Organizers: Chien-Hao Lin, Maria Vincenzi
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Oct. 6, 2022, 2:00pm (ET)
Title: TBD (21-cm cosmology)
Justin Myles (Stanford)
Nov. 3, 2022, 2:00pm (ET)
Title: TBD (Self-Organizing Map Photometric Redshift)
Past Seminars
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Chris Hirata (Ohio State University)Aug. 25, 2022, 2:00pm (ET) Calibrating infrared detectors for precision cosmologyModern weak gravitational lensing surveys have used the shape correlations of distant galaxies to infer the growth rate of cosmic structure with unprecedented precision. As we look forward to next-generation surveys, this precision must be matched by an improved treatment of systematic uncertainties from both astrophysical and observational effects. One category of observational systematics is how detector effects — that our detectors are not ideal devices that count photons in each square pixel — impact galaxy shape measurement. I will describe recent and ongoing efforts to characterize the infrared detectors for the Nancy Grace Roman Space Telescope. The infrared detectors have several effects that are familiar from visible CCD surveys, such as the “brighter-fatter” effect and pixel-to-pixel area variations, but also some new features such as capacitive cross-talk. On the other hand, the infrared detectors can be non-destructively read, which provides new opportunities to use correlations in test data to distinguish different detector effects. I will conclude with a view forward to how the Roman detector measurements can be incorporated into weak lensing analyses. |
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Justin Pierel (STScI)June 02, 2022, 2:00 PM (ET) Cosmological Tensions in the Era of Next Generation TelescopesType Ia Supernovae (SNe Ia) have been the source of many astronomical discoveries over the past several decades, perhaps most prominently the accelerated expansion of the universe by so-called “dark energy” in 1998. Today, our most precise cosmological measurements from SNe Ia in the local universe have diverged significantly from the predictions of our most successful cosmological model (ΛCDM). Upcoming surveys from the Vera C. Rubin Observatory and Nancy G. Roman Space Telescope will attempt to unravel the mysteries of dark energy, increasing our SN Ia sample by orders of magnitude. In order to fully leverage this new wealth of information, we must find new innovations for understanding and mitigating systematic uncertainties in cosmological measurements. I will discuss a series of efforts designed to reduce various systematics associated with SNIa standardization, as well as the promise of near-infrared observations provided by Roman. In addition to these traditional luminosity distance measurements, I will highlight a relatively new means of leveraging SNe for cosmology: gravitational lensing. The new era of next generation telescopes will truly enable these fully independent probes for cosmology, which provide a critical check on SNe Ia and unique constraints on dark energy, as we attempt to resolve the age of cosmological tensions. Weak lensing measurements by the Dark Energy Survey (DES) and the new generation of wide field galaxy surveys offer an exciting window on the properties and laws of the Universe. I will describe our approach to constrain non-standard cosmological models with the latest DES weak lensing data, especially focusing on tests of gravity on cosmological scales. I will then give my perspective on the lessons learnt and challenges for future tests, especially with the Rubin Observatory. I will end by presenting a new approach I propose to overcome one of these challenges and maximise the potential for discovery of new physics in the coming decade. |
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Agnès Ferté (Jet Propulsion Laboratory)April 14, 2022, 2:00 PM (EST) Tests of gravity with weak lensing surveysWeak lensing measurements by the Dark Energy Survey (DES) and the new generation of wide field galaxy surveys offer an exciting window on the properties and laws of the Universe. I will describe our approach to constrain non-standard cosmological models with the latest DES weak lensing data, especially focusing on tests of gravity on cosmological scales. I will then give my perspective on the lessons learnt and challenges for future tests, especially with the Rubin Observatory. I will end by presenting a new approach I propose to overcome one of these challenges and maximise the potential for discovery of new physics in the coming decade. |
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Kyle Boone (eScience Institue, University of Washington)August 3, 2021, 2:00 PM (EST) Modeling supernova light curves with physics-enabled deep learningUpcoming cosmological surveys such as the LSST at the Rubin Observatory will discover millions of supernovae and other transients. To take advantage of these large datasets, we have developed a deep generative model of transient light curves. Our model combines deep learning to model the unknown physics of the sources with an explicit physics model of how light propagates through the universe and is observed on a detector. I’ll discuss several applications of such a model, including classification of transients, identifying new kinds of transients, and how to perform supernova cosmology without classification. |
