Complex Structure of the Superwind-Driven Nebula around the Ultraluminous Infrared Galaxy Arp 220

Youichi Ohyama (NAOJ-Subaru), Yoshiaki Taniguchi (Tohoku Univ), J. E. Hibbard (NRAO), William D. Vacca (MPIfE), Michitoshi Yoshida (NAOJ-OAO), Nobunari Kashikawa (NAOJ).

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.

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• draft 8/01: .ps.gz, (??Mb)
• Fig. 1: Optical & Halpha morphology
• Fig. 2: Spectra, velocities, dispersions, line ratios

The Cold-Gas superwind of Arp 220 Traced by NaD5890 Line

• Fig. 1: Continuum, Line, and Spectra
• Fig. 2: Spectra at various positions