Ultraviolet signposts of resonant dynamics in the starburst-ringed Sab galaxy M94 (NGC 4736)

The dynamic orchestration of star-birth activity in the starburst-ringed ga laxy M94 (NGC 4736) is investigated using images from the Ultraviolet Imagi ng Telescope (UIT; far-ultraviolet [FUV] band), Hubble Space Telescope (HST ; near-ultraviolet [NUV] band), Kitt Peak 0.9 m telescope (H alpha, R, and I bands), and Palomar 5 m telescope (B band), along with spectra from the I nternational Ultraviolet Explorer (IUE) and the Lick 1 m telescope. The wid e-field UIT image shows FUV emission from (1) an elongated nucleus, (2) a d iffuse inner disk, where H alpha is observed in absorption, (3) a bright in ner ring of H II regions at the perimeter of the inner disk (R = 48 " = 1.1 kpc), and (4) two 500 pc size knots of hot stars exterior to the ring on d iametrically opposite sides of the nucleus (R = 130 " = 2.9 kpc). The HST F aint Object Camera image resolves the NUV emission from the nuclear region into a bright core and a faint 20 " long "minibar" at a position angle of 3 0 degrees. Optical and IUE spectroscopy of the nucleus and diffuse inner di sk indicates a similar to 10(7)-10(8) yr old stellar population from low-le vel star-birth activity blended with some LINER activity. Analysis of the H alpha-, FUV-, NUV-, B-, R-, and I-band emissions, along with other observe d tracers of stars and gas in M94, indicates that most of the star formatio n is being orchestrated via ring-bar dynamics, involving the nuclear miniba r, inner ring, oval disk, and outer ring. The inner starburst ring and bisy mmetric knots at intermediate radius, in particular, argue for bar-mediated resonances as the primary drivers of evolution in M94 at the present epoch . Similar processes may be governing the evolution of the "core-dominated" galaxies that have been observed at high red-shift. The gravitationally len sed "Pretzel Galaxy" (0024+1654) at a redshift of similar to1.5 provides an important precedent in this regard.