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:


December 2016
Dec 1, Thursday
4 pm (Astronomy Colloquium)
Alexie Leauthaud, Santa Cruz
1 Le Conte
Lensing is Low: Cosmology, Galaxy Formation, or New Physics?
A fundamental goal in observational cosmology is to understand the link between the luminous properties of galaxies and the dark matter halos in which they reside. Weak lensing, which relies simply on the laws of gravity, is a unique method that can be used to directly probe the dark matter components of galaxies. In this talk, I will present new high signal-to-noise weak lensing measurements for galaxies from the BOSS “CMASS" sample. By comparing this signal with predictions from mock catalogs trained to match observables including the stellar mass function and the projected and two dimensional clustering of BOSS galaxies, I will show that the clustering of CMASS, together with standard models of the galaxy-halo connection, robustly predicts a lensing signal that is 20-40\% larger than observed. I will discuss several effects that may explain this mis-match including, a low value of the amplitude of low redshift structure compared to Planck2015, assembly bias, the effects of baryons on the matter distribution, and the effects of massive neutrinos. Towards the end of this talk, I will show some early results from the new Hyper Suprime Cam (HSC) survey, an ambitious multi-wavelength (g,r,i,z,y) weak-lensing program to map out 1500 square degrees of the sky with the 8.2m Subaru Telescope to i∼26 mag.
Dec 2, Friday
12 pm (INPA talk, noon, not 12:10)
Sebastian Cantalupo, Zurich
LBNL 50-5132
Direct imaging of the Dark Universe with the help of supermassive black-holes and Integral Field Spectroscopy
Gravitational collapse during the Universe's first billion years transformed a nearly homogeneous matter distribution into a network of filaments - the Cosmic Web - where galaxies form and evolve. Because most of this material is too diffuse to form stars, its study has been mostly limited so far to one-dimensional absorption probes against background sources or to three-dimensional studies limited however by relatively poor spatial resolution. In this talk, I will show how deep narrow-band imaging on Keck and Integral Field Spectroscopy with VLT/MUSE around bright quasars is providing us a completely new window for the study of the high-redshift Universe. In particular, using quasars and bright galaxies as external “sources of illumination”, we are now finally able to directly map in Ly-alpha emission and at high spatial resolution the diffuse gas that traces the sites of early galaxy formation (“dark galaxies”), the circumgalactic medium, as well as intergalactic filaments extending up to several hundred of kpc around massive galaxies. I will discuss the importance of the new instrumentation such as MUSE (and the Keck Cosmic Web Imager in the next future) for the tremendous discoveries and advancements in the last few years in this new field and I will present our first attempts to advance in parallel our physical understanding of baryonic structure formation as traced by the intergalactic Ly-alpha emission.
Dec 6, Tuesday
1:10 pm (Cosmology/ BCCP)
Sukhdeep Singh, CMU
Campbell 131
Galaxy-Lensing Cross Correlations: Measurements and Applications
Weak lensing has emerged as an important cosmological probe for our understanding of dark matter and dark energy. Galaxy-lensing cross correlations map the matter distribution around galaxies and provide important information about matter correlations and the growth of large scale structure. I will present our measurements of galaxy-galaxy lensing and galaxy-CMB lensing cross correlations using SDSS-BOSS spectroscopic samples with SDSS galaxy lensing and Planck CMB lensing. I will also address some of the issues in covariance estimation for these measurements. When combined with galaxy clustering and RSD measurements, galaxy-lensing also provides strong constraints on the standard cosmological model. As applications of these measurements, I will discuss the constraints on EG parameter, cosmological parameters and the estimation of relative calibration uncertainties between galaxy shear and CMB lensing.
Dec 8, Thursday
4 pm (RPM)
Johanna Nagy, Case Western
LBL 50-5132
“Probing Inflation with SPIDER, a Balloon-Borne CMB Polarimeter”
The generation of a stochastic gravitational wave background is a key prediction of cosmological theories of inflation. At large angular scales, these gravitational waves imprint a “B-mode” polarization pattern in the Cosmic Microwave Background, providing a new window into the physics of the early universe and helping to constrain and distinguish between inflationary models. SPIDER is a balloon-borne telescope that has been uniquely optimized to search for the inflationary B-mode signature in the CMB. Over the course of two Antarctic flights, SPIDER will make polarization maps over 10% of the sky in three frequency bands with degree-scale angular resolution. After an overview of the instrument and science goals, preliminary results from SPIDER’s 2015 flight will be presented along with a summary of progress towards the second flight.
Dec 9, Friday
12 pm (INPA talk, noon, not 12:10)
Julian Munoz, JHU
LBNL 50-5132
Probing dark matter with radio surveys
A significant part of dark matter could be compact, in particular in the form of primordial black holes. I will review the signatures of primordial black holes, both in the form of gravitational-wave events and as gravitational lenses of fast radio bursts. Alternatively, a WIMP-y dark-matter component could interact with baryons to some level. I will explain how these interactions can cause heating of the baryons, becoming observable in the 21-cm line prior to the epoch of reionization.
Dec 13, Tuesday
4 pm (RPM)
ChangHoon Hahn, NYU
LBL 50-5132
“Fundamental Physics with Galaxy Clustering”
Galaxies’ connection to the cosmic web allows us to use them to trace the matter distribution in the Universe and make precise measurements of large scale structure. The next galaxy surveys (eBOSS and DESI) will expand the cosmic volumes probed with galaxies by an order of magnitude and provide unprecedented statistical power. The main challenges for realizing their full potential are methodological. I will present how the main challenges can be solved with robust treatment of systematics (e.g. fiber collisions), accurate probabilistic inference, and higher order statistics. By overcoming these challenges and unlocking the full potential of eBOSS and DESI, I will present how we can measure the growth of structure and total neutrino mass with unprecedented precision.

