Upcoming and Previous Seminars (Past months or Previous years)

Note that if the talk's pdf or ppt is available after the talk, you can get it by clicking on the talk title.

Physics/Astronomy C290C Cosmology and Cosmology-BCCP Seminar
The Physics/Astronomy C290C series consists of the Cosmology-BCCP LBNL-Physics-Astronomy Cosmology seminars held Tuesdays 1:10-2:00 pm in room 131 Campbell Hall. Because this room is hard to keep clean, please don't bring your lunch (this is a change).
Please contact Joanne Cohn to add to this list or to suggest speakers.

Speaker/Visitor Info is here.

BOSS and Nyx
(Image by C. Stark)

Note that there are also other talks which generally might be of interest, including:

July 2019
July 26, Friday
12 pm (INPA seminar)
Chen Heinrich, Caltech
LBL 50-5026
BAO and CMB Measurements of Compensated Isocurvature Perturbations and Implications for Tensions
CMB measurements have shown that the Universe started with mostly adiabatic perturbations: different particle species fluctuate spatially in the same way. The differences between fluctuations of species (called isocurvature) is highly constrained by Planck measurements, except for one type of isocurvature called Compensated Isocurvature Perturbations (CIPs), in which baryon density fluctuations are compensated by opposite dark matter density fluctuations and therefore hard to detect. In this talk, I will review various detection techniques with the CMB and propose a new measurement method by searching for a spatial modulations of the baryon acoustic oscillation (BAO) scale. We find that a Euclid-like survey would achieve WMAP CMB sensitivity while a cosmic-variance-limited BAO survey using emission-line galaxies up to z~7 has sensitivity between stage-3 and stage-4 CMB experiments. The results could be improved with a more optimal estimator and future 21cm measurements. Finally, if CIPs exist, they can bias cosmological measurements made assuming no CIPs, by acting as a super-sample fluctuation of the baryon density. I will show how a 1 sigma and isotropic (2 sigma and radial) CIP fluctuation maximally allowed by the current 95% Planck constraints can bias BAO measurements of H(z) at the 1% (6.6%) level, partially reducing the tension with the local measurements.

August 2019
Aug 26, Monday
12:10 pm (TAC Seminar)
Peng Oh, UCLA
Campbell 131
Cold Gas in Hot Halos: The Formation and Survival of Cold Gas in Galactic Halos
In recent years, observations of the circumgalactic medium has undercovered a large reservoir of T ~ 10^4 K, photoionized gas in the much hotter halos of galaxies. Inflowing cold gas in galactic halos helps fuel star formation, whilst outflowing cold gas is our primary observational marker of feedback. However, the formation and survival of dense cold gas in the atmospheres of galaxy halos is still poorly understood. For instance, we do not yet understand how cold gas can be entrained in a hot wind, as is observed; most simulations indicate it should be shredded by hydrodynamic instabilities. The impact of a multi-phase medium on cosmic ray propagation and feedback in the halo is also poorly understood. In this talk I will highlight some recent progress on these questions.

