Welcome! The Center for AstroPhysical Surveys (CAPS) seminars are normally held on Fridays at noon central time in room 1040 at NCSA. Pizzas will be arranged.
Please contact the current seminar organizers Cynthia Trendafilova and Ayan Mitra for further details.
Location: NCSA-1040(Unless specified otherwise) Zoom: Link
SPHEREx, NASA’s latest space telescope (just launched on March 11th!), will soon commence its survey of the entire sky in 102 near-infrared spectral channels from 0.75-5 microns. This rich dataset will be used for a wide variety of science, including studies of objects in our own solar system, an inventory of water and CO2 ice in the Milky Way, and constraints on cosmic inflation and the structure of the Universe on the largest scales. Due to its orbit and scan strategy, SPHEREx will also naturally build up deep fields in the ecliptic poles, which will enable unprecedented studies of the extragalactic background light (EBL). The EBL encodes the history of galaxy formation stretching from today all the way into the Epoch of Reionization, over 13 Gyr ago. In this talk, I will provide an overview of SPHEREx, including its three core science themes (ices, inflation, and EBL) and the kinds of public data products it will provide. I will close with a deep dive on the EBL, the status of our team’s analysis pipeline, and what we hope to learn about galaxies near and far in the next few years.
The La Silla Schmidt Southern Survey (LS4) is a 5-year public, wide-field, optical survey using an upgraded 20 square degree QUEST Camera on the ESO Schmidt Telescope at the La Silla Observatory in Chile. We are using LBNL fully-depleted CCDs to maximize the sensitivity in the optical up to 1 micron. This survey, which will commence in just a few months, will complement the Legacy Survey of Space and Time (LSST) being conducted at the Vera C. Rubin Observatory in two ways. First, it will provide a higher cadence than the LSST over several thousand square degrees of sky each night, allowing a more accurate characterization of brighter and faster evolving transients to 21st magnitude. Second, it will open up a new phase-space for discovery when coupled with the LSST by probing the sky between 12–16th magnitude — a region where the Rubin Observatory saturates. In addition, a Target of Opportunity program will be able to trigger on Multi-Messenger Astronomy events with localization uncertainties up to several hundred sq. deg., in multiple colors, very quickly. This project has direct relevance to several cosmology and fundamental physics efforts including: peculiar velocity measurements, and hence fundamental constraints on general relativity, with supernova as standardized candles; gravitational wave standard sirens as probes of the expansion of the Universe and gravity; and measurements of the Hubble constant through Type Ia and II-P supernovae. It also represents a very challenging computational framework to deliver on the science both in real-time and for multi-observatory data analysis. I will provide an overview of the project and its science goals with a view towards a few novel experiments which LS4 can enable.
After a review of what we know about the inner few light years of the Galactic center, I present highlights of our study of monitoring the flux of Sgr A* with JWST/NIRCam at 2.1 and 4.8 microns. JWST observations indicate that the flux of Sgr A* is fluctuating constantly with multiple flares that indicate two distinct populations of particles producing bright synchrotron flares and low-level fluctuations. I will discuss what the spectral index, time delays at infrared wavelengths, power spectrum, and the flux distribution tell us. Modeling of the distinctive behavior of the spectral index as a function of brightness (loop diagrams) has given us a handle on localized magnetic field strengths and the electron density in the accretion flow. Time permitting, I will also discuss the origin of a strong NuSTAR X-ray flare which coincides with a NIRCam infrared flare.
Accurately modeling molecular hydrogen H2 is an important task in cosmological simulations because it affects star formation and galaxy evolution. One fundamental property of molecular hydrogen is the ability to self-shield, a phenomenon in which the Lyman-Werner UV absorption line bands become optically thick at high H2 column density, and H2 in a molecular cloud’s outer layer can shield H2 inside. Historically, numerical approximations have been utilized to avoid intensive ray-tracing calculations without significantly changing results. This paper evaluates the use of the Sobolev-like approximation in self-shielding modeling and tests whether it agrees with the results from a more rigorous ray tracing method in the cosmological simulation context. We run two sets of high-resolution zoom-in cosmological simulations, each set with two self-shielding models, to investigate the models’ effects on galaxy evolution in the early stage and the late stage of the Reionization era. We find that the approximation model underestimates the level of H2 self-shielding in a low gas density environment, causing halos to lose a lot of H2 when compared with the ray tracing model. The susceptibility of H2 against high-energy radiation in simulations with the approximation model prevents smaller halos from forming stars, while bigger halos seem to be uninfluenced by the choice of self-shielding model in terms of stellar mass. Within a halo, we show that the discrepancy between the approximation and the ray-tracing model is more prominent in the halo’s outer region due to its low gas density. On a large scale, the approximation model has fewer metal-contaminated regions in the intergalactic medium, increases IGM heating, and speeds up the reionization process. These results show that the use of Sobolev-like approximation to model H2 self-shielding alters various properties of galaxies and the large-scale universe, emphasizing a need for caution when employing this technique in running cosmological simulations.
Recent cosmic microwave background (CMB) experiments have opened the millimeter-wave (mm) regime of the electromagnetic spectrum to time-domain astrophysics. While mm observations have been conducted in the past, this is the first time that transient events have been blindly discovered in non-targeted surveys, as opposed to follow-up or pointed observations. Past mm-wave transient surveys with the South Pole Telescope (SPT) targeted the extragalactic sky and have detected hundreds of transient events, with most of them being galactic flaring stars. In this talk, we will present the first mm-wave time-domain survey towards the Galactic plane with SPT-3G (the third generation SPT camera). This survey consists of approximately 500 observations covering 100 square degrees of the Galactic plane in both 2023 and 2024, with plans for more observations in the coming years. The survey measures intensity and linear polarization in three bands centered at 95, 150 and 220 GHz. Until now, we have detected two transient events above a threshold of 5𝜎 in both 95 and 150GHz bands. Both events are associated with previous known binary systems with white dwarf accretors. Future analysis will involve lowering the detection threshold and improving the transient pipeline to be sensitive to timescales of minutes.
The measurement of the cosmic microwave background (CMB) has played a crucial role in establishing the ΛCDM cosmological model. The next frontier is exploring physics beyond the Standard Model, such as inflation, neutrino mass, and cosmic birefringence, through CMB polarization. Achieving this requires high-sensitivity observations across multiple frequencies. Space-based CMB missions provide a unique opportunity for full-sky coverage with broad frequency access, complementing ground-based telescopes. In this talk, I will introduce the scientific motivation for CMB observations from space, provide an overview of LiteBIRD, and discuss the synergy between space and ground-based experiments in advancing our understanding of fundamental physics.
