From July 28 – August 1, 2025, at the Schoodic Institute in Acadia National Park in Maine, the choir collaboration hosted their first meeting, titled: “New Data that Challenge Underlying Assumptions in Early Galaxy Evolution”.
The goal of this workshop was to re-examine long held assumptions in light of new observations and theory, within the realm of galaxy assembly. From the production of the first dust grains to the growth of supermassive black holes, paradigms of early galaxy evolution that were thought to be settled are now being contested. As galaxy evolution is revitalized, so too is the culture of astronomy through ways of creating, collaborating, and sharing knowledge. Unique to this conference was a deliberate equal emphasis on challenging scientific paradigms and critically inspecting and bettering our ways of doing science.
Throughout the week, session types ranged from more traditional talks, to workshop-wide discussions and town halls, to parallel small-group discussions and hacks, to storytelling under the stars, and more. The agenda was attendee-driven, and participants were empowered to lead these sessions on topics of their choosing, for example inclusive pedagogy, astronomy in the Global South, and disentangling feedback cycles within galaxies. The Schoodic Institute is located on the homeland of the Wabanaki, People of the Dawn; the workshop also featured Wabanaki-led storytelling sessions and space for conference participants to join calls to action recommended by the Wabanaki Alliance (see more here).
For this Astrobite, student attendees were invited to report on the science-focused content at the workshop. Across five broad themes within galaxy evolution, speakers gave “Pre-existing Foundations” talks that reviewed our past and recent understanding within the theme, followed by “Late-breaking State of the Field” talks that presented recent advances made by workshop attendees. These talks were presented in the first days of the workshop; over the next few days, a discussion and co-creation based structure was adopted to take a deeper and collaborative look at the assumptions that are being made and how to challenge them going forward.
Note: This following was written by guest authors, credited by bylines under each subsection.
Star Formation Landscape across Cosmic Time
By Isa Cox and Sadie Coffin
The very first session of our workshop this week opened with a foundational overview of the current star formation landscape by Dr. Rachel Cochrane (University of Manchester; Fig. 1). Dr. Cochrane started by highlighting the new frontiers we can reach with JWST (compared to older space telescopes like Hubble and Spitzer), including extremely distant galaxies confirmed to live only a few percent into all of cosmic time (at 300 million years after the Big Bang, or redshift z > 14). One notable result found seemingly too many bright galaxies at early times (z > 10), which challenges our standard cosmological models for how fast galaxies can grow. Dr. Cochrane explained potential reasons for the under-prediction, including the suggestion that many of these sources are in fact compact reddened active galactic nuclei (AGN) candidates, called “little red dots.” She also highlighted emerging evidence that dust and heavier elements started forming earlier than previously thought. Throughout her talk, Dr. Cochrane underscored some of the open questions in the field. Are we overgeneralizing results for entire galaxy populations when we likely only observe the most extreme objects at early times? How are our results and interpretations influenced by uncertainties in our modeling codes? And how can we better align cosmological simulations with our observations to make better predictions and comparisons?
After Dr. Cochrane’s overview, there were six short talks from other scientists. Dr. Jenna Samuel (University of Texas at Austin) spoke about BonFIRE, a new simulation that predicts star formation over the first few hundred million years of the Universe. The simulation traces the efficiency of star formation in galaxies depending on the mass of their dark matter halo birthplaces. Results from BonFIRE actually predict high star formation efficiencies for both large halo mass sources (which matches observational data) and low halo mass sources, which we’re not yet able to observe. Oge Okoronkwo (University of Washington) used a simulation called CHaNGa to focus on galactic winds and their involvement in the structure of the circumgalactic medium (CGM), or the region of gas surrounding a galaxy. Okoronkwo’s talk highlighted how gas often recycles through the CGM multiple times, and most of it only travels a short distance compared to what we expected from observations before falling back in.
Dr. Logan Jones (Space Telescope Science Institute) described a multi-wavelength study of the center of M83, a nearby barred spiral galaxy. A well-studied galaxy, M83 continues to present a fascinating site for research due to its large size and extensive data coverage. Dr. Jones found small and complex structures in the very center of M83 and detected a small, unresolved point source emitting light at energies the researchers did not expect to see in star forming galaxies. Next, Yingjie Cheng (University of Massachusetts at Amherst) presented a special example of a distant barred spiral galaxy (at z > 3). Bars, an elongated structure originating from the center of the galaxy and extending into the disk, can help us trace the growth of disk galaxies and their dark matter haloes, and they are typically observed in more nearby galaxies. When Cheng modeled the bar, she found that it had more recent star formation and an older stellar age compared to the rest of the galaxy. She explained that it now seems possible for bars to form earlier than we thought (even at z ~ 4), which could change our understanding of how these galaxies form.
