The Simons Observatory: Science goals and forecasts

Abstract: The Simons Observatory (SO) is a new cosmic microwave background experiment being built on Cerro Toco in Chile, due to begin observations in the early 2020s. We describe the scientific goals of the experiment, motivate the design, and forecast its performance. SO will measure the temperature and polarization anisotropy of the cosmic microwave background in six frequency bands: 27, 39, 93, 145, 225 and 280 GHz. The initial configuration of SO will have three small-aperture 0.5-m telescopes (SATs) and one large-aperture 6-m telescope (LAT), with a total of 60,000 cryogenic bolometers. Our key science goals are to characterize the primordial perturbations, measure the number of relativistic species and the mass of neutrinos, test for deviations from a cosmological constant, improve our understanding of galaxy evolution, and constrain the duration of reionization. The SATs will target the largest angular scales observable from Chile, mapping ~10% of the sky to a white noise level of 2 $\mu$K-arcmin in combined 93 and 145 GHz bands, to measure the primordial tensor-to-scalar ratio, $r$, at a target level of $\sigma(r)=0.003$. The LAT will map ~40% of the sky at arcminute angular resolution to an expected white noise level of 6 $\mu$K-arcmin in combined 93 and 145 GHz bands, overlapping with the majority of the LSST sky region and partially with DESI. With up to an order of magnitude lower polarization noise than maps from the Planck satellite, the high-resolution sky maps will constrain cosmological parameters derived from the damping tail, gravitational lensing of the microwave background, the primordial bispectrum, and the thermal and kinematic Sunyaev-Zel'dovich effects, and will aid in delensing the large-angle polarization signal to measure the tensor-to-scalar ratio. The survey will also provide a legacy catalog of 16,000 galaxy clusters and more than 20,000 extragalactic sources.

• The paper presents the Simons Observatory’s innovative design, combining small and large aperture telescopes to achieve noise levels of 2 μK-arcmin and 6 μK-arcmin for precise CMB measurements.
• The paper forecasts enhanced constraints on primordial perturbations by targeting a tensor-to-scalar ratio uncertainty of σ(r)=0.003 and refining neutrino mass estimates.
• The paper implies that SO's high-resolution data will synergize with surveys like LSST and DESI, advancing our understanding of cosmic structure, galaxy evolution, and reionization.

The Simons Observatory: Science Goals and Forecasts

The paper, "The Simons Observatory: Science goals and forecasts," delineates the ambitious objectives and planned methodologies of the Simons Observatory (SO), a considerable cosmic microwave background (CMB) observation initiative. Situated at Cerro Toco, Chile, the observatory is poised to begin its operations in the early 2020s. Integral to the paper is a comprehensive explication of SO's scientific endeavors, which aim to unravel fundamental cosmological phenomena such as primordial perturbations, neutrino masses, and potential deviations from a cosmological constant.

Infrastructure and Methodology

The SO features a multi-faceted apparatus combining three small-aperture 0.5-meter telescopes with a large-aperture 6-meter telescope. This configuration is anticipated to be equipped with an array of 60,000 cryogenic bolometers, targeting six frequency bands centered at 27, 39, 93, 145, 225, and 280 GHz.

• Small-Aperture Telescopes: These telescopes are engineered to map approximately 10% of the celestial sphere. They are critical for detecting large angular scales, aiming for a white noise level of 2 μK-arcmin in the 93 GHz and 145 GHz bands. Their data will predominantly contribute to measurements of the primordial tensor-to-scalar ratio, $r$, targeted at an uncertainty of $\sigma(r)=0.003$.
• Large-Aperture Telescope: Intended for a finer resolution survey over about 40% of the sky, this telescope will achieve an anticipated white noise level of 6 μK-arcmin. This high-resolution capability facilitates synergies with other large-scale surveys from the Large Synoptic Survey Telescope (LSST) and the Dark Energy Spectroscopic Instrument (DESI).

Science Objectives

SO aims to make significant contributions across several domains in cosmology:

1. Primordial Perturbations: By refining the tensor-to-scalar ratio $r$, SO will offer insights into the inflationary paradigm of the early universe.
2. Relativistic Species and Neutrino Mass: The observatory's measurements seek to constrain the effective number of relativistic species ($N_{\text{eff}}$) and assess the absolute mass scale of neutrinos, which holds profound implications for particle physics and cosmology.
3. Gravitational Lensing and Bispectrum: SO's high-resolution data will improve measurements of CMB lensing, enabling a deeper understanding of mass distribution in the universe and constraining the primordial bispectrum.
4. Sunyaev–Zel'dovich Effects: The survey will also elucidate thermal and kinematic Sunyaev–Zel'dovich effects, thereby enhancing knowledge about galaxy cluster dynamics and the thermal history of cosmic structure formation.
5. Galaxy Evolution and Reionization: By providing a comprehensive legacy catalog containing approximately 16,000 galaxy clusters and over 20,000 extragalactic sources, the data from SO will aid in constraining the epoch of reionization and improve models of galaxy evolution.

Implications and Future Directions

The Simons Observatory represents a pivotal advance in CMB research, functioning at the convergence of observational cosmology and theoretical astrophysics. By enhancing precision in CMB measurements and reducing noise levels, SO aims to set unprecedented benchmarks in the field.

Future developments in CMB research facilitated by SO data might include refining models of early universe inflation, elucidating dark energy's influence via more precise measurements of the cosmic expansion history, and further integration with complementary astrophysical surveys to unify diverse cosmological measurements under a single grand narrative.

In conclusion, the Simons Observatory endeavors to push the boundaries of cosmological research, adding a pivotal layer of understanding to fundamental questions about the universe's origins, composition, and eventual fate. Through a combination of highly detailed observational data and advanced analysis techniques, it is anticipated to contribute valuable insights into the central puzzles of modern cosmology.