The Impact of Cosmic Variance and Satellites on JWST Clustering Measurements at redshift ≈6
5 affiliations
- 1University of California Department of Physics, , Santa Barbara, CA 93106 ,
- 2Center for Astrophysics | Harvard & Smithsonian , 60 Garden St., Cambridge, MA 02138 ,
- 3Leiden Observatory, Leiden University , NL-2300 RA Leiden ,
- 4University of Michigan Department of Astronomy, , 1085 S. University Ave., Ann Arbor, MI 48109 ,
- 5Lorentz Institute for Theoretical Physics, Leiden University , PO Box 9506, NL2300 RA Leiden ,
Abstract
We present a framework for inferring the dark matter halo masses of quasars and [O III]-emitting galaxies from JWST/NIRCam Wide Field Slitless Spectroscopy (WFSS) clustering measurements at z ≈ 6. Using the FLAMINGO-10k N-body simulation, we construct mock realizations of quasar and galaxy catalogs that incorporate realistic selection functions, spatial coverage, and sensitivity limits matched to the ASPIRE survey. These mocks enable accurate measurements of the quasar–galaxy cross-correlation and galaxy auto-correlation functions, with covariance matrices derived from 1000 realizations that capture both cosmic variance and bin-to-bin correlations. We employ Bayesian inference to fit the correlation functions and infer the minimum halo masses for quasars and galaxies. Our results demonstrate that Poisson pair-count uncertainties, commonly adopted in high-redshift clustering studies, significantly underestimate the true measurement errors. The dominant missing component is cosmic variance, whose coherent large-scale modes inflate the diagonal of the covariance matrix and induce positive bin-to-bin correlations, both growing with tracer bias. In particular, 1) the commonly used Poisson error on the correlation functions underestimates the true uncertainty by a factor of ≈3; 2) the uncertainties on the inferred minimum halo masses are underestimated by a factor of ≈1.5–3 when adopting Poisson errors instead of the full covariance matrix; 3) the inferred QSO halo mass is robust to whether central and satellite [O iii]-emitters share a common mass threshold. Our framework provides a more complete error budget for JWST/WFSS clustering analyses, enabling robust constraints on the host halo masses and duty cycles of high-redshift quasars and emission-line galaxies.
Related
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BibTeX
@article{huang2026impact,
title = {{The Impact of Cosmic Variance and Satellites on JWST Clustering Measurements at redshift ≈6}},
author = {Jiamu Huang and Elia Pizzati and Joseph Hennawi and Joop Schaye and Feige Wang and Matthieu Schaller and Benjamin Snyder and Yi Kang},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = oct,
doi = {10.1093/mnras/stag1987},
url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1987/8943794},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - The Impact of Cosmic Variance and Satellites on JWST Clustering Measurements at redshift ≈6
AU - Jiamu Huang
AU - Elia Pizzati
AU - Joseph Hennawi
AU - Joop Schaye
AU - Feige Wang
AU - Matthieu Schaller
AU - Benjamin Snyder
AU - Yi Kang
PY - 2026
DA - 2026/10/19
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag1987
UR - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1987/8943794
AB - We present a framework for inferring the dark matter halo masses of quasars and [O III]-emitting galaxies from JWST/NIRCam Wide Field Slitless Spectroscopy (WFSS) clustering measurements at z ≈ 6. Using the FLAMINGO-10k N-body simulation, we construct mock realizations of quasar and galaxy catalogs that incorporate realistic selection functions, spatial coverage, and sensitivity limits matched to the ASPIRE survey. These mocks enable accurate measurements of the quasar–galaxy cross-correlation and galaxy auto-correlation functions, with covariance matrices derived from 1000 realizations that capture both cosmic variance and bin-to-bin correlations. We employ Bayesian inference to fit the correlation functions and infer the minimum halo masses for quasars and galaxies. Our results demonstrate that Poisson pair-count uncertainties, commonly adopted in high-redshift clustering studies, significantly underestimate the true measurement errors. The dominant missing component is cosmic variance, whose coherent large-scale modes inflate the diagonal of the covariance matrix and induce positive bin-to-bin correlations, both growing with tracer bias. In particular, 1) the commonly used Poisson error on the correlation functions underestimates the true uncertainty by a factor of ≈3; 2) the uncertainties on the inferred minimum halo masses are underestimated by a factor of ≈1.5–3 when adopting Poisson errors instead of the full covariance matrix; 3) the inferred QSO halo mass is robust to whether central and satellite [O iii]-emitters share a common mass threshold. Our framework provides a more complete error budget for JWST/WFSS clustering analyses, enabling robust constraints on the host halo masses and duty cycles of high-redshift quasars and emission-line galaxies.
SN - 0035-8711
SN - 1365-2966
ER -