Dr. Tim Miller (Northwestern University) discussed the morphology (or visual shape) of galaxies in the early Universe and examined how the relationship between the size and mass of galaxies has evolved. He compared galaxy sizes across cosmic time (from z = 0-13) and found that the average size of low mass galaxies rose rapidly in the early Universe before tapering off around the peak of activity in the Universe (z=2, or 3 billion years after the Big Bang). One of his takeaways was that galaxies might grow through different mechanisms at different stages in cosmic history. Finally, Dr. Nikko Cleri (Pennsylvania State University) presented on how to characterize distant objects using optical emission line ratios. Astronomers often use diagrams based on emission line ratios to distinguish different types of galaxies (e.g., star forming galaxies from AGN), but Dr. Cleri argued for re-examining these line diagnostic diagrams, which are mostly calibrated using nearby galaxies and don’t always work well for distant galaxies. He concluded that optical emission lines alone are not enough to crucially determine the ionizing source of objects at high redshift.
This session really showcased the power of JWST and new simulations to revolutionize our understanding of star formation, particularly in the early Universe.
Dust: Small grains, big impact
By Lainey Gammon and Jesse Kelley-Derzon
A main theme of this conference is the song quote “from little things, big things grow.” Dust particles are some of the smallest things we study in astrophysics but have significant effects at all scales. This was highlighted in the foundational review talk given by Dr. Jed McKinney, a NASA Hubble fellow at University of Texas Austin (Fig. 2). He started his talk by summarizing the history of dust starting with the Herschel Satellite observations of the dimming of starlight or “holes” in the night sky, through modern dust theories and our current understanding. He then outlined the fundamental roles of dust in astrophysics: it dims and re-emits light, which must be accounted for in observations, it heats gas and sets the thermal structure for the interstellar medium (ISM), and it catalyzes molecular gas formation, the key ingredient in star formation. He ends by discussing the role dust plays in galaxy evolution and how it can change at early times. This includes how the most massive galaxies produce dust throughout time, how dust obscures star formation, and different mechanisms that can form dust.
The next talk was given by Lainey Gammon, an incoming PhD student at the University of Washington. She discussed her recent work to find dust-obscured galaxies with JWST near-infrared imaging (which detects dust-reddened starlight), using a different approach than the traditional methods that rely on submillimeter imaging (which detects dust emission). Submillimeter imaging surveys primarily capture the most massive and brightest dusty galaxies, but with JWST, we can now detect fainter galaxies, potentially capturing a more complete population of dusty galaxies. Her study focuses on finding these fainter, less extreme dusty galaxies that have previously gone undetected. Her analysis suggests that these dusty galaxies are less massive than nearby counterparts, but still have high dust attenuation, which challenges pre-JWST predictions that indicated galaxies of this mass would be less dusty.
Jesse Kelley-Derzon, a PhD student at University of Florida, gave a talk on her recent simulation results demonstrating the impact of dust on the surprisingly bright distant galaxies observed with JWST. She used a selection of galaxies from a simulation called SMUGGLE which was able to match the observations of a Universe with slightly evolving starlight on average. This was a result of the dust grain size distribution modeled in the simulation which included dust formation, growth, and destruction. If a dust grain size matched to our home Milky Way Galaxy was used instead — as is often assumed — the distant galaxies were more obscured and didn’t match observations.
The next talk was given by Stephen McKay, a PhD student at University of Wisconsin. He talked about Dusty Star-Forming Galaxies (DSFGs) and how he uses complimentary data from multiple telescopes (JWST and ALMA) to better constrain important properties such as redshift (or distance), stellar mass, and age. Using JWST, he also studied the morphologies of DSFGs, which includes large disks, mergers of galaxies, and complex dust structure. His study of morphologies has revealed that the rate of DSFGs formed from merging is lower than previously predicted with the Hubble Space Telescope, which could have implications on our understanding of how dusty galaxies evolve.
The final talk of the session was from Dr. Caleb Choban, a Sullivan Prize Fellow at Indiana University Bloomington. He discussed how he’s incorporating dust models into the FIRE simulation. This includes how dust is created, destroyed, and grows. This simulation should ideally reproduce present day observations, however large uncertainties exist. He had difficulty reproducing the observed DSFGs because of the bursts of star formation ejecting massive amounts of gas, dust, and metals. The simulations could potentially match if key model assumptions about stars are changed and uncertainties on the dust mass are considered. Simulating dust is difficult and more direct comparisons between simulation and observations are needed.
These talks demonstrated the necessity of better understanding of dust in both galaxy observations and simulations. Even though dust is typically less than one percent of a galaxy’s content, the impact is significant and not fully understood yet. It is an exciting time with novel observations and simulations changing our understanding of cosmic dust in our universe.
