AdvACT
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| AdvACT | |
|---|---|
| Name | AdvACT |
| Caption | Advanced ACTPol on the Atacama Cosmology Telescope |
| Location | Atacama Desert, Chile |
| Altitude | 5190 m |
| Established | 2016 |
| Telescope type | Millimeter-wavelength polarimeter |
| Wavelength | 28–230 GHz |
| Affiliations | Princeton University, University of Pennsylvania, Columbia University |
AdvACT is an advanced polarization-sensitive receiver upgrade for the Atacama Cosmology Telescope installed on the Cerro Toco site in the Atacama Desert near San Pedro de Atacama, Chile. It was designed to measure the polarization of the cosmic microwave background with improved sensitivity, frequency coverage, and angular resolution compared with previous instruments. The project builds on technologies and scientific goals associated with a range of observatories and collaborations including the Planck (spacecraft), BICEP/Keck Array, South Pole Telescope, POLARBEAR, and SPT-3G.
Overview
AdvACT is an upgrade to the Atacama Cosmology Telescope receiver suite focused on high-precision measurements of CMB temperature and polarization anisotropies at arcminute and sub-degree scales. Its primary science goals include constraining models of cosmic inflation by searching for primordial B-mode polarization, improving measurements of gravitational lensing of the CMB tied to large-scale structure traced by surveys such as DES and eBOSS, and refining cosmological parameters complementary to results from Planck (spacecraft) and WMAP. The instrument and survey strategy were motivated by theoretical work and forecasts from groups associated with Alan Guth, Andrei Linde, Viatcheslav Mukhanov, and experimental frameworks like those of John Mather and George Smoot.
Instrument and Technology
The AdvACT receiver employs large arrays of transition-edge sensor (TES) bolometers fabricated in collaboration with facilities such as NIST, Brookhaven National Laboratory, and microfabrication groups at NASA Goddard Space Flight Center. The focal plane combines multichroic pixels enabling simultaneous bands at roughly 28, 41, 90, 150, and 230 GHz, following design principles used by ACTPol, SPTpol, and POLARBEAR-2. Cryogenic cooling to ~100 mK is provided by dilution refrigerators similar to those used in experiments like Planck (spacecraft)'s bolometers and ground-based arrays at South Pole. Readout uses frequency-domain multiplexing and microwave SQUID multiplexers informed by developments at SLAC National Accelerator Laboratory and Lawrence Berkeley National Laboratory. Optical coupling employs anti-reflection-coated silicon lenses and meta-material surfaces inspired by designs tested at Princeton University and University of Chicago.
Observations and Survey Strategy
AdvACT conducted multi-season observations from the Atacama Desert targeting both deep fields and wide surveys. The strategy combined deep integrations on fields overlapping with surveys from Herschel Space Observatory, WISE, and optical/near-infrared surveys like DES and HSC to facilitate cross-correlation studies. Scanning patterns and elevation strategies were coordinated with operations at the Atacama Cosmology Telescope to mitigate atmospheric noise sources characterized in studies by Rafael Rebolo and teams at Instituto de Astrofísica de Canarias. Observing campaigns were scheduled to complement southern-hemisphere experiments such as BICEP/Keck Array at the South Pole and northern facilities like Planck (spacecraft)'s full-sky maps, enabling joint likelihood analyses with teams including members from Harvard University and University of California, Berkeley.
Data Processing and Analysis
Data reduction for AdvACT follows pipelines developed in collaboration with software groups at Princeton University, Columbia University, and University of Pennsylvania. Time-ordered data cleaning removes atmospheric and instrumental systematics using algorithms related to those used by SPT-3G and BICEP/Keck Array, with pointing reconstruction tied to star camera solutions and encoders validated against catalogs from GAIA and Two-Micron All-Sky Survey. Map-making employs maximum-likelihood and destriping techniques adopted in analyses by Planck (spacecraft) teams and adapted for ground-based correlated noise. Component separation leverages multi-frequency data to remove foregrounds such as thermal dust traced by Herschel Space Observatory and synchrotron emission constrained by WMAP, using methods from studies by Angélica de la Cruz, Shaul Hanany, and collaborators. Lensing reconstruction and delensing use quadratic estimators and iterative techniques similar to those developed by Wayne Hu, Matias Zaldarriaga, and the Planck (spacecraft) lensing consortium.
Scientific Results
AdvACT has produced high-resolution measurements of the polarized microwave sky that constrain the amplitude of lensing B-modes and improve limits on primordial gravitational waves characterized by the tensor-to-scalar ratio r. Results have been combined with data from Planck (spacecraft), BICEP/Keck Array, South Pole Telescope, and galaxy surveys like DES to tighten bounds on neutrino mass sums and effective relativistic species N_eff, connecting to particle-physics constraints from CERN and neutrino experiments such as Super-Kamiokande. Cross-correlation studies with maps from Herschel Space Observatory and optical surveys have yielded measurements of the thermal Sunyaev–Zel'dovich effect associated with galaxy clusters found in catalogs from ROSAT and the Sloan Digital Sky Survey. AdvACT maps have also informed component-separation efforts used in inflationary-model selection analyses connected to the work of Andrei Linde and Paul Steinhardt.
Collaborations and Funding
The AdvACT project is a collaboration of institutions including Princeton University, University of Pennsylvania, Columbia University, NIST, University of Chicago, Harvard University, and international partners. Funding and support have come from agencies and organizations such as the National Science Foundation, Department of Energy (United States), and institutional grants, alongside contributions from national laboratories including Brookhaven National Laboratory and Lawrence Berkeley National Laboratory. Technical partnerships and fabrication resources were provided through collaborations with NASA Goddard Space Flight Center and university microfabrication facilities. The instrument operations and data releases have engaged the broader CMB community including teams from BICEP/Keck Array, POLARBEAR, SPT-3G, and the Planck (spacecraft) consortium.