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Correcting correlation functions for redshift-dependent interloper contamination

Farrow, Daniel J. and Sánchez, Ariel G. and Ciardullo, Robin and Cooper, Erin Mentuch and Davis, Dustin and Fabricius, Maximilian and Gawiser, Eric and Grasshorn Gebhardt, Henry S. and Gebhardt, Karl and Hill, Gary J. and Jeong, Donghui and Komatsu, Eiichiro and Landriau, Martin and Liu, Chenxu and Saito, Shun and Snigula, Jan and Wold, Isak G. B. (2021) Correcting correlation functions for redshift-dependent interloper contamination. Monthly Notices of the Royal Astronomical Society, 507 (3). pp. 3187-3206. ISSN 0035-8711. doi:10.1093/mnras/stab1986.

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The construction of catalogues of a particular type of galaxy can be complicated by interlopers contaminating the sample. In spectroscopic galaxy surveys this can be due to the misclassification of an emission line; for example in the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) low-redshift [O II] emitters may make up a few per cent of the observed Ly α emitter (LAE) sample. The presence of contaminants affects the measured correlation functions and power spectra. Previous attempts to deal with this using the cross-correlation function have assumed sources at a fixed redshift, or not modelled evolution within the adopted redshift bins. However, in spectroscopic surveys like HETDEX, where the contamination fraction is likely to be redshift dependent, the observed clustering of misclassified sources will appear to evolve strongly due to projection effects, even if their true clustering does not. We present a practical method for accounting for the presence of contaminants with redshift-dependent contamination fractions and projected clustering. We show using mock catalogues that our method, unlike existing approaches, yields unbiased clustering measurements from the upcoming HETDEX survey in scenarios with redshift-dependent contamination fractions within the redshift bins used. We show our method returns autocorrelation functions with systematic biases much smaller than the statistical noise for samples with at least as high as 7 per cent contamination. We also present and test a method for fitting for the redshift-dependent interloper fraction using the LAE–[O II] galaxy cross-correlation function, which gives less biased results than assuming a single interloper fraction for the whole sample.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Farrow, Daniel J.0000-0003-2575-0652
Sánchez, Ariel G.0000-0003-1198-831X
Ciardullo, Robin0000-0002-1328-0211
Cooper, Erin Mentuch0000-0002-2307-0146
Davis, Dustin0000-0002-8925-9769
Fabricius, Maximilian0000-0002-7025-6058
Gawiser, Eric0000-0003-1530-8713
Grasshorn Gebhardt, Henry S.0000-0002-8158-0523
Gebhardt, Karl0000-0002-8433-8185
Jeong, Donghui0000-0002-8434-979X
Komatsu, Eiichiro0000-0002-0136-2404
Landriau, Martin0000-0003-1838-8528
Liu, Chenxu0000-0001-5561-2010
Saito, Shun0000-0002-6186-5476
Snigula, Jan0000-0003-4044-5357
Wold, Isak G. B.0000-0002-0784-1852
Additional Information:© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Accepted 2021 July 2. Received 2021 June 29; in original form 2021 April 9. Published: 16 July 2021. The authors acknowledge the feedback from the internal HETDEX referees and the anonymous journal referee. We acknowledge useful discussions with Humna Awan, Jiamin Hou, Martha Lippich, Andrea Pezzotta, Agne Semenaite, Martín Crocce, Román Scoccimarro, and the HETDEX cosmology science working group. Henry S. Grasshorn Gebhardt is a National Aeronautics and Space Administration (NASA) Postdoctoral Program Fellow. KG acknowledges support from the National Science Foundation (NSF) via grant NSF-2008793. EG was supported by the Department of Energy via grant DE-SC0010008. EK’s work was supported in part by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC-2094 – 390783311. DJ was supported at Pennsylvania State University by the NASA ATP program (80NSSC18K1103). We acknowledge the use of the PYTHON libraries MATPLOTLIB (Hunter 2007), ASTROPY (Astropy Collaboration et al. 2013, 2018), NUMPY (Harris et al. 2020), and SCIPY (Virtanen et al. 2020). This research also used TOPCAT (Taylor 2005), STILTS (Taylor 2006); and the GNU Scientific Library (GSL); URL: HETDEX is led by the University of Texas at Austin McDonald Observatory and Department of Astronomy with participation from the Ludwig-Maximilians-Universität München, Max-Planck-Institut für Extraterrestrische Physik (MPE), Leibniz-Institut für Astrophysik Potsdam (AIP), Texas A&M University, Pennsylvania State University, Institut für Astrophysik Göttingen, The University of Oxford, Max-Planck-Institut für Astrophysik (MPA), The University of Tokyo, and Missouri University of Science and Technology. In addition to Institutional support, HETDEX is funded by the National Science Foundation (grant AST-0926815), the State of Texas, the US Air Force (AFRL FA9451-04-2-0355), and generous support from private individuals and foundations. The observations were obtained with the Hobby-Eberly Telescope (HET), which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen. The HET is named in honour of its principal benefactors, William P. Hobby and Robert E. Eberly. The authors acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing high performance computing, visualization, and storage resources that have contributed to the research results reported within this paper; URL: This research made use of NASA’s Astrophysics Data System Bibliographic Services. Data Availability: The HETDEX data are currently proprietary, but public releases are planned for the future. The authors will respond to reasonable requests for access to the simulation data used in this paper, so long as no unreleased proprietary data is involved.
Funding AgencyGrant Number
NASA Postdoctoral ProgramUNSPECIFIED
Department of Energy (DOE)DE-SC0010008
Deutsche Forschungsgemeinschaft (DFG)EXC-2094 - 390783311
Pennsylvania State UniversityUNSPECIFIED
Air Force Research Laboratory (AFRL)FA9451-04-2-0355
Subject Keywords:methods: data analysis – cosmology: observations – large-scale structure of the Universe
Issue or Number:3
Record Number:CaltechAUTHORS:20211116-183346911
Persistent URL:
Official Citation:Daniel J Farrow, Ariel G Sánchez, Robin Ciardullo, Erin Mentuch Cooper, Dustin Davis, Maximilian Fabricius, Eric Gawiser, Henry S Grasshorn Gebhardt, Karl Gebhardt, Gary J Hill, Donghui Jeong, Eiichiro Komatsu, Martin Landriau, Chenxu Liu, Shun Saito, Jan Snigula, Isak G B Wold, Correcting correlation functions for redshift-dependent interloper contamination, Monthly Notices of the Royal Astronomical Society, Volume 507, Issue 3, November 2021, Pages 3187–3206,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111900
Deposited By: Tony Diaz
Deposited On:16 Nov 2021 22:30
Last Modified:16 Nov 2021 22:30

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