Sample Variance in Cosmological Observations with a Narrow Field-of-View

Abstract

Surveys with a narrow field-of-view can play an important role in probing cosmology, but inferences from these surveys suffer from large sample variance, arising from random fluctuations around the cosmic mean. The standard method for computing the sample variance is based on two key approximations: treating perturbations linearly and the survey geometry as a box. We demonstrate that it can lead to a significant underestimate of the sample variance in narrow surveys. We present a new method for accurately computing the sample variance and apply our method to the recent observations of the warm-hot intergalactic medium (WHIM) based on spectroscopic measurements of blazars. We find that the sample variances in these surveys are significantly larger than the quoted measurement errors; for example, the cosmic mean baryon density contained in the WHIM could be lower by $54\%$ at $1\text{-}\sigma$ fluctuation than estimated in one observation. Accurately quantifying the sample variance is essential in deriving correct interpretations of the measurements in surveys with a small field-of-view.

arXiv comment6 pages, 2 figures, accepted for publication in ApJ

References in corpus (36)

• The Sloan Digital Sky Survey: Technical Summary
• The cosmological simulation code GADGET-2
• The 2dF Galaxy Redshift Survey: Spectra and redshifts
• The Cosmic Linear Anisotropy Solving System (CLASS) II: Approximation schemes
• The Baryon Oscillation Spectroscopic Survey of SDSS-III
• Planck 2018 results. I. Overview and the cosmological legacy of Planck
• The Cosmic Baryon Budget
• Power Spectrum Analysis of Three-Dimensional Redshift Surveys
• The Halo Occupation Distribution: Towards an Empirical Determination of the Relation Between Galaxies and Mass
• Baryons in the Warm-Hot Intergalactic Medium
• Transients from Initial Conditions in Cosmological Simulations
• A census of baryons in the Universe from localized fast radio bursts
• The Baryon Census in a Multiphase Intergalactic Medium: 30% of the Baryons May Still Be Missing
• Multi-Phase Galaxy Formation: High Velocity Clouds and the Missing Baryon Problem
• Sample Variance Considerations for Cluster Surveys
• Precision big bang nucleosynthesis with improved Helium-4 predictions
• Statistical Analysis of Galaxy Surveys - I. Robust error estimation for 2-point clustering statistics
• Cosmic Variance and Its Effect on the Luminosity Function Determination in Deep High z Surveys
• The Search for the Missing Baryons at Low Redshift
• Cosmic Variance in the Great Observatories Origins Deep Survey
• Observations of the MIssing Baryons in the warm-hot intergalactic medium
• A Cosmic Variance Cookbook
• A Lower Bound on the Cosmic Baryon Density
• Quantifying cosmic variance
• The Growth of Correlations in the Matter Power Spectrum
• On the Baryon Fractions in Clusters and Groups of Galaxies
• On the Hot Gas Content of the Milky Way Halo
• Emulation of baryonic effects on the matter power spectrum and constraints from galaxy cluster data
• Measuring the Cosmic Equation of State with Counts of Galaxies II: Error Budget for the DEEP2 Redshift Survey
• Simulating the X-ray Forest
• Detection of the Missing Baryons toward the Sightline of H1821+643
• The ugrizYJHK luminosity distributions and densities from the combined MGC, SDSS and UKIDSS LAS datasets
• Random Distance Distribution for Spherical Objects: General Theory and Applications to n-Dimensional Physics
• The Morphological decomposition of Abell A868
• The challenge of measuring and mapping the missing baryons
• Cosmological Information Contents on the Light-Cone