September 2019
Sep 3, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Georgios Valogiannis, Cornell
Campbell 131
“Testing gravity with cosmology: efficient simulations, novel statistics and analytical approaches"
In the era of precision cosmology, a wide range of cosmological surveys, such as the LSST, DESI, Euclid and WFIRST will precisely probe the large-scale structure of the universe, shedding light on the nature of the dark sectors. Given how sensitively the growth of structure depends on the nature of the underlying gravitational field, this will be a unique opportunity to constrain the so-called Modified Gravity models (MG), that are theoretical alternatives to dark energy, which attempt to explain cosmic acceleration through a large-scale modification to general relativity. In order to fully utilize the wealth of incoming data, however, theoretical predictions of structure formation in such alternative scenarios are necessary. Due to the existence of an additional degree freedom, that these models introduce, N-body simulations prove to be highly computationally expensive. In the first part of the talk, I will discuss how we can overcome this issue by using Lagrangian hybrid techniques, which can lead to a speed-up by 2 orders of magnitude. Then I will proceed to introduce novel statistics that can help us more confidently detect MG signals hidden in cosmic density fields, by up-weighting the significance of cosmic voids, where the MG-ΛCDM degeneracy is broken. When structure formation is analytically tractable, finally, I will show that we can make accurate analytical predictions for the two-point statistics using Lagrangian perturbation theory and the Gaussian Streaming Model, simultaneously capturing the effects of both halo-bias and redshift space distortions, effects crucial in the context of spectroscopic surveys, for the first time in modified gravity.
Sep 5, Thursday
4 pm (RPM)
David Schlegel, LBL
LBL 50-5132
MegaMapper: a spectroscopic instrument for the study of Inflation and Dark Energy
MegaMapper is a proposed ground-based experiment to measure Inflation parameters and Dark Energy from galaxy redshifts at 2 < z <5. A 6.5-m Magellan telescope coupled with DESI spectrographs achieves a multiplexing of 20,000. MegaMapper would be located at Las Campanas Observatory to fully access LSST imaging for target selection.
Sep 9, Monday
12:10 pm (TAC Seminar)
Rick Mebane, UCLA
Campbell 131
Population III Star Formation and the Cosmic 21-cm Background
The first generation of stars to have formed in the universe were likely very different than the stars we observe today. These Population III stars formed from pristine gas with no metals, and their formation was crucial to the early evolution of galaxies. While we have yet to observe a Population III star forming halo directly, we may be able to see them indirectly through their supernovae or their effect on the cosmological 21-cm background. I will present a set of semi-analytic models studying the formation of these Population III stars and the transition of their halos to metal-enriched star formation. I will also discuss the prospects of observing this mode of star formation, focusing on their effect on the cosmological 21-cm background and comparing our results to the recent claimed detection of a 21-cm signal by the EDGES experiment.
Sep 10, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Phil Mansfield, Chicago
Campbell 131
Why Do Dark Matter Haloes Die Together? The Causes of Halo Assembly Bias at Galaxy Masses
At a constant mass, old dark matter haloes and young dark matter haloes cluster differently from one another. This fact, known as "assembly bias," severely complicates the construction of mock catalogues and serves as a major challenge for structure formation models. In this talk, I test and synthesize the many competing explanations for this phenomenon into a single cohesive story with a strong focus on low mass haloes.
Sep 13, Friday
12 pm (INPA seminar)
Suhail Dhawan, Stockholm
LBL 50-5026
Dark energy and the Hubble constant with standard candles and standard clocks
In this talk, I will summarise our recent results on constraining dark energy and measuring the local expansion rate, i.e. the Hubble constant, with Type Ia supernovae and gravitationally lensed transients. Despite growing evidence of accelerated expansion of the universe, the physical mechanism driving this phenomenon is poorly understood. Using geometric probes, we find no significant evidence suggesting a paradigm outside standard cosmology, i.e. dark energy as a cosmological constant, however, we obtain moderate evidence disfavouring some of the non-standard models.
Sep 17, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Tae-Hyeon Shin , Penn
Campbell 131
The boundary of galaxy clusters and its implications on SFR quenching of satellite galaxies”
Infalling particles form a sharp physical boundary around their first apocenters around the parent halo, which is called "splashback radius". The previous measurements of splashback radius using optical clusters reported a ~20% discrepancy against the theory prediction. Here, using galaxy clusters detected by SZ surveys (ACT, SPT), we present the detection of the splashback radius and its consistency with respect to N-body simulations, by cross-correlating the galaxy clusters to the DES galaxies. On the other hand, it is known that the infalling galaxies around galaxy clusters experience enhanced star formation quenching. Using galaxy samples split on their colors, we also present the possibility of constraining the quenching parameters in quenching models we adopt (e.g. quenching timescale), making use of N-body simulations.
Sep 19, Thursday
3:45 pm (Astronomy Colloquium)
Matt Dobbs, McGill
LeConte 1
A New Era of Transients and Cosmic Structure on the Radio Sky
Technology advances have opened a new era of radio observations. We are now monitoring the sky at millisecond cadence and discovering a vast catalog of new fast radio transients while simultaneously making deep maps of structure in the universe using hydrogen intensity mapping as a tracer. While these fields are still in their infancy, early results are rolling out, fuelling discovery and motivating the design for new instruments.
I will present an overview of the Canadian Hydrogen Intensity Mapping Experiment (CHIME), describing the project's status and early results. I’ll conclude by introducing the next generation experiment, CHORD, now being designed.
Sep 23, Monday
12:10 pm (TAC seminar)
Christopher Reynolds, Cambridge
131 Campbell
Particle physics beyond the Standard Model (and other fun) with clusters of galaxies
Clusters of galaxies provide superb laboratories for exploring new particle physics. They represent the most massive dark matter objects in the Universe, making them an important laboratory for probing dark matter decay and annihilation signatures. However, in this talk, I will highlight how the transparency (or lack thereof) of the magnetized intracluster medium (ICM) to X-rays can be a powerful probe of axion-sector physics. I will present new data from the Chandra X-ray Observatory for the Perseus cluster which already allows us to set constraints on the existence of low-mass axion-like particles which exceed those possible from the next-generation laboratory and ground-based searches. After discussing the future prospects and limitations of these studies, I will briefly discuss the other astrophysical implications of the new Chandra data for our understanding of AGN feedback and fuelling in Perseus.
Sep 24, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Keir Rogers, Nordita
Campbell 131
Tests of new physics with the Lyman-alpha forest
The Lyman-alpha forest (the correlated absorption seen in the spectra of high-redshift quasars) is a uniquely powerful probe of new physics in the cosmological model — whether that be properties of the neutrino, the nature of cosmic inflation or the phenomenology of dark matter. The challenge lies in robustly disentangling the cosmology and the astrophysics of the intergalactic medium from which it is sourced. I will discuss new models and methods that can achieve the statistical inference sufficiently accurate for current and upcoming spectroscopic surveys (e.g., eBOSS, DESI). These exploit the most sophisticated simulations of the Universe to-date and innovative machine-learning algorithms (Bayesian emulator optimisation). Deviation from the standard model of cold, collisionless dark matter would leave a characteristic suppression in the linear matter power spectrum that the Lyman-alpha forest can reveal. I will present preliminary bounds on the shape of this suppression and discuss the implications for the allowed range of dark matter candidates.
Sep. 27, Friday
12 noon (INPA talk)
Romain Graziani, Universite Blaise Pascal
LBL 50-5132
Peculiar Velocities in Cosmology
The Universe is not homogenous. Since the early times, its structures have grown and moved under the laws of gravity. By measuring these motions today we are able to trace the history of the Universe expansion and gravity laws and hence test the General Relativity. Peculiar velocity measurements rely on precise extragalactic distances estimation, which can be provided by type Ia supernovae observations. Because peculiar velocities of galaxies are deviations from the Hubble expansion law, they have poor signal to noise ratio and are particularly sensible to usual systematic uncertainties such as calibration errors, selection effects and unknown covariances. During this presentation I will show how a precise forward modeling of observations allow us to overcome these caveats and that peculiar velocities analyses can be considered as a powerful cosmological probe. In particular, I will detail how the statistical methods I developed during my thesis can handle extragalactic distance measurements and lead to - e.g. - a velocity field reconstruction of our Local Universe from Type Ia Supernovae, so as constraints on General Relativity.

