August 2017
Aug 29, Tuesday
1:10 pm (Cosmology/ BCCP)
Elisabeth Krause, Stanford
Campbell 131
Cosmology Results from the Dark Energy Survey Year 1
This talk presents cosmology constraints from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 deg2 of griz imaging data from the first year of the Dark Energy Survey (DES Y1). The analysis combines (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. These three measurements yield consistent cosmological results, and provide constraints on the amplitude of density fluctuations (S8 = 0.794+0.029-0.027) and dark energy equation of state (w = -0.80+0.20-0.22) that are competitive with those from Planck cosmic microwave background measurements.
I will describe the validation of measurements and modeling from catalogs to cosmology, and highlight cosmology constraints from the combination of DES Y1 with external data sets.
Based on DES Collaboration 2017 (1708.01530) and supporting papers
September 2017
Sep 5, Tuesday
1:10 pm (Cosmology/ BCCP)
Jordan Mirocha, UCLA
Campbell 131
Metrics for Disentangling PopII and PopIII Contributions to the 21-cm Background
The first generations of stars to form after the Big Bang are expected to have dramatically different properties than stars today. Most notably, in the absence of heavy elements, fragmentation in the Universe's first proto-stellar clouds was likely minimal, resulting in perhaps only one or a few massive stars. This idea has surfaced in many contexts over the last two decades, as very massive stars could kick-start reionization, provide the seeds of today's super-massive black holes, and give rise to abnormal abundance patterns in metal-poor stars in our own Galaxy. Unfortunately, directly detecting these so-called Population III stars (or clusters of them) may be impossible, even with the next generation of optical/near-IR space-based observatories. In this talk, I will focus on the prospects for detecting PopIII sources indirectly using the sky-averaged ("global") 21-cm background, which is currently being targeted by several experiments on the ground. I will describe first a new set of predictions for the global signal calibrated to match high-z galaxy luminosity functions (i.e., "normal" PopII galaxies), and then move on to the subtle -- but persistent -- modulations of the shape of the global signal induced by the addition of PopIII sources. Such modulations may even be accessible to experiments operating at frequencies above 100 MHz (z < 13), at which point PopIII star formation has become subdominant to PopII in most models.
Sep 12, Tuesday
1:10 pm (Cosmology/ BCCP)
Tobias Schmidt, MPIA/UCSB
Campbell 131
Quasar Lifetime and Obscuration Constraints from the HeII Transverse
Proximity Effect
The reionization of helium at z~3 is the final phase transition of the
intergalactic medium and supposed to be driven purely by quasars. The HeII
transverse proximity effect - enhanced HeII transmission in a background
sightline caused by the ionizing radiation of a foreground quasar -
therefore offers a unique opportunity to probe the morphology of HeII
reionization and to investigate the emission properties of quasars, e.g.
ionizing emissivity, lifetime and beaming geometry. I will present results
from the first statistical analysis of the HeII transverse proximity
effect. We use the most-recent HST/COS far-UV dataset and conducted a
dedicated optical spectroscopic survey to find foreground quasars around
22 HeII sightlines. We find a large object-to-object variance and a
surprising absence of strong transmission peaks for the strongest
foreground quasars. However, using a stacking analysis we find statistical
evidence for the HeII Transverse Proximity Effect which places a
geometrical constraint on the quasar lifetime of t_Q > 25 Myr. With a more
detailed modeling based on post-processing of cosmological hydrodynamic
simulations we derive joint constraints on quasar age and obscuration for
the four strongest foreground quasars, suggesting that three of them are
highly obscured or relatively young.
Sep 14, Thursday
4 pm (RPM)
Cora Dvorkin, Harvard
LBL 50-5132
"Discovering New Physics Beyond the Standard Model with Cosmological Data Sets"
Cosmological observations have provided us with answers to age-old questions, involving the age, geometry, and composition of the universe. However, there are profound questions that still remain unanswered. I will describe ongoing efforts to shed light on some of these questions.
In the first part of this talk, I will explain how we can use measurements of the CMB and the large-scale structure of the universe to reconstruct the detailed physics of much earlier epochs, when the universe was only a tiny fraction of a second old. In particular, I will show how we can probe the shape of the inflationary potential, extra degrees of freedom during inflation, and the signature of possible particles with mass and spin during this period.
In the last part of the talk, I will discuss how we can use observations at large scales and sub-galactic scales (through strong gravitational lensing) to improve our understanding of another open question in fundamental physics: the particle nature of dark matter.
Sep 19, Tuesday
1:10 pm (Cosmology/ BCCP)
Julien Carron, Sussex
Campbell 131
Planck CMB delensing and beyond
The deflection of CMB photons by large-scale structures smooths the observed CMB acoustic peaks and introduces a sizeable white noise component in the polarization B-mode.
In order to achieve best constraints on the inflationary perturbations tensor to scalar ratio, upcoming low-noise polarization-based experiments must be able to undo these deflections, an operation called delensing.
I will present the first detection of B-mode delensing, and first internal delensing of the CMB that we recently performed on Planck public maps, as well as discuss methods and prospects for the future.
Sep 21, Thursday
4 pm (RPM)
Kev Abazajian, Irvine
LBL 50-5132
Candidate Signals and Stringent Constraints from Dark Matter in the Sky
I will discuss analyses leading to two recent candidate detections of photons from dark matter. Specifically, these are: first, gamma rays in a continuum “bump” at a few GeV which can be due to WIMP-like dark matter annihilation in the Galactic Center; and, second, X-rays from clusters of galaxies and Andromeda consistent with monoenergetic 3.55 keV photons from dark matter decay such as that predicted from sterile neutrino dark matter. Commensurately, there are also stringent constraints on these signals. I will discuss the particle and cosmological model implications of both.
Sep 21, Thursday
4:10 pm (Astronomy Colloquium)
Risa Wechsler, Stanford
LeConte Hall 1
Cosmology from the Dark Energy Survey and Beyond
A new generation of sky surveys are beginning to map the universe’s expansion history and evolution of structure over the last ~ 12 billion years, using statistical constraints from hundreds of millions of galaxies.
I will present cosmological constraints from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 deg^2 of griz imaging data from the first year of the Dark Energy Survey (DES Y1). The analysis combines (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. These three measurements yield consistent cosmological results, and provide constraints on the amplitude of density fluctuations (S8 = 0.794+0.029-0.027) and dark energy equation of state (w = -0.80+0.20-0.22) that are competitive with those from Planck cosmic microwave background measurements. I will also describe the extensive validation of the measurements and modeling, with a particular focus on the role of cosmological simulations and modeling of the connection between galaxies and dark matter, highlighting where these efforts will need to go in the future to keep up with the exciting cosmological measurements expected from DES, DESI, LSST and other future galaxy surveys.
Sep 26, Tuesday
1:10 pm (Cosmology/ BCCP)
Andrina Nicola, ETH Zurich
Campbell 131
Integrated approach to cosmology
Recent progress in observational cosmology and the establishment of ΛCDM have relied on the combination of different cosmological probes. These probes are not independent, since they all measure the same physical fields. The resulting cross-correlations allow for a robust test of the cosmological model through the consistency of different physical tracers and for the identification of systematics. Integrated analyses taking into account both the auto- as well as the cross-correlations between cosmological probes therefore present a promising analysis method for both current as well as future data.
