Welcome! The Center for AstroPhysical Surveys (CAPS) seminars are normally held on Friday’s at noon central time in room 1040 at NCSA. Pizzas will be arranged.
Please contact the current seminar organizers Cynthia Trendafilova and Alisha Funkhouser-Walker for further details.
Location: NCSA-1040(Unless specified otherwise) Zoom: Link
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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