41 research outputs found
CosmoSpec: Fast and detailed computation of the cosmological recombination radiation from hydrogen and helium
We present the first fast and detailed computation of the cosmological
recombination radiation released during the hydrogen (redshift z ~ 1300) and
helium (z ~ 2500 and z ~ 6000) recombination epochs, introducing the code
CosmoSpec. Our computations include important radiative transfer effects,
500-shell bound-bound and free-bound emission for all three species, the
effects of electron scattering and free-free absorption as well as interspecies
(HeII --> HeI --> HI) photon feedback. The latter effect modifies the shape and
amplitude of the recombination radiation and CosmoSpec improves significantly
over previous treatments of it. Utilizing effective multilevel atom and
conductance approaches, one calculation takes only ~ 15 seconds on a standard
laptop as opposed to days for previous computations. This is an important step
towards detailed forecasts and feasibility studies considering the detection of
the cosmological recombination lines and what one may hope to learn from the ~
6.1 photons emitted per hydrogen atom in the three recombination eras. We
briefly illustrate some of the parameter dependencies and discuss remaining
uncertainties in particular related to collisional processes and the neutral
helium atom model.Comment: 14 pages, 10 figures, submitted to MNRA
Cosmology with the Highly Redshifted 21cm Line
In addition to being a probe of Cosmic Dawn and Epoch of Reionization
astrophysics, the 21cm line at is also a powerful way to constrain
cosmology. Its power derives from several unique capabilities. First, the 21cm
line is sensitive to energy injections into the intergalactic medium at high
redshifts. It also increases the number of measurable modes compared to
existing cosmological probes by orders of magnitude. Many of these modes are on
smaller scales than are accessible via the CMB, and moreover have the advantage
of being firmly in the linear regime (making them easy to model theoretically).
Finally, the 21cm line provides access to redshifts prior to the formation of
luminous objects. Together, these features of 21cm cosmology at provide
multiple pathways toward precise cosmological constraints. These include the
"marginalizing out" of astrophysical effects, the utilization of redshift space
distortions, the breaking of CMB degeneracies, the identification of signatures
of relative velocities between baryons and dark matter, and the discovery of
unexpected signs of physics beyond the CDM paradigm at high redshifts.Comment: Science white paper submitted to Decadal 2020 surve