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

Phillipps, S.; Ali, S. S.; Bremer, M. N.; de Propris, R.; Sansom, A. E.; Cluver, M. E.; Alpaslan, M.; Brough, S.; Brown, M. J.I.; Davies, L. J.M.; Driver, S. P.; Grootes, M. W.; Holwerda, B. W.; Hopkins, A. M.; James, P. A.; Pimbblet, K.; Robotham, A. S.G.; Taylor, E. N.; Wang, L.

Abstract

© 2019 The Author(s) 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.

Citation

Phillipps, S., Ali, S. S., Bremer, M. N., de Propris, R., Sansom, A. E., Cluver, M. E., Alpaslan, M., Brough, S., Brown, M. J., Davies, L. J., Driver, S. P., Grootes, M. W., Holwerda, B. W., Hopkins, A. M., James, P. A., Pimbblet, K., Robotham, A. S., Taylor, E. N., & Wang, L. (2020). Galaxy and Mass Assembly (GAMA): Defining passive galaxy samples and searching for the UV upturn. Monthly notices of the Royal Astronomical Society, 492(2), 2128-2139. https://doi.org/10.1093/mnras/stz3552

• Journal Article Type: Article
• Acceptance Date: Dec 17, 2019
• Online Publication Date: Dec 19, 2019
• Publication Date: Feb 1, 2020
• Deposit Date: Dec 17, 2020
• Publicly Available Date: Dec 17, 2020
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 492
• Issue: 2
• Pages: 2128-2139
• DOI: https://doi.org/10.1093/mnras/stz3552
• Keywords: Galaxies -- evolution; Galaxies -- star formation; Galaxies -- stellar content
• Public URL: https://hull-repository.worktribe.com/output/3497412
• Publisher URL: https://academic.oup.com/mnras/article-abstract/492/2/2128/5681402?redirectedFrom=fulltext