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
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 Portilla, 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 3, Tuesday
1:10 pm (Cosmology/ BCCP)
Alexandra Amon, Edinburgh
Campbell 131
Oct 10, Tuesday
1:10 pm (Cosmology/ BCCP)
Charlotte Mason, UCLA
Campbell 131
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
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