| Tuesday, August 29, 2023 |
03:30pm |
Jorge Moreno, Pomona College |
The Intriguing Lives of Galaxies Lacking Dark Matter
Abstract
The standard cold dark matter plus cosmological constant model predicts that galaxies form within dark-matter haloes, and that low-mass galaxies are more dark-matter dominated than massive ones. The unexpected discovery of two low-mass galaxies lacking dark matter immediately provoked concerns about the standard cosmology and ignited explorations of alternatives, including self-interacting dark matter and modified gravity. Apprehension grew after several cosmological simulations using the conventional model failed to form adequate numerical analogues with comparable internal characteristics (stellar masses, sizes, velocity dispersions and Sérsic indices). Here we show that the standard paradigm naturally produces galaxies lacking dark matter with internal characteristics in agreement with observations. Using a state-of-the-art cosmological simulation and a meticulous galaxy-identification technique, we find that extreme close encounters with massive neighbours can be responsible for this. Moreover, these encounters occur when the satellite is still gas-rich, suggesting that gas-rich interactions may explain the peculiar globular cluster populations in these galaxies. We predict that ∼30% of massive central galaxies (with at least 10e11 solar masses in stars) harbour at least one dark-matter-deficient satellite (with 10e8 -10e9 solar masses in stars). This distinctive class of galaxies provides an additional layer in understanding how tidal stripping and star formation triggering unfolds under these extreme conditions. Future observations surveying galaxies in the aforementioned regime will provide a crucial test of this scenario. If time allows, I will also mention recent results on the radial acceleration relation and challenges to MOND.
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| Tuesday, September 05, 2023 |
03:30pm |
Darryl Seligman, Cornell University |
Interstellar Interlopers and Dark Comets
Abstract
In recent years, two entirely new classes of planetesimals have been discovered in the solar system: interstellar interlopers and dark comets. These still-enigmatic objects are challenging our understanding of the behavior and properties of comets and asteroids. In this talk, I will review what has been learned to date from the known interstellar objects and dark comets, highlighting the attributes that are difficult to reconcile with previous models of planetesimal behavior. I will present recent hypotheses that can explain their unusual behavior through natural mechanisms, including the acceleration of 1I/`Oumuamua via release of radiolytically produced and entrapped molecular hydrogen. One of the dark comet candidates, 1998 KY26, is already the target for the extended Hayabusa2 mission and exhibits favorable viewing geometry before 2025. The forthcoming Rubin Observatory Legacy Survey of Space and Time (LSST) is poised to further transform our understanding of these classes of objects, and I will discuss the feasibility of future discoveries via ground-based observations as well as possible intercept missions.
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| Tuesday, September 12, 2023 |
03:30pm |
1-Minute Colloquium |
Astronomy Department and McDonald Observatory Personnel present overviews of their work
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| Tuesday, September 19, 2023 |
03:30pm |
Jamie Tayar, University of Florida |
Red Giant Chemistry: Interactions, Interiors, and Galactic Evolution
Abstract
Red giants can be great tracers of galactic chemical evolution since they can be studied to large distances. However, the mixture of elements they were born with can be altered over the course of their lifetimes due to creation, destruction, and mixing. In this talk, I will discuss the current state of our ability to get precise ages for these stars using asteroseismology, and how they can be used to map galactic chemical evolution. I will discuss observed changes in surface chemistry that occur at the first dredge up and above the red giant branch bump, and our current understanding of the physical mechanisms for these changes. Finally, I will discuss some of the impacts that binary interactions can have on these abundances and whether they can be used as one tracer of current or past binary interactions.
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| Tuesday, September 26, 2023 |
03:30pm |
Stephanie Douglas, Lafayette College |
From the Surface Rotation of Stars to Their Interiors, Magnetism, and Beyond
Abstract
Open clusters, such as the Pleiades, Praesepe, and the Hyades, are critical benchmarks for calibrating stellar properties such as rotation and magnetic activity. As stars approach the main sequence, they contract and spin more rapidly; once they reach the main sequence, they stop contracting and their spin speed decreases. This spin-down is caused by angular momentum lost via stellar winds, but details of stellar wind torques and any internal angular momentum transport are still uncertain. I will discuss recent results constraining the rotation of old, low-mass stars along with young, solar-mass stars. I will show how we can use these clusters and a new, statistically robust fitting method to distinguish between models of stellar rotational evolution.
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| Tuesday, October 03, 2023 |
03:30pm |
Chris Hayward, Flatiron Institute |
What Can High-Redshift, Infrared-Luminous Galaxies Tell Us About Galaxy Formation Physics and Cosmology?
Abstract
nterstellar dust is pervasive throughout the Universe, and most light from young, massive stars is absorbed by dust and reradiated as thermal emission in the infrared. Submillimeter galaxies (SMGs), a class of very infrared-luminous distant galaxies, are some of the most extreme star-forming galaxies known, forming stars at rates hundreds or even thousands of times greater than our own Milky Way. I will review our understanding of this enigmatic population, which has challenged galaxy formation theories since their discovery in the late 1990s. I will highlight how the population provides novel constraints on galaxy formation physics, cosmology, and possibly even the nature of dark matter. I will also show how they serve as beacons of galaxy clusters in the process of formation.
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| Tuesday, October 10, 2023 |
03:30pm |
Erika Hamden, University of Arizona |
Title: TBA
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| Tuesday, October 17, 2023 |
03:30pm |
Gwen Rudie, Carnegie Observatories |
Title: TBA
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| Tuesday, October 24, 2023 |
03:30pm |
Adrienne Erickcek, University of North Carolina |
Title: TBA
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| Tuesday, October 31, 2023 |
03:30pm |
BashFest Symposium |
No talk scheduled
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