its simple appearance. In Ha+[NII] image, we identify two more pairs of smaller shell-like morphological features within the twin bubbles previously known. By analyzing the kinematical structure along the major axis of the nebula, we find that the inner region between 6" ~ SE and 2" ~ NW shows a broad emission-line component whose full width at half maximum (FWHM) varies from ~500 km/s to 1200 km/s as well as the narrow one with FWHM ~250 km/s. On one hand, a double-peaked narrow profile is found at 6-9" SE, ~12" SE, and 11" NW and a single narrow blue-shifted profile is found in the remaining parts. These complex morphological and kinematical properties are difficult to be interpreted simply as the effect of the expanding twin bubbles. Rather, a model of overlapping multiple bubbles each of which has different size and kinematical structure seems to be more preferred since each shell-like structure seems to have its own kinematical characteristics. It is therefore suggested that Arp 220 experienced multiple starburst events in its central region. Back to Arp 220 page
The Cold-Gas superwind of Arp 220 Traced by NaD5890 Line
Youichi Ohyama (NAOJ-Subaru), Yoshiaki Taniguchi (Tohoku Univ),
William D. Vacca (MPIfE), J. E. Hibbard (NRAO).
R data obtained from the UH 88" in 6/95
Keck LRIS Spectra obtained from Keck II with W. D. Vacca in 4/97
Ha+[NII] imaging from Subaru by Y. Ohyama in 2/00
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