2023 Astrophysics Symposium

January 26-27, 2023 in SPL 57


  • ChangHoon Hahn (Princeton University)
  • Elena Massara (University of Waterloo)
  • Chiara Mingarelli (University of Connecticut and Flatiron Institute)
  • Chirag Modi (Flatiron Institute)
  • Rohan Naidu (MIT)
  • Anowar Shajib (University of Chicago)

January 26 - Hahn, Massara, Shajib

in SPL 57

9:00 a.m. Coffee

9:30 a.m. ChangHoon Hahn (Princeton University) Probing Dark Energy and Neutrinos with 40 million Galaxies

Abstract: The three-dimensional spatial distribution or clustering of galaxies encodes key cosmological information that can be used to probe the nature of dark energy and measure the sum of neutrino masses. The next generation of galaxy surveys, such as the Dark Energy Spectroscopic Instrument (DESI) and the Prime Focus Spectrograph (PFS), will observe >40 million galaxies over unprecedented cosmic volumes and produce the most precise measurements of galaxy clustering across 10 billion years of cosmic history. Current analyses focus on the two-point clustering of galaxies (power spectrum) and on large, linear, scales. In my talk, I will demonstrate that we can extract more than double the cosmological information from galaxy surveys by analyzing galaxy clustering on small, non-linear, scales and using higher-order statistics. Although these regimes are inaccessible to current analyses due to the limitations of analytic models and observational systematics, I will demonstrate that we can overcome these challenges with Simulation-Based Inference (SBI) and Machine Learning techniques. Furthermore, I will present cosmological constraints from a recent SBI analysis of existing observations from the SDSS-III: BOSS survey. Lastly, I will present the status of the DESI and PFS surveys and discuss upcoming SBI analyses that will probe dark energy and measure the sum of neutrinos masses with unprecedented precision.

10:30 a.m. Elena Massara (University of Waterloo), Cosmology with Galaxy Surveys

Abstract: Galaxy surveys have been very successful in probing the expansion history and content of the Universe. On large scales the galaxy field is close to Gaussian, thus all the information is contained in its two-point function, which became the standard summary statistic to analyze surveys in the past years. Future galaxy surveys, such as Euclid and the Roman Space Telescope, will map the large-scale structure of the Universe in great detail, allowing us to probe smaller scales. On those scales, the galaxy field is non-Gaussian, and there is cosmological information beyond the two-point function. To fully exploit the information in future datasets, we are in need of novel techniques that will allow us to use the small non-linear scales and statistics beyond the standard two-point functions. In this talk I will discuss recent advances in the field and promising statistics to analyze the data from future missions—void-related statistics and marked power spectra—and new developments in understanding and mitigating systematics that are peculiar to these new galaxy surveys.

11:30 a.m.  Anowar Shajib (University of Chicago), At the intersection of Astrophysics and Cosmology: strong lensing by galaxies as a probe of the Hubble constant

Abstract: The  Lambda Cold Dark Matter (LCDM) cosmological model has been highly successful in explaining a wide range of observations at different scales. However, recent challenges have emerged, one of the most significant being the “Hubble tension.” This is the discrepancy by more than 5 standard deviations between the Hubble constant (H_0) measured using the Cepheid-calibrated distance ladder of type Ia supernovae and that extrapolated using the LCDM model from the cosmic microwave background. To confirm new physics beyond the LCDM model as the source of this disagreement, another independent probe is paramount to rule out any unknown systematic in the abovementioned ones. Strong-lensing time delay is such a probe that can independently constrain H_0 to 1% precision and accuracy in the future. The major hurdle to achieving this accuracy, by avoiding potential systematic from mass model assumptions, is constraining the lens galaxy’s mass profile shape using non-lensing observables such as stellar dynamics. I will describe how we can constrain the baryonic and dark matter distributions and thus the total mass profile in elliptical galaxies to 1% precision using data from the JWST, HST, and Keck telescopes for large samples of strong lenses discovered from current and future surveys. Thus uncovering the internal structure of elliptical galaxies will not only deliver a distinguishing answer to the “Hubble tension” but also provide key insights into galactic astrophysical processes that have shaped these galaxies, such as mergers and baryonic feedbacks.

January 27 - Mingarelli, Modi, Naidu

in SPL 57

9:00 a.m. Coffee

9:30a.m. Chiara Mingarelli (University of Connecticut and Flatiron Institute), Taking the pulse of the Universe

Abstract: Galaxy mergers are a standard aspect of galaxy formation and evolution, and most (likely all) large galaxies contain supermassive black holes. As part of the merging process, the supermassive black holes should in-spiral together and eventually merge, generating a background of gravitational radiation in the nanohertz to microhertz regime. An array of precisely timed pulsars spread across the sky can form a galactic-scale gravitational wave detector in the nanohertz band. I describe the current efforts to develop and extend the pulsar timing array concept, together with recent limits which have emerged from international efforts to constrain astrophysical phenomena at the heart of supermassive black hole mergers.

10:30a.m. Chirag Modi (Flatiron Institute), Forward Modeling approaches for Cosmological Analysis

Abstract: Upcoming cosmological surveys will probe our Universe at the largest volumes with a variety of cosmological observables such as galaxy clustering (DESI), weak lensing (LSST) and more. The statistical power of these datasets provides an exciting opportunity to constrain cosmological parameters with unprecedented precision and answer longstanding fundamental questions about the birth, evolution and the nature of our Universe. However, current approaches to cosmological analysis will be insufficient in extracting all the information from this high quality data. In this talk, I will discuss the limitations of traditional methods, and motivate how they can be overcome using computational forward models. I will then present two forward modeling approaches to analysis in detail. The first approach is “field-level inference”, which promises to be the optimal way of doing cosmological analysis, and simultaneously infers cosmological parameters and the initial conditions of the Universe. The second approach is “simulation-based inference”, which allows us to use new, powerful summary statistics without having access to theoretical models and analytic likelihood for the data. I will discuss the advances made in cosmology, statistics and machine learning over the last 5 years that have made these approaches possible. Finally, I will present challenges in applying forward modeling approaches at the scale necessary for the next generation of cosmological surveys and outline strategies to address them.

11:30 a.m. Rohan Naidu (MIT), The First Glimpse of the First Galaxies with JWST

Abstract: One of the last great unknowns in our history of the Universe is when and how the first galaxies emerged after the Big Bang. These galaxies transformed the cosmos – they illuminated the invisible scaffolding of dark matter that underpins the Universe, they ionized the intergalactic reservoirs of hydrogen, and they synthesized the elements that would one day seed life on Earth. Thanks to JWST, these enigmatic galaxies are finally coming into view. In this talk I will present early results on these systems, and preview upcoming experiments I am leading. I will discuss: (i) new classes of galaxies being revealed by JWST, with a focus on remarkably luminous early galaxies that are challenging our models of galaxy evolution; (ii) novel strategies to hone in on the elusive sources of cosmic reionization, the last major phase transition of the Universe. I will end by sharing my vision for the upcoming decade for science at the highest redshifts, which promises a once-in-a-generation expansion of the astrophysical frontier to the brink of the Big Bang.

Contact: Reina Maruyama (AstrophysicsSearch@mailman.yale.edu)