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Anna Porredon (The Ohio State University)July 15, 2021, 2:00 PM (EST) Lens sample optimization for multi-probe cosmological analysesThe cosmological information extracted from photometric surveys is most robust when multiple probes of the large-scale structure of the universe are used. Two of the most sensitive probes are galaxy clustering and the tangential shear of background galaxy shapes produced by foreground (or lens) galaxies, so-called galaxy-galaxy lensing. The optimal choice of lens galaxies is governed by the joint but conflicting requirements to obtain accurate redshift information and large statistics. I will show how we optimized the selection of one of the lens samples in the Dark Energy Survey Year 3 analysis and the resulting cosmological constraints from the combination of galaxy clustering and galaxy-galaxy lensing. I will also discuss the application of such optimization to the Euclid survey. |
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Ross Cawthon (University of Wisconsin-Madison)February 25, 2021, 2:00 PM (EST) Calibrating Photometric Redshifts for Cosmic SurveysCosmic surveys like the Dark Energy Survey (DES) and the upcoming Rubin Observatory Legacy Survey of Space and Time (LSST) observe hundreds of millions to billions of galaxies. These large surveys help us study the composition and history of the Universe as well as the properties of dark matter, dark energy, gravity, and potentially new physics. A major limitation to these surveys is redshift accuracy. These large imaging surveys attempt to get redshift information from just a few color bands, rather than full spectra. I will discuss three major classes of techniques to get redshift information in these surveys: photometric redshifts, which use color information, clustering redshifts, which use spatial information, and 'self-calibration' techniques, which infer redshifts from typical cosmological measurements like galaxy clustering and galaxy-galaxy lensing. I will highlight recent work in DES. |
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Kimmy Wu (SLAC)December 10, 2020, 2:00 PM (EST) Improved constraint on primordial gravitational waves with delensingAbstract: Inflation generically predicts a background of primordial gravitational waves, which generate a primordial B-mode component in the polarization of the cosmic microwave background (CMB). The measurement of such a B-mode signature would lend significant support to the paradigm of inflation. Observed B modes also contain a component from the gravitational lensing of primordial E modes, which can obscure the measurement of the primordial B modes. We reduce the sample variance in the BB spectrum contributed from this lensing component by a process called 'delensing.' In this talk, I will show results from the first demonstration in an improved constraint on primordial gravitational waves with delensing using data from BICEP/Keck, the South Pole Telescope (SPT), and Planck. In addition, I will provide an outlook of joint-analysis efforts of the BICEP/Keck and the SPT collaborations (the South Pole Observatory) to constrain primordial gravitational waves. |
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Sihao Cheng (Johns Hopkins University)October 8, 2020, 2:00 PM (EST) CNN without training: a new vocabulary for patterns and its cosmological applicationsAbstract: Textures and patterns are ubiquitous in astronomical data but challenging for quantitative analysis. I will present a new tool, called the “scattering transform”. It borrows ideas from convolutional neural nets (CNNs) while sharing advantages of traditional statistical estimators. As an example, I will show its application to weak lensing data for constraining cosmological parameters and show that it outperforms classic statistics. It is a powerful new approach in astrophysics and beyond. |
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Eli Rykoff (SLAC)September 10, 2020, 2:00PM - 3:00PM (EST) The Magic of Red GalaxiesAbstract: Red elliptical galaxies are not exciting. All the action is long past, their star formation ended billions of years ago, they have retired from their busy mergers, and now they are made up of old stars, fading away. These properties make them uniquely valuable tools for tracing the history of structure formation in the Universe. Both on their own and gathered into galaxy clusters, the largest peaks in the cosmic density field, they track the growth of structure over a large mass range. |
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Richard Kessler (Kavli Institute for Cosmological Physics)June 18 2020, 2:00PM - 3:00PM (EST) (reprogrammed) Tutorial on Supernova Analysis Software (SNANA)Abstract: |
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Jonathan Blazek (Ecole Polytechnique Federale de Lausanne)March 26 2020, 2:00PM - 3:00PM Galaxies Far, Far Away... |
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