Data from: Galaxy And Mass Assembly (GAMA): Defining passive galaxy samples and searching for the UV upturn

Full description

We use data from the GAMA and GALEX surveys to demonstrate that the UV upturn, an unexpected excess of ultraviolet flux from a hot stellar component, seen in the spectra of many early-type galaxies, arises from processes internal to individual galaxies with no measurable influence from the galaxies' larger environment. We first define a clean sample of passive galaxies without a significant contribution to their UV flux from low-level star formation. We confirm that galaxies with the optical colours of red sequence galaxies often have signs of residual star formation, which, without other information, would prevent a convincing demonstration of the presence of UV upturns. However, by including (NUV−u) and WISE (W2-W3) colours, and FUV data where it exists, we can convincingly constrain samples to be composed of non-star-forming objects. Using such a sample, we examine GALEX photometry of low-redshift GAMA galaxies in a range of low-density environments, from groups to the general field, searching for UV upturns. We find a wide range of (NUV−r) colours, entirely consistent with the range seen - and attributed to the UV upturn - in low-redshift red sequence cluster galaxies. The range of colours is independent of group multiplicity or velocity dispersion, with isolated passive galaxies just as likely to have blue UV-to-optical colours, implying significant upturn components, as those in richer groups and in the previous data on clusters. This is supported by equivalent results for (FUV−r) colours which are clear indicators of upturn components.

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External Organisations
University of Bristol; Cardiff University; National Institutes of Natural Sciences - National Astronomical Observatory of Japan; University of Turku; Australian National University; University of New South Wales; University of Central Lancashire; University of the Western Cape; Swinburne University of Technology; NASA Ames Research Center; National Aeronautics & Space Administration (NASA); New York University; Australian Astronomical Observatory; ARC Centre of Excellence for All-sky Astrophysics; University of Sydney; ARC Centre of Excellence for Astrophysics in Three Dimensions (ASTRO3D); ARC Centre of Excellence for Gravitational Wave Discovery; Monash University (Australia); European Space Agency - ESA; ESTEC; ESA/ESTEC SCI-S; University of Sussex; Max Planck Institute for Nuclear Physics; Netherlands eScience Center; University of Louisville; Leiden University; Sydney Institute for Astronomy; Macquarie University; Australian Astronomical Optics; Liverpool John Moores University; University of Hull; Centre for Astrophysics and Supercomputing; SRON Netherlands Institute for Space Research; University of Groningen

Associated Persons
Steven Phillipps (Creator); S. S. Ali (Creator); Malcom N. Bremer (Creator); Roberto De Propris (Creator); Anne E. Sansom (Creator); Michelle E. Cluver (Creator); Mehmet Alpaslan (Creator); Sarah Brough (Creator); Michael J.I. Brown (Creator); Meiert W. Grootes (Creator); Benne W. Holwerda (Creator); Andrew M. Hopkins (Creator); P. A. James (Creator); Kevin Pimbblet (Creator); E. N. Taylor (Creator); Lingyu Wang (Creator)