In this talk, I will present an integrated analysis of CMB temperature anisotropies, CMB lensing, galaxy clustering and weak lensing as well as background probes. I will describe the cosmological probe combination framework, the obtained results and illustrate how this analysis has provided a confirmation of ΛCDM through the consistency of different probes. Furthermore, I will discuss possible tensions between the derived constraints on cosmological parameters and existing ones.
Sep 29, Friday
12 noon (INPA)
Stephen Portillo, Harvard
LBL 50-5132
Improved Source Detection in Crowded Fields using Probabilistic Cataloging
Cataloging is challenging in crowded fields because sources are extremely covariant with their neighbors and blending makes even the number of sources ambiguous. We present the first optical probabilistic stellar catalog, cataloging a crowded (~0.1 sources per pixel) Sloan Digital Sky Survey r band image from M2. Probabilistic cataloging returns an ensemble of catalogs inferred from the image and thus can capture source-source covariance and deblending ambiguities. By comparing to a traditional catalog of the same image and a Hubble Space Telescope catalog of the same region, we show that our catalog ensemble better recovers sources from the image. It goes more than a magnitude deeper than the traditional catalog while having a lower false discovery rate brighter than 20th magnitude. Future telescopes will be more sensitive, and thus more of their images will be crowded. We detail our efforts to extend probabilistic cataloging to galaxies, making the method applicable to the data that will be collected in the Large Synoptic Survey Telescope era.
October 2017
Oct 2, Monday
12:10 pm (TAC)
Xiancheng Ma, Caltech
Campbell 131
"Simulating galaxies at the epoch of reionization"
Galaxies at z>5 are thought to be the dominant sources for cosmic reionization, but current knowledge on their abundance, property, and contribution to reionization is still limited. With JWST to be launched next year, it allows us to study high-redshift galaxies in much detail. I will introduce a new suite of high-resolution cosmological zoom-in simulations of z>5 galaxies, taking advantage of the realistic models of the multi-phase ISM, star formation, and stellar feedback from the FIRE project. These simulations provide a more realistic sample of model galaxies, which can be very useful to predict and understand future observations. I will show the predicted galaxy scaling relations, mass functions, and luminosity functions at z>5. I will also discuss some applications using these simulations, including understanding the escape fraction of ionizing photons, high-redshift galaxy morphologies and their implications for the Hubble Frontier Field observations, dust extinction and the bright-end galaxy UV luminosity functions, etc.
Oct 3, Tuesday
1:10 pm (Cosmology/ BCCP)
Alexandra Amon, Edinburgh
Campbell 131
Weak Lensing with the ESO Kilo-Degree Survey
The Kilo Degree Survey, (KiDS) is an ongoing weak lensing survey that will span 1500 square degrees, on completion, in nine optical-NIR bands. I will summarize the recent cosmology results from our analysis of the first third of the survey area, and detail an important test for the robustness of our weak lensing analysis, where I compare our fiducial high-quality KiDS multi-band dataset with 815 square degrees of the overlapping, shallower KiDS i-band-only survey. I will conclude by presenting a new test of General Relativity, measuring the "gravitational slip" statistic, E_G, in a joint analysis of KiDS with the same-sky spectroscopic surveys; BOSS and the recently completed 2dF Lensing Survey.
Oct 5, Thursday
4 pm (RPM)
Simeon Bird, JHU
LBL 50-5132
Strong Absorbers in the Lyman-alpha Forest and Primordial Black Holes
Strong HI absorbers are essentially the largest foreground contamination for Lyman alpha forest surveys, and so a better understanding of them is necessary for achieving the goals of future Lyman alpha cosmology surveys. I will talk about a new automated technique for generating a probabilistic catalogue of strong absorbers for the entire survey, allowing more robust cleaning of the foreground. Since no technique can entirely remove strong absorbers, I will discuss new templates for characterising their effect on the flux power spectrum. A secondary systematic is induced by interpolation error between theoretical models, and I will discuss techniques to mitigate this error with refining Gaussian Process emulators. Lastly I will discuss the interesting possibility that the surprisingly common mergers of ~30 solar mass black holes observed by LIGO could be primordial black hole dark matter, which is intriguingly (still) not convincingly ruled out.
Oct 6, Friday
12 noon (INPA)
Marie Lau, Santa Cruz
LBL 50-5132
Quasars Probing Quasars: the Circumgalactic Medium Surrounding z ~ 2 Quasars
Understanding the circumgalactic medium--the gaseous halo surrounding a galaxy, is an integral part to understanding galaxy evolution. The z ~ 2-3 universe is interesting as this is when the star formation rate and AGN activity peak. My work concludes the decade-long Quasars Probing Quasars survey designed for studying massive galaxy formation and quasar feedback. I use background quasar sightlines that pass close to foreground quasars to study the circumgalactic medium of quasar-host galaxies in absorption. My sample of 149 quasar pairs involve spectra taken with 17 different optical and near IR instruments. I present results on the statistical and physical properties of the quasar circumgalactic medium. My results pose challenges for cosmological hydrodynamic simulations to produce a substantial cool gas reservoir surrounding quasars, that is also enriched and exhibits extreme kinematics.
I will discuss other science goals that can be facilitated using the spectral databases and absorption-line analysis tools built. If there is interest, I will show preliminary results on a peculiar tidal disruption event and evidence for deep internal mixing in red giants.
Oct 10, Tuesday
1:10 pm (Cosmology/ BCCP)
Charlotte Mason, UCLA
Campbell 131
What Can Galaxies Tell Us About The Epoch of Reionization?
The reionization of neutral hydrogen in the intergalactic medium (IGM) in the universe's first billion years was likely driven by the first stars and galaxies, and its history encodes information about their properties. But the timeline of reionization is not well-measured and it is unclear whether galaxies alone can produce enough ionizing photons. I will describe two ways in which galaxies at our current observational frontiers can constrain reionization. One tool is the UV luminosity function (LF), which traces the evolution of star-forming galaxies and their ionizing photons. I will describe a simple, but powerful, model for LF evolution and its implications for reionization and z>10 surveys with JWST. Secondly, Lyman alpha (Lya) emission from galaxies is a potential probe of the IGM, but requires disentangling physics on pc to Gpc scales. I will introduce a new forward-modeling Bayesian framework which combines IGM simulations with models of interstellar medium conditions to infer the average neutral hydrogen fraction from Lya observations. I will present our new measurement of the neutral fraction at z~7 and place it in the context of other constraints on the reionization history. I will describe ongoing efforts to build larger samples of Lya emitting galaxies with the HST survey GLASS, and future prospects with JWST.