January 2017
Jan 24, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Campbell 131

Jan 31, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Campbell 131


February 2017
Feb 7, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Campbell 131

Feb 14, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Campbell 131

Feb 21, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Campbell 131

Feb 28, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Campbell 131


March 2017
Mar 7, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Campbell 131

Mar 14, Tuesday
1:10 pm (Cosmology/ BCCP)
Steve Finkelstein, Texas
Campbell 131

Mar 21, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Campbell 131

Mar 28, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Spring break, no talk


April 2017
Apr 4, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Campbell 131

Apr 11, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Campbell 131

Apr 18, Tuesday
1:10 pm (Cosmology/ BCCP)
Yashar Hezaveh, Stanford
Campbell 131

Apr 25, Tuesday
1:10 pm (Cosmology/ BCCP)
Rychard Bouwens, Leiden
Campbell 131

Apr 27, Thursday
4 pm (Astronomy Colloquium)
Rychard Bouwens, Leiden
Le Conte





Past Months ( Previous Years )


August 2016
Aug 29, Monday
12:10 pm (TAC)
Dan Whalen, ICG, Portsmouth
Campbell 131
Finding the First Cosmic Explosions
Primordial stars formed about 200 Myr after the Big Bang, ending the cosmic dark ages. They were the first great nucleosynthetic engines of the universe and may be the origins of the supermassive black holes (SMBHs) found in most massive galaxies today. In spite of their importance to the evolution of the early universe not much is known for certain about the properties of Pop III stars. But with the advent of JWST, Euclid, WFIRST and the ELTs it may soon be possible to directly observe their supernovae in the NIR and thus unambiguously constrain the properties of the first stars. I will present radiation hydrodynamical calculations of the light curves of the first SNe in the universe and discuss strategies for their detection. I will also describe how some high-z SNe may already have been found in surveys of galaxy cluster lenses such as CLASH and Frontier Fields. I will conclude my talk with new calculations of the evolution and collapse of supermassive primordial stars that constrain the masses of the first quasars at birth.
Aug 31, Wednesday
12 pm (INPA talk, noon, not 12:10)
Dan Whalen, ICG, Portsmouth
LBL 50-5026
How Supermassive Black Holes Form by z ~ 7
Over 100 quasars have now been discovered at z > 6, less than a Gyr after the Big Bang. The discovery of supermassive black holes (SMBHs) by this epoch posed severe challenges to current theories of structure formation because it is not known how objects so massive appeared by such early times. However, we have now developed numerical simulations that show that these quasars can form from direct collapse black holes at z ~ 20 if they are fed by strong, cold accretion streams, like those thought to fuel the rapid growth of some galaxies at later epochs. I will discuss these simulations and formation channels for DCBHs at high redshift. I will also discuss prospects for their detection in the NIR and at 21 cm by Euclid, JWST and the SKA.

September 2016
Sep 6, Tuesday
1:10 pm (Cosmology/ BCCP)
Miguel Aragon-Calvo, Riverside
Campbell 131
A cosmic web model of galaxy formation and some adventures in data visualization
The cosmic web is the stage where galaxy formation and evolution occurs. However, current models of galaxy formation ignore the effect of cosmic environment beyond basic descriptors and rely on crude approximations that do not capture the complex interplay between galaxies and their environment. In this talk I will discuss the Cosmic Web Detachment (CWD) model recently proposed to describe the effect of cosmic environment on galaxy formation and evolution. The CWD model can naturally reproduce a range of galaxy properties and provides a framework to interpret observations in a truly cosmological context.
During the talk I will make use of innovative visualization techniques including stereo 3D , 3D printing and natural interaction and discuss how data visualization can be used as a driver for scientific discovery.
Sep 13, Tuesday
1:10 pm (Cosmology/ BCCP)
Andrea Petri, Columbia
Campbell 131
Cosmology with Weak Gravitational Lensing: the information beyond the Power Spectrum ,
also movies here and here

