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تسجيل مستخدم جديدGalaxy And Mass Assembly: Deconstructing Bimodality - I. Red ones and blue ones
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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 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 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 possibility of an upturn, of the red galaxy mass function below log M* ~ 9. Points 1-4 provide meaningful targets for models of galaxy formation and evolution to aim for.
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