The Neutral Hydrogen Disk of Arp 10 (=VV 362) : A Non-equilibrium Disk Associated with a Galaxy with Rings and Ripples

Abstract

We present VLA \ion{H}{1} 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 for optical shells or ripples in the outer isophotes of the galaxy reminiscent of the ripples seen in some early type systems. The small elliptical originally believed to be the companion is shown to be a background galaxy. The \ion{H}{1} 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 \ion{H}{1} structures do not exactly trace the optical morphology. In the outer parts, the \ion{H}{1} distribution does not correlate well with the optical ripples. Even the inner \ion{H}{1} disk does not correspond well morphologically nor kinematically to the optical rings. These peculiarities lead us to believe that the potential in which the \ion{H}{1} disk resides is significantly out of equilibrium --- a situation which 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 \ion{H}{1} rich disk and a gas-poor disk system. As such, it may represent an example of a class of mergers which lies intermediate between the ``ripple and shell'' accretion systems and the head-on collisional ring galaxies.