Deconstructing the galaxy stellar mass function with UKIDSS and CANDELS: the impact of colour, structure and environment

MNRAS 447, 2–24 (2015) doi:10.1093/mnras/stu2403 Deconstructing the galaxy stellar mass function with UKIDSS and CANDELS: the impact of colour, structure and environment Alice Mortlock,1,2‹ Christopher. J. Conselice,1 William G. Hartley,1,3 Ken Duncan,1 Caterina Lani,1 Jamie R. Ownsworth,1 Omar Almaini,1 Arjen van der Wel,4 Kuang-Han Huang,5 Matthew L. N. Ashby,6 S. P. Willner,6 Adriano Fontana,7 Avishai Dekel,8 Anton M. Koekemoer,9 Harry C. Ferguson,9 Sandra M. Faber,10 Norman A. Grogin10 and Dale D. Kocevski11 of Nottingham, School of Physics and Astronomy, Nottingham NG7 2RD UK Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK 3 ETH Zürich, Institut für Astronomie, Wolfgang-Pauli-Str. 27, CH-8093 Zürich, Switzerland 4 Max-Planck Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg, Germany 5 Department of Physics, University of California Davis, One Shields Avenue, Davis, CA 95616, USA 6 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 7 INAF–Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monte Porzio Catone, Italy 8 Racah Institute of Physics, The Hebrew University, Jerusalem 91904, Israel 9 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 10 UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA 11 Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506, USA 2 SUPA† Accepted 2014 November 12. Received 2014 November 11; in original form 2014 July 20 ABSTRACT We combine photometry from the Ultra Deep Survey (UDS), Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) UDS and CANDELS the Great Observatories Origins Deep Survey-South (GOODS-S) surveys to construct the galaxy stellar mass function probing both the low- and high-mass end accurately in the redshift range 0.3 < z < 3. The advantages of using a homogeneous concatenation of these data sets include meaningful measures of environment in the UDS, due to its large area (0.88 deg2 ), and the high-resolution deep imaging in CANDELS (H160 > 26.0), affording us robust measures of structural parameters. We construct stellar mass functions for the entire sample as parametrized by the Schechter function, and find that there is a decline in the values of φ and of α with higher redshifts, and a nearly constant M∗ up to z ∼ 3. We divide the galaxy stellar mass function by colour, structure, and environment and explore the links between environmental overdensity, morphology, and the quenching of star formation. We find that a double Schechter function describes galaxies with high Sérsic index (n > 2.5), similar to galaxies which are red or passive. The low-mass end of the n > 2.5 stellar mass function is dominated by blue galaxies, whereas the high-mass end is dominated by red galaxies. This shows that there is a possible link between morphological evolution and star formation quenching in high mass galaxies, which is not seen in lower mass systems. This in turn suggests that there are strong mass-dependent quenching mechanisms. In addition, we find that the number density of high-mass systems is elevated in dense environments, suggesting that an environmental process is building up massive galaxies quicker in over densities than in lower densities. Key words: galaxies: evolution – galaxies: formation – galaxies: luminosity function, mass function – galaxies: structure. 1 I N T RO D U C T I O N E-mail: † Scottish Universities Physics Alliance The galaxy stellar mass function (galaxy SMF) is an important tool for exploring galaxy evolution and the growth of stellar mass over cosmic time. By investigating the galaxy SMF of different populations we can begin to understand the physical processes  C 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society 1 University The galaxy SMF in the UDS and CANDELS The environment in which the galaxy resides is also a key parameter which affects the build-up of galaxy stellar mass. A galaxy in a dense environment may interact with the surrounding galaxies and may build up stellar mass through mergers or be quenched via gas stripping or merger driven feedback. This in turn can affect galaxy properties such as morphology and structure (e.g. Dressler 1980; Bamford et al. 2009; Maltby et al. 2010; Skibba et al. 2012; Lani et al. 2013) or SF properties and colour (e.g. Cooper et al. 2007; van der Wel 2008; Chuter et al. 2011; Grützbauch et al. 2011a,b). However, it is difficult to discern whether it is the environmental processes or internal processes (e.g. in situ SF or feedback) which are driving mass growth and the truncation of SF. By constructing the galaxy SMF with respect to environment and SF history, it is possible to explore how both internal and external processes are driving the growth of galaxies of different stellar masses. Measuring the environment of a galaxy is, however, a non-trivial problem which requires either a large survey area or targeted observations of cluster, group and field galaxies. Therefore there has only been a handful of work to date which examines the galaxy SMF in different environments (e.g. Balogh et al. 2001; Kodama & Bower 2003; Bundy et al. 2006; Bolzonella et al. 2010; Vulcani et al. 2011). The main conclusion of these studies is that the number densities of galaxies in the highest density regions are dominated by massive, early-type galaxies. This result is another way of exploring the already well-established morphology–density relation (Dressler 1980; Postman & Geller 1984; Treu et al. 2003; Nuijten et al. 2005; Postman et al. 2005; Holden et al. 2007). Peng et al. (2010b) find that out to redshifts of z ∼ 1 observations can be explained by the effects of environment and stellar mass being separable, and that these two effects halt SF in galaxies. The evolution of the shape of the galaxy SMF of star-forming and passive galaxies in the SDSS supports their proposed forms of quenching. Furthermore, the evolution of the UltraVISTA galaxy SMF of blue and red galaxies can also be explained as a mixture of mass and environment quenching (Ilbert et al. 2013). The United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS; Lawrence et al. 2007) Ultra Deep Survey (UDS) is the ideal data set to test the effect of environment on the galaxy SMF, as the large area covered (∼1 deg2 ) allows us to probe different galaxy environments. The build-up of stellar mass in a galaxy also links with galaxy structure. Recent advances in observations allow us to probe galaxy structure at high redshift with high-resolution imaging. By investigating the galaxy SMF with respect to galaxy structure we can infer how the morphologies of galaxies change as a function of stellar mass and redshift. Furthermore, several studies have previously noted that there is strong c (...truncated)