The LambdaCDM model of the Universe has been proven tremendously successful in explaining experimental data with only a few free parameters. While observations from a variety of sources (CMB, Supernovae IA, BAO, Large Scale Structure) have done an outstanding job in constraining the standard parameter space, the Dark Energy equation of state, w, remains essentially unconstrained. Weak Gravitational Lensing (WL) is a promising observational technique in this sense, because of its sensitivity to late universe physics, when Dark Energy dominates. Because of late time non-linearities, WL observables are not Gaussian distributed, and quadratic statistics such as Power Spectra likely miss some of the cosmological information contained in observations. Possible complementary statistics one could consider include higher order moments, peak counts and topological descriptors. I will review the fundamentals of WL, as well as the ray--tracing formalism on which our numerical simulations are based. I will also summarize our efforts in improving parameter constraints using a variety of higher order statistics, with both galaxy and CMB lensing data. I will also outiline some recent results on analytical prediction and origin of WL convergence peaks. To conclude, I will discuss some of the numerical subtleties that one must take into consideration when using higher order statistics to analyze WL data sets.
Sep 15, Thursday
4 pm (RPM)
Nick Kaiser, Hawaii
LBL 50-5132
The Physics of Gravitational Redshifts in Clusters of Galaxies
Wojtak, Hansen and Hjorth and others have measured the long-predicted gravitational redshift of light escaping from galaxy clusters using Sloan Digital Sky Survey data. The effect is very small, corresponding to a velocity shift of only ~10 km/s in clusters with internal random motions of order 600 km/s, but the result appears to be robust and is in good agreement with general relativity predictions and possibly in conflict with some alternative theories. It was soon realised that the interpretation of this measurement is more complex than initially thought as one needs to allow for the transverse Doppler (TD) redshift. In this talk I will describe how there are actually two more rather subtle and unexpected physical effects that need to be considered in interpreting these observations; there is a `light cone' effect that augments the TD shift, and there is a competing effect that reverses the sign of the transverse Doppler effect so that we actually observe a transverse Doppler blue-shift. I will discuss how these observations constrain gravitation theory, and along the way discuss some issues concerning the interpretation of astronomical redshifts in a broader context.
Sep 15, Thursday
4:10 pm (Astronomy Colloquium)
Freeke van de Voort, UCB and Taiwan
1 Le Conte
Cosmic gas flows: the key to understanding galaxy formation
The evolution of galaxies is critically linked to the gas flows in and the assembly history of their surrounding haloes. Although observationally gas is harder to detect than stars, it lies at the heart of our understanding of galaxy formation. The circumgalactic medium provides the gas reservoir to fuel star formation in galaxies, but galaxies do not just grow passively. Strong outflows driven by supernovae and supermassive black holes heat and enrich the galaxy's environment, thus completely changing its evolution. And it doesn't end there: galaxies can also grow through merging and they can be stripped of their gas and stars when they become satellites. I will discuss results from cosmological, hydrodynamical simulations and focus on the interaction of galactic feedback and gas accretion, their effect on the growth of galaxies, and on ways to probe this baryonic cycle observationally.
Sep 16, Friday
12 pm (INPA talk, noon, not 12:10)
Nick Kaiser, Hawaii
LBNL 50-5132
The Effect of Gravitational Lensing on Cosmological Parameter Estimation
A very long standing question in cosmology is whether gravitational lensing biases the distance-redshift relation D(z) or the mean flux density of sources. Interest in this has been rekindled by recent results in 2nd order relativistic perturbation theory which, if correct, would have profound implications for cosmological parameter estimation from both SN1a and the CMB. In this talk I shall first review the somewhat confusing history of the subject, going back to the early '60s and including both Weinberg's 1976 argument that there should be no effect on grounds of flux conservation and the general relativistic "focusing theorem" of the '80s that foreshadows the more recent results. I then show how the claimed subtle relativistic effects actually result from confusion between different types of averaging (specifically between averaging over sources and averaging over directions on the sky). I also show that while Weinberg's argument conceals a hidden loop-hole, in that he assumes that the area of a surface of constant redshifts is unaffected by lensing, the error incurred is only a one part in a million effect. This result validates conventional methods for analysis of the CMB and shows that, counter to claims in the literature, the focusing theorem does not in fact reveal an intrinsic tendency for structure to cause focusing of light rays.