Very Long Baseline Interferometry (VLBI) is intimately linked to black holes and their astrometry. This relation goes both ways: VLBI astrometry has, for instance, enabled exquisitely accurate determinations of (i) black hole properties through precise distance measurements, (ii) the motion of the supermassive black hole at the center of the Milky Way, and (iii) the (local) Hubble constant value thanks to megamaser sources. Conversely, distant black holes are the anchors used for all VLBI astrometry. In this colloquium, I will provide a review of these topics, and discuss how the intimate relationship between black holes and astrometry will change with the advent of the future generation of VLBI arrays (particularly the ngEHT and the ngVLA).
Astronomy is a science driven by observation. Since 1609, those observations have required ever more sensitive and exquisite hardware. In the 20th century, advances in technology and creativity allowed for the creation of space observatories. These space observatories have opened entirely new areas of science and play a vital role in the advancement of the field. In the early 21st century, the space industry is poised on the cusp of a revolution, the 3rd space age. In this talk we will discuss the development of predominantly large space observatories, such as Chandra, James Webb and the Habitable Worlds Observer. We will examine what makes development of these space observatories challenging and how the coming revolution in technology may ameliorate some of these challenges. Also discussed will be the roles of all manner of technical professionals, engineers and scientists in the development process.
In October 2024, the VLA Sky Survey (VLASS) completed its third full epoch, observing ~34,000 deg^2 of the northern sky at a frequency of 3 GHz, a sub-mJy (7σ) sensitivity, and a resolution of ~2.5 arcseconds, for the third time since 2017.
One of the main science goals of VLASS is to uncover the diversity of phenomena in the dynamic radio sky. In this talk, I will give an overview of the several thousand slow radio transients that VLASS has detected to date: how they were discovered, what types of multi-wavelength counterparts they are (and aren’t) associated with, and what they might teach us about the astrophysical particle accelerators that emitted them. With the scale of the VLASS sample, we are starting to assemble a statistical picture of common transient classes, including radio supernovae, AGN flares, tidal disruption events, and magnetic activity in stars. For each of these classes, I will discuss their rates and properties, and how they might open new windows on classic problems such as massive stellar evolution, the growth of supermassive black holes, and the properties of strongly magnetized stars.
Explosive growth in digital technology has created a radio interferometry renaissance, enabling current and upcoming astronomical facilities such as ALMA, ngVLA, SKA, and DSA-2000. Crucially, these facilities are all computational telescopes, which rely on increasingly performant computing clusters to process the data, calibrate the instrument, and even form images. These same breakthroughs led to the Event Horizon Telescope (EHT), a global very-long-baseline interferometry (VLBI) network that produced the first images of black holes. I will summarize our major EHT discoveries, which have led to new insights in black hole accretion and jet formation. I will also describe ongoing efforts to develop the Black Hole Explorer (BHEX), a mission that will produce the sharpest images in the history of astronomy by extending the EHT to space. BHEX will reveal the bright and narrow “photon ring” that is predicted to exist in images of black holes, produced from light that has orbited the black hole before escaping. BHEX is enabled by recent technological breakthroughs, including the development of 100 Gb/s downlink using laser communications, and it demonstrates the extraordinary potential for computation-enabled discovery in astronomy and physics in the coming decades.
When interstellar water was first detected in 1969 (through its 22 GHz maser transition), only five other molecules were known to exist in interstellar space, only eight planets beyond the Earth were known, the manner in which our solar system formed was unclear, and whether life might be possible beyond the Earth and our solar system was pure speculation. In the intervening 55 years, the advances have been nothing short of breathtaking. We now know of more than 330 interstellar and circumstellar molecules and molecular ions, some of which are complex organic building blocks of life. We also know of more than 5,700 confirmed extrasolar planets, including 963 multi-planet systems, and we routinely observe other solar systems in the making. All these discoveries encourage the belief that the chemistry in interstellar space is rich, and the products of this chemistry are likely inherited by a multitude of solar systems, some with Earth-like planets and moons in their habitable zones. As the ubiquity of this arc of evolution from molecular cloud to protoplanetary disk comes into increasing focus, the role of water and other key biological ingredients have assumed even greater interest, particularly the role of ices as the major conveyor of these key species to newly forming planets. I will review a few highlights of this journey to understand water’s indispensable role and the giant next steps we hope to take with SPHEREx, a NASA Medium-class Explorer Mission. Scheduled for launch in February 2025, SPHEREx is designed to conduct an all-sky spectroscopic survey between 0.75 µm and 5 µm. Among its goals, SPHEREx will carry out an unprecedented study of the abundance and distribution of biologically important ices throughout the Milky Way by means of absorption spectroscopy. This talk will discuss the impact of increasing the number of ice sightlines observed from a current value of several hundred to more than 9.9 million.
The direct detection of gravitational waves in 2015 opened up a new window in astronomy and astrophysics and provided new opportunities to study fundamental physics that is not accessible in the lab. I will describe what we have learned about our universe through observing merging black holes and neutron stars with LIGO and Virgo. I will also discuss ongoing observations and the prospects for new discoveries going forward.
The modern generation of telescopes are sharp enough to observe chemical inhomogeneities in the interstellar medium of galaxies on a range of spatial scales, allowing us to directly see the small-scale processes that play a critical role in shaping how galaxies grow and evolve. In this talk, I present a selection of novel statistical techniques that can be used to model galaxy data, characterise the spatial chemical distribution of galaxies, and make meaningful comparisons to both analytical and simulated models. For well-resolved data (finer than ~200 pc per pixel), I introduce the geostatistical modelling framework that allows the multiscale metallicity structure of galaxies to be modelled and key physical parameters to be extracted. For data that is more coarsely resolved, I demonstrate the power of forward-modelling to fit more accurate metallicity gradients, as well as asymmetrical models that capture more details on a galaxy’s evolutionary history. Finally, I discuss a way to infer the presence of metallicity variations in unresolved sources by combining absorption and emission-based spectroscopy in host galaxies of gamma-ray bursts. These results shed light on the evolution of the interstellar medium of galaxies throughout cosmic time and hold great promise for use in the analysis of future data sets.
Hierarchical Bayesian models provide a powerful framework for addressing complex problems in astrophysics by integrating multiple sources of uncertainty to infer population-level information. In this talk, I will present two applications of hierarchical Bayesian modelling to distinct astrophysical problems.