Oct 12, Thursday
4 pm (RPM)
Barnabas Poczos, CMU
LBL 50-5132
Distribution Regression and its Applications
The most common machine learning algorithms operate on
finite-dimensional vectorial feature representations. In
many applications, however, the natural representation of the data
consists of more complex objects,
for example functions, distributions, and sets, rather than
finite-dimensional vectors. In this talk
we will discuss machine learning algorithms that can operate directly
on these complex
objects. For this purpose, we use nonparametric statistical methods
that can consistently estimate the inner product, distance, and
certain kernel functions between distributions, sets, and other
objects. We will discuss applications in various scientific areas
including cosmology (e.g. estimating the mass of galaxy clusters,
finding anomalous galaxy clusters, estimating the cosmological
parameters of our Universe, accelerating cosmological simulations),
fluid dynamics (finding anomalous events in turbulence data),
neuroimaging, and agriculture.
Oct 13, Friday
12 noon (INPA)
Michael Walther, MPIA/UCSB
LBL 50-5132
New Constraints on Thermal Evolution in the IGM from the Small Scale Ly α Forest Power Spectrum
The line-of-sight power spectrum (P_F(k)) of the Ly-α forest has proven to be a valuable tool for doing cosmological observations. It also not only allows to constrain cosmological parameters, but enables us to measure the thermal state of the IGM at redshifts z>1.8. While at large scales (k<0.02 s/km) P_F(k) has been accurately measured using the large number (10^3-10^5) of quasar sightlines from SDSS and BOSS, there are much less spectra available at smaller scales (larger k). Prior power spectrum measurements from high-resolution data only used several times less (QSO) spectra in our redshift range about 15 years ago whereas a few hundred became available in the meantime. We therefore performed a new measurement using 74 quasar sightlines with 1.8 < z< 3.4 significantly improving the precision of the small-scale P_F(k). Using this additional precision on small scales combined with the BOSS measurements on large scales enables us to accurately constrain the thermal cutoff scale of the IGM set by a combination of temperature broadening of Ly-α forest lines, and 'Jeans' smoothing due to baryonic pressure support. We perform an MCMC analysis based on Gaussian process based techniques for interpolation between a grid of high-resolution hydrodynamical simulations and using our new high-resolution dataset, the BOSS data, a recent X-SHOOTER analysis, and a previous HIRES/MIKE analysis at higher redshifts. This allows us to measure thermal evolution in the IGM from z=5.4 to z=1.8 showing a suggestive peak at z~3.3 that might be attributed to He reionization. These constraints will help solving the existing discrepancies in the IGM thermal evolution between different works using different techniques as existing degeneracies between different thermal parameters in the existing measurements can be broken in our analysis.and can be used to place limits on possible exotic sources of heating. Additionally a better knowledge of thermal evolution will also lead to better constraints of e.g. the nature of dark matter or neutrino masses by breaking degeneracies in those measurements and thereby improve our knowledge of the underlying cosmology.
Oct 17, Tuesday
1:10 pm (Cosmology/ BCCP)
Emanuela Dimastrogiovanni, CWRU/Perimeter
Campbell 131
Exploring the early Universe: possible signatures and tests
I will describe some interesting scenarios for the generation of gravitational waves from inflation and their characteristic imprints (at the level of both the power spectrum and the bispectrum), that can be tested with upcoming observations. I will then move on to discuss techniques that may help us learn more about the early Universe by gathering additional information on large scales. Specifically this is done with cross-correlations of secondary CMB anisotropies from kinetic and polarized Sunyaev–Zel'dovich effects with tracers of the large scale structure.
Oct 19, Thursday
4 pm (RPM)
Anthony Pullen, NYU
LBL 50-5132
Revealing CII Emission with LSS Cross-correlations
In this talk, I will present our joint measurement of cosmic infrared background (CIB) and CII line emission from large scales at redshift z=2.5 using an MCMC analysis of cross-correlations of the 3 high-frequency Planck bands with both SDSS-III quasars at z=2-3.2 and SDSS-III CMASS galaxies at z=0.43-0.7. The CII emission is expected to correlate with the quasars and appear in the Planck 545 GHz band, while the other cross-correlations are assumed to mostly be attributable to CIB-LSS correlations. We report an excess emission inconsistent with the null result at 95% confidence, with an intensity value favoring the higher range of CII models. I will also forecast potential CII intensity constraints from Planck cross-correlated with DESI quasars.
Oct 20, Friday
12 noon (INPA talk)
Prabhat, NERSC
LBL 50-5132
Deep learning for science
Deep Learning has revolutionized the fields of computer vision, speech recognition and control systems. Can Deep Learning (DL) work for scientific problems? This talk will explore a variety of DOE/LBL applications that are currently benefiting from Deep Learning. We will review classification and regression problems in astronomy, cosmology, neuroscience, genomics and high-energy physics. We will outline several short and long-term challenges at the frontier of DL research, and speculate about the future of DL for data-intensive science.
Oct 23, Monday
12:10 pm (TAC)
Sarah Loebman, Davis
Campbell 131
Simulating the Evolving Milky Way: From Disk to Halo
The Milky Way is the most observationally accessible galaxy in our Universe. In many ways it is also a "typical galaxy," making it an important benchmark for studying galaxy formation and testing LCDM. For this reason, uncovering the formation history of the Milky Way is the key goal of major ongoing surveys such as APOGEE and Gaia. However, observations of the Milky Way span a complex multi-dimensional space which necessitates sophisticated modeling to interpret. In this talk, I will highlight some recent achievements utilizing state-of-the-art simulations to aid in our exploration of the Milky Way's formation and evolution. In particular, I will discuss recent APOGEE observations of the Milky Way's disk and the role radial migration has played in redistributing stars within it. I will also discuss observations and simulations of kinematics in the Milky Way's stellar halo, emphasizing how measurements of kinematic moments hold power for constraining the merger history of the Milky Way. Finally, I will discuss a strong prediction of LCDM - that stellar halos are radially anisotropic - and I will highlight the potential Gaia holds for testing this prediction in the Milky Way.
Oct 24, Tuesday
1:10 pm (Cosmology/ BCCP)
Phil Bull, UCB
Campbell 131
Cosmological tests of gravity with radio telescopes
GR is astoundingly well-tested in the small-scale, weak-field limit, and constraints in the strong field limit are not far behind thanks to recent gravitational wave and binary pulsar observations. The cosmological regime remains a viable, well-motivated hiding place for possible deviations from GR though. I discuss how radio telescopes are particularly well-suited to the task of determining the nature of gravity on cosmological scales. As well as constraining background expansion at high redshift and providing new ways of measuring the weak lensing signal, radio surveys will be able to make the first practical measurements of clustering at the Hubble scale at late times. I will also describe several novel observational strategies that will make these measurements possible, and discuss how they can be supported experimentally.
Oct 27, Friday
12 noon (INPA talk)
Jason Prochaska, Santa Cruz
LBL 50-5132
Deep Learning of Quasar Spectra
I will describe our development of a convolutional
neural network (CNN) to learn to search for and characterize
absorption lines in quasar spectra. Specifically, the algorithm
discovers and measures the redshift and Hydrogen column
density of damped Lya systems (DLAs). These systems dominate
the neutral hydrogen gas of the universe, trace the interstellar
medium of distant galaxies, and offer cosmological constraints
on the build up of gas and heavy elements across cosmic time.
