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Effects of [N II] and Hα line blending on the WFIRST Galaxy redshift survey

Martens, Daniel and Fang, Xiao and Troxel, M. A. and DeRose, Joe and Hirata, Christopher M. and Wechsler, Risa H. and Wang, Yun (2019) Effects of [N II] and Hα line blending on the WFIRST Galaxy redshift survey. Monthly Notices of the Royal Astronomical Society, 485 (1). pp. 211-228. ISSN 0035-8711. doi:10.1093/mnras/stz391.

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The Wide Field Infrared Survey Telescope (WFIRST) will conduct a galaxy redshift survey using the Hα emission line primarily for spectroscopic redshift determination. Due to the modest spectroscopic resolution of the grism, the Hα and the neighbouring [N II] lines are blended, leading to a redshift bias that depends on the [N II]/Hα ratio, which is correlated with a galaxy’s metallicity, hence mass and ultimately environment. We investigate how this bias propagates into the galaxy clustering and cosmological parameters obtained from the WFIRST. Using simulation, we explore the effect of line blending on redshift-space distortion and baryon acoustic oscillation (BAO) measurements. We measure the BAO parameters α∥, α⊥, the logarithmic growth factor f_v, and calculate their errors based on the correlations between the line ratio and large-scale structure. We find Δα∥ = 0.31±0.23 per cent (⁠0.26±0.17 per cent⁠), Δα⊥ = −0.10±0.10 per cent per cent (⁠−0.12±0.11 per cent⁠), and Δf_v = 0.17±0.33 per cent (⁠−0.20±0.30 per cent⁠) for redshift 1.355–1.994 (0.700–1.345), which use approximately 18  per cent per cent⁠, 9  per cent per cent⁠, and 7  per cent per cent of the systematic error budget in a root-sum-square sense. These errors may already be tolerable but further mitigations are discussed. Biases due to the environment-independent redshift error can be mitigated by measuring the redshift error probability distribution function. High-spectral-resolution reobservation of a few thousand galaxies would be required (if by direct approach) to reduce them to below 25  per cent per cent of the error budget. Finally, we outline the next steps to improve the modelling of [N II]-induced blending biases and their interaction with other redshift error sources.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Fang, Xiao0000-0002-5054-9566
Hirata, Christopher M.0000-0002-2951-4932
Wechsler, Risa H.0000-0003-2229-011X
Additional Information:© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2019 February 6. Received 2019 January 19; in original form 2018 April 21. Published: 08 February 2019. We would like to thank Paul Martini for input on galaxy mass–metallicity relations. We appreciate the many useful conversations with Ami Choi, Niall MacCrann, and Heidi Wu. Further thanks to Paulo Montero-Camacho, Benjamin Buckman, Ben Wibking, and Matthew Digman. We thank Ashley J. Ross for his contributions to our correlation function pipeline. We would also like to thank James Rhoads and Sangeeta Malhotra for providing feedback on our results and taking part in discussions on ideas for future work. We are also grateful for suggestions from an anonymous referee which improved the paper. DM, XF, and CMH are supported by the Simons Foundation, the U.S. Department of Energy, the Packard Foundation, the NSF, and NASA. RHW and JD received partial support through NASA contract NNG16PJ25C, from NASA ROSES ATP 16-ATP16-0084 grant, and from the U.S. Department of Energy under contract number DE-AC02-76SF00515. This research used computational resources at SLAC National Accelerator Laboratory, a U.S. Department of Energy Office; the authors thank the support of the SLAC computational team. Many computations in this paper were run on the CCAPP condo of the Ruby Cluster at the Ohio Supercomputer Center (Ohio Supercomputer Center 1987). This research made extensive use of the arXiv and NASA’s Astrophysics Data System for bibliographic information.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Simons FoundationUNSPECIFIED
Department of Energy (DOE)DE-AC02-76SF00515
David and Lucile Packard FoundationUNSPECIFIED
NASAATP 16-ATP16-0084
Subject Keywords:line: identification – surveys – cosmology: observations
Issue or Number:1
Record Number:CaltechAUTHORS:20190523-134602668
Persistent URL:
Official Citation:Daniel Martens, Xiao Fang, M A Troxel, Joe DeRose, Christopher M Hirata, Risa H Wechsler, Yun Wang, Effects of [N II] and H α line blending on the WFIRST Galaxy redshift survey, Monthly Notices of the Royal Astronomical Society, Volume 485, Issue 1, May 2019, Pages 211–228,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95765
Deposited By: Tony Diaz
Deposited On:23 May 2019 21:06
Last Modified:16 Nov 2021 17:15

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