Seminar - Jose María Ezquiaga (U Chicago) and Rohan Naidu (Harvard)


Monday, November 15, 2021, 11:00am to 12:00pm



" Probing the standard cosmological model with the population of binary black-holes"

Gravitational-wave (GW) detections are rapidly increasing in number, enabling precise statistical analyses of the population of compact binaries. In this talk I will show how these population analyses cannot only serve to constrain the astrophysical formation channels, but also to learn about cosmology. The three key observables are the number of events as a function of luminosity distance, the stochastic GW background of unresolved binaries and the location of any feature in the source mass distribution, such as the expected pair instability supernova (PISN) gap. Given data from LIGO-Virgo observations, I will present constraints in cosmological modifications of gravity. I will also discuss future prospects on measuring $H_0$ given a possible population of black holes above the PISN gap. These novel tests of the standard cosmological model require GW data only and will become increasingly relevant as GW catalogs grow, specially if multi-messenger events remain elusive.


" Double Bubble Lyman Trouble: Indirect Tracers of Escape Fractions from Near & Far for the JWST Era"

The protagonists of the last great phase transition of the universe - cosmic reionization - remain elusive. Whether a minority of bright galaxies (the ``oligarchs") drove reionization or whether it was copious ultra-faint galaxies ("democratic reionization") hinges on their ionizing photon escape fractions (fesc). Direct measures of fesc during reionization are impossible due to the opaque intervening intergalactic medium. In this talk I will present two indirect strategies for progress. First, I will show results from a controlled experiment to isolate indirect tracers of fesc that may be measured at z>6 (e.g., [OIII]/[OII]) based on the "X-SHOOTER Lyman-alpha Survey at z~2" ("XLS-z2") that has collected deep, high-resolution (R~4000) spectra spanning the rest-frame UV to optical (covering LyA to Ha). These long sought for tracers will inform deep spectroscopic programs to unravel reionization with JWST. In the latter part of this talk I will preview two Cycle 1 programs I'm leading (#1933, #2279) that will conduct blind grism spectroscopy of ionized bubbles, one towards the end (z~6.6, in COSMOS) and another at the beginning (z~9, in EGS) of reionization. Decomposing the ionizing field in these bubbles will enable indirect inferences about the relative contributions of bright & faint galaxies. These programs will produce some of the deepest grism pointings in Cycle 1 and enable a vast variety of z~1-9 science.

See also: Seminars, 2021-22