Narrow Results

The South Pole Telescope (SPT) is a 10-meter telescope designed to survey the millimeter-wave sky, taking advantage of the exceptional observing conditions at the Amundsen-Scott South Pole Station. The telescope and its ground-breaking 960-element bolometric camera finished surveying 2500 square degrees at 95. 150, and 220 GHz in November 2011. We have discovered hundreds of galaxy clusters in the SPT-SZ survey through the Sunyaev-Zel’dovich (SZ) effect. The formation of galaxy clusters the largest bound objects in the universe is highly sensitive to dark energy and the history of structure formation. I will discuss the cosmological constraints from the SPT-SZ galaxy cluster sample as well as future prospects with the soon to-be-installed SPT-3G camera.

Measurements of redshifted 21cm emission of neutral hydrogen at $\lesssim 30$MHz have the potential to probe the cosmic “dark ages,” a period of the universe’s history that remains unobserved to date. Observations at these frequencies are exceptionally challenging because of bright Galactic foregrounds, ionospheric contamination, and terrestrial radio-frequency interference. Very few sky maps exist at $\lesssim 30$MHz, and most have modest resolution. We introduce the Array of Long Baseline Antennas for Taking Radio Observations from the Sub-Antarctic (ALBATROS), a new experiment that aims to image low-frequency Galactic emission with an order-of-magnitude improvement in resolution over existing data. The ALBATROS array will consist of antenna stations that operate autonomously, each recording baseband data that will be interferometrically combined offline. The array will be installed on Marion Island and will ultimately comprise 10 stations, with an operating frequency range of 1.2–125MHz and maximum baseline lengths of $\sim 20$km. We present the ALBATROS instrument design and discuss pathfinder observations that were taken from Marion Island during 2018–2019.

We present new cosmic microwave background (CMB) spectral distortions constraints on low mass (10⁻¹⁰-10⁴ eV) dark matter particles that decay into photons. The constraints are first presented in a model-independent manner and then applied to axions and decaying excited states. For the first time, we place constraints using the full distortion spectra compared to the COBE/FIRAS and EDGES measurements. This proceeding summarizes results obtained with Jens Chluba and Richard Battye, and published in MNRAS 507 (2021).

Various observations have shown that dark energy accounts for nearly two-thirds of the energy density of the Universe. The simplest model to explain the nature of dark energy is the cosmological constant (ΛCDM) model. Although Planck observations supports using ΛCDM model as the base cosmological model, there exist some inconsistencies in parameter estimates when compared with independent observations. The most important is the inconsistency in the H₀ estimates from the Planck collaboration which reports $H_0={67.5}_{-0.5}^{+0.5}{\text{kms}}^{-1}Mp{c}^{-1}$, a considerably lower value when compared with the direct local distance ladder measurements. This value shows a discrepancy at the level greater than 4σ with the constraints reported by SH0ES collaboration in 2019, $H_0={74.3}_{-1.42}^{+1.42}km{s}^{-1}Mp{c}^{-1}$. These disagreements, called the Hubble tension, point towards a new physics that deviates from the standard ΛCDM model and to resolve this various methods have been proposed. In this work, a quintessence scalar field with an inverse power potential (V(ϕ)∽ ϕ⁻ⁿ) is assumed as a description of dark energy and we focus on an interacting dark energy dark matter model where the interacting term is taken to be linear in the field (Φ). We study in detail the evolution of the model and provide constraints on the model parameters using low redshift cosmological observations of Type Ia Supernovae (SN), baryon acoustic oscillations (BAO), direct measurements of Hubble parameter (Hz) and high redshift HII galaxy measurements (HIIG). We find that the model agrees with the existing values of the nonrelativistic matter density parameter, Ω_m and dark energy equation of state parameter, w₀. The analysis shows that the observations prefer a negative value of coupling constant and gives the best fit value of $H_0={69.9}_{-1.02}^{+0.46}{\text{kms}}^{-1}{\text{Mpc}}^{-1}$ and thereby can be used to alleviates the H₀ tension between Planck measurements and the observations considered.

We consider the simplest model of modulation of the 3D Gaussian field in k-space by a non-uniformly oscillating function f₁(k) that imitates the baryon acoustic oscillations (BAO), and a model function f₂(k) reproducing the smoothed power spectrum of a galaxy clustering. This model is applied to statistical simulations of radial (shell-like) distributions with calculations of 1D power spectra and auto-correlation functions. It is shown that the radial distributions simulated relatively to different centres in a region of study include quasi-periodical components with a characteristic (BAO) scale 2π/k ∼ 100 h⁻¹ M_pc which can appear with rather high probability depending on a sampling length L_R and an amplitude A_m of the modulation. The averaging of a number of 1D correlation functions built from different centres of radial distributions leads to the mean 1D correlation function, which is qualitatively consistent with the standard 3D correlation function. Both the functions are characterized by a single wide peak at the BAO scale. We apply 1D statistical procedures to the sample of spectroscopic redshifts of the brightest cluster galaxies (BCGs) and show that the results turn out to be consistent with those obtained in our model simulations.