Galaxy and Mass Assembly (GAMA)

Defining passive galaxy samples and searching for the UV upturn

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

*Corresponding author for this work

Research output: Contribution to journalArticle

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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.

Original languageEnglish
Pages (from-to)2128-2139
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume492
Issue number2
DOIs
Publication statusPublished - 1 Feb 2020

Bibliographical note

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 492, Issue 2, February 2020, Pages 2128–2139, https://doi.org/10.1093/mnras/stz3552. Copyright 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

Keywords

  • galaxies: evolution
  • galaxies: star formation
  • galaxies: stellar content

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