Sep 19, Monday
12:10 pm (TAC)
Sarah Wellons, Harvard/CfA
Campbell 131
The diverse progenitors and descendants of (compact elliptical) galaxies in cosmological simulations
bservations of the high-redshift universe have revealed a population of galaxies which are already very massive (~10^11 Msun at z=2) and have typical sizes of < 2 kpc, much smaller than their counterparts in the local universe. How such dense, massive galaxies form, and why they appear to be less common at low redshift, have been questions of interest for both theorists and observers. I will discuss these questions in the context of the Illustris simulation, a hydrodynamical cosmological simulation in which tens of thousands of galaxies form, evolve, and interact with each other, situated within a cosmological context. I select a group of massive compact galaxies at z=2 in the simulation and trace them back and forth in time to discover both how they formed at high redshift, and what they evolve into at the present day. I find a variety of both progenitors (our compact galaxies form either via central starbursts generally brought on by mergers, or by racing out to the tip of the SF main sequence and forming very early) and descendants (many formerly-compact galaxies lurk at the core of a more massive galaxy today, others were consumed in mergers, and some evolve passively and undisturbed). Finally, I will discuss the implications of these results for observational methods of connecting galaxy populations across redshifts - in particular, the assumption of a constant cumulative comoving number density - and suggest an improvement to this method which takes the complexity and variety of galaxy evolutionary paths into account.
Sep 20, Tuesday
1:10 pm (Cosmology/ BCCP)
Hy Trac, CMU
Campbell 131
New Ways to Use Dynamical Measurements of Galaxy Clusters
Galaxy clusters contain large amounts of cold dark matter, hot ionized gas, and tens to hundreds of visible galaxies. The abundance of clusters as a function of mass and redshift can be used to probe the growth of structure and constrain cosmological parameters. Dynamical measurements probe the entire mass distribution, but standard analyses yield unwanted high mass errors. First we show that modern machine learning algorithms can improve mass measurements by more than a factor of two compared to using standard scaling relations. Support Distribution Machines are used to train and test on the entire distribution of galaxy velocities to maximally use available information. Second we show that cluster abundance can be quantified with the distribution of direct observables rather than inferred mass to avoid uncertainties in the mass-observable relation. A novel statistic called the velocity distribution function (VDF) is constructed by stacking the probability distribution of galaxy velocities for a select number of clusters in a given volume. The VDF can be measured directly and precisely, and produces unbiased constraints on cosmological parameters. Finally we discuss how our approaches can be generalized to multi-wavelength observations of gravitational lensing, SZ effect, and X-ray emissions.
Sep 27, Tuesday
1:10 pm (Cosmology/ BCCP)
Emmanuel Schaan, Princeton
Campbell 131
Understanding large-scale structure from the CMB
In this seminar, I will present two promising ways in which the cosmic microwave background (CMB) sheds light on critical uncertain physics and systematics of the large-scale structure.
Shear calibration with CMB lensing (arXiv:1607.01761): Realizing the full potential of upcoming weak lensing surveys requires an exquisite understanding of the errors in galaxy shape estimation. In particular, such errors lead to a multiplicative bias in the shear, degenerate with the matter density parameter and the amplitude of fluctuations. Its redshift-evolution can hide the true evolution of the growth of structure, which probes dark energy and possible modifications to general relativity. I will show that CMB lensing from a stage 4 experiment (CMB S4) can self-calibrate the shear for an LSST-like optical lensing experiment. This holds in the presence of photo-z errors and intrinsic alignment.
Evidence for the kinematic Sunyaev-Zel'dovich (kSZ) effect (arXiv:1510.06442); cluster energetics: Through the kSZ effect, the baryon momentum field is imprinted on the CMB. I will report significant evidence for the kSZ effect from ACTPol and peculiar velocities reconstructed from BOSS. I will present the prospects for constraining cluster gas profiles and energetics from the kSZ effect with SPT-3G, AdvACT and CMB S4. This will provide constraints for galaxy formation and feedback models.
Sep 29, Thursday
4:00 pm (Astronomy Colloquium)
Joop Schaye, Leiden
Le Conte
Simulating the formation of galaxies
The realism of hydrodynamical simulations of the formation and evolution of populations of galaxies has improved considerably in recent years. I will try to give some insight into the reasons behind this success, focusing in particular on the importance of subgrid models and the associated limitations. I will also present recent results from the cosmological EAGLE simulations as well as from other projects.

