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.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.accessioned2021-10-08T07:20:39Z
dc.date.available2021-10-08T07:20:39Z
dc.date.issued2013
dc.description.abstractIn the local Universe, 10% of massive elliptical galaxies are observed to exhibit a peculiar property: a substantial excess of ultraviolet emission (UVX) over what is expected from their old, red stellar populations. Several origins for the UVX have been proposed, including a population of hot young stars, or 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 ultraviolet excess (UVX) in a selection of 49 nearby E/S0-type galaxies by measuring the extended photometry in the UV-midIR with GALEX, SDSS and WISE. We compare UV/optical and UV/mid-IR colors with the Flexible Stellar Population Synthesis with EHB models (Conroy & Gunn 2010). 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 EHB fraction. There are strong color gradients with the outer radii bluer than the inner half-light radii by ~1 magnitude. This color difference is easily accounted for with a BHB fraction increase of 0.25 with radius. We estimated 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 ~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 ~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~1
dc.identifier.apacitationPetty, S. M., Neill, J. D., Jarrett, T. H., Blain, A. W., Farrah, D. G., Rich, R. M., ... Wright, E. L. (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. <i>The Astrophysical Journal</i>, 146(4), 77 - 177. http://hdl.handle.net/11427/34975en_ZA
dc.identifier.chicagocitationPetty, S M, J D Neill, T H Jarrett, A W Blain, D G Farrah, R M Rich, C W Tsai, et al "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." <i>The Astrophysical Journal</i> 146, 4. (2013): 77 - 177. http://hdl.handle.net/11427/34975en_ZA
dc.identifier.citationPetty, S.M., Neill, J.D., Jarrett, T.H., Blain, A.W., Farrah, D.G., Rich, R.M., Tsai, C.W. & Benford, D.J. 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. <i>The Astrophysical Journal.</i> 146(4):77 - 177. http://hdl.handle.net/11427/34975en_ZA
dc.identifier.issn0004-637X
dc.identifier.issn1538-4357
dc.identifier.ris TY - Journal Article AU - Petty, S M AU - Neill, J D AU - Jarrett, T H AU - Blain, A W AU - Farrah, D G AU - Rich, R M AU - Tsai, C W AU - Benford, D J AU - Bridge, C R AU - Lake, S E AU - Masci, F J AU - Wright, E L AB - In the local Universe, 10% of massive elliptical galaxies are observed to exhibit a peculiar property: a substantial excess of ultraviolet emission (UVX) over what is expected from their old, red stellar populations. Several origins for the UVX have been proposed, including a population of hot young stars, or 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 ultraviolet excess (UVX) in a selection of 49 nearby E/S0-type galaxies by measuring the extended photometry in the UV-midIR with GALEX, SDSS and WISE. We compare UV/optical and UV/mid-IR colors with the Flexible Stellar Population Synthesis with EHB models (Conroy & Gunn 2010). 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 EHB fraction. There are strong color gradients with the outer radii bluer than the inner half-light radii by ~1 magnitude. This color difference is easily accounted for with a BHB fraction increase of 0.25 with radius. We estimated 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 ~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 ~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~1 DA - 2013 DB - OpenUCT DP - University of Cape Town IS - 4 J1 - The Astrophysical Journal LK - https://open.uct.ac.za PY - 2013 SM - 0004-637X SM - 1538-4357 T1 - 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 TI - 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 UR - http://hdl.handle.net/11427/34975 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/34975
dc.identifier.vancouvercitationPetty SM, Neill JD, Jarrett TH, Blain AW, Farrah DG, Rich RM, et al. 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 Astrophysical Journal. 2013;146(4):77 - 177. http://hdl.handle.net/11427/34975.en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Astronomy
dc.publisher.facultyFaculty of Science
dc.sourceThe Astrophysical Journal
dc.source.journalissue4
dc.source.journalvolume146
dc.source.pagination77 - 177
dc.source.urihttps://dx.doi.org/10.1088/0004-6256/146/4/77
dc.subject.othergalaxies: elliptical and lenticular
dc.subject.othercd
dc.subject.othergalaxies: evolution
dc.subject.othergalaxies:
dc.subject.otherformation
dc.subject.otherinfrared: galaxies
dc.subject.otherultraviolet: galaxies
dc.subject.otherrecent star-formation
dc.subject.otherstandard stellar library
dc.subject.otherinitial mass function
dc.subject.othergiant branch stars
dc.subject.othertp-agb models
dc.subject.otherelliptic galaxies
dc.subject.othersauron project
dc.subject.otherevolutionary synthesis
dc.subject.otherultraviolet-radiation
dc.subject.otherdisk galaxies
dc.subject.otherArticle
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.typeJournal Article
uct.type.publicationResearch
uct.type.resourceJournal Article
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