Moffett, Amanda J. and Kannappan, Sheila J. and Baker, Andrew J. and Laine, Seppo (2012) Extended Ultraviolet Disks and Ultraviolet-bright Disks in Low-mass E/S0 Galaxies. Astrophysical Journal, 745 (1). Art. No. 34. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20120418-103132454
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We have identified 15 extended ultraviolet (XUV) disks in a largely field sample of 38 E/S0 galaxies that have stellar masses primarily below ~4 × 10^(10) M_☉ and comparable numbers on the red and blue sequences. We use a new purely quantitative XUV-disk definition designed with reference to the "Type 1" XUV-disk definition found in the literature, requiring UV extension relative to a UV-defined star formation threshold radius. The 39% ± 9% XUV-disk frequency for these E/S0s is roughly twice the ~20% reported for late-type galaxies (although differences in XUV-disk criteria complicate the comparison), possibly indicating that XUV disks are preferentially associated with galaxies experiencing weak or inefficient star formation. Consistent with this interpretation, we find that the XUV disks in our sample do not correlate with enhanced outer-disk star formation as traced by blue optical outer-disk colors. However, UV-Bright (UV-B) disk galaxies with blue UV colors outside their optical 50% light radii do display enhanced optical outer-disk star formation as well as enhanced atomic gas content. UV-B disks occur in our E/S0s with a 42^(+9)_–8% frequency and need not coincide with XUV disks; thus their combined frequency is 61% ± 9%. For both XUV and UV-B disks, UV colors typically imply <1 Gyr ages, and most such disks extend beyond the optical R_(25) radius. XUV disks occur over the full sample mass range and on both the red and blue sequences, suggesting an association with galaxy interactions or another similarly general evolutionary process. In contrast, UV-B disks favor the blue sequence and may also prefer low masses, perhaps reflecting the onset of cold-mode gas accretion or another mass-dependent evolutionary process. Virtually all blue E/S0s in the gas-rich regime below stellar mass M_t ~ 5 × 10^9 M_☉ (the "gas-richness threshold mass") display UV-B disks, supporting the previously suggested association of this population with active disk growth.
|Additional Information:||© 2012 American Astronomical Society. Received 2011 June 25, accepted for publication 2011 October 26 Published 2011 December 28. We thank S. Jogee for her role in acquiring the Spitzer data, M. Haynes for the early release of GALEX imaging of NGC 3773, and the anonymous referee for suggestions that motivated substantial improvements to this work. We also thank D. Stark for helpful conversations on the topic of refining data analysis codes. We thank C. Clemens, K. Eckert, A. Leroy, M. Norris, and L. Wei for useful discussions as well. A.J.M. acknowledges support from the NASA Harriett G. Jenkins Predoctoral Fellowship Program. This work uses observations made with the NASA Galaxy Evolution Explorer. GALEX is operated for NASA by Caltech under NASA contract NAS5-98034. We acknowledge support from the GALEX Guest Investigator program under NASA grant NNX07AT33G. This work uses observations made with the Spitzer Space Telescope, operated by the Jet Propulsion Laboratory, Caltech under a contract with NASA. Support for this work was also provided by NASA through an award issued by JPL/Caltech. This work uses observations from the SDSS; funding for the SDSS and SDSSII has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web site is http://www.sdss.org/. Facilities: GALEX, Spitzer|
|Subject Keywords:||galaxies: elliptical and lenticular, cD; galaxies: evolution; ultraviolet: galaxies|
|Official Citation:||Extended Ultraviolet Disks and Ultraviolet-bright Disks in Low-mass E/S0 Galaxies Amanda J. Moffett et al. 2012 ApJ 745 34|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||18 Apr 2012 17:51|
|Last Modified:||26 Dec 2012 15:04|
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