October 2019
Oct 1, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Jose Manuel Zorrilla Matilla, Columbia
Campbell 131
Learning from small scales in weak lensing and CMB data
Weak lensing of photons by large scale structure is sensitive to both the growth of the (lensing) structures and the expansion history of the universe. The large number of modes available on small scales have the potential to constrain cosmological parameters beyond what is achievable in the linear regime, but extracting this information from weak lensing surveys is not straightforward. I will review how to do so emphasizing the use of non-Gaussian observables and discuss how deep convolutional neural networks offer a viable alternative. The amount of information is limited by our ability to model the matter density field on small scales, including baryonic effects. I will end by explaining how future high resolution CMB experiments can inform simulations by measuring the angular momentum of baryons in the circumgalactic medium.
Oct 4, Friday
12 pm (INPA seminar)
Daniel Whiteson, UCI
LBL 50-5132
What has the Machine Learned?
Recent advances in artificial intelligence offer opportunities to disrupt the traditional techniques for data analysis in high energy physics. I will describe the new machine-learning techniques, explain why they are particularly well suited for particle physics, present selected results that demonstrate their new capabilities, and present a strategy for translating their learned strategies into human understanding.
Oct 7, Monday
12:10 pm (TAC seminar)
Wolfgang Kerzendorf, MSU
Campbell 131
"Machine learning and theoretical astrophysics"
Machine Learning is currently one of the hot new topics of our time. Advancements in computing and algorithms have made incredible progress. However, the paradigms of machine learning are often seemingly at odds with our goals as physicists: Machine-learning techniques techniques are used to interpolate and extrapolate from given large data sets without prior knowledge. Physical analysis applies statistical methods and prior physical understanding to large data sets to infer the fundamental laws shaping them. While there are differences between these too approaches there are also many commonalities.
In this talk, I will showcase several examples how machine learning can aid in astrophysics research. Specifically, I will focus on the area of data model comparisons and exploration of parameter spaces: High computing costs limit the exploration of the high-dimensional spaces required to understand the details in today’s astrophysical problems. Exploring the full viable parameter space is often needed to reliably identify new mechanisms. A good example for this is the modelling the spectral time series. The expensive radiative transfer codes needed to find the complex mechanisms are too expensive to marginalize the high dimensional parameter space. Physical models are mostly continuous allowing parameter interpolation. Emulators are machine learning con- structs that combine dimensionality reduction with interpolation algorithms. These constructs are geared towards exploration of high dimensional spaces with a minimum of pre-computed grid points. Some emulators even feature means to quantify the uncertainty that arises due to interpolation.
I will conclude my talk by giving an outlook of the possible future synergies of machine learning and theoretical astrophysics.
Oct 8, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Digvijay Wadekar, NYU
Campbell 131
"Analytic covariance of the redshift-space galaxy power spectrum"
A robust analysis of the covariance of the galaxy power spectrum is crucial for cosmological parameter estimation. The traditional process of obtaining the covariance involves simulating thousands of mocks. I will present an analytic approach for the full covariance matrix which is more than four orders of magnitude faster than mocks. Our analytic approach includes shot noise, redshift-space distortions, higher-order galaxy bias and non-linear structure formation. The dominance of shot noise at quasi-linear scales greatly simplifies the analytic approach and makes it useful for future surveys like DESI and Euclid. I will also show that the effect of super-survey modes for a redshift survey is stronger than previously considered in the literature.
Oct 15, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Lucas Secco, Penn
Campbell 131
"Cosmic Shear in the Year-3 DES data: 2-point and 3-point correlations"
The cosmology analyzes of the Year-3 (Y3) data from the Dark Energy Survey (DES) is at full speed ahead. Our preliminary weak lensing sample contains 120 million objects over 4200 square degrees of sky and is the largest shape catalog to date. This statistical power comes at a price: the cosmic shear measurements are more sensitive not only to the signal but also to potential systematics. In this talk, I will present our prospects for the 2-point cosmic shear cosmology analysis and some of the leading systematics that must be under control, in particular the Intrinsic Alignment of galaxies. Additionally, I will talk about a preliminary detection of a shear 3-point correlation in the DES-Y3 simulations and data which is unprecedented in weak lensing surveys.
Oct 22, Tuesday
1:10 pm (BCCP/Cosmology seminar)
George Stein, UCB
Campbell 131
Mocking the Universe & Machine Learning Approaches to Large-Scale Structure
Efficient generation of accurate mock observations of the sky, tailored specifically to near-future large-scale structure and cosmic microwave background surveys, is a key technical challenge in cosmology. I will first discuss the creation of these synthetic observations, or mocks, through the use of rapid so-called ‘approximate’ simulation techniques, with a focus on the Websky extragalactic CMB simulations. Next, I will overview a few recent applications of machine learning in cosmology, including the use of deep learning techniques to speed up cosmological simulations, and the possible failure of supervised methods when trained on mocks with the goal of extracting information from data.
Oct 23, Wednesday
2 pm (Particle Seminar)
Francis Yan Cyr-Racine, UNM
LBL 50 5132
Rock 'n' Roll, Jazzy and Classical Solutions to the Hubble Tension
Local measurements of the Hubble parameter are increasingly in tension with the value inferred from a LCDM fit to the cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) data. A general class of solutions to this tension involves temporarily increasing the energy density of the Universe close to the epoch of matter-radiation equality to reduce the size of the baryon-photon sound horizon at recombination. In the literature, various models for this energy injection have been proposed, ranging from rolling and oscillating scalar fields, new relativistic species with nonstandard properties, or extra matter components that subsequently decay. We describe the appealing and problematic features of these proposed solutions, showing that it is in general challenging to resolve the tension between CMB, BAO, and distance ladder measurements without either introducing new tensions with other cosmological datasets or requiring particle physics models that are significantly fine-tuned. We argue that none of the currently proposed solutions are entirely satisfactory, but identify important properties that a complete solution should have.
Oct 29, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Patricia Larsen, ANL
Campbell 131
From dark matter to observed skies, creating a universe with state-of-the-art simulations
Preparations for upcoming cosmological surveys such as LSST can benefit greatly from the use of simulated observations, however creating realistic galaxy catalogs is an incredibly complex and challenging task. In this talk I will first discuss how such simulations can aid in the interpretation of modern cosmological datasets. I will then detail the creation of the cosmoDC2 synthetic sky catalog built for the LSST-DESC collaboration, with a particular focus on the development of the weak lensing pipeline. Finally I will discuss lessons learnt in the context of a future synthetic galaxy catalog currently in the early stages of development.

