The Atacama Cosmology Telescope (ACT) is a six-meter telescope located at an altitude of 5190 meters (17,028 ft) on Cerro Toco in the Atacama Desert in Chile. ACT was built to survey the cosmic microwave background (CMB) from 28 to 230 GHz.  Three generations of cameras have been used with ACT, all relying on transition-edge-sensor (TES) bolometers, time-devision multiplexing (TDM) superconducting quantum interference devices (SQUIDs), and silicon lenses. The final camera, Advanced ACTPol (AdvACT), has finished observations, and ACT is now being decommissioned. Observations with ACT have mapped primary and secondary CMB anisotropies in intensity and polarization at a resolution of a few arcminutes, and this data is enabling precision cosmological constraints as well as a wide array of cross-correlation science to probe the expansion history of the universe and the growth of large scale structure. ACT data products are available publicly on LAMBDA (link). 

My work for ACT has involved device testing, remote observing, and data analysis, now focusing on the latter. As a remote observer, I took 24-hour shifts of control over the telescope and coordinating with Team Toco down at the site. Using our lab’s dilution refrigerator and Multi-Channel Electronics (MCE) I screened SQUID multiplexing chips and tested TESes. By analyzing ACT data in combination with optical surveys for highly sensitive measurements of galaxy halos, we are now working towards novel constraints on dark energy, general relativity, neutrino mass, and galaxy feedback models. Our 2021 5.4 sigma detection with data from ACT, Planck, and the Sloan Digital Sky Survey (SDSS) is the highest significance pairwise kinetic Sunyaev-Zel’dovich (kSZ) effect measurement yet, providing a tracer of the gravitational field on cosmological scales. By measuring galaxy halo properties with the thermal Sunyaev-Zel’dovich (tSZ) effect, I am working to break the optical depth degeneracy in pairwise kSZ measurements so that we can constrain cosmology with future data sets. These tSZ measurements will also inform open questions in galaxy cluster astrophysics.  

Select publications: 

E. M. Vavagiakis, P. A. Gallardo, V. Calafut, S. Amodeo et al. 2021, “The Atacama Cosmology Telescope: Probing the Baryon Content of SDSS DR15 Galaxies with the Thermal and Kinematic Sunyaev-Zel’dovich Effects,” Phys. Rev. D 104, 043503, arXiv:2101.08373.

V. Calafut, P. A. Gallardo, E. M. Vavagiakis et al. 2021, “The Atacama Cosmology Telescope: Detection of the Pairwise Kinematic Sunyaev-Zel’dovich Effect with SDSS DR15 Galaxies,” Phys. Rev. D 104, 043502, arXiv:2101.08374.

J. C. Hill, E. Calabrese et al. 2021, “The Atacama Cosmology Telescope: Constraints on Pre-Recombination Early Dark Energy,” Phys. Rev. D 105, 123536, arXiv:2109.04451.

M. Hilton, C. Sifón, S. Naess, M. Madhavacheril, M. Oguri, E. Rozo, E. Rykoff et al. 2021, “The Atacama Cosmology Telescope: A Catalog of >4000 Sunyaev-Zel’dovich Galaxy Clusters,” ApJS 253 (1), arXiv:2009.11043.

F. De Bernardis, S. Aiola, E. M. Vavagiakis, M. D. Niemack, N. Battaglia et al. 2017, “Detection of the pairwise kinematic Sunyaev-Zel’dovich effect with BOSS DR11 and the Atacama Cosmology Telescope,” JCAP 03, 008, arXiv:1607.02139.



The ACT Collaboration at our 2022 meeting.


The ACT Collaboration at our 2018 meeting.

Header Image Credit: Mark Devlin/University of Pennsylvania