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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

We present the first far-ultraviolet (FUV; λ ~ 1500 A) image of the nearby peculiar SAB(r)bc galaxy NGC 3310. The small 15'' (945 pc) diameter circumnuclear starburst ring is the most luminous structure, producing 30% of the total observed FUV luminosity. Diffuse emission from the inner disk (20'' < R < 40'') contributes another ~20% of the observed FUV flux. A linear feature (the "arrow") appears to be a star-forming tidal feature. A diffuse arc observed at optical wavelengths (the "bow") is not visible in the FUV and is probably a tidally induced shell composed of older stars. Mean star formation rates range from 0.031 M☉ yr-1 kpc-2 in the arrow to 2.1 M☉ yr-1 kpc-2 at the brightest FUV source. The striking similarity between the R1/4 law behavior of the FUV and B-band surface brightness profiles, combined with the very blue colors of NGC 3310, strongly argues that the present morphology is the result of a global starburst triggered by a merger with a dwarf companion.

We have undertaken an imaging survey of 34 nearby galaxies in far-ultraviolet (FUV, ~1500A) and optical (UBVRI) passbands to characterize galaxy morphology as a function of wavelength. This sample, which includes a range of classical Hubble types from elliptical to irregular with emphasis on spirals at low inclination angle, provides a valuable database for comparison with images of high-z galaxies whose FUV light is redshifted into the optical and near- infrared bands. Ultraviolet data are from the UIT Astro-2 mission. We present images and surface brightness profiles for each galaxy, and we discuss the wavelength-dependence of morphology for different Hubble types in the context of understanding high-z objects. In general, the dominance of young stars in the FUV produces the patchy appearance of a morphological type later than that inferred from optical images. Prominent rings and circumnuclear star formation regions are clearly evident in FUV images of spirals, while bulges, bars, and old, red stellar disks are faint to invisible at these short wavelengths. However, the magnitude of the change in apparent morphology ranges from dramatic in early--type spirals with prominent optical bulges to slight in late-type spirals and irregulars, in which young stars dominate both the UV and optical emission. Starburst galaxies with centrally concentrated, symmetric bursts display an apparent ``E/S0'' structure in the FUV, while starbursts associated with rings or mergers produce a peculiar morphology. We briefly discuss the inadequacy of the optically-defined Hubble sequence to describe FUV galaxy images and estimate morphological k-corrections, and we suggest some directions for future research with this dataset., Accepted for publication in the ApJS. 15 pages, 17 JPEG figures, 10 GIF figures. Paper and full resolution figures available at http://nedwww.ipac.caltech.edu/level5/Kuchinski/frames.html

Far ultraviolet FUV imagery of the edge-on, Sc/SBd galaxy, NGC 4631 reveals very strong FUV emission, resulting from active star formation, uniformly distributed along the galactic mid- plane. Multi-band imagery, HI and HII position-velocity curves and extinction considerations all imply that the emission is from the outer edges of the visible galaxy. The overall FUV morphology of this edge-on disk system is remarkably similar to those of the so-called "chain galaxies" evident at high redshift, thus suggesting a similar interpretation for at least some of those distant objects. FUV, U, B and V magnitudes, measured for 48 star forming regions, along with corresponding H-alpha and H-beta measurements are used to construct diagnostic color-color diagrams. Although there are significant exceptions, most of the star forming regions are less massive and older than 30 Doradus. Comparison with the expectations from two star formation models yields ages of 2.7 to 10 Myr for the instantaneous burst (IB) model and star formation cut-off ages of 0 to 9 Myr for the continuous star formation (CSF) model. Interpreted in terms of the IB model the photometry implies a total created mass in the 48 star forming regions of 25 million solar-masses. When viewed as resulting from constant star formation the photometry implies a star formation rate of 0.33 solar-masses/yr. These results are compared to those derived from FIR and radio observations. Corrections for FUV emission reprocessed by interstellar grains are estimated., Comment: 29 pages including 6 encapsulated Postscript figures; accepted for publication in ApJ; changed table format

The Ultraviolet Imaging Telescope (UIT) has returned the first significant sample of ultraviolet imagery of galaxies combining a large field-of-view and spatial resolution comparable to ground-based observatories. During the Astro Spacelab missions, UIT obtained spatially-resolved far-UV (λλ 1500 A) imagery of ∼35 disk galaxies. We have utilized the FUV light profiles and morphology to characterize the high-mass stellar populations in these systems. A variety of radial light profiles are found, including two systems, NGC 4214 and NGC 3310, which exhibit R1/4 profiles produced by their Population I stellar components.

Recent rest-frame ultraviolet imaging of galaxies at apparently high redshift have revealed a population of very blue galaxies with aspect ratios approaching 30 which have been interpreted to be chains of star formation regions in the initial stages of galaxy formation [1]. We compare these optical observations with rest-frame far-ultraviolet observations of nearby edge-on galaxies with a view to illustrating their noteworthy similarities. For the comparison we use far ultraviolet (FUV) images of NGC 253 (SAB(s)c), NGC 891 (SA (s)b), NGC 3034 (M82)(I0), NGC 4248 (I0), UGC 6697 (Im), and NGC 4631 (SB(s)d) which were recorded by the Ultraviolet Imaging Telescope. We focus primarily on NGC 4631, 7.5 Mpc distant, which in the FUV exhibits a linear beaded structure, an axial ratio of ∼24 and a (λλ 1520 A)-U color of −0.70. At z≈1.9 (λλ 1520 A)-U would approximate (B–I) and would appear to be very blue. NGC 4248 and UGC 6697 are additional examples of edge-on galaxies which give the appearance of “chain galaxie...

Results of a deep near-infrared imaging survey of low-luminosity cold IRAS sources in the Taurus dark cloud are discussed. The images involved identify the compact sources energizing the IRAS sources, identify infrared nebulosity around numbers of the invisible sources, and reveal the large-scale (about 1000 to 10,000 AU) morphology of this nebulosity. Some of the invisible sources show a clear bipolar or monopolar morphology suggesting a close relation of the nebulosity with a bipolar mass outflow. It is concluded that the nebulosity is likely due to scattering of radiation from the central source by the dust associated with the mass outflow extending to the poles of a circumstellar dust disk.

H-alpha, R, and I band CCD images of the posteruptive irregular galaxy NGC 1569 are presented. The discovery of two archlike structures of diffuse H-alpha emission located more than 1 kpc beyond the star-forming bar is reported. These features are used to estimate an age for the near-nuclear starburst that created them along with other filamentary and armlike structures previously seen in H-alpha photographs. The gravitational and kinematic energies associated with the H-alpha arcs are estimated to be orders of magnitude higher than can be provided by a single supernova explosion. Coherent outbursts involving thousands of supernovae each could explain the diffuse H-alpha features without exceeding the starbirth rate inferred from the total H-alpha luminosity of the galaxy. 46 refs.

H-alpha (6563 A) and near-infrared forbidden S III line (9532 A) data are presented for the Sc galaxy NGC 253. Anomalous enhancements in the forbidden S III/H-alpha emission ratio throughout the inner disk may indicate the presence of concealed H II regions. Visual extinctions range from 3-7 mag. The results suggest that within the inner 7 kpc of the disk roughly 95 percent of the ionized gas is obscured from view at H-alpha, and that on large scales the massive star formation depends linearly on the available molecular gas. NGC 253 differs from other Sc-type galaxies by the stronger concentration of star-forming activity toward the nucleus, the richer presence of massive star formation, and the higher overall star-forming efficiency. 50 references.