November 2019
Nov 4, Monday
12:10 pm (TAC Seminar)
Mark Voit, MSU
Campbell 131
Nov 5, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Guochao (Jason) Sun , Caltech
Campbell 131
Understanding cosmological evolution of galaxies with intensity mapping
Line-intensity mapping (LIM) is an emerging observational technique to study the large-scale structure of the universe. LIM measurements are sensitive to the aggregate line emission from the entire galaxy population, therefore placing important integral constraints on galaxy evolution in a cosmological context. In the first part of this talk, I will provide a status update of the Tomographic Ionized-carbon Mapping Experiment (TIME), a forthcoming instrument designed to measure the star formation rate during cosmic reionization by observing the redshifted 158-micron [CII] line in tomography. Over the same spectral coverage, it can simultaneously study the abundance of molecular gas during the era of peak star formation by observing the rotational CO lines. I will discuss the constraining power TIME will offer on various physical quantities, such as the escape fraction of ionizing photons and the evolution of cosmic molecular gas density. In the second part, I will present a simple, analytic framework to self-consistently model multiple emission lines in the context of using multi-line intensity mapping to dissect the multi-phase ISM of galaxies.
Nov 8, Friday
2 pm (INPA seminar), moved due to run-around
Solene Chabanier, IRFU, CEA, Universite Paris-Saclay
LBL 50-5132
Toward precision cosmology with the Lya forest
Neutral hydrogen in the Intergalactic Medium produces a collection of Lya absorptions, called the Lya forest, seen in the spectra of background objects. According to the common paradigm, neutral hydrogen in the IGM evolves from primordial density fluctuations in a low density and photo-ionized environment. It, therefore, acts as a direct tracer of Dark Matter (DM). However, it also implies that temperature and density are tightly coupled, giving rise to degeneracies between parameters describing either cosmology or the IGM thermal history. The Lya forest 1D power spectrum is sensitive to clustering on small scales, and as such to the smoothing scale of relativistic particles. It has been used to put the strongest constraints on the sum of the neutrino masses and to study DM models. To infer cosmological constraints and to test our models at the percent level accuracy, the measurements need to be compared to state-of-the-art hydrodynamical simulations. We also need to refine our understanding of the impact of galactic feedbacks on the IGM temperature.
I will present the analysis that leads to the most recent P1D measurement. As the current uncertainties are at the percent level, and will even shrink further in the DESI era, the P1D becomes sensitive to complex mechanical effects known as AGN feedback. We use Adaptative Mesh Refinement (AMR) hydrodynamical simulations, the Horizon-AGN and Horizon-noAGN simulations, to evaluate its impact on the P1D and prevent degeneracies with neutrino effects. Finally, I will present current constraints on the mass of active neutrinos and on Warm Dark Matter models.
Nov 12, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Anowar Shajib,UCLA
Campbell 131
Measuring the Hubble constant from time-delays of strongly lensed quasars
The recent tension between early- and late-Universe measurements of the Hubble constant highlights the necessity for independent and precise probes such as the time-delay cosmography. The measured time-delays between the lensed images of a background quasar depend on the absolute physical scales in the lens configuration. Thus, the time-delays allow measurements of these scales to infer the Hubble constant, H_0. Due to a number of great advancements over the past decade in both the data quality and modeling techniques, the measurement of H_0 from the time-delays has fulfilled its promise to be competitive with other traditional methods such as the cosmic distance ladder. This is evident from the recent 2.4% blind measurement of H_0 from only six lenses (Wong et al. 2019). Simulation shows that a sample of nine lenses shrinks the uncertainty on this measurement to 2% (Shajib et al. 2018). I will present the Hubble constant measured from a newly analyzed lens system taking the sample size to seven. In addition, I will present the future roadmap of time-delay cosmography to independently reach 1% precision within a few years.
Nov 19, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Selim Hotinli, Imperial
Campbell 131
Upcoming probes of fundamental physics: Utilising small-scale signatures in the Universe
In the next few years, the field of cosmology will see an influx of new and high quality data from surveys of cosmic microwave background (CMB) and large-scale structure (LSS). In particular, there is overwhelming evidence that measuring the late time effects on the CMB photons (secondaries) will provide new and valuable information for cosmological inference upon cross-correlating with LSS surveys. Simultaneously, surveys of the 21cm hydrogen line will achieve sufficient accuracy for cosmological inference for the fist time. In this talk, I will describe how these cosmological probes will provide opportunities to study fundamental problems. I will focus on the so-called ‘moving lens effect’, a CMB modulation due to changing gravitational potentials as a result of cosmological structure moving transverse to the line of sight (Hotinli et al 2019, PRL). I will also discuss prospects of utilising velocity acoustic oscillations (so-called VAOs) in the 21cm hydrogen line. I will describe how these observables can be used to constrain various classes of early Universe models beyond the standard LCDM.
Nov 21, Thursday
4 pm (RPM)
Zhaodi Pan, Chicago
LBL 50-5132
“Instrument and science for the SPT-3G cosmic microwave background receiver”
SPT-3G is a third-generation camera for the 10-meter diameter South Pole Telescope (SPT), which is designed to measure the cosmic microwave background (CMB). To achieve a high mapping speed, we have developed a new multichroic receiver with a total of 16,000 polarization-sensitive detectors. SPT-3G began a 6-year 1500 square degree survey in February 2018, which will produce measurements of CMB temperature and polarization anisotropies with an unprecedented combination of angular resolution and sensitivity. In this talk, I will summarize the instrument status and highlight the development of the most compact millimeter-wavelength Fourier transform spectrometer, which was used for SPT-3G and is also a prototype for the proposed PIXIE satellite. I will also discuss the science goals and current data analyses, with a focus on the gravitational lensing analysis using SPT-3G’s first-year data.
Nov 22, Friday
12 noon (INPA talk)
Chirag Modi, UCB
LBL 50-5132
Reconstruction of Cosmological Fields in Forward Model Framework - Galaxy Clustering and Intensity Mapping
In this talk, I will outline the forward model approach to reconstruct cosmological fields in a Bayesian framework. I will focus on two examples - galaxy clustering and neutral hydrogen intensity mapping. In galaxy clustering example, I will use the observations of galaxy surveys to reconstruct the initial Lagrangian field. Here, we develop a novel framework with neural networks to forward model halo masses and positions and demonstrate that our method outperforms standard reconstruction in both real and redshift space. This reconstructed initial field has enhanced signal for baryon acoustic oscillations and can enhance science returns for surveys like DESI. For neutral hydrogen surveys, we lose over 50% of the modes at high redshifts due to foregrounds and it severely hampers their feasibility for cosmological analysis. With a novel bias framework for the forward model, I will show that we are able to reconstruct over 90% of these modes and this recovers cross-correlations with photo-z surveys like LSST and tracers like CMB lensing. Lastly, I will briefly touch upon assumptions made in this reconstruction framework regarding noise models and likelihood. I will discuss preliminary ways to improve upon them using deep learning.
Nov 26, Tuesday
no talk

