Events Daily

Thursday, April 25, 2024

Galaxy Simulations as Ground Truth for Validating Cosmological Inferences
Nicholas Faucher
Event Type: Oral Defense
Time: 1:00 PM - 2:30 PM
Location: 726 Broadway, 940, CCPP Seminar
Abstract: This thesis presents a comprehensive investigation into the accuracy of spectral energy distribution (SED) modeling inferences of galaxy star-formation histories. SED modeling is an essential tool for inferring star-formation histories from nearby galaxy observations, but it is fraught with difficulty due to our incomplete understanding of stellar populations, chemical enrichment processes, and the nonlinear, geometry-dependent effects of dust on our observations. The dust attenuation curve of a galaxy, defined as the ratio of the total observed to emitted flux as a function of wavelength, depends on the chemical composition and grain size distribution of the dust as well as the geometry of the stars and dust relative to the observer. Utilizing hydrodynamic simulations and radiative transfer calculations, we generate simulated galaxy SEDs spanning far-ultraviolet (FUV) through far-infrared (FIR) wavelengths that account for the geometry-dependent effects of dust. These simulations enable the validation of SED modeling techniques against galaxies with known ground truth. We find that subgrid post-processing recipes that mitigate limitations in the temporal and spatial resolution of the simulations are required for producing FUV to FIR photometry that statistically reproduce the colors of galaxies in the nearby Universe. These simulations demonstrate a large variation in attenuation laws among galaxies, and that energy balance between dust attenuation and re-emission can be violated by up to a factor of 3. Inspired by the diversity among these simulated attenuation laws and the inability of commonly used existing models to reproduce them, we propose a novel dust attenuation model with three free parameters that can accurately recover the simulated attenuation curves as well as the best-fitting curves from the commonly used models. This new model is fully analytic and treats all starlight equally, in contrast to two-component dust attenuation models. Finally, we use our simulated observations to test the accuracy of SED modeling techniques. We find that the combined effect of model mismatches for high mass galaxies leads to inferred star-formation rates (SFRs) that are on average underestimated by a factor of 2 when fit to UV through IR photometry, and a factor of 3 when fit to UV through optical photometry. These biases lead to significant inaccuracies in the resulting sSFR-mass relations, with UV through optical fits showing particularly strong deviations from the true relation of the simulated galaxies. In the context of massive existing and upcoming photometric surveys, these results highlight that star-formation history inference from broadband photometry remains imprecise and inaccurate, and that there is a pressing need for more realistic testing of existing techniques. Professor Michael Blanton (Thesis Advisor) Professor Kyle Cranmer Professor David Hogg Professor Anthony Pullen Professor Jeremy Tinker

The Quantum Revolution: Emerging Technologies at the Atomic Scale
David Awschalom, University of Chicago
Event Type: Physics Dept Colloquium
Time: 4:00 PM - 5:30 PM
Location: 726 Broadway, 940, CCPP Seminar
Abstract: Traditional electronics are rapidly approaching the length scale of atoms and molecules. In this regime, a single atom out of place can have outsized negative consequences and so scaling down classical technologies requires ever-more perfect control of materials. Surprisingly, one of the most promising pathways out of this conundrum may emerge from current efforts to embrace these atomic ‘defects’ to construct devices that enable new information processing, communication, and sensing technologies based on the quantum nature of electrons and atomic nuclei. In addition to their charge, individual defects in semiconductors and molecules possess an electronic spin state that can be employed as a quantum bit. These qubits can be manipulated and read using a simple combination of light and microwaves with a built-in optical interface and retain their quantum properties over millisecond to second timescales. With these foundations in hand, we discuss emerging opportunities and the importance of collaborating with industry to atomically-engineer qubits for nuclear memories, entangled registers, sensors and networks for science and technology.