We have CCAPP seminar today at 11:30. Today’s talk will be inperson in the Cliffhanger room, PRB 4138 (with zoom option as usual). For this seminar we will have two more OSU grad students sharing their work with us, Grace Olivier and Hui Kong!
Link for the CCAPP Seminar Zoom Option:
Zoom link:https://osu.zoom.us/j/96209154804?pwd=d1lWZnRueGVVa2tabUZTak4xSkpaQT09password: CCAPP-2021
password: CCAPP-2021
Speaker: Grace Olivier
Evolution of Stellar Feedback from Reionization to The Milky Way: A Diverse Toolset of Imaging, Spectroscopy, and Modelling for Understanding the Impact of Massive Stars
Massive stars contribute incredible amounts of energy to their surroundings across a variety of environments in the universe. Before their exciting deaths, massive stars produce feedback through a number of mechanisms that are frequently used in subgrid physics models in galaxy simulations to create realistic galaxies. Observations are a key to anchoring these simulations in reality, but there has been limited work on this front, especially for the youngest, embedded HII regions. I explore the effects of direct radiation pressure, dust-processed radiation pressure, photoionization heating and shock-heating from stellar winds in a sample of young HII regions (sources with radii < 0.5 pc) and determine which is the most important for very young stars. This analysis suggests radiative feedback on dust drives the earliest stages of HII region expansion. Additionally, I study the effects of radiative feedback in an exciting population of extremely low-metallicity star-forming galaxies that have been discovered in the local universe which are analogues to Reionization Era galaxies. During the Epoch of Reionization radiative feedback played a significant role in shaping the universe, and such analogues give us a detailed laboratory to explore the effects from feedback. I present deep FUV and optical spectra of two of these extreme emission line galaxies that have strong very-high-ionization optical and FUV emission lines (e.g., CIV, HeII, [FeV], [ArIV]). I demonstrate that canonical photoionization models, using typical stellar population models, catastrophically fail to reproduce the high-ionization emission lines. I constrain the stellar population properties using the FUV spectral features and explore the deficiencies of current stellar models. By simultaneously fitting the stellar and nebular emission within these extremely high-ionization emission line galaxies, I provide new observational benchmarks of radiative feedback for the next generation of stellar models at very low metallicity. By studying the effects of stellar feedback from single stars in the Milky Way to entire stellar populations in analogues to the first galaxies we can begin to build a coherent picture of stellar feedback as it impacts the vast scales of the universe.
Speaker: Hui Kong
Image simulation and sample characterization of DESI LRGs'
DESI is about to measure the most accurate 3D map of the large scale structure of the universe. DESI targets are selected from imaging surveys, and this selection inevitably generates imaging systematics. Control and possibly mitigation of these systematic uncertainties is crucial for our understanding of large scale structure. Galaxy clustering is a very rich topic providing a wealth of information. On large scales, for example, it contains information of the very early universe such as the nature of the primordial density fluctuation during the period of inflation. These scales, however, are highly contaminated by aforementioned imaging systematics. In order to control these uncertainties, we developed a novel simulation tool that inserts simulating galaxies in the imaging survey data. Using the same pipeline that produces photometric catalogs, this method allows us to study the fluctuations in galaxy features at the pixel level. I will present the simulation tool we have developed for this purpose, demonstrate how it can be used to characterize the sample of large red galaxies used by DESI for cosmological analyses and present an outlook of how a better control of the imaging systematics improves measurements of the f_nl parameter that describes primordial density fluctuations