December 2019
Dec 3, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Chia-Hsun Chuang, Stanford
Campbell 131
Accurate and precise cosmological constraints from the large-scale structure of galaxy clustering
Ongoing and future galaxy surveys, e.g., DESI, Euclid, WFIRST, etc., are going to collect >100M galaxy redshifts and reach sub-percentage precision on the cosmological measurements, e.g., Baryon Acoustic Oscillations, growth rates of large-scale structure, etc. We look forward to obtaining tighter constraints on the cosmological parameters, e.g., Hubble constant, equation of state of dark energy, etc. But meanwhile, we have to ask: are we ready to analyze such a massive data set? Are we sure that the systematics are under control? In this talk, I will report on what we have done and been doing towards this goal.
Dec 4, Wednesday
2 pm (Particle Theory Seminar)
Cora Dvorkin, Harvard
LBL 50-5132
“Unveiling the Nature of Dark Matter with Cosmological Observables”
Measurements of the Cosmic Microwave Background and the large-scale structure of the universe have made it possible to determine with great precision the universe’s inventory, as well as properties of its initial conditions. However, there are profound questions that remain unanswered.
Cosmological observations and galaxy dynamics seem to imply that 84% of all matter in the universe is composed of dark matter, which is not accounted for by the Standard Model of particles. The particle nature of dark matter is one of the most intriguing puzzles of our time. The wealth of knowledge which is and will soon be available from cosmological surveys will reveal new information about our universe. I will discuss how we can use new and complementary data sets to improve our understanding of the particle nature of dark matter both at large and small scales.
Dec 5, Thursday
4 pm (RPM)
Peter Timbie, Wisconsin
LBL 50-5132
21cm Intensity Mapping: A New Cosmological Tool?
The 21 cm line from neutral hydrogen gas has many useful properties for mapping large volumes of the cosmos. These maps will give us a view of the Universe when the first luminous objects formed through gravity – the Cosmic Dawn and the Epoch of Reionization, and later, the post-Reionization Universe. They may even allow us to map the epoch before these luminous objects, the cosmic dark ages. The large volumes of these maps promise dramatic improvements in estimation of cosmological parameters. Data is flowing now from a new generation of radio telescopes optimized for this task. Unfortunately, the main challenge for all of them is that the astrophysical radio foregrounds are ~10,000 times brighter than the expected hydrogen signal. In this talk I will focus on current and planned efforts to use the new technique of` ‘hydrogen intensity mapping’ to make tomographic maps of the post-Reionization universe. In particular, I will describe the first measurements from an instrument in China, called the Tianlai (‘Cosmic Sound’) Pathfinder.
Dec 6, Friday
12 noon (INPA talk)
Suk Sien Tie, OSU
LBL 50-5132
Cosmology with the Lya forest: beyond two-point statistics, DESI instrumentation
The Lyman-alpha forest is currently the only probe of cosmology and the state of the intergalactic medium (IGM) between redshifts of z=2 and 6. Its higher-order clustering, specifically its three-point correlation function (3PCF), contains information that can help to constrain fluctuations in the ionizing background and temperature fields of the IGM, thus providing a novel way to constrain their effects on cosmological analyses of the LyA forest. In this talk, I will present theoretical predictions of the 3PCF of the LyA forest, considering both a uniform and spatially varying UV background. I will discuss the exciting possibilities that future surveys like DESI will enable in this area. Finally, I will present my instrumentation work on the DESI sky camera and the fiber positioner anti-collision algorithm, and how they facilitate the DESI survey to achieve its science goals.

January 2020
Jan 10, Friday
12 pm (INPA seminar)
Samuel Hinton, Queensland
LBL 50-5132
Challenges and pathways forward in supernova cosmology
Using the DES photometric supernova cosmology analysis as groundwork, I will summarise our current analysis methodologies, from simulations, to transient classification, selection effect treatment, and cosmology. Despite recent improvements in analysis methods, there still exist fundamental challenges in areas spanning the initial empirical SN Ia model all the way to failing approximations built into cosmology fitters. I will highlight potential solutions to these challenges, to allow the next generation of surveys to lower the systematic floor and provide improved cosmological constraints. Additionally, I will also summarise my BAO and pipeline work for surveys like DESI, and discuss ways I’ve improved scientific workflow to allow more efficient use of researcher time.
Jan 13-15, Mon-Wed
BCCP Workshop:
Spectroscopic Surveys: Are We Ready For the Future?

