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

Authors

S. Phillipps, University of Bristol
S. S. Ali, University of Bristol
M. N. Bremer, University of Bristol
R. de Propris, Turun yliopisto
A. E. Sansom, University of Central Lancashire
M. E. Cluver, Swinburne University of Technology
M. Alpaslan, The Center for Cosmology and Particle Physics
S. Brough, UNSW Sydney
M. J.I. Brown, Monash University
L. J.M. Davies, The University of Western Australia
S. P. Driver, The University of Western Australia
M. W. Grootes, Netherlands eScience Center
Benne W. Holwerda, University of LouisvilleFollow
A. M. Hopkins, Macquarie University
P. A. James, Liverpool John Moores University
K. Pimbblet, University of Hull
A. S.G. Robotham, The University of Western Australia
E. N. Taylor, Swinburne University of Technology
L. Wang, SRON Netherlands Institute for Space Research

Document Type

Article

Publication Date

2-1-2020

Department

Physics and Astronomy

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.

ThinkIR 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.I.; Davies, L. J.M.; Driver, S. P.; Grootes, M. W.; Holwerda, Benne W.; Hopkins, A. M.; James, P. A.; Pimbblet, K.; Robotham, A. S.G.; Taylor, E. N.; and Wang, L., "Galaxy and Mass Assembly (GAMA): Defining passive galaxy samples and searching for the UV upturn" (2020). Faculty and Staff Scholarship. 479.
https://ir.library.louisville.edu/faculty/479

DOI

10.1093/mnras/stz3552

ORCID

0000-0002-4884-6756