The first model involves the spectrophotometric calibration of 32 faint DA white dwarf (DAWD) standards alongside the three CALSPEC primary standards across a broad wavelength range (1100 Å to 1.8 μm). By jointly inferring photometric zeropoints and WD parameters using both photometric and spectroscopic data, the model reaches sub-percent precision. This allows for the correction of instrument-dependent variations, such as HST cycle-dependent zeropoints and count rate non-linearity and supports population-level dust analysis for validating priors. The results are critical for ensuring precise calibration of upcoming surveys like the Vera Rubin Observatory’s LSST and the Nancy Grace Roman and Euclid surveys.
The second model addresses the challenge of Malmquist bias in cosmological distance estimation using Type Ia Supernovae (SNe Ia). This selection effect skews detected samples towards brighter SNe at higher redshifts, leading to biased distance measurements and incorrect cosmological parameter constraints if untreated. I will outline a novel hierarchical Bayesian approach that combines simulation-based inference to correct for this bias. Our method generalizes well to real survey selection effects, providing more accurate estimates of cosmological parameters where traditional analytical corrections fail.
The launch of the James Webb Space Telescope (JWST) has ignited a revolution in our understanding of the early universe. Its exquisite infrared capabilities have allowed observers to find galaxies at higher redshifts and measure their stellar properties better than ever before. I will describe how, intriguingly, observations in these different arenas appear to be in tension with our models. I will discuss the higher-than-expected abundance of early (z>9) galaxies in JWST, and show how clustering measurements are key for understanding how these galaxies formed. Then, I will show how recent JWST determinations of the ionizing properties of the first galaxies are in tension with CMB and Lyman-alpha forest observations. If time allows, I will discuss the road ahead with future observatories including 21-cm telescopes.
The last decade witnessed an explosion of cloud technology in the tech sector. Dominated by a few key players (e.g., AWS), their managed infrastructure products allow even small teams of software developers to create powerful web applications for consumers and businesses. Furthermore, an ever increasing number of cloud-centric open source frameworks have been adopted in the technology sector, further accelerating both the utility and the adoption of the cloud.
As a platform, Camber brings the benefits of cloud computing to researchers in a way that is easy to use, collaborative, accessible and cost-effective. With a pythonic interface, you can spin up MPI clusters for simulations, Apache Spark for big data analysis as well as several managed science engines to run popular science libraries on distributed computing infrastructure. In addition, our managed version of cloud object store allows for teams to collaboratively efficiently use big data tooling.
When stars approach the tidal radius of a supermassive black hole (SMBH) and find themselves unraveled, the resulting debris stream spirals toward the SMBH and creates a flare whose light can outshine the host galaxy. TDEs have recently offered us glimpses into the sub-parsec local environments near SMBHs. AT 2020mot is a typical UV/optical TDE, but is uniquely bright in the near-infrared and even shows a later enhancement in brightness along the tail of the light curve. This could be the first TDE to show two “dust echoes,” indicative of concentric rings of thin dust within 0.1 parsecs of a SMBH, among the smallest scales at which dust has been inferred near SMBHs. Similarly, the event AT 2022upj is an extreme coronal line emitter (ECLE) that shares emission line diagnostics in common with the small subset of ECLEs believed to be “light echoes” of TDEs in gas-rich environments. Events like AT 2020mot and AT 2022upj are novel opportunities to peer into the closest material of otherwise invisible black holes in quiet galaxies. Studying these events will explore the fundamental connections between supermassive black holes, galaxy evolution, and accretion mechanics.
Active galactic nuclei (AGN), residing at the center of massive galaxies, are the ideal laboratories for studying accretion physics, black hole-galaxy-halo relations, and interstellar/circumgalactic medium (ISM/CGM) evolution. Driven by accretion onto the central supermassive black holes (SMBH), AGN can expel substantial energy into the surrounding environment through radio jets and direct heating of ISM/CGM. Recent deep imaging and spectroscopic surveys have revealed interesting connections between AGN, host galaxies, and their surrounding ISM/CGM. Meanwhile, stochastic quasar variability monitored by time-domain surveys can provide constraints on geometry and dynamics in the innermost region of AGNs. In this talk, I will highlight recent discoveries from the Cosmic Ultraviolet Baryon Survey (CUBS) and the Sloan Digital Sky Survey Reverberation Mapping Project (SDSS-RM). I will also present a flexible inference framework using simulation-based inference and deep learning to constrain accretion disk physics for the upcoming Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST). Finally, I will discuss the importance of leveraging novel methodologies to tackle large datasets in future astronomy surveys.
GW170817 was the first confirmed binary neutron star merger (NSM) with an associated kilonova. Observations of this event was revolutionary as kilonovae and NSMs are excellent laboratories for studying r-process nucleosynthesis, multi-messenger astronomy, cosmology, the equation of state of neutron stars, and more. Its discovery was made possible by the LIGO-Virgo-KAGRA (LVK) gravitational wave network; however, based on recent predictions for Observing runs 4 and 5, there will only be a handful of EM counterparts will be detectable for LVK-detected NSMs. As a result, we cannot wholly rely on gravitational wave detections to do KN science. Given the faint nature of KN, we propose leveraging bright short gamma ray burst afterglows to identify candidate NSM events in large scale optical surveys like Legacy Survey of Space and Time (LSST). By overlaying existing afterglow and kilonova models, we find at ~5 days post-merger the combined UV emission can be up to 2 magnitudes brighter than the kilonova alone. This enhancement can enable a study of NSM hosts and their environments by expanding the possible search volume and the time to find these events.
Recently, cosmic microwave background (CMB) experiments have opened the millimeter-wave (mm) regime of the electromagnetic spectrum to time domain astrophysics. While many observations in the mm have occurred in the past, this is the first time that transient events have been blindly discovered in blank-field surveys, as opposed to follow-up or pointed observations. The dominant source of time variability in the mm extragalactic sky are blazars. In the galaxy, the mm transient signal is dominated by stellar flares ~1e5 times more energetic than flares from our own Sun. The South Pole Telescope (SPT) has recently conducted the first mm-wave time domain survey of the Galactic plane. This survey consists of ~500 observations over 125 square degrees of the Galactic plane. The survey measures intensity and linear polarization in three bands centered at 95, 150 and 220 GHz. Preliminary data reduction and analysis are currently underway and I will present the first preliminary results of our survey in this talk.
While astronomy is rich with compelling imagery that excites both researchers and the public, the datasets underlying many significant results are often easily interpreted only by the researchers themselves. Effective science communication often relies on science-based illustrations to both engage audiences and provide important visual context for understanding the text of a press release, museum exhibit, etc. I will talk through the methodologies we have found most effective in balancing science, communications, and aesthetic concerns when developing “space art” in support of NASA science results. Case studies will include Milky Way structure, black holes, and exoplanets.
