Session V13: Large Scale Structure & CMB

CMB Lensing Measurements with Two Years of Data from the SPT-3G Survey

The South Pole Telescope (SPT) is a 10 m offset Gregorian telescope designed to observe the Cosmic Microwave Background (CMB) and astrophysical foregrounds at millimeter wavelengths. Radiation from the CMB is gravitationally lensed by large scale structure as it travels through the cosmos, complicating the analysis of the primordial CMB but also embedding information about the evolution and structure of the universe at more recent times. Measurements of the lensing potential can be used to constrain cosmological parameters (e.g. Ω_M, σ_8, and the sum of neutrino masses) and to remove lensing contamination from CMB B-mode polarization maps in the search for primordial gravitational waves. The SPT-3G experiment surveys 1500 deg² of the southern sky with ~1 arcminute angular resolution, allowing for high signal-to-noise measurements of the lensing potential out to sub-degree scales that can probe the nonlinear regime of the lensing power spectrum. In this talk I will present preliminary results from the latest SPT lensing analysis using data from the 2019 and 2020 observing seasons. The resulting lensing maps will be some of most sensitive made to date, and will be combined with BICEP/Keck data to tighten the constraints on the amplitude of primordial gravitational waves.   

Constraining Primordial Gravitational Waves with the BICEP/Keck Series of CMB Polarization Experiments

The BICEP/Keck series of experiments have set leading limits on

primordial gravitational waves (PGW) though over 15 years of cosmic

microwave background (CMB) polarization measurements from the geographic

South Pole. BICEP/Keck consists of a series of small-aperture

refracting telescopes observing the CMB at a range of frequencies from 30 to

270 GHz. Measurements of the "B-mode" polarization of the CMB provide

a unique observational tool through which to characterize PGW, and

thus understand the physics of cosmic inflation in the very early

Universe. Such measurements have allowed BICEP/Keck to set the most

stringent limits to date on the primordial tensor-to-scalar ratio,

r, and thus on models of cosmic inflation. The most recent

publication, containing data up through 2018, has set the limit

r_0.05<0.036 (95% C.L.), with an uncertainty σ(r)=0.009. In

this talk, I will detail the progress of the BICEP/Keck program, our

current constraints, efforts at astrophysical foreground and polarized

systematic characterization and mitigation, limitations, and future

directions including the development and analysis of data from the new

BICEP Array and delensing of CMB B-mode data in conjunction with

SPT-3G.   

Scaling of polarization noise with number of simultaneous detector pairsin BICEP/Keck data

The BICEP/Keck collaboration has set constraints on the tensor-to-scalar ratio

r using a series of CMB polarization telescopes at the South Pole. BICEP

Array, the next stage of the experiment, will operate with an order of

magnitude more detectors than the previous stage, and is projected to reach a

sensitivity of σ(r) ≤ 0.003 using data upto 2027. This will be possible only if the

polarized noise scales down as expected with the increase in number of

simultaneously observing detector pairs. As the BICEP/Keck telescopes are

ground-based, the atmosphere acts as an unavoidable source of noise.

Large-scale atmospheric noise is correlated across detectors and, if it has a

polarized component, might cause a deviation from simple noise scaling,

impeding the progress of the experiment. We check for this “failure to scale”

in our polarization datasets. We observe that polarized noise in the high-l

regime, corresponding to small scale structures, scales well but that there is

a failure to scale in the low-l regime. We show that this issue can be

potentially addressed by down-weighting periods of elevated 1/f noise in the

pair difference timestreams, which results in a reduction in the low-l noise

excess in the final maps.

    

The SPT-3G+ Experiment: Science Goals and Current Status of MKID Development

I will present an overview of the design and science goals of SPT-3G+, the fourth-generation survey camera for the South Pole Telescope (SPT) and then discuss the development of microwave kinetic inductance detectors (MKIDs) for SPT-3G+. The SPT is a 10-meter submillimeter (sub-mm) quality telescope designed to observe the cosmic microwave background (CMB), which has undertaken a series of large area mm-wavelength surveys (SPT-SZ, SPTpol, SPT-3G). The SPT-3G+ receiver is designed measure polarized light at 220, 285, and 345 GHz, and will map 1500 sq. degrees of sky, overlapping with the existing SPT-3G and BICEP Array surveys. The science goals for the SPT-3G and SPT-3G+ combined data sets include: constraining reionization through measurements of the kinematic Sunyaev-Zel'dovich effect, improving constraints on inflation through characterization of polarized galactic dust, extending SPT astrophysical transient observations into the sub-mm, and potentially observing the first Rayleigh scattering of the CMB off of neutral hydrogen in the early universe, which would provide constraints on recombination. The necessary sensitivity for this instrument will be achieved using MKIDs, which are highly multiplexable, allowing for high detector density in the focal plane.   

Analysis of CMB Temperature and E-mode Polarization Anisotropies with 2019 and 2020 Data from the South Pole Telescope

Autocorrelation and cross-correlation spectra of the temperature and E-mode polarization anisotropies (EE/TE/TT) of the CMB provide a wealth of information on the composition and evolution of the universe. While the Planck satellite experiment has already constrained parameters of the ΛCDM cosmological model to sub-percent precision using the anisotropies at relatively large angular scales, better measurements at small angular scales by a ground-based telescope such as the South Pole Telescope (SPT) can serve as a powerful consistency check and potentially discover evidence of new physics. The SPT-3G camera was installed in 2016/17 austral summer and was a significant upgrade from its predecessor, the SPTpol camera, with ten times more detectors. The instrument has been taking data stably at full capacity since 2019. Several analysis projects using the 2019 and 2020 dataset are underway, including substantially improving existing measurements of the EE/TE spectra and constraints on cosmological models from the SPT. In this talk, I will describe the status of the 2019 and 2020 EE/TE/TT analysis, show preliminary measurements of the spectra, and outline our next steps.   

Cosmic density field reconstruction with machine learning and applications

Nonlinear evolution of the late-time Universe limits the precision of parameter estimates produced from large galaxy surveys. In baryon acoustic oscillation (BAO) analysis, for example, nonlinear evolution dampens and broadens the acoustic peak in the matter correlation function and erases higher harmonics in the power spectrum, thereby decreasing the precision of BAO distance measurement by a factor of three at the present day. This effect can be partially recovered by a process called reconstruction. The standard reconstruction algorithm has been used in large galaxy survey analyses for about a decade and has achieved an improvement in the precision of BAO measurement by about a factor of two on average. The ever higher precision of the ongoing and upcoming surveys, such as the Dark Energy Spectroscopic Instrument, Nancy Grace Roman Space Telescope, and Euclid, will greatly benefit from improvements in reconstruction to more fully realize their potential of probing cosmology. We present a method that uses convolutional neural networks to augment the traditional reconstruction algorithms. We show the improvement of this method over traditional reconstruction algorithms with various metrics. We also present applications of this method beyond BAO analysis with two-point statistics.