A search for Extended Ultraviolet Disk (XUV-disk) galaxies in the local universe

David A. Thilker, Luciana Bianchi, Gerhardt Meurer, Armando Gil De Paz, Samuel Boissier, Barry F. Madore, Alessandro Boselli, Annette M.N. Ferguson, Juan Carlos Muńoz-Mateos, Greg J. Madsen, Salman Hameed, Roderik A. Overzier, Karl Forster, Peter G. Friedman, D. Christopher Martin, Patrick Morrissey, Susan G. Neff, David Schiminovich, Mark Seibert, Todd SmallTed K. Wyder, José Donas, Timothy M. Heckman, Young Wook Lee, Bruno Milliard, R. Michael Rich, Alex S. Szalay, Barry Y. Welsh, Sukyoung K. Yi

Research output: Contribution to journalArticlepeer-review

267 Citations (Scopus)


We have initiated a search for extended ultraviolet disk (XUV-disk) galaxies in the local universe. Here we compare GALEX UV and visible-NIR images of 189 nearby (D < 40 Mpc) S0-Sm galaxies included in the GALEX Atlas of Nearby Galaxies and present the first catalog of XUV-disk galaxies. We find that XUV-disk galaxies are surprisingly common but have varied relative (UV/optical) extent and morphology. Type 1 objects (≳20% incidence) have structured, UV-bright/optically faint emission features in the outer disk, beyond the traditional star formation threshold. Type 2 XUV-disk galaxies (∼10% incidence) exhibit an exceptionally large, UV-bright/optically low surface brightness (LSB) zone having blue UV-Ks outside the effective extent of the inner, older stellar population, but not reaching extreme galactocentric distance. If the activity occurring in XUV-disks is episodic, a higher fraction of present-day spirals could be influenced by such outer disk star formation. Type 1 disks are associated with spirals of all types, whereas Type 2 XUV-disks are predominantly found in late-type spirals. Type 2 XUV-disks are forming stars quickly enough to double their (currently low) stellar mass in the next Gyr (assuming a constant star formation rate). XUV-disk galaxies of both types are systematically more gas-rich than the general galaxy population. Minor external perturbation may stimulate XUV-disk incidence, at least for Type 1 objects. XUV-disks are the most actively evolving galaxies growing via inside-out disk formation in the current epoch, and may constitute a segment of the galaxy population experiencing significant, continued gas accretion from the intergalactic medium or neighboring objects.

Original languageEnglish
Pages (from-to)538-571
Number of pages34
JournalAstrophysical Journal, Supplement Series
Issue number2
Publication statusPublished - 2007 Dec

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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