Jan 17, Friday
12 pm (INPA seminar)
Arnaud De Mattia, Saclay
LBL 50-5132
The extended Baryon Oscillation Spectroscopic Survey: clustering measurements, lessons, and prospects
In this talk, I will present the clustering analysis of the ELG (Emission Line Galaxy) sample from the eBOSS (extended Baryon Oscillation Spectroscopic Survey) program of the Sloan Digital Sky Survey and review the other clustering analyses of the eBOSS program, dedicated to Luminous Red Galaxies and Quasars. I will discuss theoretical, observational and analysis systematics, how they were estimated and mitigated, focusing on the improvements over the last release of the BOSS program in 2016. Specifically, I will start by presenting the extensive work of the eBOSS collaboration to test model predictions against N-body simulations. The different observational systematics of the eBOSS samples will be reviewed, as well as the adopted correction schemes and the new analysis techniques used to mitigate residual systematics. Different analysis assumptions and their impact on the clustering signal will be discussed. After a review of eBOSS legacy cosmological measurements, I will finish by drawing lessons and prospects for future galaxy surveys.
Jan 21, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Michelle Ntampaka, CfA
Campbell 131
A Hybrid Deep Learning Approach to Cosmological Constraints From Galaxy Redshift Surveys
I will present a new technique for accurately determining sigma_8 and Omega_m from mock 3D galaxy surveys. The method is a hybrid technique; it merges deep machine learning with physics. The method is trained and tested on mock surveys that are built from the AbacusCosmos suite of N-body simulations, comprising 40 cosmological-volume simulations spanning a range of cosmological models. These simulations are populated with galaxies according to a flexible generalized halo occupation distribution (HODs) to capture a wide range of galaxy formation models. In addition to describing the advantages of this hybrid approach, I will also discuss best practices and lessons-learned for training deep models more generally.
Jan 24, Friday
12 pm (INPA seminar)
Jiamin Hou, MPE
LBL 50-5132
Clustering measurements in the final eBOSS quasar sample and their cosmological implications
In this talk I present the clustering analysis of the final extended Baryon Oscillation Spectroscopic Survey (eBOSS) quasar sample at redshift 0.8< z< 2.2, which bridges the redshift gap between the eBOSS LRG and Lyman-alpha measurements. Mapping the evolution of the expansion and growth of structure histories of our Universe provides us with a crucial test of the standard LCDM cosmological scenario. Our analysis includes a detailed modelling of the impact of the non-linear evolution of density fluctuations, bias, and redshift-space distortions on the two-point correlation function. Using numerical simulations designed to reproduce the uniqueness of the quasar sample, we perform extensive validation tests to characterise potential systematic errors induced by theoretical and observational effects. The constraints obtained from anisotropic clustering measurements can be used to test models of gravity on large-scales. However, these tests require the validation of our analysis techniques in modified gravity scenarios. I present an example of such tests, based on large numerical simulations of standard and modified gravity models to measure galaxy clustering in redshift space.
Jan 28, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Gus Evrard, Michigan
Campbell 131
Stellar Property Statistics of Massive Halos: Common Kernel Shapes from Multiple Cosmological Hydrodynamics Simulations
In the last decade, the astrophysical processes driving galaxy formation in a cosmological context at kpc scales have been incorporated, largely independently, into multiple codes developed by different simulation teams. Each simulation solves the complex evolution of baryon components (principally cold/warm/hot gas phases, metals, stars, and supermassive black holes) coupled gravitationally to dark matter, and the realization of large cosmic volumes yields populations of thousands of massive halos that host groups and clusters of galaxies.
This talk will present a recent study of stellar property statistics of massive halo populations realized by three cosmological hydrodynamics simulations: BAHAMAS+MACSIS, TNG300 of the IllustrisTNG suite, and Magneticum Pathfinder. The simulations have spatial resolutions ranging 1.5 to 6 kpc, and each generates samples of 1000 or more halos with total mass >10^{13.5} M⊙ at z = 0. Applying a localized, linear regression (LLR) method, we extract halo mass-conditioned statistics (normalizations, slopes, and intrinsic covariance) for a three-element stellar property vector consisting of: i) Nsat, the number of satellite galaxies with stellar mass >10^{10} M⊙ within radius R200c of the halo; ii) M⋆,tot, the total stellar mass within that radius, and; iii) M⋆,BCG, the gravitationally-bound stellar mass of the central galaxy within a 100 kpc radius. While there is not perfect agreement in scaling relation parameters from the three simulation teams, we find common shapes of normalized property kernels for satellite galaxy count and total stellar mass, and all simulations show an anti-correlation between BCG stellar mass and satellite galaxy count at fixed halo mass, as anticipated from age-related arguments in which the BCGs in early-forming halos grow by accreting satellites to a larger extent than those in late-forming halos. We close with some potential implications and thoughts on how such population studies could be better facilitated through common data analysis and publication practices.

