Predictions for the diffuse cosmic dipole at radio frequencies from reionization imprints
Journal
Date Issued
2019
Author(s)
Abstract
The cosmological reionization can be studied in the radio through the
tomographic view offered by the redshifted 21-cm line and the integrated
information carried out by the diffuse free-free emission, coupled to the
Comptonization distortion, relevant at higher frequencies. Current predictions
span a wide range of possibilities, while the recent EDGES observations
disagree with the standard models and call, if confirmed, for non-standard
physical processes and/or for an early population of extragalactic sources
producing a remarkable background at high redshifts almost consistent with the
ARCADE 2 claim of a significant excess of CMB absolute temperature at low
frequency. These signatures can be observed in global signal and fluctuations,
from very large to small angular scales. The observer peculiar motion with
respect to a reference frame in rest with respect to the CMB produces boosting
effects in various observable quantities, remarkable at low multipoles, and
particularly in the dipole, with frequency spectral behaviours depending on the
monopole emission spectrum. We present a novel investigation at radio
frequencies, aimed at predicting the imprints expected in the redshifted 21-cm
line signal and in the diffuse free-free emission plus the Comptonization
distortion for several models. Furthermore, we consider the same type of signal
but expected from the cosmological radio background determining the offset for
21-cm line. The combination of these signals and their relevance in the various
frequency ranges are studied. This approach, linking monopole and anisotropy
analyses, can be applied on wide sky coverage surveys as well as to sets of sky
patches. Relying only on the quality of interfrequency and relative data
calibration, it in principle by-passes the need for precise absolute
calibration, a critical point of current and future radio interferometric
facilities.
Volume
631
Start page
A61
Issn Identifier
0004-6361
Ads BibCode
2019A&A...631A..61T
Rights
open.access
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