I will discuss the lessons learned employing CNN techniques
on large spectral datasets and the prospects for future analysis.
Oct 31, Tuesday
1:10 pm (Cosmology/ BCCP)
Marko Simonovic, IAS
Campbell 131
Analytical Tools for Large-scale Structure of the Universe
The large-scale structure of the universe is becoming the leading probe of cosmology. The ongoing and future LSS surveys combined with the next generation CMB experiments aim to provide the unprecedented constraints on the statistic of the initial conditions and physics of inflation, to measure the sum of neutrino masses and to shed new light on the nature of dark matter and dark energy. The main theoretical challenge in this program is understanding the nonlinear evolution of density fluctuations induced by gravitational collapse. In this talk I will describe several analytical tools to deal with this problem. In the first part I will describe perturbation theory approach to gravitational nonlinearities, its advantages, successes and limitations. I will also present some recent progress in evaluation of higher order/loop correlation functions using scattering amplitudes of a massless QFT. In the second part I will focus on some nonperturbative results such as consistency relations for the LSS and their applications to the modeling of the nonlinear evolution of the BAO peak.
November 2017
Nov 1, Wednesday
12 pm LBL lunch
Miguel Zumalacarregui, UCB
LBL 50-4025
Constraining the abundance of primordial black holes with
magnification of type Ia SNe
Black hole mergers detected by the Laser Interferometer
Gravitational-Wave Observatory (LIGO) have revived dark matter models
based on primordial black holes (PBH) or other massive compact halo
objects (MACHO) with masses in the range 1-100 M_Sun, where previous
bounds were the weakest. I will present new constraints on the PBH
abundance and mass using the gravitational lensing magnification of
type Ia supernovae (Sne) using current datasets (JLA, Union 2.1). Our
results rule out the hypothesis of MACHO/PBH comprising the totality
of the dark matter at high significance in the mass range M > 0.01
M_Sun. Eliminating the possibility of a LIGO-mass MACHO further
strengthens the case for microscopic dark matter.
Nov 6, Monday
12:10 pm (TAC)
Brian O'Shea, Michigan State
Campbell 131
"Better living through computation: Connecting the first stars in the universe to the Milky Way using cosmological simulations"
Galaxies are complicated beasts - many physical processes operate simultaneously, and over a huge range of scales in space and time. As a result, creating accurate models of the formation and evolution of galaxies over the lifetime of the universe presents tremendous technical challenges. In this talk I will discuss these challenges and their solutions, and will explain how large-scale computational models can be used to gain insights into the very first galaxies that formed in the universe (over 13 billion years ago!), and how we can use both these computational models and observations of the Milky Way and its neighbors to infer how galaxies have grown and evolved in the intervening time.
Nov 7, Tuesday
1:10 pm (Cosmology/ BCCP)
Justin Alsing, CCA
Campbell 131
"Towards scalable likelihood-free inference for cosmology"
Many statistical models for cosmological data analysis can be simulated forwards but have intractable likelihoods, for example because of complicated reduction pipelines and systematics, or non-linear structure formation and astrophysics impacting small scales. Likelihood-free inference provides an alternative paradigm for doing Bayesian inference using forward simulations only, eliminating the need to make uncomfortable likelihood approximations and allowing us to extract information from previously inaccessible statistics and scales. Traditional Approximate Bayesian Computation (ABC) methods involve drawing parameters and forward simulating mock data, accepting the parameters if the simulated data are within some small distance \epsilon of the real data (recovering the true posterior in the limit \epsilon -> 0). These methods scale poorly with the size of the dataset and critically slow down as \epsilon -> 0, often leading to expensive analyses with overly conservative error bars. I will introduce a new approach to likelihood-free inference that is “epsilon-free”, bypassing the limitations of ABC, and use massive lossless data compression to dramatically reduce the size of the data-space; together, these advances provide a framework for performing scalable likelihood-free inference from cosmological surveys, using reasonable numbers of forward simulations.
Nov 10, Friday
12 noon (INPA)
Katelin Schutz, UCB
LBL 50-5132
Excluding a thin dark matter disk in the Milky Way with Gaia DR1: Resurrecting the Dinosaurs
If a component of the dark matter has dissipative interactions, it could collapse to form a thin dark disk in our Galaxy coincident with the baryonic disk. It has been suggested that dark disks could explain a variety of observed phenomena, including mass extinction events due to periodic comet impacts. Using the first data release from the Gaia space observatory, I will present the results of a search for a dark disk via its effect on stellar kinematics in the Milky Way. I will discuss our strong new limits that disfavor the presence of a thin dark matter disk and present updated measurements on the total matter density in the solar neighborhood.
Nov 14, Tuesday
1:10 pm (Cosmology/ BCCP)
Anze Slosar, BNL
Campbell 131
CANCELLED
Intensity mapping of the neutral hydrogen 21cm line is in principle an
extremely cheap and simple method, but has in practice proven to be a
devilishly difficult way of mapping the universe. I will argue that it
nevertheless offers the best way to complete the programmatic goal of
measuring the linear scales of the universe deep into the
pre-acceleration era after current crop of optical experiments (DESI,
LSST, Euclid, WFIRST). It will give us expansion history measurements
to z=6, which can constrain early dark energy and modified gravity,
break the w/mnu degeneracy, improve curvature constraints and help
with radiation density measurements. It could in principle also
measure the largest scales in the universe through tidal
reconstruction, reconstruct the weak-lensing field and probe the
primordial non-Gaussianity, but robust forecasts for these promises
have yet to be developed. I will discuss the scientific, technological
and programmatic issues that need to be overcome to make such
experiment a reality.
Nov 21, Tuesday
no talk
Nov 28, Tuesday
1:10 pm (Cosmology/ BCCP)
Cancelled, speaker denied entry to US,
Campbell 131
December 2017
Dec 5, Tuesday
1:10 pm (informal talk, term seminars are over)
Michael Kopp, CEICO
Campbell 131
Solving the Vlasov equation in two spatial dimensions with the Schrödinger method
I present recent progress (Kopp, Vattis & Skordis 1711.00140) to solve the Vlasov equation via the so-called Schrödinger method (Widrow & Kaiser 1993). This technique consists of solving the Schrödinger-Poisson equation, together with a prescription to construct a phase space distribution from the wave function.
For the first time, we implemented the Schrödinger method in two spatial dimensions, extending the one-dimensional previous studies.
We performed a quantitative comparison of our code and the state-of-the-art Vlasov solver ColDICE (Sousbie & Colombi 1509.07720), finding excellent agreement.
I review how the fully fledged phase space dynamics is encoded in a wave function with its mere 2 spatial degrees of freedom, and how the cumulants of the phase space distribution, including vorticity and velocity dispersion, can be easily decoded from the wave function in a way that completely avoids the cumbersome high-dimensional phase space.
As an application we evaluate the background pressure induced by the non-linearity of large scale structure formation, thereby estimating the magnitude of cosmological backreaction. We find that it is negligibly small and has time dependence and magnitude compatible with expectations from the effective field theory of large scale structure.
