%0 Journal Article
%T Ultraviolet Signatures of Tidal Interaction in the Giant Spiral Galaxy, M101
%A William H. Waller
%A Ralph C. Bohlin
%A Robert H. Cornett
%A Michael N. Fanelli
%A Wendy L. Freedman
%A Jesse K. Hill
%A Barry F. Madore
%A Susan G. Neff
%A Joel D. Offenberg
%A Robert W. O'Connell
%A Morton S. Roberts
%A Andrew M. Smith
%A Theodore P. Stecher
%J Physics
%D 1996
%I arXiv
%R 10.1086/304057
%X We present new evidence for tidal interactions having occurred in the disk of M101 in the last 10^8 - 10^9 years. Recent imaging of the far-ultraviolet emission from M101 by the Shuttle-borne Ultraviolet Imaging Telescope (UIT) reveals with unprecedented clarity a disk-wide pattern of multiple linear arm segments (``crooked arms''). The deep FUV image also shows a faint outer spiral arm with a (``curly tail'') feature that appears to loop around the supergiant HII region NGC 5471 - linking this outlying starburst with the rest of the galaxy. These FUV-bright features most likely trace hot O & B-type stars along with scattered light from associated nebular dust. Counterparts of the outermost ``crooked arms'' are evident in maps at visible wavelengths and in the 21-cm line of HI. The inner-disk FUV arms are most closely associated with H$\alpha$ knots and the outer (downstream) sides of CO arms. Comparisons of the ``crooked arm'' and ``curly tail'' morphologies with dynamical simulations yield the greatest similitude, when the non- axisymmetric forcing comes from a combination of ``external interactions'' with one or more companion galaxies and ``internal perturbations'' from massive objects orbiting within the disk. We speculate that NGC 5471 represents one of these ``massive disturbers'' within the disk, whose formation followed from a tidal interaction between M101 and a smaller galaxy.
%U http://arxiv.org/abs/astro-ph/9612165v1