From Seeds to Giants: Insights into Black Hole Growth
By Madisyn Brooks and Annie Giman
One thing that astronomers tend to agree on is the presence of a black hole (BH) at the center of almost every massive galaxy. How those BHs grow and evolve with their host galaxy remains an open question in astrophysics that is being tackled from a multitude of different perspectives, including multiple-wavelength observations and large theoretical simulations. Dr. Pallavi Patil, a postdoctoral fellow at Johns Hopkins University, kicked off the BH growth session at the choir conference with a review that stretched from the definition of a BH in the 1960s to the major open questions proposed by astronomers in the early 2010s (Fig. 3).
The current paradigm in extragalactic astrophysics relates the total stellar mass, bulge mass (the mass of stars, gas, and dust in the center of a galaxy), and velocity dispersion (the spread of velocities in a galaxy) of a host galaxy to the mass of its central BH. “BH-galaxy co-evolution” is the term used to describe the study of how these galactic and BH properties relate to each other. When the central BH is accreting enough material to produce significant amounts of radiation, it is considered “active” and the region is called an active galactic nucleus (AGN). The mechanisms that drive the interactions between the large-scale galaxy and the small-scale BH — and how these two phenomena might communicate with each other — is the main topic that Dr. Patil discussed in her talk. Dr. Patil described the main research areas that need attention in the BH growth landscape: fueling and accretion, feedback mechanisms, and the BH-galaxy connection. Dr. Patil’s review was followed by three talks that dove deeper into some of the novel science that is being pursued to answer these open questions.
Brian Bichang’a, a graduate student at the University of Hertfordshire, began the talks by comparing a sample of active galactic nuclei (AGN) with a control sample where he found a low interaction fraction amongst both populations, suggesting that AGN triggering could be unrelated to interactions. UMass Amherst graduate student Carlos Garcia Diaz then addressed the fueling of BHs by searching for AGN in dusty star-forming galaxies within distant clusters of galaxies, and emphasized the need for higher resolution X-ray telescopes. Jonathan Cohn, Guarini Dean’s Postdoctoral Fellow at Dartmouth, finished off the session presenting evidence for evolutionary pathway dependent BH scaling relations using the relics of small but dense “dying” galaxies called red nuggets.
A common thread throughout this session was frequent references to other talks and presentations, highlighting just how interconnected these open questions of BH-galaxy co-evolution are. For every finding these researchers presented, there were even more questions that popped up. There is so much still to learn, and with great implications at stake across extragalactic astronomy, it is an exciting time to be thinking about BH growth.
The AGN Renaissance: Discussions on Distant Active Galactic Nuclei
By Sabrina Berger and Veronica Pratt
The session on distant Active Galactic Nuclei (AGN) offered an exciting opportunity to gain a broad overview of the field and spark collaborative conversation. Dr. Erini Lambrides (a NASA Postdoctoral Fellow at NASA-Goddard) began her talk (Fig. 4) asking the all important question: are we on the cusp of an AGN renaissance? AGN are highly active supermassive black holes (SMBH) at the centers of galaxies. To understand what AGN are, it’s helpful to first consider what qualifies as an AGN. For example, the SMBH at the center of the Milky Way has an accretion disk but is not an AGN as its luminosity does not rival its host. On the other hand, the brightest AGN accrete so much matter that they completely outshine their hosts by 100 times or more.
Dr. Lambrides went on to discuss past surveys that searched for AGN. Classically, astronomers based their search criteria on the most luminous unobscured AGN in nearby galaxies; they assumed they didn’t have to worry about how AGN appearance evolves across cosmic time. However, AGN appearance does in fact change over time, since as distance away (or redshift) increases so does gas and dust coverage in host galaxies. She went on to say that after JWST’s launch, many of the new findings disagreed with past predictions. To name a few, scientists found an overabundance of AGN, strange AGN spectra opening up the subfield of Little Red Dots (LRDs), and a surplus of black holes that were overmassive compared to their host galaxy.
To conclude, Dr. Lambrides highlighted some key challenges in the AGN-subfield. By using the same methods for inferring properties such as black hole mass and accretion rate for distant objects that were developed for nearby ones, we may not be inferring these properties robustly. She also noted that most JWST AGN samples are not deep nor resolved enough at key wavelengths, making it difficult to form a complete sample.
