Title: Star formation and evolution in AGN disks, with application to Little Red Dots

Abstract: Study of stellar objects embedded in AGN accretion disks has been motivated by i) the disk(s) of stars that possibly formed in-situ in the galactic center; ii) the super-solar metallicity of classical quasars independent of redshift, as well as possible AGN+star origin of Little Red Dots; iii) quasi-periodic eruptions connected to star-disk collisions; and iv) LIGO-Virgo gravitational wave sources potentially born in gas rich environments. 

In this talk, I will introduce some recent progress on radiation hydrodynamic simulations of stellar evolution in AGN disks, focusing on their formation from fragmentation of a gravitationally unstable disk and their accretion process in a stratified gas-rich background. We argue that a population of such stars is able to power the extended, optically thick and marginally gravitationally stable disk to generate a big red bump of universal Teff~5000K in the disk SED, which can be invoked to explain continuum features of Little Red Dots.

Title: A novel view of the Milky Way disk and outer Solar system

Abstract: Combining big survey data with advanced statistical analysis is a fruitful approach to new discoveries. I will present two examples.   (1) One is a new mapping technique to provide for the first time a clear and flat view of the phase space of Milky Way disk. Applying it to Gaia data, we found sharp new structures with order-of-unity contrast in number density and metallicity. It opens a new window to study galactic dynamics, calling for theoretical explanation and observational search for similar structures in other disk galaxies.  (2) Another example is a new algorithm searching for moving objects from imaging survey. Applying it to cosmological surveys, I found a dwarf planet with the widest orbit in the Solar system, which places an interesting challenge to the Planet Nine / Planet X hypothesis.

Title: Warm ionized gas filaments in non-central early-type galaxies

Abstract: Filamentary multiphase gas is nearly ubiquitous within the brightest cluster galaxies (BCGs) of cool-core clusters and is likely related to the feeding and feedback of their supermassive black holes. Determining how such filaments form is crucial to understanding the interplay between baryon cycling, active galactic nucleus (AGN) feedback, and the evolution of early-type galaxies (ETGs). However, BCGs account for only a small fraction of all ETGs and their gaseous atmospheres are thought to be strongly influenced by the extreme, dense cluster environments in which they reside. In this talk, I will present the results of our multiwavelength analysis of 126 nearby ETGs that sit outside of the immediate cores of galaxy groups and clusters (hereafter “non-central” ETGs) - with the aim of connecting our current understanding of filamentary multiphase gas formation to the greater ETG population. Using archival VLT-MUSE observations, we detect warm ionized gas in 54 of the 126 non-central ETGs. Most of these systems (35/54) host ordered, rotating gas disks, while the remainder (19/54) show extended filamentary structures that resemble the multiphase filaments seen in BCGs. I will discuss how the MUSE data, in tandem with archival Chandra X-ray observations, support an interpretation in which the warm filaments condense out of cooling, thermally unstable hot halos. Furthermore, I will present emission-line diagnostics that test the ionization mechanisms capable of powering the filaments.

Title: Reading Between the Bumps: Unexplained Features in Optical Extinction Curves

Abstract: The features of interstellar extinction curves serve as powerful diagnostics for interstellar dust, revealing information about its composition, size distribution and the physical and chemical processes that shape it. Extinction features tend to be categorized based on width as they probe different carriers. 

These extinction features include narrow interstellar absorption features from Na, Ca and K and diffuse interstellar bands (DIBs) with widths on the scale of ~0.1-1.0 nm. On the intermediate scale, the well-known 2175A with a width of ~427A is thought to originate from carbonaceous grains. Massa et al 2020, reported three new intermediate-scale structures (ISS). Their analysis found that strength two of the three of these ISS features correlate with the 2175A bump strength, but none were correlated with the total-to-selective extinction ratio, R(V). \

Since then, three additional candidate ISS features were identified in the literature at 0.770, 0.540, 0.850 micron, all with widths greater than any known DIB. To help identify their carriers, I used 74 different lines-of-sight to study the three original ISS features as well as the candidate features. Furthermore, in this study I identified 10 more candidate ISS features observed in these sightlines. Lastly, I present an analysis of all these ISS features on how they relate to the extinction curve parameters, to each other and to the 2175A bump feature.

Title: Using the Metallicity of Simulated Galaxies to Understand Galaxy Evolution

Abstract: Numerical simulations are an invaluable tool for understanding how galaxies form and evolve. Yet, the current generation of simulations suffers from significant modeling uncertainties, rooted in divergent predictions from different codes using similar prescriptions and in a lack systematic comparisons between qualitatively different models. In this talk, I will highlight the oftentimes underappreciated differences between popular cosmological simulations (e.g., IllustrisTNG, EAGLE, FIRE) through examining their metal content. Metals serve as powerful observational tracers of the galactic baryon cycle and are highly sensitive to the details of feedback physics. I will show that even for nominally similar simulation models (e.g., IllustrisTNG and EAGLE), the overall metal budget of the galaxy can be significantly different. Moreover, distinct physical implementations (e.g., IllustrisTNG and FIRE) make very different predictions for the spatial distribution of metals within galaxies. Together, these predictions provide a theoretical framework through which we can leverage the wealth of observational data on metals to gain deeper insight into the processes driving galaxy evolution.