The space-time distortion caused by supermassive black holes provides a unique laboratory for violent physical processes like stellar tidal disruption, highly relativistic jets, and turbulent accretion flows. Synthesizing observations across many wavelengths and studying their time variability at slow and rapid timescales promises a new, dynamic, thorough understanding of how black holes form and grow, how they consume material, how they construct powerful relativistic jets, and how they bend the evolution of galaxies to a path that matches our observations of the Universe. I will discuss how both high-resolution radio imaging surveys of outflows and star formation and timing observations with breakthrough instruments like the NICER instrument on the ISS and the TESS exoplanet-hunting missions have provided new intersectional insights and promise a fertile new temporal phase space for exploring the detailed phenomenology and cosmological implications of active galactic nuclei. In my talk, I will discuss results from my 22 GHz radio survey of 268 radio-quiet BAT AGN and implications for both the origin of radio emission in non-jetted objects and galaxy-wide star formation suppression. I will also discuss time domain results in progress from my large TESS program, including searching for unique signatures of binary supermassive black holes, the high-energy astrophysics of relativistic jets, and more.
The diversity of the exoplanet population is beyond our imagination. The more than 5000 known exoplanets vastly differ in mass, size, orbital period, dynamics, and host type. Demographic studies, however, aim to find patterns in the population that inform us about their origin, composition, and evolution. Among these features, perhaps the most surprising is the abundance of planets with no analog in the solar system, also known as sub-Neptunes. In this talk, I will review the state-of-the-art regarding the detection and characterization of such planets and what we know today about their enigmatic nature. A definitive answer, however, seems within reach during this decade thanks to the game-changing observations that will be provided by JWST.
A complete theory of galaxy formation requires understanding the details of how gas is converted into stars over cosmic time, which is affected by gas supply, star formation, and feedback-driven outflows. I will present a physical picture for galaxy formation that exhibits two distinct phases: at high redshift, stellar feedback causes all-star-forming galaxies to undergo rapid fluctuations in their star formation rates on ~10-Myr timescales. Bursts of star formation are followed by strong outflows, which cause the star formation rate to drop precipitously. Fresh gas supply from galactic fountains rejuvenates star formation and restarts the cycle. At z ~ 1, simulations of massive galaxies exhibit a qualitative transition: outflows are no longer driven effectively, and the galaxies transition to steadily star-forming, well-order disk galaxies. I will discuss the physical causes of busty star formation and the aforementioned transition to time-steady star formation, in addition to some implications for JWST observations of high-redshift galaxies. I will also describe how we can test this theoretical picture via more sophisticated comparisons between theoretical models and observations than are currently performed.
CMB-S4 [1] is the next generation of ground-based cosmic microwave background (CMB)
experiments. With a total of 21 telescopes at the South Pole and the Atacama desert, this
campaign is going to observe the accessible sky at millimeter wavelengths for a duration of
seven years. Our research goal is to better understand what new physics we can derive from
the CMB-S4 data in the context of Solar System Objects (SSOs). Observations of asteroids in
mm wavelengths [2] have reported consistently lower fluxes than predicted by modeling their
surface temperature profiles with IR data. Since the mm wave radiation has a significant
contribution from subsurface emission, researchers have noted that it might be an indication of
a large temperature gradient in the immediate subsurface region. To address this anomaly, we
have developed a thermophysical solver that can predict asteroid temperatures (and thus flux)
of asteroids throughout the body, given a set of material properties, the shape and orbit position
with respect to the Sun. We are comparing our new model against IR observations as well as
observations of asteroids from the South Pole Telescope. Our objective is to reconcile the
observed and predicted flux, thus unraveling the underlying factors contributing to the disparity.
Once we successfully resolve this discrepancy, and achieve accurate predictions of asteroid
fluxes in mm wavelengths, we will run the Sorcha solar system simulator [3], slated for release
this summer, which will ultimately let us predict the prospect of CMB-S4 in terms of observability
and discoverability of SSOs.
References:
[1] CMB-S4 – CMB-S4 Next Generation CMB Experiment. https://cmb-s4.org/
[2] Chichura, P. M., Foster, A., Patel, C., Ossa-Jaen, N., Ade, P. A. R., Ahmed, Z., … & Young,
M. R. (2022). Asteroid measurements at millimeter wavelengths with the South Pole telescope.
The Astrophysical Journal, 936(2), 173.
[3] Sorcha. https://github.com/dirac-institute/sorcha.
Tidal disruption events (TDEs) are unique astrophysical phenomena that occur when the orbit of stars brings them close enough to super-massive black holes (SMBHs) for their self-gravity to be overpowered by tidal forces. This disruption and subsequent accretion onto SMBHs produces a bright flare of radiation, providing a means to probe quiescent black holes lying at the center of most galaxies which would otherwise remain observationally inaccessible. Current neural network classification systems for TDEs are limited by the lack of a unifying physical model for the expected behavior of TDEs, are unable to adapt to new observations once a network has been trained, and struggle in the regime of small data where good uncertainty estimation is needed. Alternatives like Gaussian processes take a probabilistic approach by using stochastic processes and are often preferred for their ability to describe the uncertainty of the function domain. However, Gaussian processes scale poorly with the amount of data and/or dimensionality of the problem, and are sensitive to the chosen kernel. A new approach has emerged in recent years to address both these shortcomings: Neural Processes (NPs). NPs are stochastic processes parameterized by neural networks. Similar to GPs, NPs learn distributions over functions, but differ by implicitly learning the kernel function through observed data. NPs use a neural network to parameterize and learn a mapping from the observed data to posterior predictive distributions. Given the lack of conclusive physical models from which to draw explicit kernel functions, and the often sparse data accompanying TDEs, NPs are a prime framework for establishing a predictive model for quickly identifying potential TDEs in survey observations. I will discuss the status of an on-going project to apply NPs to TDEs and develop an adaptive solution to identifying TDEs for use in current and upcoming astronomical surveys.
The cosmic microwave background (CMB), the relic radiation left over from the Big Bang, has been a cornerstone of our cosmological model of the Universe for more than 50 years. Observations and analysis of the CMB tell us the composition of the Universe and have been crucial for understanding the existence of dark matter and dark energy. I will present an overview of the rich scientific questions currently being pursued by CMB experiments, which ties together the most disparate scales possible in science: quantum mechanics and cosmology; the beginning of the universe to the present day. I will discuss astrophysics being done with CMB surveys, including followup studies of high-redshift galaxy evolution with the Atacama Large millimeter/submillimeter Array (ALMA) and the James Webb Space Telescope (JWST) and the nascent field of mm-wave time-domain surveys. I will conclude by describing current efforts in line intensity mapping (LIM), including a description of the Terahertz Intensity Mapper (TIM), and the prospect for the future.