February 2020
Feb 4, Tuesday
1:10 pm (BCCP/Cosmology seminar)
no talk

Feb 10, Monday
12:10 pm (TAC talk)
Matt McQuinn, Washington
Campbell 131
Welcome to the era of fast radio burst “cosmology”!
Fast radio bursts are frequent, bright millisecond bursts of radio emission that have fortunately turned out to not be from microwave ovens or alien light sails, but rather to be some new extragalactic phenomenon likely associated with neutron stars. Radio astronomers are beginning to localize these bursts to specific galaxies, opening up new extragalactic observables — the bursts' dispersion, scattering, and Faraday rotation. Dispersion in particular yields the intervening column of electrons, providing a unique tool to probe the 95% of the baryons that sit outside of galaxies (the vast majority of which are invisible using other observational methods). I will present the first ever applications of diffuse baryon science with these bursts, using data from the ASKAP telescope. Even with fewer than ten localized bursts, we are able to make interesting inferences about circumgalactic gas and the "missing baryons".
Feb 11, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Matt McQuinn, Washington
Campbell 131
Cosmology from the diffuse baryons between galaxies
The field of cosmology has to make do with a theory of structure that is incomplete in the ``ultraviolet'' -- we lack a precise understanding of the cosmologically minute scales on which galaxies form and affect their surroundings. I will review methods to circumvent this limitation, with a particular focus on using the ultra-dilute gas that lies far from galaxies as probed by intergalactic hydrogen absorption. This absorption provides our strongest constraints on the warmness/fuzziness of the dark matter, and it has untapped potential for revealing when the first galaxies formed and ionized the Universe. The standard picture is that, other than the cosmological model, the only other property that matters for shaping this absorption is the gas temperature. Indeed, the temperature is the major impediment for using this absorption to constrain the warmness/fuzziness of the dark matter, and precisely measuring the temperature from this absorption would reveal when the first galaxies formed. I will discuss my group's work to finalize the often elegant rules that shape the temperature of intergalactic gas, as well as these rules' implications for existing measurements. I will conclude provocatively, by questioning the standard picture for intergalactic gas; I will present a preliminary measurement and a research program pursuing further tests of this picture.
Feb 13, Thursday
12:30 pm (Astro Colloquium)
Jerry Ostriker, Princeton
Campbell 131
“The Hidden Life of Massive Elliptical Galaxies”
This talk will show the results of very high resolution simulations of massive systems that discovered formation in all of them of cold, dense central discs hosting star formation.
Feb 18, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Aaron Ewall-Wice, UCB
Campbell 131
Chasing Ancient Demons: The Quest to detect 21cm fluctuations from X-ray sources before reionization
Two important chapters in our Universe’s history remain, for the most part, unexplored by direct observations. During the “dark ages”, cooling gas clouds left over from the big bang collapsed into dark-matter halos to form the first bound objects and where conditions were right, the first stars ignited, heralding in the “Cosmic Dawn”. These first generations of galaxies heated, ionized, and enriched the intergalactic medium, forever changing the nature of stars and galaxies that could form in the future. Unfortunately, the majority of sources that drove this transformation are too faint to detect directly with optical and infrared facilities any time soon. A promising avenue to illuminating the cosmic dawn is to observe the impact of early sources on 21cm emission from the abundant HI that existed before reionization. Today, a number of radio facilities are being commissioned to detect the redshifted HI signal.
I will present an overview of 21cm experiments along with the systematics challenges that they face and the strategies being adopted to overcome these challenges including the adoption of spectrally smooth RF signal chains and novel calibration techniques. I will also report progress by the Hydrogen Epoch of Reionization Array (HERA) in realizing these strategies.
I will finish with a discussion of work exploring whether the recently claimed detection of a 78MHz cosmic dawn absorption feature by EDGEs might be explained by rapidly accreting radio loud black holes in the early Universe and the potential of power spectrum measurements by HERA to check whether the absorption feature is cosmological.
Feb 25, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Boryana Hadzhiyska, Harvard
Campbell 131
"Limitations to the 'basic' HOD model and beyond"
We make use of the IllustrisTNG cosmological, hydrodynamical simulations to test fundamental assumptions of the mass-based Halo Occupation Distribution (HOD) approach to modelling the galaxy-halo connection. By comparing the clustering of galaxies measured in the 300 Mpc TNG box (TNG300) with that predicted by the standard (``basic'') HOD model, we find that, on average, the ``basic'' HOD model underpredicts the real-space correlation function in the TNG300 box by ~15\% on scales of 1 Mpc/h < r < 20 Mpc/h, which is well beyond the target precision demanded of next-generation galaxy redshift surveys. We perform several tests to establish the robustness of our findings to systematic effects, including the effect of finite box size and the choice of halo finder. In our exploration of ``secondary'' parameters with which to augment the ``basic'' HOD, we find that the local environment of the halo, the velocity dispersion anisotropy and the product of the half-mass radius and the velocity dispersion, sigma^2 R_halfmass, are the three most effective measures of assembly bias that help reconcile the ``basic'' HOD-predicted clustering with that in TNG300. In addition, we test other halo properties such as halo spin, formation epoch and halo concentration. We also find that at fixed halo mass, galaxies in one type of environment cluster differently from galaxies in another. We demonstrate that a more complete model of the galaxy-halo connection can be constructed if both the mass and information regarding the local environment in which a halo is embedded are combined.

March 2020
Mar 3, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Liang Dai, IAS
Campbell 131
Einstein’s Microscope: Uncovering Small-Scale Dark Matter Structures with Novel Gravitational Lensing Probes
The physical nature of the astrophysical dark matter (DM) is a fundamental question in cosmology. The clustering structure of DM on sub-galactic scales is key to distinguishing between various viable DM models which all make successful predictions about the large-scale structure and galaxy formation, but empirical tests have been fundamentally hindered by the lack of electromagnetic tracers of sub-galactic structures. In this talk, I aim to introduce novel and practical gravitational-lensing based methods which can be employed to push forward this research frontier. I will first discuss the new phenomenon of extremely magnified cosmological sources as deep imaging of strong lensing clusters has recently started to uncover, and explain how this phenomenon can be exploited as a sensitive probe of compact halo objects, non-luminous DM subhalos smaller than those who host dwarf galaxies, and even (sub-)planetary mass DM minihalos as expected in the axion DM scenario. The full scientific potential of these new ideas will be realized as forthcoming photometric surveys will greatly expand the catalog of highly magnified lensed galaxies and deep follow-up observations with space-borne or ground-based optical/infrared telescopes will enable detailed studies of their lensed appearances. I will also discuss the exciting prospect to exploit lensing of alternative extragalactic sources such as gravitational waves from merging black holes to probe small-scale DM lenses. In particular, I will explain how one can extract unique information by observing wave diffraction of gravitational waves, which would be typically infeasible with electromagnetic sources.
Mar 10, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Elena Massara, Waterloo
by Zoom (online lecture) due to coronavirus
Higher signal from lower densities
The standard way to extract cosmological information from the large-scale structure is to measure two point functions. This statistic is mostly sensitive to the high density regions, which are highly nonlinear objects. Thus, their clustering properties are highly correlated on small scales and the cosmological information in them is limited. On the hand, cosmic voids — the less dense patches of the Universe — are mildly nonlinear regions that are expected to maintain most of their initial cosmological information. Moreover, being devoid of dark matter, voids are sensitive to diffuse components such as neutrinos — the last particles of the Standard Model whose masses are still unknown. The properties of voids are not well contained within, or easily extracted from, standard two point functions. In this talk I will discuss marked two point statistics, which are two point functions where each point is weighted by a mark. The mark can be a function of the local density around each point and can be used to up-weight points in low density regions compared to points in high density regions; this helps to extract cosmological information from voids. In particular, I will present the results of a Fisher analysis performed on the Quijote simulations; this analysis quantifies the cosmological information that can be extracted from the matter density field using marked power spectra.
CANCELLED Mar 17, Tuesday
1:10 pm (BCCP/Cosmology seminar-CANCELLED)
Ben Thorne, UC Davis
Campbell 131
Mar 24, Tuesday
No talk, spring break
CANCELLED Mar 31, Tuesday
Adam Lidz , Penn

