UV-BRIGHT NEARBY EARLY-TYPE GALAXIES OBSERVED IN THE MID-INFRARED: EVIDENCE FOR A MULTI-STAGE FORMATION HISTORY BY WAY OF WISE AND GALEX IMAGING

• Published in: The Astronomical journal Vol. 146; no. 4; pp. 1 - 17
• Main Authors: Petty, S M, Neill, J D, Jarrett, T H, Blain, A W, Farrah, D G, Rich, R M, Tsai, C-W, Benford, D J, Bridge, C R, Lake, S E, Masci, F J, Wright, E L
• Format: Journal Article
• Language: English
• Published: United States 01.10.2013
• Subjects: Astronomical models; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COLOR; GALACTIC EVOLUTION; Galaxies; Horizontal; Inclusions; INFRARED SURVEYS; MASS TRANSFER; PHOTOMETRY; SKY; SPATIAL DISTRIBUTION; STARS; Stellar atmospheres; STELLAR WINDS; Ultraviolet; ULTRAVIOLET RADIATION; UNIVERSE; VISIBLE RADIATION
• ISSN: 0004-6256; 1538-3881; 1538-3881
• DOI: 10.1088/0004-6256/146/4/77

Several origins for this ultraviolet excess (UVX) have been proposed including a population of hot young stars and a population of old, blue horizontal branch or extended horizontal branch (BHB or EHB) stars that have undergone substantial mass loss from their outer atmospheres. We explore the radial distribution of UVX in a selection of 49 nearby E/S0-type galaxies by measuring their extended photometry in the UV through mid-infrared (mid-IR) with the Galaxy Evolution Explorer (GALEX), the Sloan Digital Sky Survey, and the Wide-field Infrared Survey Explorer (WISE). We compare UV/optical and UV/mid-IR colors with the Flexible Stellar Population Synthesis models, which allow for the inclusion of EHB stars. We find that combined WISE mid-IR and GALEX UV colors are more effective in distinguishing models than optical colors, and that the UV/mid-IR combination is sensitive to the EHB fraction.