Organizers: Chien-Hao Lin, Maria Vincenzi
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Seminars are usually held every other Thursday in Physics 298. Travel instructions for speakers and visitors: Location: Physics Building, faculty lounge (298) |
Upcoming
Justin Myles (Stanford)
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Past Seminars
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Isobel Hook (Lancaster University)Sep. 28, 2023, 2:00pm (ET) Title: |
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Supernovae with TiDES and EuclidIn 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. |
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Roohi Dalal (Princeton University)May 25, 2023, 2:00pm (ET) Title: Cosmology from Cosmic Shear Power Spectra with Hyper Suprime-Cam Year 3 DataThe Hyper Suprime-Cam (HSC) survey is the deepest Stage III weak lensing experiment, going to ~26 mag with exquisite seeing. The depth and image quality achieved by HSC allow us to probe cosmology using weak lensing up to high redshifts, and the analyses serve as important preparatory studies for the next generation of weak lensing surveys. I will discuss our constraints on cosmological parameters using weak lensing cosmic shear power spectra measured from the Year 3 shear catalog of HSC. The shear catalog, prepared by Li et al. 2022, covers 416 square degrees of the northern sky, with a mean i-band seeing of 0.59 arcsec and an effective galaxy number density of 15 arcmin^-2. With an i-band magnitude limit of 24.5 mag, and four tomographic redshift bins spanning 0.3<z<1.5, we obtain a high-significance measurement of the cosmic shear power spectra in the multipole range 300<\ell<1800. I will describe our cosmological analysis, including the steps we take to prevent confirmation bias as well as our modeling of various sources of systematic uncertainties. I will then discuss our new constraint on the S8 parameter, and how it informs our understanding of the apparent 2-3 sigma tension between constraints on S8 from weak lensing experiments and those from the CMB. Finally, I will discuss ongoing and future work that can further shed light on the S8 tension, including an improved modeling of baryonic feedback at small scales. |
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James Trussler (The University of Manchester)May 04, 2023, 2:00pm (ET) Title: JWST's first glimpse of the first galaxiesJWST has ushered in a great new golden age of astronomy, opening the possibility of discovering and characterising primordial galaxies deep within the epoch of reionisation (EoR). In this talk I will therefore highlight how JWST has already begun to transform our understanding of the formation and evolution of the first galaxies in the Universe. First, I will discuss the first images and spectra taken by JWST - centred on the now-famous galaxy cluster SMACS 0723 - which immediately demonstrated that intense star formation and extreme nebular conditions are likely the norm, rather than the exception, for galaxies in the EoR. Second, I will discuss our search for EoR galaxies exhibiting two strong spectral breaks in their photometry, providing evidence for evolved stellar populations in these galaxies, and thus enabling us to indirectly infer the epoch when the first galaxies began to form. Third I will introduce a set of photometric and spectroscopic diagnostics that I have developed to identify potential first galaxy candidates, i.e. chemically pristine Population III galaxies in the EoR. Finally, I will close by revealing whether any convincing Pop III candidates have been identified from the early Webb data. |
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Bastien CarreresApr. 20, 2023, 2:00pm (ET) Title: Growth-rate measurement with type Ia supernovaeMeasurements of the growth rate of structures have the potential to detect potential deviations from General Relativity. The growth rate can be measured using its link to the cosmological velocity field. In the past decade, the majority of growth-rate measurements were performed indirectly by using redshift space distortions on clustering. However, due to a lack of statistics, this method isn't precise at low redshift. An efficient method to measure the growth rate at low redshift is to directly estimates velocities from redshift and distance indicators. Until today the statistics of SN Ia was too law to be used in such analysis and galaxies were used as distance indicators. New generation of surveys will provide sufficient number of SN Ia to do the growth-rate measurement. In this talk, I will present our work on the growth-rate measurement using SN Ia simulation from the ZTF survey. |