January 2018
Jan 10-12
BCCP Meeting, Modeling the Extragalactic Sky
Program here and
Slides here (slides listed by speaker)
Jan 16, Tuesday
1:10 pm (Cosmology/ BCCP)
Francois Lanusse, CMU
Campbell 131
Facing the challenges of modern cosmological surveys with deep learning
The upcoming generation of cosmological surveys such as LSST or DESI will aim
at shedding some much needed light on the physical nature of dark energy and
dark matter by mapping the Universe in great detail and on an unprecedented scale.
While this implies a great potential for discoveries, it also involves new and
outstanding challenges at every step of the science analysis, from image processing
to the modeling of astrophysical systematics.
In this talk I will illustrate how recent advances in Deep Learning open new
perspectives for addressing some of theses challenges and for exploiting this
wealth of data in new and exciting ways. As a first example, I will present
our work on automated strong gravitational lens detection, a problem where deep
learning essential eliminates the need for human visual inspection (which would
have intractable at the scale of LSST). In a second example of applications, I will
illustrate how data driven deep generative models can be used to complement
a physical modeling in two different cases: image simulations with realistic galaxy
morphologies for the calibration of weak lensing shape measurement algorithms,
and the production of mock galaxy catalogs with realistic intrinsic alignments
learned from hydrodynamical simulations.
Jan 23, Tuesday
1:10 pm (Cosmology/ BCCP)
Chihway Chang, Chicago
Campbell 131
Mapping the Cosmos with the Dark Energy Survey
The first year data from the Dark Energy Survey (DES Y1) provides the most powerful optical survey dataset to date. In this talk I will first give an overall summary of the cosmology results from the DES Y1 dataset combining galaxy clustering and weak gravitational lensing. Next, I will describe our work in generating and testing the wide-field weak lensing mass maps from the galaxy shape measurements and some exciting applications for the maps. I will end with thoughts on how weak lensing could also inform us on various topics of galaxy formation, which is essential for completing the story behind the Universe we see today.
Jan 23, Tuesday
4:00 pm (RPM)
Chihway Chang, Chicago
LBL 50-5132
Cosmic Surveys in the Next Decade: Mapping the Landscape of the Universe
Cosmology in the next decade will be driven by data. Exploiting the information one can extract from the ongoing and upcoming large surveys will give us the power to stress-test the LCDM model with unprecedented precision and open up windows for new physics. In this talk I will present some of our work in the Dark Energy Survey Collaboration and the Large Synoptics Survey Telescope Dark Energy Science Collaboration, to analyse state-of-the-art galaxy survey data as well as getting ready for the next generation of data. I will focus on topics surrounding weak lensing analyses, including cosmology from 2-point functions, generating weak lensing mass maps, and measuring the mass profiles at the outskirts of galaxy clusters.
Jan 30, Tuesday
1:10 pm (Cosmology/ BCCP)
Alex Drlica-Wagner, FNAL
Campbell 131
Small Galaxies, Big Science: The Booming Industry of Milky Way Satellite Galaxies
The satellite galaxies of the Milky Way are some of the most ancient, most chemically pristine, and most dark-matter-dominated galaxies known. These extreme objects provide a unique opportunity to test the standard cosmological model in the near-field limit. In addition, the relative proximity and large dark matter content of dwarf galaxies make them excellent systems for probing the fundamental properties of dark matter. Over the past several years, the unprecedented sensitivity of large CCD cameras have allowed us to double the known population of Milky Way satellites. These discoveries help address the "missing satellites problem” and can be used to test the particle nature of dark matter. I will summarize recent results, outstanding questions, and exciting prospects in near-field cosmology.
Jan 30, Tuesday
4 pm (RPM)
Alex Drlica-Wagner, FNAL
LBL 50-5132
Using Cosmic Surveys to Understand the Fundamental Nature of Dark Matter
The existence of dark matter is strong evidence for new physics beyond the Standard Model. While laboratory and collider searches for dark matter have advanced rapidly over the past several decades, astrophysical observations currently provide the only robust, positive, empirical measurement of dark matter. Astrophysical observables can be directly linked to the fundamental properties of dark matter, such as particle mass, self-interaction cross section, and self-annihilation rate. In this talk, I will discuss how the Fermi Large Area Telescope (LAT) and the Dark Energy Survey (DES) have advanced our understanding of dark matter from observations of the smallest and most dark-matter-dominated galaxies. In addition, I will discuss opportunities to build a cohesive dark matter program with the Large Synoptic Survey Telescope (LSST).
February 2018
Feb 1, Thursday
4:10 pm (Astronomy Colloquium)
Adrian Liu, UCB
LeConte Hall 1
Accessing Cosmic Dawn via the Hydrogen Epoch of Reionization Array
Although it is a crucial pat of our cosmic timeline, Cosmic Dawn—when the first stars and galaxies formed and systematically reionized the intergalactic medium—remains relatively unexplored. By tracing the distribution and state of neutral hydrogen, 21cm cosmology promises to provide the first direct observations of Cosmic Dawn. The Hydrogen Epoch of Reionization Array (HERA) is a low-frequency radio interferometer that is poised to realize this promise within the next few years by making large-scale observations of the 6 < z < 20 universe. In this talk, I will provide an overview of the scientific capabilities of HERA as well as a status update on high-z 21cm cosmology. Along the way, I will also describe our recent efforts in modeling foreground contaminants in the data, how machine learning can be used in our data analyses, and how 21cm cosmology may complement Cosmic Microwave Background observations with better constraints on reionization.
Feb 6, Tuesday
NO TALK
Feb 8, Thursday
4:00 pm (RPM)
Daniel Scolnic, U Chicago
LBL 50-5132
“Measuring Dark Energy with Supernovae and Kilonovae”
The next decade will be the golden age of cosmology with transients. In this talk, I will present new analyses of Type Ia Supernovae that mark the most precise measurement of dark energy to date. I will go over how this analysis ties together with the analysis of the local value of the Hubble constant, for which tension persists with the inferred value from the CMB – an exciting hint at possible departures from the standard cosmological model. I will then discuss the first measurements of the Hubble constant with kilonovae and gravitational waves. I will review the large amount of overlap between the issues that must be tackled for future progress using supernovae and kilonovae to measure cosmological parameters. Finally, I will discuss the roles that surveys like LSST and WFIRST will play and how we can harness the millions of transients discovered to make generation-defining cosmological measurements.
Feb 12, Monday
12:00 pm (INPA)
Danielle Leonard, CMU
LBL 50A-5132
Measuring the scale-dependence of intrinsic alignments using multiple shear estimates
The next generation of cosmological surveys promises significant advancements in the field of weak gravitational lensing. As such, it is crucial that relevant systematic effects such as the intrinsic alignment of galaxies are well-understood. I will discuss a new method for measuring the scale-dependence of the intrinsic alignment contamination to the galaxy-galaxy lensing signal, which takes advantage of multiple shear estimates applied to the same data set. For a galaxy-galaxy lensing measurement which uses LSST sources and DESI lenses, the signal-to-noise on the intrinsic alignment signal measured by our method is forecast to improve on an existing method (Blazek et al. 2012) by a factor of >2, for optimally chosen pairs of shear estimates.
