Postdoc Colloquium

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Postdoc Colloquium

Tuesday, February 14, 2023, 03:30pm - 04:30pm

This repeat is an exception to the normal repeat pattern

Will Best, The University of Texas at Austin
Toward the Bottom of the IMF: JWST Spectroscopy of Brown Dwarfs in the Westerlund 2 Star-Forming Region

Abstract

As the lowest-mass objects created by star formation processes, brown dwarfs are essential to a complete understanding of star formation in our galaxy. Leading models of the Initial Mass Function (IMF) differ most dramatically at the extreme low-mass tail, making brown dwarfs and free-floating planets the most sensitive test population for identifying the IMF's shape and possible variations. However, the low-mass IMF remains poorly constrained due to meager samples of these faint objects in the Solar neighborhood and nearby, relatively small star-forming regions. Leveraging deep HST photometry of the star-forming nebula surrounding the massive young Westerlund 2 cluster, we have obtained JWST/NIRSpec multi-object spectroscopy of 131 candidate low-mass stars and brown dwarfs, the most distant observed spectroscopically to date. I will describe our initial findings from our ongoing analysis of these remarkable spectra and their surrounding environment.

Ryan Endsley, The University of Texas at Austin
Revealing the Nature of Reionization-era Galaxies with JWST

Abstract

The epoch of hydrogen reionization marks when structure formation began impacting the large-scale ionization state of the Universe. It has long been thought that faint, low-mass galaxies at redshifts z>6 were the dominant contributors to reionization. However, our understanding of the ionizing properties of these early galaxies has for decades been severely hindered by the sensitivity limitations of previous facilities. Within just months of the start of science operations, JWST is completely transforming our understanding of galaxies present within the first billion years of cosmic history. In this talk, I will discuss the first JWST results on the ages, stellar masses, metal content, and ionizing properties of faint galaxies at z~7-8, the epoch corresponding to the halfway point of hydrogen reionization. By combining these JWST results with those of the much more luminous z~7-8 galaxy population probed by wide-area surveys, I will discuss whether early faint galaxies indeed appear to be the likely drivers of reionization. I will also comment on the surprising presence of dust and AGN within some z~7-8 objects and discuss how future observations with JWST and ALMA can continue to deliver rich insight into the initial formation of massive galaxies.

Jenna Samuel, The University of Texas at Austin
A Jolt to the System: Quenching low-mass galaxies via ram pressure

Abstract

Low-mass galaxies are highly susceptible to quenching effects from both internal stellar feedback and external environment. We explore the role of ram pressure in the environmental quenching of low-mass galaxies in zoom-in hydrodynamic simulations of Milky Way (MW) mass hosts. Ram pressure is highly variable across different environments, within individual MW halos, and for individual low-mass galaxies over time. The impulsiveness of ram pressure -- the maximum ram pressure scaled to the integrated ram pressure prior to quenching -- correlates with whether a galaxy is quiescent or star-forming. The time-scale between maximum ram pressure and quenching is anticorrelated with impulsiveness, such that high impulsiveness corresponds to quenching time-scales under 1 Gyr. Galaxies in low-mass groups outside of MW halos experience typical ram pressure only slightly lower than ram pressure on MW satellites, helping to explain effective quenching via group pre-processing. Furthermore, at small angles off the host galaxy disk, the ambient gas density, ram pressure, and quiescent fraction of satellites around paired Local Group-like hosts are elevated relative to isolated hosts, signaling anisotropic quenching via ram pressure.

Location: PMA 15.216B and online