Colloquia & Current Events 2021 - 2022

Colloquia Abstracts
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A&P Colloquium series

To obtain the Zoom link for any online event, please email the Astronomy and Physics Department Secretary, Shannon Rhode, at  

Shocking tales of structure formation:
Evolving galaxies and black holes in evolving environments

Andra Stroe (Center for Astrophysics | Harvard & Smithsonian)
Date: Friday 19 November 2021
Time: 3:00 -4:00 PM (AST)
Location: Atrium 101 or Zoom

Understanding the interplay between galaxy evolution, star formation, and black hole activity from the perspective of structure formation remains one of the most fascinating challenges in modern astrophysics. On the largest scales, pairs of galaxy clusters colliding drive the growth of structure. Cluster mergers are the most energetic events since the Big Bang, which release 1064 ergs over 1-2 billion years and produce dramatic, long-lasting effects. By bringing together panchromatic observations, I will discuss how the merger of galaxy clusters can trigger star formation and black hole activity in cluster galaxies, shape the evolution of cluster galaxies, and reverse typical environmental trends observed in relaxed clusters at low redshift. With approximately half the galaxy clusters in the local Universe undergoing mergers, this recent work has revealed gaps in our understanding of the growth of structure in the Universe and showed the potential for discovery in this understudied field. I will draw parallels between the fundamental drivers of galaxy and black hole evolution in low-redshift clusters and the processes relevant in the context of proto-clusters and high-redshift clusters, where mergers and associated non-thermal phenomena were far more common than in the nearby Universe. A treasure trove of cluster samples at increasingly large redshifts will be delivered by new generation of instruments, including eROSITA, GMT, ELT, ATHENA, Lynx, and SKA. The detail with which we can study clusters in the nearby Universe provides us the calibration for the physics of high redshift events and helps guide discoveries in the field of galaxy and black hole evolution at the epoch when structures first formed.


Attila Krasznahorkay (Atomki, Hungary)
26 November: TBA


Dr. Andrew Newman (Carnegie Institution for Science) 
3 December 2021


Probing Dynamic Intracluster Medium: Insights from X-ray Surface Brightness Fluctuations

Irina Zhuravleva (University of Chicago)
Date: Friday 22 October 2021
Time: 3:00 -4:00 PM (ADT)
Location: Loyola 173 or Zoom

Clusters of galaxies are mainly filled with dark matter and hot, Xray emitting gas. They evolve through matter accretion along cosmic filaments, violent mergers, feedback from active galactic nuclei (AGN). Despite being very dynamic environments, the processes that drive gas motions in the intracluster medium (ICM), the properties of turbulence and relevant plasma physics remain poorly explored. In this talk, I will mainly focus on observational efforts to probe these physics. A recent analysis of X-ray surface brightness fluctuations in the central regions of bright, nearby galaxy clusters provided constraints on velocity power spectra, effective equation of state of small-scale perturbations produced by AGN feedback, and directly probed how magnetic fields modify small-scale density perturbations of the gas, affecting its transport properties. At the end of the talk, exciting possibilities to probe gas motions and plasma physics in the ICM with near-future XRISM observatory will be discussed.

Stellar Populations and Formation Histories of Massive Galaxies
Derived from Deep Hubble Space Telescope Grism Data 

Vicente Estrada-Carpenter (Saint Mary’s University)
Date: 15 October 2021
Time:3:00 - 4:00 PM (ADT)
Location: Atrium 101, in-person (Zoom available only upon request, contact

A key question in the field of galaxy evolution is: How do massive quiescent galaxies form in the early universe? Many works have shown the existence of massive quiescent galaxies up to redshifts of z > 3 (when the age of the universe was < 2.2 Gyr). These galaxies are puzzling because they have been able to form massive amounts of stellar mass (log(M/M☉) > 10) in a relatively rapid fashion, even simulations have struggled to recreate these galaxies. Therefore we are lacking some knowledge about the formation of massive galaxies. My research has focused on understanding the star-formation, chemical, morphological, and quenching histories of high redshift (0.7 < z < 2.5) massive quiescent galaxies using HST WFC3 grism spectra + photometry from the CLEAR (CANDELS Lyman-α Emission at Reionization) survey. By studying these massive quiescent galaxies at high redshift we can better constrain their star-formation histories as the uncertainty on age constraints is ~ logarithmic. My work has touched upon topics such as the mass - stellar metallicity relationship (showing that this relationship does not evolve with redshift up a z = 1.7), the link between a galaxies formation redshift and its morphology (providing evidence that the most compact galaxies get their compact morphologies from having formed in the early universe), and the evolution of galaxies as they cross the green valley (showing that galaxies form more rapidly at high redshift and that fast quenching occurs more in high mass galaxies).

