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Foregrounds for 21-cm observations of neutral gas at high redshift

Oh, S. Peng and Mack, Katherine J. (2003) Foregrounds for 21-cm observations of neutral gas at high redshift. Monthly Notices of the Royal Astronomical Society, 346 (3). pp. 871-877. ISSN 0035-8711. doi:10.1111/j.1365-2966.2003.07133.x.

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We investigate a number of potential foregrounds for an ambitious goal of future radio telescopes such as the Square Kilometer Array (SKA) and the Low Frequency Array (LOFAR): spatial tomography of neutral gas at high redshift in 21-cm emission. While the expected temperature fluctuations due to unresolved radio point sources is highly uncertain, we point out that free–free emission from the ionizing haloes that reionized the Universe should define a minimal bound. This emission is likely to swamp the expected brightness temperature fluctuations, making proposed detections of the angular patchwork of 21-cm emission across the sky unlikely to be viable. Hα observations with JWST could place an upper bound on the contribution of high-redshift sources to the free–free background. An alternative approach is to discern the topology of reionization from spectral features due to 21-cm emission along a pencil-beam slice. This requires tight control of the frequency-dependence of the beam in order to prevent foreground sources from contributing excessive variance. We also investigate potential contamination by galactic and extragalactic radio recombination lines (RRLs). These are unlikely to be show-stoppers, although little is known about the distribution of RRLs away from the Galactic plane. The mini-halo emission signal is always less than that of the intergalactic medium (IGM), making mini-haloes unlikely to be detectable. If they are seen, it will be only in the very earliest stages of structure formation at high redshift, when the spin temperature of the IGM has not yet decoupled from the cosmic microwave background.

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Additional Information:© 2003 RAS. Accepted 2003 August 20. Received 2003 August 6; in original form 2003 February 10. KM thanks Mark Gordon, Bill Erickson, Peter Shaver, Harry Payne, Miller Goss, and Rod Davies for helpful correspondence, and the Caltech Summer Undergraduate Research Fellowship (SURF) office at Caltech for financial support. SPO was supported by NSF grant AST-0096023. We thank the anonymous referee for pointing out that Hα observations with JWST could identify free–free sources below the SKA flux cut-off.
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Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Subject Keywords:galaxies: formation, cosmology: theory, large-scale structure of Universe
Issue or Number:3
Record Number:CaltechAUTHORS:20180413-161003284
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Official Citation:S. Peng Oh, Katherine J. Mack; Foregrounds for 21-cm observations of neutral gas at high redshift, Monthly Notices of the Royal Astronomical Society, Volume 346, Issue 3, 11 December 2003, Pages 871–877,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85860
Deposited By: George Porter
Deposited On:16 Apr 2018 15:12
Last Modified:15 Nov 2021 20:32

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