Welcome! The Center for AstroPhysical Surveys (CAPS) seminars are normally held on Friday’s at noon central time in room 1040 at NCSA. Pizzas and sodas will be arranged.
Please contact the current seminar organisers Srinivasan Raghunathan and Jay Alameda for further details.
Location: NCSA-1040(Unless specified otherwise) Zoom: Link
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.
(Unless specified otherwise)
