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

Taylor, EN and Hopkins, AM and Baldry, IK and Bland-Hawthorn, J and Brown, MJI and Colless, M and Driver, S and Norberg, P and Robotham, ASG and Alpaslan, M and Brough, S and Cluver, ME and Gunawardhana, M and Kelvin, LS and Liske, J and Conselice, CJ and Croom, S and Foster, C and Jarrett, TH and Lara-Lopez, M and 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). pp. 2144-2185. ISSN 0035-8711

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Abstract

We measure the mass functions for generically red and blue galaxies, using a z < 0:12 sample of logM_ > 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 characterise 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 logM_ _ 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 logM_ _ 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 logM_ _ 9:3. Points 1–4 provide meaningful targets for models, of galaxy formation and evolution to aim for.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record "Galaxy And Mass Assembly (GAMA): deconstructing bimodality - I. Red ones and blue ones", MNRAS, 446(2), pp.2144-2185 is available online at: http://dx.doi.org/10.1093/mnras/stu1900
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: OXFORD UNIV PRESS
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Date Deposited: 26 Oct 2015 15:10
Last Modified: 26 Oct 2015 15:10
DOI or Identification number: 10.1093/mnras/stu1900
URI: http://researchonline.ljmu.ac.uk/id/eprint/1721

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