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Swift UV/Optical Telescope Imaging of Star Forming Regions in M81 and Holmberg IX

Hoversten, EA; Gronwall, C; Berk, DEV; Basu-Zych, AR; Breeveld, AA; Brown, PJ; Kuin, NPM; ... Siegel, MH; + view all (2011) Swift UV/Optical Telescope Imaging of Star Forming Regions in M81 and Holmberg IX. The Astronomical Journal , 141 (6) , Article 205. 10.1088/0004-6256/141/6/205. Green open access

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Abstract

We present Swift UV/Optical Telescope (UVOT) imaging of the galaxies M81 and Holmberg IX. We combine UVOT imaging in three near-ultraviolet (NUV) filters (uvw2: 1928 Å; uvm2: 2246 Å; uvw1: 2600 Å) with ground-based optical imaging from the Sloan Digital Sky Survey to constrain the stellar populations of both galaxies. Our analysis consists of three different methods. First, we use the NUV imaging to identify UV star-forming knots and then perform spectral energy distribution (SED) modeling on the UV/optical photometry of these sources. Second, we measure surface brightness profiles of the disk of M81 in the NUV and optical. Lastly, we use SED fitting of individual pixels to map the properties of the two galaxies. In agreement with earlier studies, we find evidence for a burst in star formation in both galaxies starting ~200 Myr ago coincident with the suggested time of an M81-M82 interaction. In line with theories of its origin as a tidal dwarf, we find that the luminosity-weighted age of Holmberg IX is a few hundred million years. Both galaxies are best fit by a Milky Way dust extinction law with a prominent 2175 Å bump. In addition, we describe a stacked median filter technique for modeling the diffuse background light within a galaxy and a Markov chain method for cleaning segment maps generated by SExtractor.

Type: Article
Title: Swift UV/Optical Telescope Imaging of Star Forming Regions in M81 and Holmberg IX
Open access status: An open access version is available from UCL Discovery
DOI: 10.1088/0004-6256/141/6/205
Publisher version: http://dx.doi.org/10.1088/0004-6256/141/6/205
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Science & Technology, Physical Sciences, Astronomy & Astrophysics, galaxies: individual (M81, Holmberg IX), galaxies: star formation, H II regions, INITIAL MASS FUNCTION, DIGITAL SKY SURVEY, H-II REGIONS, DWARF IRREGULAR GALAXIES, MILKY-WAY, INFRARED-EMISSION, SPIRAL GALAXIES, GALACTIC NUCLEI, EXTINCTION LAW, DUST
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/1330216
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