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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

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dc.contributorVirginia Techen
dc.contributor.authorPetty, S. M.en
dc.contributor.authorNeill, J. D.en
dc.contributor.authorJarrett, T. H.en
dc.contributor.authorBlain, A. W.en
dc.contributor.authorFarrah, Duncanen
dc.contributor.authorRich, R. M.en
dc.contributor.authorTsai, C. W.en
dc.contributor.authorBenford, D. J.en
dc.contributor.authorBridge, C. R.en
dc.contributor.authorLake, S. E.en
dc.contributor.authorMasci, F. J.en
dc.contributor.authorWright, E. L.en
dc.contributor.departmentPhysicsen
dc.date.accessed2014-02-05en
dc.date.accessioned2014-02-25T13:57:01Zen
dc.date.available2014-02-25T13:57:01Zen
dc.date.issued2013-10en
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.en
dc.description.sponsorshipNational Aeronautics and Space Administration NAS5-98034en
dc.description.sponsorshipAlfred P. Sloan Foundationen
dc.description.sponsorshipNational Science Foundationen
dc.description.sponsorshipU.S. Department of Energyen
dc.description.sponsorshipJapanese Monbukagakushoen
dc.description.sponsorshipMax Planck Societyen
dc.description.sponsorshipHigher Education Funding Council for Englanden
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:10.1088/0004-6256/146/4/77en
dc.identifier.doihttps://doi.org/10.1088/0004-6256/146/4/77en
dc.identifier.issn0004-637Xen
dc.identifier.urihttp://hdl.handle.net/10919/25530en
dc.identifier.urlhttp://iopscience.iop.org/1538-3881/146/4/77/pdf/1538-3881_146_4_77.pdfen
dc.language.isoen_USen
dc.publisherIOP Publishing Ltd.en
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectgalaxies: elliptical and lenticular, cden
dc.subjectgalaxies: evolutionen
dc.subjectgalaxies:en
dc.subjectformationen
dc.subjectinfrared: galaxiesen
dc.subjectultraviolet: galaxiesen
dc.subjectrecent star-formationen
dc.subjectstandard stellar libraryen
dc.subjectinitial mass functionen
dc.subjectgiant branch starsen
dc.subjecttp-agb modelsen
dc.subjectelliptic galaxiesen
dc.subjectsauron projecten
dc.subjectevolutionary synthesisen
dc.subjectultraviolet-radiationen
dc.subjectdisk galaxiesen
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 imagingen
dc.title.serialAstronomical Journalen
dc.typeArticle - Refereeden

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