Ethan: Unlocking Star Formation in Galactic Photometry
Understanding star-formation conditions and its associated Initial Mass Function (IMF) is critical to deriving galactic properties and their evolution in the universe. Although the IMF has traditionally been inconclusive beyond the local universe, recent research at DAWN parameterized the IMF in the EAZY photometric fitting code. Here, we employ the same IMF parameterization in LePhare, a fundamentally different method of fitting photometry. Results from fitting thousands of galaxies in extensive catalogs suggest systematic variations in the IMF over time that are similarly consistent with EAZY, further verifying that most galaxies exhibit top-heavier stellar populations than in the Milky Way. In addition, LePhare extracts relationships of the variable IMF with properties of star-forming and quenched populations, yielding a more complete and accurate picture of galactic evolution.
Thomas: Constraints and Predictions on Alternatives to Dark Energy
Recent studies find that measurements of the Hubble constant (H0) determined from the Cosmic Microwave Background are ~9% lower than measurements of H0 from much lower-redshift supernova observations. Several possible modifications to the standard ΛCDM cosmological model have been proposed to explain this discrepancy. A re-analysis of the supernova dataset finds that there are actually two discrepancies: one in H0 but another in the composition of the Universe as well. We show that the models designed to fix this “Hubble Tension” are incapable of correcting each simultaneously. And in a different, simple class of dark energy models, we show these quantities are not only preserved, but meet other observations including Ωmh2. These models predict drastic differences for the future of the Universe than those under ΛCDM—possibly even in the present.
