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Measures of galaxy environment - I. What is ‘environment’?

Stuart I. MuldrewSchool of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RDDarren J. CrotonCentre for Astrophysics & Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122, AustraliaRamin A. SkibbaSteward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USAFrazer R. PearceSchool of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RDHong Bae AnnDivision of Science Education, Pusan National University, Busan 609-735, South KoreaIvan K. BaldryAstrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LDSarah BroughAustralian Astronomical Observatory, PO Box 296, Epping, NSW 1710, AustraliaYun-Young ChoiDepartment of Astronomy and Space Science, Kyung Hee University, Gyeonggi 446-701, South KoreaChristopher J. ConseliceSchool of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RDNicolas B. CowanNorthwestern University, Dearborn Observatory, 2131 Tech Drive, Evanston, IL 60208, USAAnna GallazziDark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, DenmarkMeghan E. GraySchool of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RDRuth GrützbauchI-Hui LiCentre for Astrophysics & Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122, AustraliaChangbom ParkKorea Institute for Advanced Study, 87 Hoegiro, Dongdaemun-Gu, Seoul 130-722, South KoreaSergey V. PilipenkoAstro Space Center, Lebedev Physical Institute, Russian Academy of Sciences, 117997 Moscow, RussiaBret J. PodgorzecSchool of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RDAaron S. G. RobothamSchool of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS 13 Max-Planck-Institut fr Extraterrestrische Physik, Giessenbachstrae, D-85748 Garching, GermanyDavid J. WilmanXiaohu YangKey Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory (the Partner Group of MPA), Nandan Road 80, Shanghai 200030, ChinaYoucai ZhangKey Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory (the Partner Group of MPA), Nandan Road 80, Shanghai 200030, ChinaStefano ZibettiDark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark

2011en

ABI

Аннотация

The influence of a galaxy's environment on its evolution has been studied and compared extensively in the literature, although differing techniques are often used to define environment. Most methods fall into two broad groups: those that use nearest neighbours to probe the underlying density field and those that use fixed apertures. The differences between the two inhibit a clean comparison between analyses and leave open the possibility that, even with the same data, different properties are actually being measured. In this work, we apply 20 published environment definitions to a common mock galaxy catalogue constrained to look like the local Universe. We find that nearest-neighbour-based measures best probe the internal densities of high-mass haloes, while at low masses the interhalo separation dominates and acts to smooth out local density variations. The resulting correlation also shows that nearestneighbour galaxy environment is largely independent of dark matter halo mass. Conversely, aperture-based methods that probe superhalo scales accurately identify high-density regions corresponding to high-mass haloes. Both methods show how galaxies in dense environments tend to be redder, with the exception of the largest apertures, but these are the strongest at recovering the background dark matter environment. We also warn against using photometric redshifts to define environment in all but the densest regions. When considering environment, there are two regimes: the 'local environment' internal to a halo best measured with nearest neighbour and 'large-scale environment' external to a halo best measured with apertures. This leads to the conclusion that there is no universal environment measure and the most suitable method depends on the scale being probed.

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DOI: 10.1111/j.1365-2966.2011.19922.x

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