SPTpol

SPTpol
Name	SPTpol
Location	South Pole
Coordinates	90, S
Altitude	2835 m
Established	2011
Telescope type	Polarization-sensitive camera on a 10-meter telescope

SPTpol

The SPTpol instrument is a polarization-sensitive camera installed on the 10-meter South Pole Telescope at the Amundsen–Scott South Pole Station, designed to measure the polarization of the Cosmic microwave background across small angular scales. Built to probe signals from inflationary cosmology, gravitational lensing, and galaxy clusters via the Sunyaev–Zel'dovich effect, the instrument operated contemporaneously with projects such as Planck (spacecraft), Atacama Cosmology Telescope, and BICEP2/Keck Array to constrain parameters in Lambda-CDM model and search for primordial gravitational waves.

Overview

SPTpol was commissioned on the 10-meter telescope at Amundsen–Scott South Pole Station as an upgrade to the original South Pole Telescope camera to achieve high sensitivity to linear polarization; development involved teams from institutions including University of Chicago, Argonne National Laboratory, Fermi National Accelerator Laboratory, California Institute of Technology, and Stanford University. The project targeted both E-mode and B-mode polarization signals to test theories from inflation (cosmology), measure the lensing potential (cosmology), and detect clusters via the Sunyaev–Zel'dovich effect while complementing measurements by Wilkinson Microwave Anisotropy Probe and Planck (spacecraft). Operations integrated logistical support from National Science Foundation, United States Antarctic Program, and international collaborators such as University of British Columbia and University of Melbourne.

Instrumentation and Design

The instrument employed arrays of polarization-sensitive transition-edge sensor (TES) bolometers fabricated at facilities like NIST and read out with multiplexing developed at SLAC National Accelerator Laboratory and Argonne National Laboratory; optical design included cold reimaging optics, anti-reflection coatings, and band-defining filters to observe at approximately 90 GHz and 150 GHz. The SPTpol focal plane architecture drew on detector technologies advanced for experiments including POLARBEAR, SPT-3G, and BICEP Array, while cryogenic systems used pulse-tube coolers similar to those in Herschel Space Observatory and Planck (spacecraft). The 10-meter primary provided angular resolution akin to that of Atacama Cosmology Telescope enabling cross-correlation studies with catalogs from Sloan Digital Sky Survey and Dark Energy Survey.

Observations and Data Acquisition

Survey strategy combined deep, small-area fields and wider, shallower patches to balance sensitivity to primordial B-modes and lensing B-modes; observations were scheduled during austral winters at Amundsen–Scott South Pole Station to exploit stable atmospheric conditions and low precipitable water vapor seen also by teams at ALMA and South Pole Telescope (SPT) for continuum mapping. Pointing calibration referenced sources cataloged by ATCA and Very Large Array, while flux and polarization calibration used celestial standards such as Jupiter (planet) and bright radio galaxies in the NRAO VLA Sky Survey; data acquisition systems synchronized time-stamps with standards from National Institute of Standards and Technology and employed telemetry channels coordinated with National Science Foundation logistics.

Scientific Results

SPTpol produced measurements that refined constraints on the scalar spectral index and tensor-to-scalar ratio, complementing limits from Planck (spacecraft), BICEP2/Keck Array, and WMAP. It delivered high signal-to-noise observations of E-mode polarization and detected lensing B-modes, contributing to mass maps used to study large-scale structure traced in surveys like Dark Energy Survey and Baryon Oscillation Spectroscopic Survey. The instrument discovered and characterized galaxy clusters via the Sunyaev–Zel'dovich effect, yielding catalogs cross-matched with ROSAT, Chandra X-ray Observatory, and XMM-Newton observations, and provided constraints on neutrino mass when combined with datasets from Planck (spacecraft) and Baryon Oscillation Spectroscopic Survey.

Data Processing and Analysis Methods

Data reduction pipelines adapted time-ordered data techniques developed in experiments such as ACT (Atacama Cosmology Telescope), BICEP2/Keck Array, and POLARBEAR; steps included flagging, deglitching, common-mode subtraction, and mapmaking using maximum-likelihood and iterative solvers similar to those used by Planck (spacecraft) teams. Power spectrum estimation employed pseudo-Cl and cross-spectrum estimators used in analyses by WMAP and Planck (spacecraft), with lensing reconstruction using quadratic estimators akin to methods from Hirata and Seljak and delensing techniques pioneered in joint analyses with BICEP2/Keck Array. Systematic error mitigation referenced beam characterization methods from Atacama Cosmology Telescope and polarization calibration strategies developed by POLARBEAR and BICEP Array collaborations.

Collaborations and Related Experiments

The SPTpol collaboration included researchers from institutions such as University of Chicago, Fermi National Accelerator Laboratory, Argonne National Laboratory, University of California, Berkeley, and McGill University, and coordinated analyses with teams from Planck (spacecraft), BICEP2/Keck Array, Atacama Cosmology Telescope, POLARBEAR, and the later SPT-3G upgrade. Related projects addressing complementary science goals included the Dark Energy Survey, Baryon Oscillation Spectroscopic Survey, eROSITA, and ground-based facilities like ALMA and Very Large Array for follow-up, while funding and logistics were supported by agencies including National Science Foundation and national labs such as Brookhaven National Laboratory and Lawrence Berkeley National Laboratory.

Category:Cosmic microwave background experiments