THE NEUTRAL HYDROGEN DISK OF ARP 10 (=VV 362): A NONEQUILIBRIUM DISK ASSOCIATED WITH A GALAXY WITH RINGS AND RIPPLES

摘要

We present VLA H Ⅰ and optical spectra of the peculiar galaxy Arp 10. Originally believed to be an example of a classical colliding ring galaxy with multiple rings, the new observations show a large, disturbed neutral hydrogen disk extending 2.7 times the radius of the bright optical ring. We also present evidence of optical shells or ripples in the outer isophotes of the galaxy, reminiscent of the ripples seen in some early-type systems. The small elliptical galaxy originally believed to be the companion is shown to be a background galaxy. The H Ⅰ disk consists of two main parts: a very irregular outer structure and a more regular inner disk associated with the main bright optical ring. In both cases, the H Ⅰ structures do not exactly trace the optical morphology. In the outer parts, the H Ⅰ distribution does not correlate well with the optical ripples. Even the inner H Ⅰ disk does not correspond well morphologically or kine-matically to the optical rings. These peculiarities lead us to believe that the potential in which the H Ⅰ disk resides is time-varying—a situation that would inherently produce rings of star formation. We suggest that Arp 10 is the result of the intermediate stage of a merger between a large H Ⅰ-rich disk and a gas-poor disk system. As such, it may represent an example of a class of mergers that lies intermediate between the " ripple and shell" accretion systems and the head-on collisional ring galaxies.