Colloquia

Colloquia & Current Events 2026 - 2027

Colloquia Abstracts
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A&P Colloquium series

Colloquia are not recorded.

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The World of Webb, the Cosmic Circle of Life, and Seeing through the Eyes of Einstein

Rogier Windhorst
Arizona State University

Date: Friday 23 October 2026
Time: 3pm - 4pm (ADT)
Venue: AT 101

The 6.5 meter NASA James Webb Space Telescope (JWST) is the near--mid-IR sequel to Hubble, and was successfully launched from French Guiana on December 25, 2021. This talk summarizes the main and most dramatic discoveries by JWST: how much cosmic star-formation has produced its own dust, and has been hidden in its own dust. Webb has revealed the ``Cosmic Circle of Life'', where stars and their planetary systems are formed in this environment of cosmic dust, while stars return their own dust at the end of their lifetimes. In cosmic perspective, the formation of the Sun and Earth occurred 4.5 billion years ago when other galaxies were already twice as old! In random deep fields and Webb's stunning deep lensing galaxy cluster fields, the earliest galaxies have been detected up to redshifts z=15, when the universe was barely 270 Myr old. (Super)massive black hole growth may have started even before that time --- often shrouded by dense gas or dust --- and triggered surrounding galaxy formation through powerful outflows that include relativistic jets. At very high redshifts, (super)massive black hole growth appears to outpace the process of galaxy assembly, with the mysterious Little Red Dots (LRDs) as possible massive black hole progenitors due to direct collapse or (super)Eddington accretion. Very high redshift galaxies --- lensed through massive galaxy clusters up to half the Hubble time in distance --- are being imaged by Webb at light year scales --- physical scales not resolvable without lensing. Perhaps even more stunning, individual stars are now being discovered in significant numbers at very high magnification (mu~1000--10,000) up to redshifts z~6 when going across the cluster caustics, constraining the the stellar mass function directly, and perhaps also the nature of (Wave) Dark Matter. Finally, Webb has detected some lensed high redshift multiply-imaged Supernovae (SNe), whose relativistic time delay helped address the Hubble tension.

Inside the nucleus, inside the stars : Experimental constrains on X-ray Bursts and proton-rich nucleosynthesis with MUSIC

Eilens Lopez-Saavedra
Argonne National Laboratory

Date: Friday 30 October 2026
Time: 3pm - 4pm (ADT)
Venue: AT 101

 

Understanding dense stellar environments with gravitational wave catalogs

Aditya Vijaykumar
Canadian Institute for Theoretical Astrophysics
Chicago

Date: Friday 6 November 2026
Time: 3pm - 4pm (AST)
Venue: AT 101

Fall Break - No TalkFriday 13 November

 

Jason Hessels
McGill University

Date: Friday 20 November 2026
Time: 3pm - 4pm (AST)
Venue: AT 101

 

Monitoring Pluto’s Atmospheric Evolution via Stellar Occultation Data

Michael Person
MIT

Date: Friday 27 November 2026
Time: 3pm - 4pm (AST)
Venue: AT 101

 

A 3-dimensional holographic picture of the pion

Ruben Sandapan
Acadia University

Date: Friday 20 November 2026
Time: 3pm - 4pm (AST)
Venue: AT 101

 

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Illuminating the First Galaxies and the Epoch of Reionization: New Insights from JWST

Lily Whitler
Cambridge

Date: Friday 16 October 2026
Time: 3pm - 4pm (ADT)
Venue: AT 101

In the first billion years of cosmic time, the earliest luminous sources -- stars and accreting black holes in galaxies -- formed and drove a global phase transition of hydrogen in the intergalactic medium known as the Epoch of Reionization. In recent years, JWST observations have shifted the paradigm of our understanding of these earliest galaxies, which played a key role in shaping the Universe as we know it today. In this talk, I will review a sampling of recent results probing the reionization process with observations of z≳8 galaxies. In particular, I will discuss the unexpectedly large abundance of luminous galaxies at unexpectedly high redshifts discovered by JWST, potentially pointing to previously unknown physical processes governing early star formation and a large population of galaxies driving the reionization process. I will then discuss these results in context with insights into the properties of ionized bubbles at z≳7 obtained from JWST spectroscopy of Lyman-alpha emission in reionization-era galaxies. I will particularly emphasize the power of simultaneously studying reionization and the properties of the earliest galaxies, and will discuss prospects and challenges for making the connection between galaxies and reionization with JWST and near-future facilities.

 

Caffe AP

Date: Friday 9 October 2026
Time: 3pm - 4pm (ADT)
Venue: AT 101

 

Evidence for the First Globular Cluster Stellar Stream beyond the Milky Way

Julie Kiel Holm
Copenhagen

Date: Friday 2 October 2026
Time: 3pm - 4pm (ADT)
Venue: AT 101

Globular clusters can lose stars because of a galaxy’s gravity, creating stellar streams—long trails of stars that can reveal information about the galaxy’s dark matter and gravitational structure.