October 2016
Oct 4, Tuesday
1:10 pm (Cosmology/ BCCP)
Irene Shivaei, Riverside
Campbell 131
A Multi-Wavelength Census of Star Formation and Dust in Galaxies at z ~ 2
Redshift of z ~ 2 is an important era in the history of the universe, as it contains the peak of star formation rate density and quasar activity. I will talk about the properties of galaxies during this era from two different, yet complementary, aspects: star formation and mass assembly, and galactic dust enrichment. In this study, I use a wealth of spectroscopic data obtained by the MOSDEF survey. I will introduce the MOSDEF survey, which is a multi-institutional project that uses the near-IR MOSFIRE spectrograph on the Keck I telescope to characterize the gaseous and stellar contents of ~ 1500 rest-frame optically selected galaxies at 1.37 < z < 3.80. Furthermore, I incorporate the mid- and far-IR data from the Spitzer and Herschel telescopes to obtain a complete census of obscured and unobscured star formation in galaxies. Specifically, I explore the star-formation rate and stellar mass relation at z ~ 2, using multi-wavelength star-formation rate tracers (UV, Hα, 24 micron, and far-IR). Moreover, I investigate, for the first time, the variation of the PAH emission at 7.7 micron, traced by Spitzer/MIPS 24 micron, in galaxies spanning a wide range in metallicity at z ~ 2. Our results have important implications for high-redshift studies that adopt 24 micron flux to derive total IR luminosity and star-formation rate.
Oct 11, Tuesday
1:10 pm (Cosmology/ BCCP)
Derek Inman, CITA
Campbell 131
Non-linear neutrino effects in large scale structure
Detecting the cosmic neutrino background, either through observation or experiment, has proven to be a substantial challenge due to the very small neutrino mass. Typical cosmological studies rely on two point statistics and must distinguish small neutrino effects from much larger cold dark matter (CDM) and baryonic ones. Higher order statistics, in which generic CDM effects can be cancelled by design, are a promising avenue to improve constraints on neutrino properties. However, utilizing them requires an accurate understanding of neutrino co-evolution with the non-linear CDM. Surprisingly, the low neutrino mass makes this computation a significant numerical challenge. I will describe our N-body simulations that study this problem, including the TianNu simulation, which contains nearly three trillion particles. I will then describe three non-linear effects: the evolution of the neutrino power spectrum, the relative velocity dipole between neutrinos and cold dark matter, and differential neutrino condensation onto halos.
Oct 18, Tuesday
1:10 pm (Cosmology/ BCCP)
Chen He Heinrich, Chicago
Campbell 131
Complete Reionization Constraints from Planck 2015 Polarization
I will present a recent analysis of the Planck 2015 data that is complete in the reionization observables from large angle CMB polarization measurements using principal components. By allowing for an arbitrary ionization history, this technique tests the robustness of total optical depth inferences from the usual instantaneous reionization assumption. A reliable measurement of the total optical depth is important for the interpretation of many other cosmological parameters such as the dark energy and neutrino mass. We found that Planck 2015 data not only allow a high redshift z>15 component to the optical depth but prefer it at the 2σ level. This high redshift component contributes to a higher total optical depth than in the instantaneous reionization analysis, illustrating the need for a complete treatment of reionization observables. I will further demonstrate the power of the principal component method to efficiently constrain models given predictions of ionization history by applying our effective likelihood code.
Oct 20, Thursday
4 pm (RPM)
Marilena LoVerde, Stony Brook
LBL 50-5132
Neutrinos, Quintessence and Structure Formation in the Universe
The large-scale structure of our universe (the distribution of galaxies on very large-scales for instance) contains a wealth of information about the origin, evolution, and matter content of the universe. Extracting this information relies crucially on understanding how galaxies and other biased objects trace the large-scale matter distribution. In a universe such as our own, with both cold dark matter and massive neutrinos, or in alternative cosmologies with clustered quintessence, this problem is much more complicated. I will discuss new tools that my group has developed to study gravitational evolution in cosmologies with multiple fluids, the novel signatures we have identified including a new probe of neutrino mass, and the broader implications for models of large-scale structure.
Oct 21, Friday
12 pm (INPA talk, noon, not 12:10)
Enea Di Dio,
LBNL 50-5132
Relativistic effects on LSS: power spectrum and bispectrum
I will discuss the Large Scale Structure power spectrum and bispectrum in a relativistic framework. To first order, a relativistic description includes terms beyond the Kaiser approximation (Doppler effects and galaxy evolution), gravitational potentials and integrated terms (cosmic magnification, integrated Sachs-Wolfe and Shapiro time-delay). I will show how they can be isolated by correlating different probes, or by using the so-called multi-tracer technique. Through this technique future surveys may be able to detect some relativistic contributions. I will also discuss relativistic effects beyond linear theory, the relativistic bispectrum and how the lensing deflection angle smears out the BAO wiggles.
Oct 25, Tuesday
1:10 pm (Cosmology/ BCCP)
Alessandro Manzotti, Chicago
Campbell 131
Delensing CMB B-modes: results from SPT
A promising signature of cosmic inflation is the presence of a "B-mode" component in the polarization of the Cosmic Microwave Background (CMB) induced by primordial gravitational waves. For many inflation models, this B-mode signal is predicted to be at a level detectable in the near future. However current searches are limited by a "lensing B-mode" component that is produced by gravitationally lensing primordial E modes. In order to potentially detect the inflationary signal from B-mode measurements, lensing B modes must be characterized and removed in a process referred to as "delensing." This process has been studied extensively theoretically and with simulations, but has not been performed on polarization data. In this talk, we present the results of CMB B-mode delensing using polarization data from the South Pole Telescope polarimeter, SPTpol. Furthermore, using realistic simulations that include filtering and realistic CMB noise, we will show what is currently limiting the delensing efficiency and how it will rapidly improve in the near future.
Oct 27, Thursday
4 pm (Astronomy Colloquium)
Shirley Ho, LBL
1 Le Conte
Digging into the Large Scale Structure: Galaxies, Filaments and Neutral Hydrogen
Galaxy spectroscopic surveys provide the means to map out this cosmic large-scale structure in three dimensions, furnishing a cornerstone of observational cosmology. The information is given in the form of galaxy locations, and is typically condensed into a single function of scale, such as the galaxy correlation function or power-spectrum. However, galaxy correlation functions are not the only information those surveys provide. One of the most striking features of N-body simulations is the network of filaments into which dark matter particles arrange themselves. We however traditionally only use the information contained in the positions of the galaxies, and in some occasions, we look at other cosmic structures of the Universe such as voids.
In this colloquium, I explore the information beyond the galaxy positions in large sky surveys combining novel ideas with recent techniques in statistical methods and machine learning algorithms. In particular, we will investigate the following two topics: the "cosmic web" that are mostly ignored in any large scale structure analyses in the Universe and how it affects the surrounding galaxies; and Damped Lyman Alpha absorbers that are hidden within the observed quasar spectra, which dominates the neutral hydrogen budget after reionization.
Oct 28, Friday
**1 pm** (INPA talk), time change due to runaround
Samuel Flender, Argonne
LBNL 50-5132
The kinematic Sunyaev-Zel'dovich effect as a cosmology probe?
Future data from galaxy redshift surveys, combined with high-resolutions maps of the cosmic microwave background, will enable measurements of the pairwise kinematic Sunyaev-Zel'dovich (kSZ) signal with unprecedented statistical significance. This signal probes the matter-velocity correlation function, scaled by the average optical depth (tau) of the galaxy groups and clusters in the sample, and is thus of fundamental importance for cosmology. However, in order to translate pairwise kSZ measurements into cosmological constraints, external constraints on tau are necessary. In this talk I will present the current state of kSZ measurements, including a recent measurement by SPT and DES, insights from simulations, as well as recent progress in modeling the tau profile of galaxy clusters.