Stellar halos are amazingly rich records of their host galaxy’s history. During the hierarchical galaxy formation process smaller galaxies are stripped apart in the outskirts of their larger hosts, leaving their stars as tracers of their origin. This tidal debris survives for Gigayears as stellar streams and substructures and is sensitive to the underlying gravitational potential, providing constraints on the nature of dark matter as well as galaxy formation physics. Upcoming large surveys such as those from the Rubin Observatory and the Roman Space Telescope will provide an unprecedented deep and wide view of this low-surface brightness discovery space, and will be able to detect stellar halo substructure for numerous galaxies in our nearby universe. In this talk I will highlight how using a variety of modeling techniques can aid in understanding and disentangling key physical processes in hierarchical galaxy formation and their link to observational signatures. These insights and predictions will facilitate the interpretation of observations by the next generation of telescopes.
We propose a new method to search for dark matter using dark forest/absorption features across the full electromagnetic spectrum, especially in the bands where there is a desert i.e. regions where no strong lines from baryons are expected. These unique signatures can arise for dark matter models with a composite nature and internal electromagnetic transitions. In the presence of a background source, such as a quasar, such interactions in the dark matter halos can produce a series of closely spaced absorption lines, which we call the dark forest. The dark forest feature is a sensitive probe of the dark matter self-interactions and the halo mass function, especially at the low mass end. There is a large volume of parameter space where dark forest is more sensitive compared to the best current and proposed direct detection experiments. Further, the electromagnetic transitions in dark matter due to CMB photons can give rise to unique features in the spectrum of the CMB. In particular, dark matter transition energies ~10^{-4} eV can produce a global absorption signal in the CMB which is consistent with the anomalous absorption feature detected by the EDGES collaboration.
We develop a new theoretical framework for studying the pairwise and cross-pairwise polarised kinetic Sunyaev Zeldovich (pkSZ) effect arising from the transverse peculiar velocity of galaxy clusters. The pkSZ effect is second order in peculiar velocities and has a spectrum that can be decomposed into y-type and blackbody components. We consider pairing of clusters with other clusters as well as cross-pairing of clusters with galaxies from spectroscopic galaxy surveys. We develop and compare estimators of the pairwise pkSZ effect and study the detectability of the pairwise signal with cluster catalogs consisting of a few hundred thousand clusters expected from surveys such as eROSITA and CMB-S4. We find that cross-pairing clusters with galaxies from a large overlapping spectroscopic survey having a few billion galaxies will enable us to detect the pairwise pkSZ effect with CMB-S4. The cross-pairwise pkSZ effect will thus open up a new window into the large-scale structure of the Universe in the coming decades.
Supermassive black holes (SMBHs) reside in the centers of all massive galaxies, yet are notoriously difficult to study. However, in the current era of all-sky surveys, an increasing diversity and number of nuclear transients are being identified. These events can arise from the accretion of gas through a disk, shocks between an orbiting star and an accretion disk, or the tidal disruption of clouds or stars. Studying active phases of SMBH growth during periods of active galactic nucleus (AGN) activity gives insight into physics governing the accretion disk and broad line region. Stars orbiting within the disk give further constraints on the properties of the disk through their quasi-periodic interactions. Nevertheless, other transients, such as tidal disruption events (TDEs), are required for us to study the ~90% of SMBHs that are otherwise quiescent. In this talk I will detail our current understanding of nuclear transients and present promising future research directions. I will also discuss how nuclear transients serve as excellent probes of SMBH physics and the only viable probe of quiescent SMBHs at great distances.
The cosmic microwave background (CMB) provides an unparalleled opportunity to advance our understanding of the fundamental physics of the universe. Recent and ongoing experiments have contributed to our understanding of neutrinos, dark energy, and dark matter through measurements of large-scale structure imprinted on the CMB and constrained the conditions in the early universe, tightly restricting inflationary and other cosmological models through measurements of CMB polarization. Next-generation CMB experiments like CMB-S4 will further constrain the sum of the neutrino masses and the number of relativistic species, expand our understanding of dark energy and dark matter, and set new constraints on cosmological models describing the first moments of the universe. The polarization in the CMB is faint, so future experiments must be at least an order of magnitude more sensitive than current experiments. These unprecedented levels of sensitivity require improved systematic mitigation via modeling and novel calibration techniques. I will give an overview of the science achievable with these next-generation experiments and the advances in technology that are critical for its this leap in performance.
In this talk I will discuss the future prospects for observing distant supernovae. I will focus on the expected advances in Type Ia supernova cosmology enabled by the Time Domain Extragalactic Survey (TiDES) which will use the 4MOST instrument to obtain spectra tens of thousands of supernovae and host galaxies. I will also give an update on the ESA Euclid mission following its launch in July, and will describe prospects for supernova science with Euclid.
Stockholm University and University of Texas at Austin
Various aspects of the early and primordial universe have been probed by the cosmic microwave background (CMB). Large-scale structure (LSS) observations and their theoretical description have now become precise enough to complement these constraints beyond the baryon acoustic oscillation scale. In this talk, I will discuss how careful theoretical consideration of the underlying physics allows us to gain new insights into the early universe from CMB and LSS power spectra. To illustrate this, I will present theoretical background, data analyses and forecasts for the free-streaming nature of neutrinos, primordial non-Gaussianity beyond the local type and oscillatory features in the primordial power spectrum.
The world of artificial intelligence (AI) and machine learning (ML) has undergone what some scientists refer to as the “3rd Age of AI” due to the confluence of developments in Algorithms, Computing Resources, and Big Data. Particle Physics has benefitted from, and in many ways strengthened and advanced, progress in AI/ML for decades due to its proliferation of enormous data sets, complex instrumentation, and enormous computing infrastructure. However, there exist both known and unknown deficiencies in our ability to explain “why” some AI/ML models yield a certain result. In this talk, I will discuss some of the context and applications of AI/ML in experimental particle physics. I will then focus on a few projects ongoing in my group that we believe target important problems relevant to the use of machine learning, symmetries, and domain knowledge in particle physics.
Millimeter-wave and far-infrared astronomical surveys have revolutionized our understanding of the evolution of the universe through measurements of the Cosmic Microwave Background (CMB) such as PLANCK as well as the formation and evolution of galaxies through far-infrared surveys such as HERSCHEL. Future ground-based,balloon-borne and space-based instruments such as the Simons Observatory, CMB-S4, CCAT, Toltec, EXCLAIM, TIM, PRIMA and FIRSST will provide a large increase in survey mapping speed compared to previous instruments and produce a corresponding increase in scientific data through developments in the technology for large format superconducting detector arrays and readout electronics. I will give an overview of the technology development and examples of key science capabilities from these new surveys.