Feb 13, Tuesday
1:10 pm (Cosmology/ BCCP)
Tom Collett, Portsmouth
Campbell 131
Cosmology with Strong Gravitational Lensing
Local measurements of the expansion rate are in tension with those inferred from observations of the distant Universe. Is this the first sign of new physics or merely a sign of systematic errors within individual probes? This key question remains unsolved, because there are only a handful of established probes. Here I will talk about how strong gravitational lensing offers a new window on precision cosmology, shining a new light on the dark Universe.
I will present strong lensing constraints on the expansion rate of the Universe and the equation of state of dark energy. I will also show how lensing combined with stellar dynamics yields the most precise test to date of the validity of General Relativity on extragalactic scales.
Feb 20, Tuesday
1:10 pm (Cosmology/ BCCP)
Ferah Munshi, U Oklahoma
Campbell 131
The MARVELous Dwarfs meet the Justice League: Constraints on dwarf galaxies using a heroically large simulated sample
I will present results from high resolution, fully cosmological simulations of 4 cosmic sheets that contain many (isolated) dwarf galaxies [MARVEL dwarfs] as well as dwarfs drawn from 4 volumes containing a Milky Way analogue [the Justice League]. Together, they create the largest collection of simulated dwarf galaxies to date, with z=0 stellar masses comparable to the LMC or smaller. In total, we have simulated ~100 luminous dwarf galaxies, forming a sample of simulated dwarfs which span a wide range of physical (stellar and halo mass), evolutionary properties (merger history) and environment. I will show how these dwarfs can be calibrated against a wealth of observations of nearby galaxies including star formation histories, HI masses and kinematics, as well as stellar and gas-phase metallicities. I will present preliminary results answering the following key questions: What is the slope of the stellar mass function at extremely low masses? Do halos with HI and no stars exist? What is the scatter in the stellar to halo mass relationship as a function of dwarf mass? What drives the scatter? With this large suite, we can begin to statistically characterize dwarf galaxies and identify the types and numbers of outliers to expect.
Feb 27, Tuesday
1:10 pm (Cosmology/ BCCP)
Anna Christina Eilers, MPIA
Campbell 131
High Redshift Quasars: Constraining their Lifetime and the Epoch of Reionization
One of the major goals in observational cosmology today is to understand how our Universe transitioned from the "dark ages", following recombination, into the ionized universe we can observe today. For this purpose we compiled a new data set of 34 high redshift (5.8 < z< 6.5) quasar spectra of moderate resolution, containing several new and unpublished objects, and reduced these spectra in a coherent and homogeneous way. The analysis of this rich data set enables new insights into the early evolutionary phase of our Universe and the early stages of AGN and galaxy formation traced by the intergalactic gas.
We analyse the proximity zones of the quasars in our data set, i.e. the regions surrounding the quasars that have been ionized by their own radiation, in order to set constraints on the onset and duration of the reionization process as well as the lifetime of these quasars. We find several objects showing exceptionally small proximity zones and argue that only a very short lifetime (t_Q < 10^5 years) can be causing these small zones by comparing our measurements to radiative transfer simulations. We analyze the implications of such short quasar lifetimes on their ionizing power, their black hole accretion rates and highlight tensions with current black hole formation theories. Additionally we discuss the imprints of the intergalactic medium (IGM) on the spectra of the quasars and constrain the evolution of the IGM opacity as well as its neutral gas fraction. We highlight their implications regarding the timing of the epoch of reionization, the morphology of the UV background radiation, and the temperature-density relation of the high-redshift IGM.
Feb 27, Tuesday
4:00 pm (RPM)
Julien Guy, LBL
LBL 50-5132
The DESI Project, Construction Status and Prospects for Precise Cosmological Distance Measurements with Lyman-Alpha Forests
The Dark Energy Spectroscopic Instrument is a multi-object spectrograph composed of a wide field corrector, a 5000 robotically positioned fiber system, and 10 3-arms spectrographs. The instrument is installed this year on the Mayall 4-m diameter telescope at Kitt Peak, Arizona. Operations will start next year. In 5 years, DESI will measure spectra and redshifts of more than 30 million galaxies and quasars. This catalog will be used to measure the expansion history of the Universe and the growth rate of structure in the past 10 billion years with sub-percent precision. I will present the construction status and give some insight on the Lyman-alpha BAO analysis.
March 2018
Mar 6, Tuesday
1:10 pm (Cosmology/ BCCP)
Viraj Sanghai, Dalhousie
Campbell 131
Using the post-Newtonian formalism to understand theories of gravity in cosmology
I am going to split up my talk into two parts. In the first part I am going to show how we can use an extended version of the parameterized post-Newtonian formalism to parameterize theories of gravity in the cosmological background, as well as in the perturbations on non-linear and horizon-scales. This covers a range of scales that we don't think has been consistently parameterized before. In the second part of my talk I will discuss how we perform numerical ray-tracing simulations in a post-Newtonian cosmology (within general relativity) to understand the effect of inhomogeneities on the Hubble diagram.
Mar 9, Friday
12:00 pm (INPA)
Giorgia Pollina, LMU
LBL 50-5132
Unveiling cosmic voids in large-scale structure surveys: the impact of tracer bias
The large-scale structure of the Universe can only be observed directly via luminous tracers of the underlying matter density field. However, luminous tracers, such as galaxies, do not precisely mirror the clustering statistic of the bulk of the cold dark matter distribution: their correlation function (or power spectrum) is biased and depends on various properties of the tracers themselves. Although on small scales this bias is an unestablished function of space and time, on very large scales it results in a constant offset in the clustering amplitude, known as linear bias. In this talk we focus on the bias of luminous objects within and around cosmic voids, enormous under-dense regions of the Universe that occupy the vast majority of its volume. As a remarkable result, we find that, within voids, the relation between matter and galaxy density is always linear and determined by a multiplicative constant. Furthermore, the value of this constant decreases with the increase of the size of voids and asymptotes to the linear bias. This result opens to the possibility of using such simple relation in other voids studies, allowing to extend our theoretical understanding of voids (typically defined as depressions in the matter density field) to voids that are identified using galaxies as tracers of the matter density. Ultimately we aim to test these findings with observations, using the Dark Energy Survey data currently available.
Mar 12, Monday
4:15 pm (Physics Colloquium)
Jo Dunkley, Princeton
1 LeConte
Neutrino physics from Cosmological Surveys
Measurements of the Cosmic Microwave Background radiation, and of the large scale structure in the universe, have taught us a great deal about the orgins and content of the universe, but there is still so much to learn. In the next decade we anticipate using new microwave background data, combined with cosmological measurements of the positions and shapes of galaxies, to measure the total mass of the neutrino particles. I will describe a path to making this indirect detection of the absolute neutrino mass scale using the Atacama Cosmology Telescope, Simons Observatory and the Large Synoptic Survey Telescope, which will complement direct measurements. I will also describe how different views of the universe will help us disentangle the signature of neutrinos from signatures of non-standard cosmologies.
