Session G14: High Redshift Probes and Surveys

New Results from The Cosmic Dawn (CoDa) Project: Simulating Reionization and Galaxy Formation

I summarize the latest progress in modelling reionization by large-scale simulations by The Cosmic Dawn (“CoDa”) Project.  When the first galaxies formed stars whose UV radiation escaped into the cold, neutral intergalactic medium, they created giant H II regions that grew in size and number until they overlapped.  Reionization and its back-reaction on the galaxies that caused it were fundamentally inhomogeneous in space and time.  This means galaxy formation and reionization were correlated and fully-coupled from the beginning, imprinting each other with observable consequences. Star formation suppression, for example, may explain the underabundance of Local Group dwarfs relative to CDM N-body predictions.  The CoDa Project recently achieved a new milestone – CoDa III -- the largest radiation-hydrodynamics simulation to date of fully-coupled reionization and galaxy formation, in a ~ 1 0 0  c M p c  volume,  large enough to model b o t h  global and local  reionization, with 8192^3 particles and cells, enough resolving power to follow all atomic-cooling galactic halos. CoDa III required running hybrid CPU-GPU code RAMSES-CUDATON on Oak Ridge supercomputer Summit for 10 days, on 131,072 processors and 24,576 GPUs.  Its results and observational predictions will be presented.     

The First Galaxy Cluster Catalog from the SPT-3G 1500 deg2 Survey

Because the formation history of galaxy clusters is expected to have strongly depended on the universe's physical conditions through time, measuring the abundance, richness, and redshifts of galaxy clusters provides a unique way to probe the universe’s large-scale structure and underlying physics across cosmic timescales. High-resolution (arcminute-scale) cosmic microwave background (CMB) surveys are capable of detecting galaxy clusters across all redshifts due to a CMB scattering process known as the Sunyaev-Zeldovich (SZ) effect. This effect occurs when CMB photons inverse-Compton scatter off energetic, ionized particles present in the clusters, thereby resulting in arcminute-scale intensity distortions in the CMB at locations where galaxy clusters exist. I will present a first catalog of SZ-selected galaxy clusters from an analysis of two years of data from the SPT-3G 1500 deg² CMB survey, and also forecast expected improvements from the full multiyear SPT-3G dataset.  These cluster catalogs will contribute towards improved cosmological constraints on models of dark energy, modified gravity, and neutrino mass.   

Technology for SPT-SLIM and Line-Intensity Mapping

LIM at millimeter wavelengths is a potentially powerful probe of large-scale structure, but achieving meaningful constraints on cosmological parameters requires focal planes with orders of magnitudes more detectors than existing instruments. SPT-SLIM is an upcoming experiment to demonstrate line-intensity mapping (LIM) of CO at 0.5 < z < 2.0 using on-chip spectrometers with kinetic inductance detectors (KIDs), a technology that should enable scaling to much larger arrays of detectors. In 2023, SPT-SLIM will deploy on the South Pole Telescope with 9,000 KIDs arranged into filter-bank spectrometers coupled to 18 dual-polarization spatial pixels and new room-temperature microwave readout electronics. I will describe the overall experimental design and the technology development for detectors, readout, and cryogenics that will enable SPT-SLIM to realize its significant improvements in mapping speed.   

A Systematics-Robust 21 cm Foreground Removal Algorithm

The 21 cm line of neutral hydrogen is a promising probe of large-scale structure of the universe. However, cosmological 21 cm signal is extremely challenging to observe due to bright astrophysical foregrounds. Using the smooth spectral character of foregrounds, traditional linear filters can optimally remove foregrounds so long as the telescope response is accurately known. However, such methods are sensitive to telescope systematics such as antenna gain errors, leaving foreground residuals that dominate the signal. I will present a systematics-robust foreground removal technique that combines a traditional linear filter with a nonlinear method. We first roughly separate the signal and foregrounds using a linear filter. Then, by cross-correlating the residual-contaminated signal channel with the foregrounds, we estimate the systematics-induced contamination, which is subsequently subtracted. In simulations, we find the method suppresses contamination up to first order in systematic errors, making the experiment two orders of magnitude more robust to these errors. Our results suggest that the method can ease the requirement on telescope characterization for 21 cm cosmology experiments such as the Canadian Hydrogen Intensity Mapping Experiment (CHIME).   