Nearly two decades of reverberation mapping (RM) studies on nearby AGN have revealed a tight correlation between the size of the Hbeta broad-line region (BLR) and the optical luminosity of the AGN, known the R-L relation. However, recent RM measurements have revealed a systematic offset from the canonical R-L relation. In this talk, I will present my current work on spectral analysis and theoretic photoionization modeling to understand the observed deviations from the R-L relation. This work would provide insight into the AGN accretion activity and photoionization models of the BLR.
All quasars show a common stochastic variability, seen across various observed wavelengths and timescales. The origin of this variability is still uncertain, though variability in the optical is thought to stem from processes in the accretion disk and other structures close to the supermassive black hole (SMBH). Time-series and spectral variability analysis present unique ways to probe a quasar’s geometry and dynamics, including the mass of the SMBH. Much of the analysis used for measuring these structures involves assumed models of radiation and kinematics, which necessitate testing through high-quality, high-cadence data. We present results from modeling quasar optical variability, using high-quality, 20-year-long light curve data, and how it informs our view of the innermost structures around SMBHs. In particular, we find evidence of a characteristic timescale near days long in the optical, and slow, inward-moving propagations in the quasar accretion disk. We mention the future of variability studies, involving high-cadence surveys such as LSST, and multi-epoch spectroscopy campaigns, as well as the finely resolved reverberation mapping data that can be produced.
Seated high atop Cerro Chajnantor in the Atacama desert of Chile, The Prime-cam instrument on the 6 meter Fred Young Submillimeter Telescope, will map the sky at mm/sub-mm wavelengths with imaging polarimeters and spectrometers. Making use of the telescope’s wide field of view and large optical throughput requires high detector count focal planes exceeding 100,000. The main enabling technologies such as kinetic inductance detectors, cryogenic low noise amplifiers, and RFSoC based readout electronics will be discussed along with some historical background of their development. Current progress with prototype detector arrays and the RFSoC based readout electronics will also be presented.
Using computational methods to study social structure and behavior at scale requires researchers to make a plethora of decisions, including how to sample and preprocess data, implement algorithms, and validate results. I present findings and lessons learned from my group’s work on assessing the impact of some of these choices, especially related to data provenance and selecting variables and metrics, on understanding research collaborations and validating social science theories in contemporary settings. I highlight sources of biases and strategies for mitigating biased insights.
The Variables and Slow Transients Survey (VAST) on the Australian Square Kilometre Array Pathfinder (ASKAP) is designed to detect highly variable and transient radio sources on timescales from 5 s to 5 yr. We present the survey description, observation strategy and initial results from the VAST Phase I Pilot Survey. This pilot survey consists of ~162 h of observations conducted at a central frequency of 888 MHz between 2019 August and 2020 August, with a typical rms sensitivity of 0.24 mJy/beam, angular resolution of 12-20 arcseconds, and 5-13 repeats covering 5000 square degrees. An initial search of 1646 square degrees revealed 28 highly variable and/or transient sources, including known pulsars, flaring stars, active galactic nuclei, and sources with no multi-wavelength counterpart. Targeted searches including circular polarization of the Galactic Center and Magellanic Clouds further identified a Galactic Center Radio Transient and a very luminous pulsar. We discuss these findings and plans for a full 5-year survey which started in late 2022.
Rubin Observatory’s Legacy Survey of Space and Time (LSST) will deliver the deepest, widest image of the optical-infrared Universe ever seen. The ten-year LSST has been designed to revolutionize our understanding of the Universe on scales from our Solar System to galaxies to dark matter and dark energy. To enable this revolution, LSST has been developed as more than a telescope. Rubin’s LSST is a full system that will deliver science-ready data products, analysis tools, and computing resources to a world-wide community. These qualities, combined with LSST’s massively wide-spread data rights and open-source software, position it to be the most productive astronomy experiment of all time.
We are less than two years away from Rubin Observatory’s first light, and the start of LSST. The LSST Ecosystem includes (i) the federally-funded Rubin project that is building and operating the LSST, (ii) the self-governed international LSST science collaborations, and (iii) LSSTC – a non-profit coalition of member institutions invested in LSST science and community building (UIUC is a member!). My talk will focus on the role and activities of LSSTC in maximizing the scientific and societal impact of Rubin’s LSST. I will highlight ways that LSSTC programs can help you and your students prepare for science with LSST, and ways that LSSTC is designing its programs to set a new normal of inclusive participation in astrophysics.
Institute of Cosmology and Gravitation, University of Portsmouth
Galaxy redshift surveys that map the large-scale structure of the Universe contain a vast amount of information. Measurements of the clustering of galaxies and the Baryon Acoustic Oscillation feature imprinted within it have delivered major advances in cosmology over the last 20 years. I will describe exciting new methods that have recently been developed to extract even more information from these datasets. Two closely related methods are based on analysing the clustering separately in regions of different background density – I will discuss in particular information from anisotropies in the distribution of galaxies around low-density regions known as cosmic voids. The third method is based on advances in modelling correlations in the Lyman-alpha forest absorption from very high redshift quasars. I will present current results from these methods applied to the latest available data from the Sloan Digital Sky Survey (SDSS), and discuss ongoing work for these measurements in the next generation surveys DESI and Euclid.
Inter-University Centre for Astronomy and Astrophysics, India
We perform a rigorous cosmology analysis on simulated type Ia supernovae (SN~Ia) and evaluate the improvement from including photometric host-galaxy redshifts compared to using only the “zspec” subset with spectroscopic redshifts from the host or SN. We use the Deep Drilling Fields (~50 deg^2) from the Photometric LSST Astronomical Time-Series Classification Challenge (PLaSTiCC), in combination with a low-z sample based on Data Challenge2 (DC2). The analysis includes light curve fitting to standardize the SN brightness, a high-statistics simulation to obtain a bias-corrected Hubble diagram, a statistical+systematics covariance matrix including calibration and photo-z uncertainties, and cosmology fitting with a prior from the cosmic microwave background. Compared to using the zspec subset, including events with SN+host photo-z results in i) more precise distances for z>0.5, ii) a Hubble diagram that extends 0.3 further in redshift, and iii) a 50 % increase in the Dark Energy Task Force figure of merit (FoM) based on the w0-wa CDM model. Analyzing 25 simulated data samples, the average bias on w0 and wa is consistent with zero. The host photo-z systematic of 0.01 reduces FoM by only 2 % because i) most z<0.5 events are in the zspec subset, ii) the combined SN+host photo-z has X 2 smaller bias, and iii) the anti-correlation between fitted redshift and color self corrects distance errors. To prepare for analysing real data, the next SNIa-cosmology analysis with photo-z’s should include non SN-Ia contamination and host galaxy mis-associations.