Mar 13, Tuesday
1:10 pm (Cosmology/ BCCP)
Gabriele Trevisan, NYU
Campbell 131
IR-resummation in the EFTofLSS
In this talk I will discuss the “non-linear” infrared effects that plagues Standard Perturbation Theory for Large Scale Structure. Understanding and resumming these contributions is essential to achieve a detailed description of the correlation functions around the BAO scale.
Mar 16, Friday
12:00 pm (INPA)
Ana Bonaca, Harvard-CfA
LBL 50-5132
What are the tidal streams constraining?
Cold stellar streams, remnants of tidally disrupted globular clusters,
have been employed as exquisite tracers of dark matter in the Milky
Way. Because of their different positions in phase space, different
ages, and different levels of observational scrutiny, different
streams tell us different things about the Galaxy. We employ a
Cramer--Rao or Fisher-matrix approach to understand the quantitative
information content in the known streams. In simple, static, analytic
models of the Milky Way, streams on eccentric orbits contain the most
information about the dark-matter shape. For any individual stream,
there are near-degeneracies between dark-matter halo properties and
parameters describing the Galactic bulge, disk and the stream
progenitor itself, but we find that simultaneous fitting of multiple
streams ought to constrain all parameters to a precision of a few
percent. At this level, simulated dark matter halos deviate from
analytic parametrizations, so we chart the way forward by discussing
constraints streams place on more flexible models of the Galactic
gravitational potential.
Mar 20, Tuesday
1:10 pm (Cosmology/ BCCP)
no 1:10 pm talk, go to 4 pm talk
Mar 20, Tuesday
4:00 pm (RPM)
Simone Ferraro,UCB
LBL 50-5132
“Lighting up the Dark Universe”
Recent progress in cosmological observations reveal a simple yet strange universe. Our preferred cosmological model relies on mysterious components such as Dark Matter, Dark Energy and an early period of accelerated expansion. The challenge in the next decade will be to understand the nature of these components and reveal new aspects of fundamental physics.
I will discuss the synergies between upcoming redshift and CMB experiments and show that thanks to sample variance cancellation techniques, a large improvement on constraining power is possible even at fixed volume. I will highlight the role of cross-correlations and velocity fields in increasing the statistical power of future surveys, while at the same time allowing for greater control of systematics. I will show how the combination of large-scale structure and CMB experiments hold great promise to reveal the secrets of our mysterious Universe.
Mar 22, Thursday
4:00 pm (RPM)
Andreu Font,UCL
LBL 50-5132
“Cosmology with the Lyman alpha forest: challenges and opportunities”
From 2009 to 2014, the Baryon Oscillation Spectroscopic Survey (BOSS) used the SDSS telescope to obtain spectra of 1.5 million galaxies to get very accurate measurements of the Baryon Acoustic Oscillations (BAO) scale at redshift z ~0.5. At the same time, BOSS observed over 184 000 high redshift quasars (z>2.15) with the goal of detecting the BAO feature in the clustering of the intergalactic medium, using a technique known as the Lyman alpha forest (LyaF). In this talk I will overview the final results from the LyaF working group in BOSS, including the measurement of BAO at z=2.4 both from the auto-correlation of the LyaF (Bautista et al. 2017), and from its cross-correlation with quasars (du-Mas-des-Bourboux et al. 2017). From the combination of these studies we are able to measure the expansion rate of the Universe 11 billion years ago with a 2% uncertainty.
Starting in 2019, the Dark Energy Spectroscopic Instrument (DESI) will increase this dataset by an order of magnitude. In this talk I will review the challenges that we will face in order to provide an exquisite measurement of the expansion over cosmic history, and the opportunities that we will have to study other fundamental questions: the sum of the mass of the neutrino species, properties of dark matter particles, and the shape of the primordial power spectrum of density fluctuations.
Mar 27, Tuesday
Spring Break, no talk
April 2018
Apr 3, Tuesday
1:10 pm (Cosmology/ BCCP)
Gus Evrard, Michigan
Campbell 131
Physics and Statistics of the Massive Halo Population
New observations and simulations of the most massive cosmic halos that host groups and clusters of galaxies are providing details of the interlocking physical processes that drive astrophysical evolution across this population. In the first part of this talk I will use a few cherry-picked results from last week’s SNOWCLUSTER meeting to illustrate the range and scope of progress. Property covariance — correlated intrinsic variations in observable features at fixed halo mass — is an important descriptive statistic of the massive halo population, and the second part of my talk will present recent results, both computational and empirical, on determining on- and off-diagonal components of the property covariance matrix. In particular, high mass halos at low redshift demonstrate anti-correlated hot gas and galaxy behavior, indicative of their nature as quasi-closed baryon boxes.
Apr 3, Tuesday
4:00 pm (RPM)
Brice Menard, JHU and Ting-Wen Lan, IPMU
LBL 50-5132
Twenty years of SDSS spectra: lessons for DESI
We have played with SDSS spectra for almost two decades and enjoyed performing all sorts of statistical analyses with them. In this talk we will take a critical look at these explorations and discuss what has worked well and what has not, what mistakes were made and some of the fundamental limits arising from the calibration of the data -- all of which are informative to prepare ourselves for the DESI era. Finally we will also discuss new data analysis ideas and emerging techniques that are likely to impact the way we think and manipulate spectra in the near future.
Apr 5, Thursday
4:00 pm (RPM)
Colin Hill, CCA
LBL 50-5132
“Fundamental Physics from the Foreground-Obscured Microwave Sky: Inflation, Neutrino Masses, and Beyond”
The cosmic microwave background (CMB) remains a key source from which to extract information about fundamental physics, due to its clean, well-understood origin and immense constraining power on many types of new physics. The next decade of CMB observations will yield answers to at least two fundamental questions: (1) did large-field inflation source the initial density perturbations in our universe? (2) what is the absolute mass scale of the neutrinos? In this talk, I will explain the routes by which these answers will be obtained. Both rely on highly precise measurements of the polarization of the CMB, which can be used to search for the signature of primordial gravitational waves (answering the first question) and to measure the growth of cosmic structure via gravitational lensing (answering the second question). Moreover, I will describe new methods with which to overcome the most significant challenge to this program: emission from non-primordial foreground sources. I will highlight the major role that the Simons Observatory and CMB-Stage IV experiments will play in these exciting developments. Finally, I will describe additional unique information about the distribution and properties of baryons and dark matter that these measurements will yield, providing crucial feedback for cosmological analyses with DESI and other large-scale structure surveys.
Apr 10, Tuesday
NO TALK
Apr 12, Thursday
4:00 pm (RPM)
George Smoot, UCB/LBNL
LBL 50-5132
“Reinterpreting Low Frequency LIGO/Virgo Events as Gravitationally-Lensed Magnified Stellar-Mass Black Hole Mergers at Cosmological Distances”
Though dismissed by most, we claim that strong gravitational lensing of the gravitational waves for merging black holes explains the high mass binary black hole mergers observed by LIGO/Virgo explains the apparent 30 M_Sun events better than any alternative models.
It turns out to be difficult to make large mass black hole binaries in sufficient number to explain LIGO’s results. However, strong gravitational lensing of cosmological distant mergers can naturally explain them while the redshift of the orbital frequencies amplifies the observed apparent masses.