April 2020
Cancelled! Apr 7, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Cancelled!! Brice Menard, JHU
Campbell 131
Apr 14, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Marcelle Soares-Santos , Brandeis
via ZOOM
Cosmology in the era of multi-messenger astronomy with gravitational waves
Motivated by the exciting prospect of new wealth of information arising from the first observations of gravitational and electromagnetic radiation from the same astrophysical phenomena, the Dark Energy Survey (DES) has established a search and discovery program for the optical transients associated with LIGO/Virgo events (DESGW). Using the Dark Energy Camera (DECam), DESGW has contributed to the discovery of the optical transient associated with the neutron star merger GW170817, and produced the first cosmological measurements using gravitational wave events as standard sirens. We now pursue new results from the third observing campaign, which ended just last month. In this talk, I present an overview of our results, and discuss its implications for the emerging field of multi-messenger cosmology with gravitational waves and optical survey data.
CANCELLED Apr 21, Tuesday
Cancelled 1:10 pm (BCCP/Cosmology seminar)
Kyle Dawson, Utah

Apr 24, Friday
12 pm (INPA talks)
Remi Adam, CNRS
Diffuse gas in galaxy clusters: on the thermal and non-thermal components
The clusters of galaxies represent the last step of the formation of large scale structures in the Universe. They are both useful cosmological probes and unique astrophysical laboratories. The clusters grow by accretion of surrounding structures and from the merging of subclusters, in very energetic events, eventually forming a diffuse gas phase made of a hot thermal component, but also leading to particle acceleration up to very high energies. After introducing the role of clusters in our understanding of the assembly of matter in the Universe, I will discuss how we can study the diffuse gas phase across cosmic time. The presentation will highlight results based on the NIKA/NIKA2 camera at the IRAM 30m telescope, sensitive to the thermal gas pressure via the Sunyaev-Zel’dovich effect. I will also present prospects for probing the non-thermal component in the gamma rays with the CTA observatory.
Apr 28, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Dan Gruen, Stanford/SLAC
The three most curious things from one year of DES weak lensing
The Dark Energy Survey has finished cosmological and other lensing results from one year of collected data. I will revisit three findings that were perhaps unexpected but seem curious (at least to me!), on the side of the main two-point function results on cosmology. One is the ongoing controversy on calibration of photometric redshifts. Another are the anomalously low counts and lensing signals we have measured for low-mass optically selected clusters. A third one is the first detection, and somewhat unexpected behavior, of the cross-correlation of weak gravitational lensing with extragalactic gamma- rays. I will also discuss progress towards the one most curious thing from three years of DES weak lensing data, to come out soon.
Apr 30, Thursday
12:40 pm (Astro Lunch)
Alex Krolewski, UCB

CMB lensing tomography across half the universe with 150 million infrared galaxies from the unWISE catalog
In this talk I will review and summarize my thesis work, focusing in particular on cosmological constraints from CMB lensing cross-correlations with the unWISE galaxy catalog. By measuring how galaxies lens the cosmic microwave background, CMB lensing cross-correlations offer a powerful avenue for testing the standard cosmological model across cosmic time. We have detected unWISE-CMB lensing cross-correlations at ~80σ, the highest-significance CMB lensing cross-correlation to date. This implies <2% error on the amplitude of matter clustering, σ8. The statistical power of this measurement exceeds other recent weak lensing surveys (KiDS, DES, HSC). Thus it could provide improved constraints on gravity and resolve the σ8 tension between Planck and some weak lensing surveys. Since the unWISE galaxies are selected by imaging rather than spectroscopy, their redshift distribution is uncertain. This constitutes the largest systematic error on the measurement. I measure the redshift distribution via cross-correlations with spectroscopic galaxies and quasars from the SDSS surveys and discuss how the uncertainty in the redshift distribution propagates to the lensing cross-correlation. Finally, I discuss ongoing work to constrain cosmological parameters from the unWISE cross-correlations. From simulated observations, we expect to measure σ8 to 3.5% precision and Ωm to 4.4% precision.

May 2020
Postponed! May 5, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Alexandra Amon, Stanford, Postponed
May 14, Thursday
12:40 pm (Astro Lunch)
Nick Kern, UCB By ZOOM
Mapping the Cosmic Evolution of Hydrogen: 21 cm Cosmology at the EoR with HERA
The path towards detecting the 21 cm signal from the Epoch of Reionization (EoR) and Cosmic Dawn has seen tremendous progress in recent years. Current experiments are setting increasingly stringent limits on the 21 cm power spectrum, and a tentative detection of the sky-averaged signal has been made. As the next generation of experiments are designed and built, the road towards making a detection of the power spectrum and maximizing its scientific return hinges crucially on robust analysis methods for isolating the 21 cm signal from instrumental and environmental systematics. In this PhD exit seminar, I'll discuss some of my thesis work on the commissioning and analysis of Phase I data from the Hydrogen Epoch of Reionization Array (HERA). I'll discuss some of the techniques we are employing for control of calibration and instrumental systematics, which have helped us suppress systematics in the power spectrum by orders of magnitude. I'll also share our progress in deriving HERA's first limit on the 21 cm power spectrum at z = 7.9, and will discuss the validation tests we are pushing it through to build confidence in our results.

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