Ultraviolet Signatures of Tidal Interaction in the Giant Spiral Galaxy M101

We present new evidence for the occurrence of tidal interactions in the disk of M101 during the last 108-109 yr. 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 far-ultraviolet (FUV) image also shows a faint outer spiral arm with a (“curly tail”) feature that appears to loop around the supergiant H II region NGC 5471, linking this outlying starburst with the rest of the galaxy. These FUV-bright features most likely trace hot O- and 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 H I. The inner-disk FUV arms are most closely associated with Hα 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 nonaxisymmetric 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.

[1]  E. Mash,et al.  IMPROVED SYNTHESES OF 2,2',3,3',6,6'-HEXACHLOROBIPHENYL , 1997 .

[2]  D. Kelson,et al.  The Extragalactic Distance Scale Key Project III. Teh discovery of Cephids and a New Distance to M101 Using the Hubble Space Telescope , 1996 .

[3]  R. Kennicutt,et al.  The Composition Gradient in M101 Revisited. I. H II Region Spectra and Excitation Properties , 1996 .

[4]  M. S. Roberts,et al.  The Ultraviolet Sky as Observed by the Shuttle-Borne Ultraviolet Imaging Telescope , 1995 .

[5]  M. S. Roberts,et al.  Ultraviolet imaging telescope and optical emission-line observations of H II regions in M81 , 1995 .

[6]  R. Wilson,et al.  WAVES IN ASTROPHYSICS , 1995 .

[7]  M. Greason,et al.  CORRECTING THE DISTORTION OF IMAGES TAKEN WITH THE ULTRAVIOLET IMAGING TELESCOPE , 1994 .

[8]  W. Keel,et al.  A Simulation Atlas of Tidal Features in Galaxies , 1993 .

[9]  B. Elmegreen,et al.  An interaction model for the formation of dwarf galaxies and 10 exp 8 solar mass clouds in spiral disks , 1993 .

[10]  W. Roberts.  GLOBAL, LOCAL, AND INTERMEDIATE-SCALE STRUCTURES IN PROTOTYPE SPIRAL GALAXIES , 1993 .

[11]  M. S. Roberts,et al.  Ultraviolet Imaging Telescope observations of the ScI galaxy NGC 628 (M74) , 1992 .

[12]  R. O’Connell,et al.  Ultraviolet Imaging Telescope Images of the Reflection Nebula NGC 7023: Derivation of Ultraviolet Scattering Properties of Dust Grains , 1992 .

[13]  J. D. Stolarik,et al.  The Ultraviolet Imaging Telescope - Design and performance , 1992 .

[14]  P. Scowen,et al.  The H II regions of the galaxy M101 , 1992 .

[15]  B. Elmegreen,et al.  Optical Tracers of Spiral Wave Resonances in Galaxies: II. Hidden Three-Arm Spirals in a Sample of 18 Galaxies , 1991 .

[16]  Christine D. Wilson,et al.  The star-forming disk and CO bar in M101 , 1991 .

[17]  Robert C. Kennicutt,et al.  The H II Regions of M101. I. an Atlas of 1264 Emission Regions , 1990 .

[18]  R. Sancisi,et al.  High-Velocity Gas in M101 , 1988 .

[19]  R. Humphreys,et al.  The use of the brightest blue supergiants as distance indicators - Further complications: Or the brightest 'stars' are not always stars , 1987 .

[20]  E. Skillman.  Spatial variations in the physical conditions in the giant extragalactic H II region NGC 5471 , 1985 .

[21]  R. Miller,et al.  Gravitational spurs and resonances - Effects of small mass disturbers in spiral galaxy disks , 1984 .

[22]  G. Byrd.  Gravitationally induced spurs in spiral galaxies - An example in M31 , 1983 .

[23]  R. Bohlin,et al.  Ultraviolet images of M101 - Observations of dust and inferences on the metallicity , 1982 .

[24]  Theodore P. Stecher,et al.  High-resolution photographs in the rocket ultraviolet of the Orion Nebula , 1982 .

[25]  G. Vaucouleurs.  Book Review: Lowell and Mars. William Graves Hoyt. The University of Arizona Press, Tucson, 1976. 376 pp., 8.50 paperbound, 13.95 clothbound , 1978 .

[26]  W. Hoyt.  Lowell and Mars , 1976 .

[27]  A. Sandage,et al.  Steps toward the Hubble constant. III. The distance and stellar content of the M101 group of galaxies , 1974 .