The Virtual Universe (Galaxy outflows and their circumgalactic signatures in the IllustrisTNG simulations) 

Dylan Nelson (Heidelberg University)
Date: 8 October 2021
Time: 1:00-2:00 pm (ADT)
Location: Zoom

Recently it has become possible to numerically simulate large, representative volumes of the Universe. These cosmological (magneto)hydrodynamical simulations solve for the coupled evolution of gas, dark matter, stars, and supermassive black holes interacting via the coupled equations of self-gravity and fluid dynamics, all within the context of an expanding spacetime. We can use these 'virtual universes' to study, theoretically, how galaxies form and evolve within the large-scale structure.

In particular, I will discuss our investigations into galaxy evolution, galactic-scale outflows, and the circumgalactic medium in the IllustrisTNG simulations. I will show how outflows sculpt the surrounding CGM, imprinting observable signatures in the gas, as well as in nearby satellite galaxy populations. I will highlight recent results from the high-resolution TNG50 simulation, which provides a unique look at the small-scale structure of cold, circumgalactic gas.

Learning on the Birth of the Stars with SITELLE

Laurie Rousseau-Nepton (Canada-France-Hawaii Telescope)
Date: 1 October 2021
Time: 3:00-4:00 PM (ADT)
Location: Zoom

October 2018 marked the beginning of a new large program at the Canada-France-Hawaii Telescope: SIGNALS, the Star-formation, Ionized Gas, and Nebular Abundances Legacy Survey. During the next four years and with 60 nights of telescope time in hands, our collaboration is observing more than 50,000 extragalactic star-forming regions located in different galactic environments using the instrument SITELLE, an Imaging Fourier Transform Spectrograph. In order to build this sample, we cover 40 galaxies that are actively forming stars within a distance of 10 Mpc. SITELLE was built in Canada and is the perfect instrument to survey these often extended objects.

With SIGNALS, we are seeking to increase our knowledge on how stars form in galaxies, how their birthplace affects their properties, and how multiple generations of stars transform galaxies. Stars continuously affect their environment by returning new elements to the interstellar gas. These new elements are then recycled to form new stars. Stars form in a wide variety of environments. These can be different galaxy to galaxy, location to location. The result is that each star has its own story. By studying 50,000 regions where stars actively form, we will understand what triggers their formation, how efficiently stars form, and how each generation transforms the gas around them. This will also help researchers to understand the star-formation history of the whole Universe since the Big-Bang. During this presentation, I will introduce this ambitious project and the instrument SITELLE as well as show some preliminary results.

Nuclear Physics in Stellar Environments: The Case of Radioactive 26Al in the Galaxy

Sergio Almaraz-Calderon (Florida State University)
Date: 24 September2021
Time: 3:00-4:00 PM (ADT)
Location: Zoom

The satellite-based observation of the long-lived radioisotope aluminum-26, the first of its kind made in space via the detection of its characteristic 1.809 γ-ray line, has long been recognized as direct evidence of ongoing stellar nucleosynthesis processes in the Galaxy. This observation also explains the excess of 26Mg found in presolar dust grains and meteorites. In this talk, I'll describe recent experimental efforts to understand the nucleosynthesis of this important radioisotope by studying nuclear reactions in the laboratory relevant for the production and destruction of 26Al in the stars.

The Growth & Transformation of Galaxies Over Cosmic Time

Dr. Wren Suess (University of California, Santa Cruz)
Date: Friday 17 September 2021
Time: 3:00 - 4:00 PM (ADT)

Deep surveys have allowed us to chart the evolution of galaxies from billions of years ago through to the present day with unprecedented precision. We’ve learned that the properties of both star-forming and quiescent galaxies — including stellar masses, structures, star formation rates, gas content, and kinematics — change dramatically with redshift. Despite this progress, several key questions remain unsolved in our current view of galaxy evolution. We still don’t understand how galaxies grow over cosmic time, or what physical mechanisms are responsible for shutting down star formation and creating the bimodality between star-forming and quiescent galaxies. In this talk, I’ll discuss how new insights from color gradients and half-mass radii have changed our view of galaxy growth, provide insights into how galaxies quench, and show the need to move beyond a bimodal picture of galaxy evolution. Finally, I’ll show that studying the molecular gas reservoirs and star-formation histories of recently-quenched galaxies can provide clues to the mechanisms responsible for quenching star formation in galaxies.

The Cosmic Life Cycle of Massive Galaxies

Katherine Whitaker (University of Massachusetts)
Date: Friday 29 October 2021
Time: 3:00 -4:00 PM (ADT)
Location: Atrium 101 or Zoom

Over the last few decades, we have uncovered billions of years of cosmic growth that present new challenges to galaxy formation theories. In this talk, I will review the recent innovative techniques developed to probe the distant universe, and the key observations constraining the formation histories of galaxies over the past 11 billion years. We have discovered a population of surprisingly compact and massive “red and dead” (quiescent) galaxies that are no longer actively forming stars. The physical mechanisms responsible for shutting down star formation and the subsequent buildup of this quiescent population at such early times is one of the most outstanding questions in astrophysics today. I will present promising paths forward towards solving this puzzle that leverage strong gravitational lensing and the capabilities of the Hubble Space Telescope and ALMA, as
well as a look toward the future with exciting upcoming public facilities. 


Previous Years' Abstracts


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