Simons Observatory science targets

Simons Observatory (SO) key targets are: the physics of primordial perturbations, identifying the correct model of an early inflationary epoch of the Universe; effective number of relativistic species; the sum of neutrino masses; observable deviations from the cosmological constant paradigm; galaxy evolution; redshift and duration of the reionization epoch. Simons Observatory key science targets are summarized in Table (1).

Tab.1. Projected 1σ errors as in the SO Science Overview Paper, with the addition of neutrino mass limits for an optical depth measurement of σ(τ ) = 0.002, achievable with LiteBIRD soon after SO-Nominal is concluded. Sec. 2 of the SO Science Overview paper describes our methods to account for noise properties and foreground uncertainties. A 20% end-to-end observation efficiency is used, matching what has been typically achieved in Chile. We assume SO is combined with Planck data. Further details on this table can be found in the Astro2020 APC White Paper.
b) Primarily from BICEP2-Keck collaboration and Planck collaboration. We anticipate data from existing ground-based data to improve on the ‘current’ limits by 2022. Constraints are expected to lie between the ‘current’ and SO-Nominal levels.
d) The SO observables and external datasets used, as summarized in the SO Science Overview paper except for LiteBIRD (LB) added here.
e) The SO-Goal projected uncertainty with zero foregrounds is σ(r) = 0.0007.
f) Neglecting foregrounds and possible systematic errors, σ(Σmν ) would be 0.016 eV for this case.

The 1σ forecast uncertainties on each parameter for the baseline and goal noise levels are specified. For the baseline case, we show the forecast uncertainty, and also, for each case, we inflate the uncertainty by 25% (rounding up to 1 significant figure) as a proxy for additional systematic errors, to be refined in future studies. For each science target we also give the current uncertainty to ease the comparison with expected SO performance.

The Simons Observatory has a set of secondary science goals summarized in Table (2). These include measuring additional non-Gaussian parameters describing the primordial perturbations and again identifying the correct model of an early inflationary epoch of the Universe, probing Big Bang Nucleosynthesis by measuring the primordial helium fraction, constraining interactions between dark matter particles and baryons, constraining the mass of ultra-light-axion dark matter, measuring the dark energy equation of state to cross-check constraints from optical surveys, calibrating the shear bias for LSST, and constraining the ionization efficiency in models of reionization.

The Simons Observatory is poised to advance a broad range of Galactic science. The high angular resolution maps of polarized emission from SO will enable characterization of interstellar turbulence on small spatial scales and the mapping of the structure of the magnetic field over a range of scales and environments, from diffuse regions to cold cores. With the multi-frequency SO data, we will characterize the physics of Galactic emission by improving constraints on the dust and synchrotron spectral energy distributions, including the presence of multiple dust populations, curvature in the synchrotron spectrum, and the existence of polarized anomalous microwave emission.

Finally, SO’s broader aim is to produce several high-level legacy catalogues for use by the general astronomical community. The extent of these catalogues is summarized in the first entry of Table (2).

Tab.2. Catalogs and additional science from SO. The extended version of this table can be found in the summary section of the SO Science Overview paper.