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dc.contributorVirginia Tech
dc.contributor.authorPetty, S. M.
dc.contributor.authorNeill, J. D.
dc.contributor.authorJarrett, T. H.
dc.contributor.authorBlain, A. W.
dc.contributor.authorFarrah, D. G.
dc.contributor.authorRich, R. M.
dc.contributor.authorTsai, C. W.
dc.contributor.authorBenford, D. J.
dc.contributor.authorBridge, C. R.
dc.contributor.authorLake, S. E.
dc.contributor.authorMasci, F. J.
dc.contributor.authorWright, E. L.
dc.date.accessioned2014-02-25T13:57:01Z
dc.date.available2014-02-25T13:57:01Z
dc.date.issued2013-10
dc.identifier.citationS. M. Petty et al. 2013. "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," The Astronomical Journal 146 77 doi:10.1088/0004-6256/146/4/77
dc.identifier.issn0004-637X
dc.identifier.urihttp://hdl.handle.net/10919/25530
dc.description.abstractIn the local universe, 10% of massive elliptical galaxies are observed to exhibit a peculiar property: a substantial excess of ultraviolet emission than what is expected from their old, red stellar populations. 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. There are strong color gradients, with the outer radii bluer than the inner half-light radii by similar to 1 mag. This color difference is easily accounted for with an increase in the BHB fraction of 0.25 with radius. We estimated that the average ages for the inner and outer radii are 7.0 +/- 0.3 Gyr, and 6.2 +/- 0.2 Gyr, respectively, with the implication that the outer regions are likely to have formed similar to 1 Gyr after the inner regions. Additionally, we find that metallicity gradients are likely not a significant factor in the color difference. The separation of color between the inner and outer regions, which agrees with a specific stellar population difference (e. g., higher EHB populations), and the similar to 0.5-2 Gyr age difference suggests multi-stage formation. Our results are best explained by inside-out formation: rapid star formation within the core at early epochs (>4 Gyr ago) and at least one later stage starburst event coinciding with z similar to 1.
dc.description.sponsorshipNational Aeronautics and Space Administration NAS5-98034
dc.description.sponsorshipAlfred P. Sloan Foundation
dc.description.sponsorshipNational Science Foundation
dc.description.sponsorshipU.S. Department of Energy
dc.description.sponsorshipJapanese Monbukagakusho
dc.description.sponsorshipMax Planck Society
dc.description.sponsorshipHigher Education Funding Council for England
dc.language.isoen_US
dc.publisherIOP Publishing Ltd.
dc.subjectgalaxies: elliptical and lenticular, cd
dc.subjectgalaxies: evolution
dc.subjectgalaxies:
dc.subjectformation
dc.subjectinfrared: galaxies
dc.subjectultraviolet: galaxies
dc.subjectrecent star-formation
dc.subjectstandard stellar library
dc.subjectinitial mass function
dc.subjectgiant branch stars
dc.subjecttp-agb models
dc.subjectelliptic galaxies
dc.subjectsauron project
dc.subjectevolutionary synthesis
dc.subjectultraviolet-radiation
dc.subjectdisk galaxies
dc.titleuv-bright nearby early-type galaxies observed in the mid-infrared: evidence for a multi-stage formation history by way of wise and galex imaging
dc.typeArticle
dc.identifier.urlhttp://iopscience.iop.org/1538-3881/146/4/77/pdf/1538-3881_146_4_77.pdf
dc.date.accessed2014-02-05
dc.title.serialAstronomical Journal
dc.identifier.doihttps://doi.org/10.1088/0004-6256/146/4/77


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