The physics of a magnetically confined, radiation pressure supported column of plasma plays a defining role in understanding the observations of accretion-powered X-ray pulsars, including pulsating ultraluminous X-ray sources (ULXs). Near the neutron star accretor, the accretion flow is constrained by the strong magnetic field to fall along the magnetic field lines. At a sufficiently high accretion rate, the inflow is shocked above the stellar surface and forms a columnar structure below, radiating most of accretion power via sideways emission in a so-called ‘fan-beam’ pattern. The misalignment of the anisotropic radiation emission with respect to the neutron star spin axis results in the observed pulsations. We perform radiative relativistic MHD simulations to study the nonlinear dynamics of the accretion column. The column structure is extremely dynamical and exhibits kHz quasi-periodic oscillations. The existence of the photon bubble instability is identified in simulated accretion columns but proved to be not responsible for triggering the oscillatory behaviors. Instead, the oscillations originate from the inability of the system to resupply heat to locally balance the sideways cooling. The column structure is very sensitive to the shock geometry, which directly determines the cooling efficiency. The time-averaged column structures from the simulations can be approximately reproduced by a 1D stationary model provided one corrects for the actual 2D shape of the time-averaged column. I will also discuss how reduction of scattering opacity by the magnetic field can alter the column structure and variability.
A new window into the growth and evolution of large-scale structure has opened up with the recent observations of the thermal and kinetic Sunyaev-Zel’dovich (SZ) effects. I will review recent observations of the SZ signals and highlight their expected rapid growth over the next decade with upcoming cosmic microwave background experiments, like Simons Observatory and CMB-S4. I will present ongoing work to extract SZ signals in data from the Atacama Cosmology Telescope and how they can be used to constrain the important baryonic process that govern galaxy formation. Time permitting, I will conclude by discussing the connections between these SZ observations and mitigating the modeling uncertainties associated with “baryonic effects” in future large-scale structure surveys like LSST.
Department of Astronomy, University of Illinois Urbana-Champaign
SDSS-V is the fifth generation of the Sloan Digital Sky Survey that provides dual-hemisphere, optical and near-IR (H band), time-domain spectroscopy for the Milky Way stars, ISM, the Local Group, and distant quasars. It features three “mappers”, the Milky Way Mapper, the Black Hole Mapper and the Local Volume Mapper, to address a wide range of questions from the emergence of chemical elements of the Milky Way to the flickers/flares and radical transformations of the most luminous persistent sources in the Universe. Illinois is an associated institutional member of SDSS-V and is actively involved in the BHM and LVM components. I will give a brief overview of the project, its current status, and discuss the science on SMBHs and AGNs, along with some associated efforts by UIUC postdocs/students (e.g., DECam imaging).
Current techniques for analyzing large photometric catalogs are generally forced to assume a single, universal stellar initial mass function (IMF), although the IMF should be expected to vary depending upon conditions within a star-forming galaxy. The introduction of an additional parameter into photometric template fitting allows galaxies to be fit with a range of different IMFs. Most galaxies are best fit with a bottom-lighter IMF than the Milky Way, and this change in IMF also modifies inferred properties such as stellar mass and star formation rate. Several surprising new features appear, including significant constraints on the feedback mechanisms responsible for star formation and subsequent quenching. Additionally, the same techniques might indicate that most galaxies go through an earliest phase of star formation dominated by different feedback mechanisms and centered in galactic cores prior to the more typical star formation at later times.
With dozens of telescopes at the South Pole and in the Chilean Atacama desert CMB-S4 is the next-generation ground-based cosmic microwave background experiment. Surveying the sky with over 500,000 cryogenically-cooled superconducting detectors for 7 years, CMB-S4 will deliver transformative discoveries in fundamental physics, cosmology, astrophysics, and astronomy. After a brief overview of CMB-S4 we will discuss its potential for Solar System Science.
Department of Astronomy, University of Illinois Urbana-Champaign
The latest South Pole Telescope survey, SPT-3G, is halfway through a 1500 square degree survey of the southern sky. The result is some of the richest data at millimeter (mm) wavelengths, suitable for large-scale science including cosmic microwave background (CMB) studies as well as small-scale discoveries of galaxies, galaxy clusters, and transient objects. I will present the preliminary point source catalog from three years of winter observing, consisting of over 22,000 significant emissive detections. This catalog already includes 4.5 times as many sources as the previous SPT catalog, and we are able to detect sources 3 times fainter at the central frequency than the previous survey. I will show the first results of cross-matching the 3G catalog to external catalogs, characterizing spectral types, and identifying significant sources with no counterparts as we begin to extract worthy sources for follow-up.
Department of Astronomy, University of Illinois Urbana-Champaign
TEMPLATES is a James Webb Space Telescope (JWST) Early Release Science (ERS) program designed to produce high signal-to-noise imaging and Integral Field Unit (IFU) spectroscopic data cubes for four gravitationally lensed galaxies at high redshift (1<z<4.5). The program plan is to spatially resolve the star formation in galaxies across the peak of cosmic star formation. TEMPLATES was awarded ~55 hours to comprehensively study 4 high redshift galaxies out of which ~40 hours have already been completed. At the completion of the program all four target galaxies will have 13 band imaging as well as IFU data covering nebular emission lines such as H-alpha and Paschen-alpha. In this talk, I’ll showcase the new data and discuss how we are tackling some instrumental artifacts. I’ll also give a brief overview of the first science results expected from the program.
Observations of the cosmic microwave background (CMB) have played an essential role in shaping our understanding of the history, evolution, and contents of the universe. CMB surveys planned over the next decade, including those with Simons Observatory and CMB-S4, will map the microwave sky with unprecedented precision. I will discuss how these forthcoming observations will provide characteristically new insights into particle physics, cosmology, and astrophysics, focusing especially on probes of dark sector physics enabled by CMB observations. Maximizing the scientific value of future data will require new analysis tools and techniques. Using gravitational lensing as an example, I will show how subtle effects imprinted on the CMB by cosmic structure lead to new challenges and new opportunities for upcoming surveys. I will describe tools developed to address these challenges and to make the most of the exciting opportunities provided by future CMB observations.
