Phillipps, S, Ali, SS, Bremer, MN, De Propris, R, Sansom, AE, Cluver, ME, Alpaslan, M, Brough, S, Brown, MJ, Davies, LJM, Driver, SP, Grootes, MW, Holwerda, BW, Hopkins, AM, James, PA, Pimbblet, K, Robotham, ASG, Taylor, EN and Wang, L (2019) Galaxy And Mass Assembly (GAMA): Defining passive galaxy samples and searching for the UV upturn. Monthly Notices of the Royal Astronomical Society, 492 (2). pp. 2128-2139. ISSN 0035-8711

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Abstract

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.

Item Type:	Article
Additional Information:	This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2019 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords:	0201 Astronomical and Space Sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Related URLs:	Author
Date Deposited:	05 Mar 2020 14:58
Last Modified:	04 Sep 2021 07:47
DOI or ID number:	10.1093/mnras/stz3552
URI:	https://researchonline.ljmu.ac.uk/id/eprint/12396

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