http://arxiv.org/abs/2304.09191
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. The standard method for computing the sample variance is based on two key approximations, and 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.
P. Espenshade and J. Yoo
Thu, 20 Apr 23
53/57
Comments: 6 pages, 2 figures, submitted to ApJL
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