Ultraviolet Signposts of Resonant Dynamics in the Starburst-Ringed Sab Galaxy, M94 (NGC 4736)

Abstract

M94 (NGC 4736) is investigated using images from the Ultraviolet Imaging Telescope (FUV-band), Hubble Space Telescope (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 International Ultraviolet Explorer and Lick 1-m telescopes. The wide-field UIT image shows FUV emission from (a) an elongated nucleus, (b) a diffuse inner disk, where H-alpha is observed in absorption, (c) a bright inner ring of H II regions at the perimeter of the inner disk (R = 48 arcsec. = 1.1 kpc), and (d) two 500-pc size knots of hot stars exterior to the ring on diametrically opposite sides of the nucleus (R= 130 arcsec. = 2.9 kpc). The HST/FOC image resolves the NUV emission from the nuclear region into a bright core and a faint 20 arcsec. long ``mini-bar'' at a position angle of 30 deg. Optical and IUE spectroscopy of the nucleus and diffuse inner disk indicates an approximately 10^7 or 10^8 yr-old stellar population from low-level starbirth activity blended with some LINER activity. Analysis of the H-alpha, FUV, NUV, B, R, and I-band emission along with other observed tracers of stars and gas in M94 indicates that most of the star formation is being orchestrated via ring-bar dynamics involving the nuclear mini-bar, inner ring, oval disk, and outer ring. The inner starburst ring and bi-symmetric 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 redshift. The gravitationally-lensed ``Pretzel Galaxy'' (0024+1654) at a redshift of approximately 1.5 provides an important precedent in this regard.

revised figure 1 (corrected coordinate labels on declination axis); 19 pages of text + 19 figures (jpg files); accepted for publication in AJ

References in corpus (2)

• Comparing Galaxy Morphology at Ultraviolet and Optical Wavelengths
• Non-circular Gas Kinematics and Star Formation in the Ringed Galaxy NGC 4736

Cited by in corpus (13)

• Secular Evolution and the Formation of Pseudobulges in Disk Galaxies
• The Murmur of the Sleeping Black Hole: Detection of Nuclear Ultraviolet Variability in LINER Galaxies
• Gas Inflow in Barred Galaxies - Effects of Secondary Bars
• Morphological Annotations for Groups in the FIRST Database
• Discovery of a strong spiral magnetic field crossing the inner pseudoring of NGC 4736
• Dusty Acoustic Turbulence in the Nuclear Disks of two LINER Galaxies NGC 4450 and NGC 4736
• Unveiling the nature of M94's (NGC4736) outer region: a panchromatic perspective
• FAST reveals new evidence for M94 as a merger
• The Luminosity Function of X-ray Sources in Spiral Galaxies
• The Nova Rate in M94 (NGC 4736)
• The Net Radial Flow Velocity of the Neutral Hydrogen in the Oval Distortion of NGC 4736
• The JCMT Nearby Galaxies Legacy Survey: SCUBA-2 observations of nearby galaxies
• Discovery of a deep Seyfert-2 galaxy at z = 0.222 behind NGC 300