Colloquium: Mayuri S. Rao (RSAA) "On the detection of spectral distortions in the CMB: recombination to reionization"

Date & time

11am–12pm 20 April 2017


Duffield Lecture Theatre


Mayuri S. Rao (RSAA)


The ΛCDM model of cosmology predicts inevitable, weak distortions in the spectrum of the Cosmic Microwave Background (CMB) from that of a blackbody. However, no such deviations have been measured to date. In this talk, I focus on CMB spectral distortions arising from the cosmological epochs of recombination and cosmic dawn & reionization (collectively called EoR henceforth). A detection and measurement of these CMB spectral distortions will enable a better understanding of the thermal and ionization history of the Universe and help us probe redshifts that have never been directly observed thus far. I present a feasibility study for a ground-based detection of extremely weak, ripple-like additive features in the CMB spectrum created by photons emitted during cosmological recombination (900 < z < 7000). I introduce the Maximally Smooth (MS) function, an algorithm to distinguish smooth foregrounds from the ripple like signal. Using synthetic spectra, I demonstrate the efficacy of using MS functions over polynomials to separate foregrounds from the cosmological recombination signal. I also present GMOSS: Global model for the radio sky spectrum, a physically motivated model of the low-frequency radio sky. Using GMOSS I investigate the spectral complexity expected in foregrounds and the effect of the same on detection of the global redshifted 21-cm signal from EoR (6 < z < 150). Once again, I demonstrate the advantage of using MS functions over polynomials to separate foregrounds from the global EoR signal in mock-sky spectra. I conclude the talk with a brief discussion on design criteria for radio-telescopes seeking to detect distortions in the CMB spectrum arising from the epochs of recombination through reionization.

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