Zoom Link: https://uky.zoom.us/j/82910452708

Title: Where the hot universe meets the energetic universe

Abstract: The hot circumgalactic medium (CGM), a reservoir of missing baryons, metals and energy, plays a key role in our understanding of galaxy evolution. Extraordinary observational challenges, however, make the hot CGM one of the least understood components of galaxies. 

Studying the hot CGM was not the objective of current X-ray or mm facilities during the design phase. As an excellent byproduct, however, observing the hot CGM has emerged as a promising field over the last two decades, coming at the forefront of priority science goals for the current and upcoming decades. 

I will discuss three snippets of our recent efforts to detect and characterize the hot CGM: 

1. X-raying the Milky Way: Investigating thermal and chemical anomalies.
2. Is CGM detectable? Conducting deep searches in individual external galaxies using X-ray,
3. Test for self-similarity: stacking thousands of galaxies in mm (Sunyaev-Zeldovich Effect). 

I will highlight how our findings provide insights into the impact of galactic feedback on the hot CGM, establish our confidence in leveraging current telescopes to inform theoretical simulations and set a benchmark for designing experiments with next-generation X-ray and mm facilities.

Title: Better Together: Combining the Strengths of Rubin, LS4 and Euclid for Time-domain Science and Cosmology

Abstract: We have entered an exciting decade for survey science with such space-based surveys as Euclid and such ground-based surveys as LSST and LS4 providing overlapping imaging datasets across the optical and IR.  LSST will identify thousands of tidal disruption events (TDEs) and millions of AGN and supernovae, including hundreds of gravitationally lensed supernovae (gLSNe) from which we can measure the Hubble Constant. I will discuss how joint analysis of ground and space-based data via multi-resolution forward modeling methods will enable us to search for TDEs from non-nuclear massive black holes, undertake time delay cosmography with populations of gLSNe and study the environments of supernovae and dwarf galaxy AGN.

Title: How "Little Red Dots" Broke the Universe (and how we're unbreaking it)

Abstract: One of the biggest mysteries of the early era of JWST's operation has been "Little Red Dots," compact sources with strange V shaped spectral energy distributions and broad emission lines. These sources have been incredibly hard to model, and over the course of three years, leading theories have ranged from over-massive galaxies that assembled Milky Way levels of stellar mass in the first Gyr of cosmic time to over-massive active galactic nuclei that defy models of black hole assembly. I will walk through the brief history of discover in this sources, demonstrating how we have slowly been getting closer and closer to understanding them by leveraging JWST, ALMA, and several other observatories to constrain their panchromatic spectral energy distribution. I will discuss our current best understanding of these sources, and how we might move forward to incorporate them into our picture of galaxy and black hole assembly.

Dr. Adam Smercina, Space Telescope Science Institute

Title: A New Era of Galaxy Evolution using Resolved Stars

Abstract: The varied and dynamic evolutionary histories of galaxies give rise to their stunning diversity in the present-day universe. Inferring these histories requires accessing the information encoded in their longest-lived visible components: stars. We are in an exciting new frontier, with a fleet of current and upcoming observatories capable of accessing the resolved stellar populations within and around external galaxies. In this talk, I will first summarize my efforts to chart the merger histories of nearby galaxies by surveying the stars in their accreted halos, including the exciting potential of the upcoming Roman Space Telescope. I will then discuss my efforts to trace the evolution of these galaxies star formation and structure, particularly as a consequence of their merger histories, through high-resolution surveys of their main bodies. In particular, I will highlight several large programs with JWST, which has opened up an exciting new frontier for this science. Over the next decade, these efforts with JWST and Roman have the potential to transform our view of galaxy evolution. To close, I will discuss how this current pioneering work with JWST will pave way for the next paradigm shift in resolved star science: the Habitable Worlds Observatory.

Abstract:
We now believe that every large galaxy hosts a supermassive black
hole at its core, with masses ranging from millions to billions of
times that of our Sun. At times, these black holes are actively
accreting, causing the nuclei of the galaxies to shine brightly
across the electromagnetic spectrum. However, in many, perhaps
most quasars, obscuring material along the line of sight shields
us from directly viewing the inner nucleus. This obscuring material
is heated, and emits strongly in the mid-infrared. The Wide-field
Infrared Survey Explorer, or WISE, has recently mapped the entire
sky in mid-infrared light with exquisite depth and clarity. WISE
has allowed us to find luminous quasars across the whole sky due
to this heated material, more than tripling the number of quasars
known. I will discuss several surprising new insights into quasars
that have come out of this work. In brief, the dominant paradigms
do not match our observations, with potentially important implications
for the role of quasars in the growth of galaxies. I will conclude
by discussing how these studies will be further enabled by the
Euclid and WFIRST satellites.