Galaxy And Mass Assembly (GAMA): deconstructing bimodality - I. Red ones and blue ones

Taylor, E.N.; Hopkins, A.M.; Baldry, I.K.; Bland-Hawthorn, J.; Brown, M.J.I.; Colless, M.; Driver, S.; Norberg, P.; Robotham, A.S.G.; Alpaslan, M.; Brough, S.; Cluver, M.E.; Gunawardhana, M.; Kelvin, L.S.; Liske, J.; Conselice, C.J.; Croom, S.; Foster, C.; Jarrett, T.H.; Lara-Lopez, M.; Loveday, J.

doi:10.1093/mnras/stu1900

Galaxy And Mass Assembly (GAMA): deconstructing bimodality - I. Red ones and blue ones

Taylor, E.N.; Hopkins, A.M.; Baldry, I.K.; Bland-Hawthorn, J.; Brown, M.J.I.; Colless, M.; Driver, S.; Norberg, P.; Robotham, A.S.G.; Alpaslan, M.; Brough, S.; Cluver, M.E.; Gunawardhana, M.; Kelvin, L.S.; Liske, J.; Conselice, C.J.; Croom, S.; Foster, C.; Jarrett, T.H.; Lara-Lopez, M.; Loveday, J.

Authors

E.N. Taylor

A.M. Hopkins

I.K. Baldry

J. Bland-Hawthorn

M.J.I. Brown

M. Colless

S. Driver

Professor Peder Norberg peder.norberg@durham.ac.uk
Professor

A.S.G. Robotham

M. Alpaslan

S. Brough

M.E. Cluver

M. Gunawardhana

L.S. Kelvin

J. Liske

C.J. Conselice

S. Croom

C. Foster

T.H. Jarrett

M. Lara-Lopez

J. Loveday

Abstract

We measure the mass functions for generically red and blue galaxies, using a z < 0.12 sample of log M* > 8.7 field galaxies from the Galaxy And Mass Assembly (GAMA) survey. Our motivation is that, as we show, the dominant uncertainty in existing measurements stems from how ‘red’ and ‘blue’ galaxies have been selected/defined. Accordingly, we model our data as two naturally overlapping populations, each with their own mass function and colour–mass relation, which enables us characterize the two populations without having to specify a priori which galaxies are ‘red’ and ‘blue’. Our results then provide the means to derive objective operational definitions for the terms ‘red’ and ‘blue’, which are based on the phenomenology of the colour–mass diagrams. Informed by this descriptive modelling, we show that (1) after accounting for dust, the stellar colours of ‘blue’ galaxies do not depend strongly on mass; (2) the tight, flat ‘dead sequence’ does not extend much below log M* ∼ 10.5; instead, (3) the stellar colours of ‘red’ galaxies vary rather strongly with mass, such that lower mass ‘red’ galaxies have bluer stellar populations; (4) below log M* ∼ 9.3, the ‘red’ population dissolves into obscurity, and it becomes problematic to talk about two distinct populations; as a consequence, (5) it is hard to meaningfully constrain the shape, including the existence of an upturn, of the ‘red’ galaxy mass function below log M* ∼ 9.3. Points 1–4 provide meaningful targets for models of galaxy formation and evolution to aim for.

Citation

Taylor, E., Hopkins, A., Baldry, I., Bland-Hawthorn, J., Brown, M., Colless, M., …Loveday, J. (2015). Galaxy And Mass Assembly (GAMA): deconstructing bimodality - I. Red ones and blue ones. Monthly Notices of the Royal Astronomical Society, 446(2), 2144-2185. https://doi.org/10.1093/mnras/stu1900

Journal Article Type	Article
Acceptance Date	Sep 11, 2014
Publication Date	Jan 11, 2015
Deposit Date	Feb 3, 2016
Publicly Available Date	Feb 11, 2016
Journal	Monthly Notices of the Royal Astronomical Society
Print ISSN	0035-8711
Electronic ISSN	1365-2966
Publisher	Royal Astronomical Society
Peer Reviewed	Peer Reviewed
Volume	446
Issue	2
Pages	2144-2185
DOI	https://doi.org/10.1093/mnras/stu1900
Keywords	Galaxies: evolution, Galaxies: formation, Galaxies: fundamental parameters, Galaxies: luminosity function, mass function, Galaxies: statistics, Galaxies: stellar content.

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This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.