November 2016
Nov 1, Tuesday
1:10 pm (Cosmology/ BCCP)
Alison Strom, Caltech
Campbell 131
"Star-formation history and chemical enrichment in the early Universe: clues from the rest-UV and rest-optical spectra of high-redshift galaxies"
Galaxies at the peak of cosmic star formation (z~2-3) exhibit significantly higher star formation rates and gas fractions at fixed stellar mass than nearby galaxies. These z~2-3 galaxies are also distinct in terms of their nebular spectra, reflecting important differences not only in the physical conditions of their interstellar medium (e.g., electron density and gas-phase metallicity), but also in the details of their massive stellar populations, especially their ionizing radiation fields. Jointly observing galaxies' HII regions, at rest-UV and rest-optical wavelength, and massive stars, in the rest-UV bandpass, is central to constructing a framework for understanding the differences between z~2-3 and z~0 star-forming galaxies and for self-consistently explaining the trends observed in the high-redshift population. I will present results from the Keck Baryonic Structure Survey (KBSS), which uniquely combines observations of the rest-optical spectra of ~400 individual galaxies (obtained with Keck/MOSFIRE) with deep rest-UV spectroscopy of many of the same galaxies (obtained with Keck/LRIS). These measurements represent one of the most comprehensive spectroscopic studies of z~2-3 galaxies to date and, when compared with predictions from photoionization models, offer compelling evidence that high-redshift galaxies exhibit chemical abundance patterns distinct from local galaxies, likely as the result of systematic differences in their star-formation histories.
Nov 4, Friday
12 pm (INPA talk, noon, not 12:10)
Colin Hill,
LBNL 50-5132
New Information in Ancient Photons: Novel Approaches to CMB Secondary Anisotropies
Cosmic microwave background (CMB) experiments have recently entered a new era in which cosmological and astrophysical constraints derived from the secondary anisotropies (due to late-time effects) substantially improve upon those derived from the primary anisotropies alone. In this talk, I will discuss new approaches to extract information from these signals, placed in the broader context of component separation in CMB analysis. I will describe novel methods for studying the thermal Sunyaev-Zel'dovich (SZ) effect --- the inverse-Compton scattering of CMB photons off hot electrons --- using cross-correlations, stacking, and beyond-Gaussian statistics. I will present projections for thermal SZ extraction from Advanced ACT data based on a new component-separation pipeline, as well as new foreground-marginalized forecasts for the all-sky tSZ (and $\mu$) spectral distortion monopole from the proposed PIXIE satellite. I will then present a measurement of the kinematic SZ effect (due to electrons moving with a net bulk velocity along the line-of-sight) with Planck, WMAP, and WISE data using a novel estimator that does not require redshift estimates for individual tracers. This measurement yields the tightest kinematic SZ-derived constraint on the low-redshift baryon fraction to date. The result is consistent with constraints derived from the primary CMB and Big Bang nucleosynthesis, thus resolving the long-standing "missing baryon problem".
Nov 8, Tuesday
1:10 pm (Cosmology/ BCCP)
Michael Wilson, ROE
Campbell 131
Geometric and growth rate tests of gravity with the linearised galaxy distribution
This talk will first outline the consistency of the VIPERS PDR-2 census of the galaxy distribution at z=0.8 with the expansion and growth rate histories predicted by General Relativity and a Planck (2015) cosmology. These may be inferred from the observed anisotropy of the galaxy power spectrum, which is due to both the coherent infall of galaxies towards clusters (outflow from voids) and the assumption of an expansion history differing from the true one.
I will then present the results of including a simple density transform prior to the analysis; this tackles the root-cause of non-linearity by down-weighting the most massive structures and extends the validity of theoretical models. Moreover, this weighting would amplify signatures of modified gravity in ‘shielded’ models and represents a higher-order statistic, which contains information beyond that available to the power spectrum.
Finally, the final VIPERS data release will occur on Nov 18th (http://vipers.inaf.it). I will detail the pros, and cons, of the survey and describe the breadth of the accompanying clustering analyses.
Nov 15, Tuesday
1:10 pm (Cosmology/ BCCP)
Vanessa Boehm, Garching
Campbell 131
A new bias to CMB lensing measurements
Weak gravitational lensing distorts the cosmic microwave background in a characeristic way that carries valuable information about the growth of structure and the spatial geometry of the Universe. The rapidly improving precision of measurements of this effect also requires a corresponding increase in the accuracy of theoretical modeling. A commonly made approximation is to model the CMB lensing potential as a Gaussian random field. In the work presented, we drop this assumption and analytically quantify the influence of the non-Gaussianity of the lensing potential, arising from nonlinear structure formation, on CMB lensing measurements. In particular, we evaluate the impact of the nonzero bispectrum of large-scale structure on the standard estimator for the lensing potential power spectrum. The result is a new, so far ignored, bias term that adds to the estimator and should be accounted for in future experiments. After an introduction to CMB lensing and CMB lensing measurements, I will explain the origin and structure of the bias and discuss its significance in current and upcoming surveys. I will further show updates of the published results that 1) include an improved modeling of the bispectrum of large-scale structure and 2) account for contributions to the lensing potential bispectrum from post-Born corrections. Finally, I will show preliminary results of a verification of the analytically derived bias with simulations.