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Suhail Dhawan (Cambridge)Apr. 13, 2023, 2:00pm (ET) Title: Resolving cosmological tensions with Type Ia supernovaeThe Hubble tension is arguably the biggest open question in modern cosmology. While it is the most significant signature of new cosmological physics, it is imperative to test whether unknown systematics are at play. In my talk I will summaries our recent work on developing the distance ladder with novel probes like the tip of the red giant branch to use Type Ia supernovae (SNe Ia) from the Zwicky Transient Facility for measuring the Hubble constant. Strong gravitational lensing is an independent channel with which SNe Ia weigh in on the tension. Since lensed SNe measure time delay distances this probe has complete independent systematics to the local distance ladder and hence, is a powerful way to measure H0. I will talk about our recent work with wide-field surveys to discover and characterize lensed SNe. An interlinked problem in cosmology today is the test for whether the universe is isotropic. Our recent work shows some indications for potential deviations from isotropy and forecasts suggest the exciting possibility to strongly confirm or refute this claim. |
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Hee-Jong Seo (Ohio Univ.)Feb. 16, 2023, 2:00pm (ET) Title: Accelerating expansion of the Universe through DESIOne of the most intriguing questions in physics today is the nature of dark energy that is responsible for the accelerated expansion of the Universe. Three-dimensional maps of galaxies from spectroscopic galaxy surveys provide a giant laboratory to test the nature of the Universe, including dark energy, in a way that is complementary to other cosmic surveys. DESI, being the largest galaxy redshift survey up to date, is currently preparing for the first-year cosmology analysis release in Summer 2023, In this talk, among the key science goals of DESI, I want to focus on the studies of two accelerated expansion phases of the Universe using DESI, one today due to dark energy and the other, cosmic inflation right after the Big Bang. For the former, I will show the first Baryon Acoustic Oscillation detection result using only the first two months of the DESI data. For the latter, I will discuss how we can fight the observational systematics using neural networks and derive a tight constraint on inflation using the DESI Legacy survey. |
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Justin Myles (Stanford)Nov. 3, 2022, 2:00pm (ET) Title: Novel Methods to Leverage Spectroscopic Overlap of Imaging SurveysLarge galaxy imaging surveys promise to deliver extraordinary datasets to answer open questions about the nature of dark matter and dark energy, but these surveys suffer from challenges arising from the difficulty in constraining galaxy redshift. I will discuss projects that leverage spectroscopic observations of small, well selected subsets of galaxies observed in imaging surveys to improve the utility of photometric datasets for cosmological experiments. First, I will describe the new methodology used for the Dark Energy Survey Year 3 weak lensing source galaxy redshift calibration and the resulting DES Y3 cosmology constraints. Second, I will present an algorithm for accurately propagating uncertainties of probability distributions and illustrate the application of this algorithm to redshift calibration. Third, I will show results using archival spectroscopy of redMaPPer galaxy clusters to measure the impact of projection effects on these clusters and comment on how this measurement relates to the DES Y1 cluster cosmology results. I will conclude by presenting promising paths forward to take full advantage of forthcoming surveys to constrain the cosmological model |
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Hee-Jong Seo (Ohio University)
Feb. 16, 2023, 2:00pm (ET)
Title: Baryon Acoustic Oscillations with Dark Energy Spectroscopic Instrument (tentative title)
James Trussler (University of Manchester)
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Title: High Redshift Galaxies in the Epoch of Reionization (tentative title)
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Ruby Byrne (Caltech)Oct. 6, 2022, 2:00pm (ET) Title: Understanding the Early Universe with 21 cm Cosmology: Progress, Challenges, and Next StepsMeasuring the 21 cm emission line from neutral hydrogen at high redshift has the potential to revolutionize our understanding of the universe’s evolution and early galaxy formation. These measurements would provide 3-dimensional maps of the universe during the Dark Ages, Cosmic Dawn, and Epoch of Reionization, when stars and galaxies first formed and ionized the intergalactic medium. However, 21 cm cosmology experiments have not yet overcome the challenges that will allow them to achieve their potential. In particular, these experiments struggle to separate the faint cosmological signal from intervening foreground emission that is 4-5 orders of magnitude brighter. I discuss recent progress constraining the high redshift 21 cm signal and developing new techniques to improve the precision of these 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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