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Halo histories versus galaxy properties at z = 0 II: large-scale galactic conformity

Tinker, Jeremy L. and Hahn, ChangHoon and Mao, Yao-Yuan and Wetzel, Andrew R. and Conroy, Charlie (2018) Halo histories versus galaxy properties at z = 0 II: large-scale galactic conformity. Monthly Notices of the Royal Astronomical Society, 477 (1). pp. 935-945. ISSN 0035-8711. doi:10.1093/mnras/sty666.

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Using group catalogues from the Sloan Digital Sky Survey (SDSS) Data Release 7, we measure galactic conformity in the local universe. We measure the quenched fraction of neighbour galaxies around isolated primary galaxies, dividing the isolated sample into star-forming and quiescent objects. We restrict our measurements to scales >1 Mpc to probe the correlations between halo formation histories. Over the stellar mass range 10^(9.7) ≤ M*/M⊙ ≤ 10^(10.9), we find minimal evidence for conformity. We further compare these data to predictions of the halo age-matching model, in which the oldest galaxies are associated with the oldest haloes. For models with strong correlations between halo and stellar age, the conformity is too large to be consistent with the data. Weaker implementations of the age-matching model would not produce a detectable signal in SDSS data. We reproduce the results of Kauffmann et al., in which the star formation rates of neighbour galaxies are reduced around primary galaxies when the primaries are low star formers. However, we find this result is mainly driven by contamination in the isolation criterion; when removing the small fraction of satellite galaxies in the sample, the conformity signal largely goes away. Lastly, we show that small conformity signals, i.e. 2–5 per cent differences in the quenched fractions of neighbour galaxies, can be produced by mechanisms other than halo assembly bias. For example, if passive galaxies occupy more massive haloes than star-forming galaxies of the same stellar mass, a conformity signal that is consistent with recent measurements from PRIMUS (Berti et al.) can be produced.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Mao, Yao-Yuan0000-0002-1200-0820
Wetzel, Andrew R.0000-0003-0603-8942
Conroy, Charlie0000-0002-1590-8551
Additional Information:© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2018 March 9. Received 2018 February 27; in original form 2017 March 22. Published: 15 March 2018. The authors wish to thank Michael Blanton and Risa Wechsler for many useful discussions. ARW was supported by a Caltech-Carnegie Fellowship, in part through the Moore Center for Theoretical Cosmology and Physics at Caltech. The authors thank Matthew R. Becker for providing the Chinchilla simulation used in this work. The Chinchilla simulation and related analysis were performed using computational resources at SLAC. We thank the SLAC computational team for their consistent support. The authors acknowledge the Gauss Centre for Supercomputing e.V. ( and the Partnership for Advanced Supercomputing in Europe ( for funding the MultiDark simulation project by providing computing time on the GCS Supercomputer SuperMUC at Leibniz Supercomputing Centre ( The Bolshoi simulations have been performed within the Bolshoi project of the University of California High-Performance AstroComputing Center and were run at the NASA Ames Research Center.
Group:TAPIR, Moore Center for Theoretical Cosmology and Physics
Funding AgencyGrant Number
Caltech-Carnegie FellowshipUNSPECIFIED
Caltech Moore Center for Theoretical Cosmology and PhysicsUNSPECIFIED
Subject Keywords:galaxies: evolution – galaxies: haloes
Issue or Number:1
Record Number:CaltechAUTHORS:20180606-105527709
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Official Citation:Jeremy L Tinker, ChangHoon Hahn, Yao-Yuan Mao, Andrew R Wetzel, Charlie Conroy; Halo histories versus galaxy properties at z = 0 II: large-scale galactic conformity, Monthly Notices of the Royal Astronomical Society, Volume 477, Issue 1, 11 June 2018, Pages 935–945,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86835
Deposited By: Tony Diaz
Deposited On:06 Jun 2018 18:03
Last Modified:15 Nov 2021 20:42

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