Nov 15, Tuesday
4 pm (RPM)
Emmanuel Schaan, Princeton
LBL 50-5132
“Non-linearities in the large-scale structure: noise and signal”
he primordial density perturbations seen in the cosmic microwave background have collapsed under gravity to form the large-scale structure we see in the universe today. This evolution is non-linear, and therefore introduces coupling between Fourier modes that would otherwise be independent. I will present two consequences of this non-linear coupling.
Halo sample variance (arXiv:1406.3330): Gaussian estimates for the errors in large-scale structure measurements exaggerate the scientific impact of these measurements. Non-linear evolution and finite volume effects are both significant sources of non-Gaussian covariance, which reduce the ability of power spectrum measurements to constrain cosmological parameters. I will present a joint likelihood for cluster counts, power spectrum and bispectrum, including the non-Gaussian covariances, and show that a joint analysis of these observables can reduce this “information loss”. In some cases, the resulting improvement on cosmological parameters is equivalent to doubling the survey area.
Lyman-alpha – CMB lensing bispectrum (arXiv:1607.03625): The Lyman-alpha forest seen in the spectra of quasars is a powerful tool for constraining warm dark matter models and the neutrino masses, as well as properties of the intergalactic medium. Its use as a cosmological probe relies on modeling the connection between neutral gas and dark matter. I will present the first detection of the correlation between the Lyman-alpha forest and the cosmic microwave background, using data from BOSS and Planck. This signal quantifies the non-linear response of the neutral hydrogen to a large-scale overdensity, and thus tests our understanding of the connection between neutral gas and the dark matter.
Nov 16, Wednesday
12 pm (scientific computing seminar)
Davide Martizzi, UCB
380 Soda Hall
Studying cosmic structure formation with computational methods.
In this talk I will show how the use of numerical simulations has greatly aided the study of cosmic structure formation: galaxies, groups of galaxies, galaxy clusters. I will provide motivation for the use of numerical methods in astrophysics and cosmology and describe state-of-the-art techniques used by numerical astrophysicists to solve challenging problems. Finally, I will discuss the key results achieved in the field of numerical cosmology, as well as the current physical and computational challenges that the numerical cosmology community is facing.
Nov 17, Thursday
4 pm (RPM)
Robert Kirshner, Moore Foundation
LBL 50-5132
“Doing WFIRST Science Now: Supernovae in the Infrared”
An infrared-capable 2.4m telescope is presently in orbit: the Hubble Space Telescope. This makes it possible to do rest-frame infrared observations of Type Ia supernovae. In the infrared, SN Ia are more nearly standard candles and there is less obscuration by dust. I will give a status report on RAISIN2, an HST program that tiptoes into the realm of WFIRST science today.
Nov 17, Thursday
4 pm (Astronomy Colloquium)
Michael Boylan-Kolchin, Austin
1 Le Conte
"Far-reaching Science with Near-field Cosmology"
The local Universe provides a unique and powerful way to explore galaxy formation and cosmological physics. Through measurements of the abundances, kinematics, and chemical composition of nearby systems that can be studied in exquisite detail, we can learn about the initial spectrum of cosmological density fluctuations, galaxy formation, dark matter physics, and processes at cosmic dawn that might otherwise remain unobservable. I will highlight some recent developments in this rapidly-changing discipline of “near-field cosmology”, with an emphasis on (1) the interplay between dark matter and baryons in the centers of dwarf galaxies, and (2) connections between the local Universe and high-redshift galaxies.
Nov 18, Friday
12 pm (INPA talk, noon, not 12:10)
Daniele Sorini, Heidelberg
LBL 50-5132
3D-IMS: Accurately Modeling the Lyman-alpha Forest in Collisionless Simulations
Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, I present “3D Iteratively Matched Statistics” (3D-IMS), a novel method to accurately model the Lyman-alpha forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. I compare the results given by 3D-IMS with a reference high-resolution hydrodynamic simulation, demonstrating that 3D-IMS can reproduce the probability density function (PDF), line-of-sight and 3D power spectra of the Lyman-alpha forest with high accuracy. I also show that commonly used approximate methods to model such statistics from N-body simulations are not suitable when large volumes (>~100 cMpc) are needed. The 3D-IMS method could be used to improve our understanding about the 3D correlations of the Lyman-alpha flux measured from BOSS, and their relation with the thermal state of the IGM or other small scale physics. This could increase the accuracy of the estimate of the BAO scale.
Nov 22, Tuesday
1:10 pm (Cosmology/ BCCP)
no talk
Campbell 131

