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Title: Erasing the variable: empirical foreground discovery for global 21 cm spectrum experiments

Spectral measurements of the 21 cm monopole background have the promise of revealing the bulk energetic properties and ionization state of our universe from z ∼ 6-30. Synchrotron foregrounds are orders of magnitude larger than the cosmological signal and are the principal challenge faced by these experiments. While synchrotron radiation is thought to be spectrally smooth and described by relatively few degrees of freedom, the instrumental response to bright foregrounds may be much more complex. To deal with such complexities, we develop an approach that discovers contaminated spectral modes using spatial fluctuations of the measured data. This approach exploits the fact that foregrounds vary across the sky while the signal does not. The discovered modes are projected out of each line of sight of a data cube. An angular weighting then optimizes the cosmological signal amplitude estimate by giving preference to lower-noise regions. Using this method, we show that it is essential for the passband to be stable to at least ∼10{sup –4}. In contrast, the constraints on the spectral smoothness of the absolute calibration are mainly aesthetic if one is able to take advantage of spatial information. To the extent it is understood, controlling polarization to intensity leakage atmore » the ∼10{sup –2} level will also be essential to rejecting Faraday rotation of the polarized synchrotron emission.« less
Authors:
 [1] ;  [2]
  1. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  2. Department of Astronomy, UC Berkeley, Berkeley, CA 94720 (United States)
Publication Date:
OSTI Identifier:
22370556
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 793; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; DATA ANALYSIS; DEGREES OF FREEDOM; EMISSION; FARADAY EFFECT; FLUCTUATIONS; LIMITING VALUES; POLARIZATION; ROUGHNESS; SKY; SPECTRA; STARS; SYNCHROTRON RADIATION; UNIVERSE