Next up in the distant AGN session, five speakers navigate potential solutions to some of these problems. Dr. Luca Ighina (Postdoctoral Fellow at the CfA) approached them through radio observations, which allow us to observe AGN radio jets – that can enhance black hole growth – and provide key constraints on AGN evolution not possible at other wavelengths. Then, Aidan Cloonan (PhD Student at UMass Amherst) investigated LRD morphology to try to understand what drives their unique emission pattern: an AGN-dominated system or an AGN within a larger host galaxy? Pranav Satheesh (PhD candidate at the University of Florida) came in as the first simulator, exploring what happens when black holes merge in cosmological simulations and finding that 22% of massive black hole systems form in a combination of three! Prof. Jillian Bellovary (Queensborough Community College) presented a unique view of LRDs, speculating that they could be caused by stars being ripped apart as they fall into an intermediate mass black hole (a phenomenon also known as a tidal disruption event or TDE). Finally, Dr. David Setton (Postdoctoral fellow at Princeton University) closed the session by detailing the complex spectra of LRDs, including their surprising lack of dust despite their red color.
Clearly, we are on the cusp of an AGN renaissance! We need deeper observations with both JWST and instruments at other wavelengths to unveil the mechanisms behind AGN and to overcome these key challenges. Astronomers (including all those mentioned in this Astrobite!) will continue to tackle questions with our existing datasets and improve simulations to model both new and old AGN.
Shutting Down Star Formation
By Claire Williams and Quinn Casey
As our next speaker explained, “galaxies have been dying since about redshift two,” or in other words, for the last 10 billion years.
Dr. Massissilla Hamadouche, a postdoctoral research associate at the University of Massachusetts, Amherst, opened our session on “Shutting Down Star Formation” with a talk describing the pre-existing foundations of the field (Fig. 5). These “dying” galaxies (often called “quiescent” by astronomers) have their blaze of star formation — traced by a galaxy’s brightest, youngest, and most massive stars — somehow “quenched,” or turned off. Dr. Hamadouche described the history of our understanding of these galaxies: prior to the launch of JWST, galaxies whose star formation has been quenched were observed to at least redshift z=2, corresponding to over 10 billion years ago. Given the age of the Universe (13.7 billion years), those observations imply that galaxies were born, grew to very massive sizes, and then stopped forming new stars all within the first three billion years of the Universe’s existence. In the days before JWST, which is optimized to detect extremely distant galaxies, astronomers speculated that this new telescope probably wouldn’t see any quiescent galaxies beyond redshift z=5, corresponding to about 12.5 billion years ago.
Dr. Hamadouche described how, with the launch of JWST, the community of astronomers that study quiescent galaxies was stunned by a series of incredible early Universe discoveries that repeatedly “broke the redshift barrier.” First came a quiescent galaxy at redshift 4.7, breaking the previous redshift record. Then, another team reported the discovery of an even more distant (or early) massive quiescent galaxy at redshift 4.9. Then, this record was once again beaten by a quiescent galaxy discovered at redshift 7.3, 13 billion years ago. At this time, the Universe was only 700 million years old. The authors of that paper reported that it formed the majority of its stars in an intense burst of activity that lasted 20-100 million years. This means that in roughly the same amount of time between the extinction of the dinosaurs and today, an entire galaxy’s worth of stars was created.
The incredible new observations from JWST, coupled with other telescopes on the ground, have sparked scientific interest in the study of how star formation shuts off in these galaxies. We heard from Dr. Hamadouche and the other contributors to the session about some of the breaking research results and open questions in this field.
Dr. Francisco J. Mercado (Pomona College), Silvia Rueda-Vargas (European Southern Observatory), Joseph Choi (University of Montreal/University of Michigan), and Jorge Moreno (Pomona College) each discussed the importance of AGN feedback in altering star formation. In an AGN, an accreting supermassive black hole in a galaxy’s center may power strong outflows of plasma and radiation, powerful and energetic feedback processes that can prevent continued star formation in the rest of the galaxy. In the early Universe, AGN feedback is more common and more energetic than what we observe in local galaxies which suggests a more profound impact on star formation. This feedback is necessary to reproduce the observed regions surrounding AGN host galaxies in simulations. However, our current understanding of AGN feedback is incomplete as it frequently promotes star formation while also overquenching low mass galaxies in the local Universe. Gourav Khullar (University of Washington) and Kate Whitaker (UMass Amherst) both utilize the magnification effect of gravitational lensing to increase the spatial resolution of their observations and study these lensed galaxies in more detail. They study the stellar properties of these galaxies and find diverse stellar ages which were likely broken up by epochs of quenching.
JWST continues to revolutionize our understanding of the early Universe with regards to how and when stars do, or do not, form. More observations with JWST are necessary to paint a complete picture of star formation.
For more information about the choir collaboration, to keep up with further results from the 2025 workshop, and to be notified of future choir meetings, check out the website here!
Astrobite written by: Sabrina Berger, Madisyn Brooks, Quinn Casey, Sadie Coffin, Olivia Cooper, Isa Cox, Lainey Gammon, Annie Giman, Jesse Kelley-Derzon, Veronica Pratt, and Claire Williams
Astrobite edited by: Olivia Cooper
Featured image credit: Olivia Cooper, taken from the Schoodic Institute where the conference was held.