Streaming Velocity Effects on the Post-reionization 21 cm Baryon Acoustic Oscillation Signal

The relative velocity between baryons and dark matter in the early Universe can suppress the formation of small-scale baryonic structure and leave an imprint on the baryon acoustic oscillation (BAO) scale at low redshifts after reionization. This "streaming velocity" affects the post-reionization gas distribution by directly reducing the abundance of pre-existing mini-halos (≤ 10⁷ M_⊙) that could be destroyed by reionization and indirectly modulating reionization history via photoionization within these mini-halos. In this work, we investigate the effect of streaming velocity on the BAO feature in HI 21 cm intensity mapping after reionization, with a focus on redshifts 3.5 ≤  z ≤ 5.5. We build a spatially modulated halo model that includes the dependence of the filtering mass on the local reionization redshift and thermal history of the intergalactic gas. In our fiducial model, we find isotropic streaming velocity bias coefficients b_v ranging from -0.0033 at z=3.5 to -0.0248 at z=5.5, which indicates that the BAO scale is stretched (i.e., the peaks shift to lower k). In particular, streaming velocity shifts the transverse BAO scale between 0.087% (z=3.5) and 0.37% (z=5.5) and shifts the radial BAO scale between 0.13% (z=3.5) and 0.52% (z=5.5). These shifts exceed the projected error bars from the more ambitious proposed hemispherical-scale surveys in HI (0.13% at 1σ per  △z = 0.5 bin).    

Probing the Ionized Gas Thermodynamicsin Distant Galaxieswith the Sunyaev-Zel'dovich Effect

The Sunyaev-Zel’dovich (SZ) Effect—the Doppler boost of low energy Cosmic Microwave Background photons scattering off free electrons—is an excellent probe of ionized gas residing in distant galaxies. Its two constituents are the kinematic SZ effect (kSZ), where electrons have a non-zero line-of-sight (LOS) velocity and which probes the electron line-of-sight momentum, and the thermal SZ effect (tSZ) effect, where electrons have high energies due to their temperature, and which probes the electron integrated pressure. These two effects, together with lensing measurement (which scales as the total integrated mass along the LOS), provide complementary information to constrain the thermodynamic profile of the gas residing in distant galaxies, which can be further used to understand feedback processes, a necessary ingredient to understand the evolution of LSS in our Universe. 

I measured the kSZ signal of unWISE galaxies with the projected-field estimator, which does not require spectroscopic redshift information. unWISE is a galaxy catalog consisting of three samples of mean redshifts z=0.5, 1.1, 1.5 and containing over 500 million galaxies on the full sky. I will also discuss the preliminary tSZ measurement of for unWISE, along with the Halo Occupation Distribution of these galaxies.   

SPT-SLIM and Fundamental Cosmology with Future Millimeter-Wave Line Intensity Mapping Experiments

Line Intensity Mapping (LIM) at millimeter wavelengths is a promising method for measuring the large-scale structure of the Universe over a larger redshift range than traditional galaxy surveys. However, current-generation LIM instruments are not yet sensitive enough for competitive cosmological constraints. I will discuss future science cases enabled by LIM over wide redshift ranges, including constraining the expansion history and dark energy at high redshift, measuring the sum of neutrino masses, and constraining primordial non-Gaussianity. I will then present the South Pole Telescope Summertime Line Intensity Mapper (SPT-SLIM), a pathfinder instrument that will demonstrate key technologies necessary for improving the instantaneous sensitivity of mm-wave LIM experiments including high-density on-chip spectrometers and readout electronics. Finally I will discuss the sensitivity needed to cross critical thresholds in LIM science cases, and the stages of potential future instruments based on SPT-SLIM technology.   

TES Bolometer Data Results for TIME

TIME (Tomographic Ionized-carbon Mapping Experiment) seeks to better understand the Epoch of Reionization (EoR), the time period when the first stars and galaxies ionized the intergalactic medium. This is achieved by mapping the fluctuations of the 157.7 um fine-structure line of singly ionized carbon [CII]. The experiment uses arrays of superconducting transition edge sensor (TES) bolometers to make a measurement of the [CII] power spectrum. We will present some of the recent data results from the experiment regarding load curves for the TES detectors, optical efficiency measurements, and maps.    

Detection of Cosmological 21cm Emission with CHIME

Intensity mapping of redshifted 21cm emission from neutral hydrogen holds great promise for learning about cosmology, as it provides an efficient way to map large volumes of the universe without the need to characterize individual luminous sources. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a cylinder telescope located in Western Canada that was custom-built for this purpose, and that has collected several hundred days' worth of data since it reached full observational capacity in late 2018. I will present the first 21cm science results from CHIME: the detection of a cross-correlation between CHIME sky maps and galaxy/quasar catalogs from the extended Baryon Oscillation Spectroscopic Survey (eBOSS). In particular, I will discuss our data processing pipeline and how we model the measured signal, as well as the implications and prospects for more precise future measurements.