Nov 29, Tuesday
1:10 pm (Cosmology/ BCCP)
Luke Kelley, Harvard
Campbell 131
Massive Black Hole Binary Mergers and their Gravitational Waves
Gravitational Waves (GW) from stellar-mass BH binaries have recently been observed by LIGO, but GW from their supermassive counterparts have remained elusive. Recent upper limits from Pulsar Timing Arrays (PTA) have excluded significant portions of the predicted parameter space. Most previous studies, however, have assumed that most or all Massive Black Hole (MBH) Binaries merge effectively and quickly. I will present results derived—for the first time—from cosmological, hydrodynamic simulations with self-consistently coevolved populations of MBH. We perform post-processing simulations of the MBH merger process, using realistic galactic environments, including models of dynamical friction, stellar scattering, gas drag from a circumbinary disk, and GW emission—with no assumptions of merger fractions or timescales. We find that despite only the most massive systems merging effectively (and still on gigayear timescales), the GW Background is only just below current detection limits with PTA. Our models suggest that PTA should make detections within the next decade, and will provide information about MBH binary populations, environments, and even eccentricities. I’ll also briefly discuss prospects for observations of dual-AGN, and the possible importance of MBH triples in the merger process.
Nov 30, Wednesday
12 pm (INPA talk, noon, not 12:10)
Wai Ling Kimmy Wu, UCB
LBNL 50-5132
Constraining Inflation with BICEP/Keck and SPT
Inflation generically predicts a background of stochastic gravitational waves. In the standard cosmological model LCDM, these primordial gravitational waves (PGW) are the only source to the odd-parity (curl) B-mode polarization on the Cosmic Microwave Background (CMB) at the epoch of recombination. Therefore, we can learn much about inflation by constraining or potentially detecting primordial gravitational waves. In this talk, I will present two frontiers that advance the search for primordial gravitational waves: instrumentation of BICEP3 and delensing with SPTpol. I will conclude with the future outlook of such search with CMB-S4. In the first part of the talk, I will discuss the design and performance of BICEP3 — the path-finder of BICEP/Keck program’s Stage-3 effort. The BICEP/Keck telescopes are small aperture (~0.5m) cryogenic refractors that focus on measuring the degree-angular scale feature of the PGW-generated B modes. BICEP3 has ~10x optical throughput compared to BICEP2 due to a larger field-of-view and aperture size. As a result, we adopt new designs in BICEP3 for thermal filtering, optical elements selection, and detector modules packing. We deployed BICEP3 in the Austral summer of 2014-2015 and upgraded the instrument after the first season of testing and observations. I will present the improvements of the noise levels due to this upgrade. The second part of my talk will focus on delensing SPTpol data. Gravitational lensing of primordial (curl-free) E modes generates B modes. These lensing B modes are a source of foreground contamination to detecting the PGW-generated B modes. We can characterize and reduce the lensing B-mode contribution through a technique called “delensing.” I will present results of a first demonstration of delensing on polarization data. In this work, we delens B-mode maps from multi-frequency SPTpol observations of a 100 deg^2 patch of sky by subtracting a lensing B template constructed from two components: SPTpol E-mode maps and a lensing potential map formed from a Herschel 500 μm map of the CIB. In addition, we build and use a suite of realistic simulations to study the current limitations and expected future improvements in delensing with implications for future experiments.




   
            
 
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