This talk presents evidence for what may be the first globular cluster stellar stream discovered outside the Milky Way, located in an ultra-diffuse galaxy. Researchers model the stream and use generative modelling to study the galaxy’s dark-matter halo.

The discovery is important because stellar streams are sensitive to dark-matter substructures. Future observations from the Euclid and Roman Space Telescopes are expected to find more extragalactic streams, providing new ways to study dark matter across different types of galaxies

 

SMHr-IL: A Tool for High-Resolution Integrated Light Spectroscopy

Charli Sakari
San Francisco State University

Date: Friday 25 September 2026
Time: 3pm - 4pm (ADT)
Venue: AT 101

Integrated light (IL) spectroscopy provides a way to investigate the detailed chemical abundances of distant globular clusters through high-resolution spectroscopy.  Detailed abundances of elements like Na, Mg, Ca, Ba, and Eu provide insight into the birth sites of these clusters, the assembly histories of the host galaxies, and the nature of multiple populations within the clusters.  In this talk, I will discuss work we are doing at San Francisco State University to develop a new version of the code Spectroscopy Made Hard(er), or SMHr, for IL spectroscopic analysis.  SMHr-IL enables automation and standardization of several steps of the analysis, while requiring user input during crucial steps such as line measurements.  I will discuss the progress we have made so far and our goals for the future.

 

The Frisky Infancy of Galaxy Growth Revealed with JWST

Karina Caputi
Groningen

Date: Friday 18 September 2026
Time: 3pm - 4pm (ADT)
Venue: AT 101

Low-mass galaxies (with stellar masses < 10^9 Msun) are fundamental to understand the first steps of galaxy growth. For many years, the study of dwarf galaxies in the local Universe has given us a glimpse of the conditions that would likely have applied to their analogues at early cosmic times. Now, thanks to the superb sensitivity of JWST, we can directly study in detail the properties of significant samples of low-mass sources up to the Epoch of Reionisation and beyond. In the first part of this talk I will briefly review some of the crucial aspects that we have learned about star-formation activity in low-mass galaxies in the first few billion years of cosmic time. I will particularly discuss the importance of burstiness and its effect on galaxy spectral lines and derived parameters. In the second part of the talk, I will present our study of the Pseudo-LRD-NOM, a highly magnified low-mass galaxies at z~6 with very special spectroscopic properties: a very high Balmer decrement and a complete lack of metal lines. I will argue that the simple spectrum of this source provides evidence for complex physical conditions which are similar to those of Little Red Dots (LRDs), suggesting that the Pseudo-LRD-NOM could be a precursor to one of them.

 

A Search for Narrow-line Seyfert 1 Galaxies/Narrow-line Type-1 Quasars at z > 2 with Subaru PFS


Ayumi Takahashi
Kanagawa University

Date: Friday 11 September 2026
Time: 3.30pm - 4.30pm (ADT)
Venue: SB 265

Most galaxies have supermassive black holes at their center. These black holes might have co-evolved with their host galaxies, interacting with each other across cosmic history. We can identify supermassive black holes as active galactic nuclei (AGN) and quasars, which are among the most consistently bright objects in the universe. Beyond redshift 6, quasars with black holes exceeding 1 billion solar masses have been found; these observational findings pose a challenge to our understanding of how black holes grew from their seeds within such a short timescale. We would like to keep track of this investigation. However, such massive black holes have already matured and lost the memory of their early growth. Meanwhile, theoretical models imply that black holes can only grow by a factor of a few under sub-Eddington accretion, and that super- or high-Eddington accretion is a key parameter for black hole growth. Low black hole mass, high-Eddington ratio sources would represent the missing piece in the black hole growth pathway. Narrow-line Seyfert 1 galaxies are known to be low-mass, high-Eddington accretion objects in the local universe, and they, along with their bright analogs (narrow-line Type-1 quasars; NLQ1s), may represent such a population at high redshift as well.

We therefore launched the NLS1/NLQ1 search project using the Subaru Prime Focus Spectrograph (PFS). PFS is a massively multiplexed fiber spectrograph installed at the prime focus of the 8.2-meter Subaru Telescope. This instrument covers optical and near-infrared wavelengths with ~2400 science fibers distributed over a 1.3 deg2 field of view. Since this class has traditionally been identified using the Hβ and [OIII] lines, statistical studies of NLS1s at z>2 remain largely unexplored due to the observational limitations of ground-based telescopes. To extend a comprehensive understanding of this population to the more distant universe, we searched for broad-line AGNs (quasars) whose rest-frame UV spectral shapes resemble those of local NLS1 galaxies, utilizing the Lyα line profile. As a result, four NLQ1s at 2.5 - 6.1 were identified, and this z~6 object is one of the most distant NLS1 candidates. This is the first science result from the PFS-SSP (Subaru Strategic Program) project. I will introduce the current status of Subaru/PFS and this NLS1/NLQ1 search project.

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