Published in ApJS, 132: 129-198, 2001.
For a postscript version of the article, click
here.
AN ULTRAVIOLET/OPTICAL ATLAS OF BRIGHT GALAXIES
Pamela M. Marcum 1,
Robert W. O'Connell 2,
Michael N. Fanelli 3,4,
Robert H. Cornett 4,
William H. Waller 4,5,
Ralph C. Bohlin 6,
Susan G. Neff 7,
Morton S. Roberts 8,
Andrew M. Smith 7,
K.-P. Cheng 9,
Nicholas R. Collins 4,
Gregory S. Hennessy 2,10,
Jesse K. Hill 4,
Robert S. Hill 4,
Paul Hintzen 11,
Wayne B. Landsman 4,
Raymond G. Ohl 2,
Ronald A. Parise 12,
Eric P. Smith 7,
Wendy L. Freedman13,
Leslie E. Kuchinski 14,
Barry Madore 14,
Ronald Angione 15,
Christopher Palma 2,
Freddie Talbert 15,
and Theodore P. Stecher 7
Abstract. We present wide-field imagery and photometry of 43
selected nearby galaxies of all morphological types at ultraviolet and
optical wavelengths. The ultraviolet (UV) images, in two broad bands at
1500 and 2500 Å, were obtained using the Ultraviolet Imaging
Telescope (UIT) during the Astro-1 Spacelab mission. The UV
images have ~ 3" resolution, and the comparison sets of
ground-based CCD images (in one or more of B, V, R,
and H
) have pixel scales and
fields of view closely matching the UV frames. The atlas consists of
multiband images and plots of UV/optical surface brightness and color
profiles. Other associated parameters, such as integrated photometry and
half-light radii, are tabulated. In an appendix, we discuss the
sensitivity of different wavebands to a galaxy's star formation history
in the form of "history weighting functions" and emphasize the
importance of UV observations as probes of evolution during the past
10-1000 Myr. We find that UV galaxy morphologies are usually
significantly different from visible band morphologies as a consequence
of spatially inhomogeneous stellar populations. Differences are quite
pronounced for systems in the middle range of Hubble types, Sa through
Sc, but less so for ellipticals or late-type disks. Normal ellipticals
and large spiral bulges are fainter and more compact in the UV. However,
they typically exhibit smooth UV profiles with far-UV/optical color
gradients which are larger than any at optical/IR wavelengths. The
far-UV light in these cases is probably produced by extreme horizontal
branch stars and their descendants in the dominant, low-mass, metal-rich
population. The cool stars in the large bulges of Sa and Sb spirals fade
in the UV while hot OB stars in their disks brighten, such that their
Hubble classifications become significantly later. In the far-UV,
early-type spirals often appear as peculiar, ringlike systems. In some
spiral disks, UV-bright structures closely outline the spiral pattern;
in others, the disks can be much more fragmented and chaotic than at
optical wavelengths. Contributions by bright active galactic nuclei
(AGNs) to the integrated UV light in our sample range from less than 10%
to nearly 100%. A number of systems have unusual UV-bright structures in
their inner disks, including rings, compact knots, and starburst nuclei,
which could easily dominate the UV light in high-redshift analogs. A
significant but variable fraction of the far-UV light in spiral disks is
diffuse rather than closely concentrated to star-forming regions. Dust
in normal spiral disks does not control UV morphologies, even in some
highly inclined disk systems. The heaviest extinction is apparently
confined to thin layers and the immediate vicinity of young H II
complexes; the UV light emerges from thicker star distributions, regions
evacuated of dust by photodestruction or winds, or by virtue of strong
dust clumpiness. Only in cases where the dust layers are disturbed does
dust appear to be a major factor in UV morphology. The UV-bright plume
of M82 indicates that dust scattering of UV photons can be important in
some cases. In a companion paper, we discuss far-UV data from the
Astro-2 mission and optical comparisons for another 35 galaxies,
emphasizing face-on spirals.
Key words: galaxies: evolution-galaxies: fundamental
parameters-galaxies: photometry-galaxies: structure-ultraviolet:
galaxies
Table of Contents
1 Physics and Astronomy Department, Texas
Christian University, Box 298840, Fort Worth, TX 76129;
p.marcum@tcu.edu.
2 Astronomy Department, University of
Virginia, P. O. Box 3818, Charlottesville, VA 22903-0818; rwo@virginia.edu.
3 Physics
Department, University of North Texas, Denton, TX 76203-5370; fanelli@unt.edu.
4 Raytheon
ITSS, Code 681, NASA/GSFC, Greenbelt, MD 20771.
5 Department
of Physics and Astronomy, Tufts University, Medford, MA 02155.
6 Space
Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218.
7 Laboratory for Astronomy and Solar
Physics, Code 681, NASA/GSFC, Greenbelt, MD 20771.
8 National Radio
Astronomy Observatory, Charlottesville, VA 22903.
9 Physics Department, California
State University, Fullerton, CA 92634.
10 Visiting Astronomer, Kitt Peak
National
Observatory and Cerro Tololo Inter-American Observatory of the National
Optical Astronomy Observatories, operated by the Association of
Universities for Research in Astronomy (AURA), Inc. under cooperative
agreement with the National Science Foundation.
11 US
Naval Observatory, 3450 Massachusetts Avenue, NW, Washington, DC
20392-5420.
12 Physics and Astronomy Department,
California State University, Long Beach CA 90840.
13 Computer Sciences Corporation,
NASA/GSFC, Code 684.9, Greenbelt, MD 20771.
14 Carnegie Observatories, 813 Santa
Barbara Street, Pasadena, CA 91101-1292.
15 Caltech, IPAC 100-22, Pasadena,
CA 91125.
16 Astronomy Department, San Diego
State University, San Diego, CA 92182.
