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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:


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

Oct 10, Tuesday
1:10 pm (Cosmology/ BCCP)
Charlotte Mason, UCLA
Campbell 131

Oct 13, Friday
12 noon (INPA)
Michael Walther, MPIA/UCSB
LBL 50-5132

Oct 17, Tuesday
1:10 pm (Cosmology/ BCCP)
Emanuela Dimastrogiovanni, CWRU/Perimeter
Campbell 131

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 24, Tuesday
1:10 pm (Cosmology/ BCCP)
Mackenzie Jones, Dartmouth
Campbell 131

Oct 31, Tuesday
1:10 pm (Cosmology/ BCCP)
Marko Simonovic, IAS
Campbell 131


November 2017
Nov 7, Tuesday
1:10 pm (Cosmology/ BCCP)
Justin Alsing, CCA
Campbell 131

Nov 14, Tuesday
1:10 pm (Cosmology/ BCCP)
Anze Slosar, BNL
Campbell 131

Nov 21, Tuesday

no talk


Nov 28, Tuesday
1:10 pm (Cosmology/ BCCP)
Francois Lanusse, CMU
Campbell 131


December 2017
Dec 5, Tuesday
1:10 pm (Cosmology/ BCCP)
tba,
Campbell 131





Past Months


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
   
            
 
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