Millimeter-wavelength cosmological surveys require focal planes with increasingly vast numbers of detectors in order to access new science using the CMB and emerging probes such as mm-wave line intensity mapping (LIM). Highly multiplexed kinetic inductance detectors (KIDs), arrayed as both on-chip spectrometers and wide-band photometers, provide a promising solution to these scaling challenges. I will present two new projects deploying these technologies for observations with the South Pole Telescope. SPT-SLIM is a pathfinder camera to demonstrate LIM with the CO rotational lines using on-chip spectrometers. SPT-3G+ is a camera that will measure the CMB at 220, 285, 345 GHz with diverse science goals spanning reionization history and the patchy kinematic Sunyaev-Zeldovich effect, Rayleigh scattering, and sub-millimeter sources. I will discuss both our ongoing technology development as well as the science targets of these cameras.
School of Information Sciences, University of Illinois Urbana-Champaign
Why is it so easy to watch funny cat videos but so hard to send science data? It’s because the Internet is broken! FABRIC is a midscale, International NSF project (a testbed) that enables researchers and practitioners to re-imagine a future, better Internet by enabling exploratory research in (among other things) networking, security, storage, distributed computing and machine learning. Multiple science communities are driving the first experiments on FABRIC. I’ll talk about the basic architecture of FABRIC, give a high level overview of some current experiments, and try to convince you that we can build an Internet that is good for science.
Astronomical Surveys have brought us a major advance in our understanding of the Universe and its physical laws. All observations in the sky can be described by the standard model of cosmology with just six free parameters. However, description is not the same as understanding. Despite the phenomenal progress of astronomical surveys, only. Few percentage of the sky has been surveys. Future and ongoing surveys will aim at surveying most of the sky. This rich dataset will provide us with the tools to understand the sky, rather than describe it. In this talk I will review the current status of our understanding of the Universe, the status of the “tensions” and will present new results about the nature of the energy components of the universe: dark matter and dark energy, and also about how the Universe might have originated and evolved.
Department of Astronomy, University of Illinois Urbana-Champaign
Optical variability is a key probe of the AGN population that will be instrumental for studies of AGN demographics with LSST Rubin. We have developed a phenomenological forward model that generates a mock AGN and host galaxy population and simulates light curves given the survey specifications as input. In this talk, I will show how our model can be used to constrain the local black hole mass function (BHMF) using optical variability with LSST Rubin. The ultimate goal is that this relic BHMF, when probed at low masses, will reveal the signature of how supermassive black holes were seeded at high redshifts.
Department of Astronomy, University of Illinois Urbana-Champaign
We present the Young Supernova Experiment (YSE) first data release, spanning discoveries from November 24th, 2019 to December 20, 2021. YSE is an active, three year optical time-domain survey on the Pan-STARRS1 and Pan-STARRS2 telescopes, designed to capture young, fast-rising supernovae (SNe) within a few hours to days of explosion. This YSE DR1 includes light curves and metadata for 2008 supernova-like sources, of which 441 transients are spectroscopically-classified. We then uniquely use realistic, multi-survey SNe simulations from YSE and Zwicky Transient Facility (ZTF) data to train the ParSNIP classifier for photometric classification tasks; when validating on spectroscopically-classified YSE SNe, we achieve 82% accuracy across three SN classes (SN Ia, SN II, SN Ibc) and 90% accuracy across two SN classes (SN Ia, CC SNe), with high individual completeness and purity of SN Ia. We then use our classifier to characterize our spectroscopically unclassified sample of 1567 YSE SNe, predicting ~66% SN Ia, ~34% CC SNe. We find that realistic simulations are now sufficient to exclusively train current photometric classification methods without compromising performance on real data. Though, our classifiers have particular difficulty in characterizing transients near the cores of galaxies or exhibit rare photometric or spectral features. In preparation for the forthcoming Rubin Observatory era, griz data sets such as the one presented here will be an important component of building classification and discovery algorithms for transient discovery.
A new generation of survey telescopes is allowing us to explore large volumes of the Universe in an unprecedented fashion, detecting and reporting up to tens of millions of varying objects in the sky every night. This requires fast machine learning aided discovery and classification systems, the astronomical brokers. The Automatic Learning for the Rapid Classification of Events (ALeRCE) broker is processing the alert stream from the Zwicky Transient Facility (ZTF), will soon start to process the Asteroid Terrestrial-impact Last Alert System (ATLAS) alert stream, and is an official Community Broker for the Legacy Survey of Space and Time (LSST). Since 2019, we use cloud infrastructure and machine learning to bring real-time processed products and services to the astronomical community, becoming the first public broker to systematically classify the ZTF alert stream into an astrophysically motivated taxonomy, ingesting more than 250 million alerts, classifying about 69 million objects based on their images, 1.6 objects based on their light curves, and reporting more than 13 k supernova candidates, 1.6 k of them resulting in spectroscopic classifications. In this talk I will summarize the available services (e.g., web explorer, SN hunter, data releases, watchlist) that can be used by the scientific community.
All-sky photometric time-series exoplanet missions have allowed for the monitoring of hundreds of thousands of stars, allowing for statistical analyses of stellar properties, specifically activity, across the Hertzsprung-Russell diagram. In this talk, I will discuss the convolutional neural network (CNN), stella, specifically trained to find flares in TESS short-cadence data. I will present the results of the CNN applied to 3200 young (< 1 Gyr) stars in order to evaluate flare rates as a function of age and mass. Additionally, we measure rotation periods for 1500 of our targets. The combination of flare rates and rotation periods allowed us to investigate surface starspot coverage as well as develop analytical models for magnetic field braiding to interpret differences in flare frequency distributions (FFDs). The efficiency and accuracy of the CNN allows for rapid flare detection on all stars observed at 2-minute cadence. Towards the end of my talk, I will present FFDs for 10^5 stars observed during TESS’s primary mission. By fitting the FFD for different mass bins, we find that all stars exhibit distributions of flaring events indicative of a self-organized critical state. This suggests that magnetic reconnection events maintain the topology of the coronal magnetic fields in a self-organized critical state in all stars, universally. If this is true, we will be able to infer properties of magnetic fields, interior structure, and dynamo mechanisms for all stars, which are otherwise unresolved point sources.
The smallest and faintest galaxies around the Milky Way are the most ancient, most metal-poor, and most dark-matter-dominated systems known. These extreme objects offer unique access to small scales where the stellar and dark matter content can be studied simultaneously. They hold the promise of major breakthroughs in understanding the nature of dark matter and a more complete picture of galaxy formation. Thus, their discovery and characterization are among the most important goals in the field. In this talk, I will share our ongoing observational efforts to detect these faint systems around the Milky Way and beyond, and upcoming advances in the era of deep and wide imaging instrumentation, with a focus on their implications.
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