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19 April 2024 |
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The redshifted 21-cm signal in the EDGES low-band spectrum | | Saurabh Singh
; Ravi Subrahmanyan
; | | Date: |
11 Mar 2019 | | Abstract: | The EDGES collaboration reported the finding of an unexpectedly deep
absorption in the radio background at 78~MHz based on their low-band
observations, and interpreted the dip as a first detection of redshifted 21-cm
from Cosmic Dawn. We have attempted an alternate analysis, adopting a maximally
smooth function approach to model the foreground. A joint fit to the spectrum
using such a function together with a flattened absorption profile yields a
best fit absorption amplitude of $921 pm 35$~mK with full width $19.2 pm
0.2$~MHz centered at $78.2 pm 0.1$~MHz. The depth of the 21-cm absorption
inferred by the EDGES analysis required invoking non-standard cosmology at
Cosmic Dawn and this tension between interpretation of their data and accepted
models is compounded by our analysis that suggests absorption of greater depth.
Alternatively, the measured spectrum may be equally-well fit assuming that
there exists a residual unmodeled systematic sinusoidal feature with 12~MHz
period and peak amplitude 60~mK, which leads to the option of avoiding the
discordance between the deep and flattened absorption with more accepted
astrophysical cosmology by assuming that such a sinusoidal systematic exists in
the spectrum, which has escaped their calibrations. We explore this possibility
further by examining for any additional redshifted 21-cm signal in the data.
The data then favors an absorption with Gaussian model parameters of amplitude
$133$~mK, best width at half-power $9$~MHz and center frequency $72.5$~MHz. We
also examine the consistency of the measured spectrum with plausible redshifted
21-cm models: a set of 3 of the 265 profiles in the global 21-cm atlas of
cite{2017MNRAS.472.1915C} are favored by the spectrum. We conclude that the
EDGES data may be consistent with standard cosmology and astrophysics, without
invoking excess radio backgrounds or baryon-dark matter interactions. | | Source: | arXiv, 1903.4540 | | Services: | Forum | Review | PDF | Favorites | |
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