SPT-3G+: Mapping the High-Frequency Cosmic Microwave Background Using Kinetic Inductance Detectors

TL;DR

SPT-3G+ is a new high-frequency camera for the South Pole Telescope, utilizing 34,100 kinetic inductance detectors to advance cosmic microwave background research, reionization studies, and detector technology development.

Contribution

This paper introduces the design, science goals, and technological innovations of SPT-3G+, a novel CMB observation instrument with a large detector array and modular design.

Findings

Enables new constraints on reionization and the kinematic Sunyaev-Zeldovich effect.

Serves as a pathfinder for Rayleigh scattering detection in the CMB.

Enhances existing surveys with multi-band data and technological advancements.

Abstract

We present the design and science goals of SPT-3G+, a new camera for the South Pole Telescope, which will consist of a dense array of 34100 kinetic inductance detectors measuring the cosmic microwave background (CMB) at 220 GHz, 285 GHz, and 345 GHz. The SPT-3G+ dataset will enable new constraints on the process of reionization, including measurements of the patchy kinematic Sunyaev-Zeldovich effect and improved constraints on the optical depth due to reionization. At the same time, it will serve as a pathfinder for the detection of Rayleigh scattering, which could allow future CMB surveys to constrain cosmological parameters better than from the primary CMB alone. In addition, the combined, multi-band SPT-3G and SPT-3G+ survey data will have several synergies that enhance the original SPT-3G survey, including: extending the redshift-reach of SZ cluster surveys to $z > 2$; understanding the relationship between magnetic fields and star formation in our Galaxy; improved characterization of the impact of dust on inflationary B-mode searches; and characterizing astrophysical transients at the boundary between mm and sub-mm wavelengths. Finally, the modular design of the SPT-3G+ camera allows it to serve as an on-sky demonstrator for new detector technologies employing microwave readout, such as the on-chip spectrometers that we expect to deploy during the SPT-3G+ survey. In this paper, we describe the science goals of the project and the key technology developments that enable its powerful yet compact design.