Apr 13, Friday
12:00 pm (INPA)
Helion Mas du Bourboux, University of Utah
LBL 50-5132
Baryonic Acoustic Oscillations in SDSS and DESI using the intergalactic medium absorption
We present the measurement of the Baryonic Acoustic Oscillation (BAO) scale from the correlation between absorption in the intergalactic medium and the positions of galaxies and quasars in the SDSS data and in the desi simulations.
We use the absorption by neutral Hydrogen and by Magnesium-II observed in quasar spectra to trace the underlying matter density fluctuations. Combined with galaxies and quasars, these two tracers allow to measure the 3d cross-correlation of matter from a redshift of z = 0.5 up to a redshift of z = 2.4.
Apr 17, Tuesday
1:10 pm (Cosmology/ BCCP)
Benedikt Diemer, Harvard
Campbell 131
Edge of darkness: The splashback radius as a physical halo boundary
The radii and masses of dark matter halos are an essential input for models of galaxy formation, and for the interpretation of numerous observations. These radii are typically defined through an arbitrary overdensity threshold, largely because the density profiles of halos are thought not to have a well-defined edge. In this talk, I will show that the situation is more complicated: the outer profiles of halos depend on their dynamical state, and exhibit a novel feature called the splashback radius. I will argue for this radius as a physically motivated halo boundary and discuss recent observational and theoretical results supporting this notion. I will introduce a new analysis code that tracks billions of particle orbits in cosmological simulations in unprecedented detail. Based on the resulting measurements, I will demonstrate that the splashback radius contains complex information about halos that cannot be derived from conventional radius definitions.
Apr 17, Tuesday
4:00 pm (INPA)
Heidi Newberg, RPI
LBL 50-5132
Dwarf galaxies and dark matter in the Milky Way
In the past fifteen years, dozens of tidal streams of stars pulled from dwarf galaxies and globular clusters have been discovered in the Milky Way’s stellar halo. Recently, it has been discovered that as the dwarf galaxies fall into our galaxy they perturb the stars in the disk, causing wavelike disturbances that are seen in the densities and velocities of disk stars. These disturbances could be driving force behind spiral structure in galaxies. MilkyWay@home is a petaFLOPS scale volunteer computing platform that is mapping the densities of stars in the larger tidal streams in the stellar halo and using that information to measure the mass and density profile of both the stars and the dark matter in the progenitor dwarf galaxies, using only information from the stars in the tidal streams. Eventually, MilkyWay@home will fit the shape of the Galactic potential using tidal streams.
Apr 20, Friday
12:00 pm (INPA)
Rebecca Canning, Stanford
LBL 50-5132
Understanding Active Galactic Nuclei (AGN) in the most massive cosmic laboratories
Supermassive Black Holes (SMBHs) lurk in the centers of all massive galaxies, a fraction of these SMBHs are actively accreting and this can result in powerful outbursts which have important consequences for galaxy formation and evolution. However, the conditions under which a SMBH becomes active and the manner in which it interacts with its environment are not well understood. Clusters of galaxies offer us wonderful cosmic laboratories in which we can observe these processes. I will discuss what observations of these massive galaxy clusters can tell us about the role of AGN feedback in both maintaining a delicate balance between heating and cooling and in searching for a casual link between SMBHs and galaxy co-evolution and detail the Cluster AGN Topography Survey which is undertaking a census of SMBH activity in massive galaxy clusters.
Apr 24, Tuesday
1:10 pm (Cosmology/ BCCP)
Ethan Nadler, Stanford
Campbell 131
Modeling Subhalos and Satellites in Milky Way-like Systems
High-resolution hydrodynamic zoom-in simulations of Milky Way-mass halos offer exquisite resolution and provide insights into the small-scale challenges associated with cold dark matter. However, these simulations are computationally expensive, so studying a diverse sample of simulated Milky Way analogs is currently infeasible. We present a machine learning model trained on simulations from the Feedback in Realistic Environments project that efficiently predicts surviving subhalo populations from dark-matter-only simulations, and we show that the predicted subhalo populations agree well with hydrodynamic results. We discuss several applications of this technique, including its use in modeling satellite galaxy populations around Milky Way analogs and around the Milky Way itself.
May 2018
May 1, Tuesday
1:10 pm (Cosmology/ BCCP)
Ben Wandelt, Flatiron Institute, NYC, Sorbonne University, Princeton University
Campbell 131
How to learn from cosmological data
The mysteries of the cosmic beginning, gravitational clustering, and cosmic acceleration persist. How can we distill relevant cosmological information from the next generation of data sets? Taking examples from the cosmic microwave background, large scale structure, and supernova cosmology, I will discuss inference strategies, artificial intelligence, and computational approaches that promise to extract more information from current and upcoming data sets. The philosophy is to allow maximum freedom to design realistic forward models, to be robust to systematic nuisances, to accurately combine multiple probes, move beyond simplistic likelihood assumptions, naturally allow quantitative model comparison, characterize tensions in the data, and maintain (near-)optimality whenever possible.
May 17, Thursday
4 pm (RPM)
Chris Fassnacht, Davis
LBL 50-5132
“Cosmological parameters from strong gravitational lenses”
Recent measurements of the Hubble Constant (H_0) through distance
ladder techniques have revealed a noticeable tension with the
Planck H_0 value that was obtained under the assumption of the cosmological
“standard model”, i.e., a flat Lambda cold dark matter cosmology. Is this
tension an indication that modifications to the standard model are
necessary, or is it the sign of unknown systematic effects in one or
both of the techniques? To address this question requires additional
high-precision measurements with techniques that are independent of
the distance ladder. The time delay strong lensing technique, in
which gravitational lensing by a massive galaxy produces multiple
images of a time-variable quasar, fulfills these requirements. I will
present recent results from the H0licow program, in which the analysis
of just three time-delay strong lenses has produced a 3.8% measurement
of H_0, and discuss the implications for other cosmological parameters,
including those describing dark energy. I will also discuss the
future prospects of this technique in the era of large sky surveys and
extremely large telescopes.
June 2018
Jun 4, Monday
2:00 pm (RPM)
Masashi Hazumi, KEK
LBL 50A-5132
“LiteBIRD Satellite for Tests of Cosmic Inflation and Quantum Gravity”
Cosmological inflation is the leading hypothesis to resolve the problems in the Big Bang theory. It predicts that primordial gravitational waves were created during the inflationary era, which then imprinted large-scale curl patterns in the cosmic microwave background (CMB) polarization map called the B-modes. Measurements of the CMB B-mode signals are known as the best probe to detect the primordial gravitational waves. LiteBIRD is a candidate for JAXA’s strategic large mission to map the polarization of the CMB radiation over the full sky at large angular scales with unprecedented precision, which will offer us a crucial test of cosmic inflation. It will also serve as the first crucial test of quantum gravity such as superstring theory. Precise polarization maps of LiteBIRD will also provide us with valuable pieces of information on particle physics and astrophysics. In this talk, I will give an overview of the science and design of LiteBIRD.
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