December 2013:
Dec. 3, Tuesday
1:10 pm (Cosmology-BCCP)
Joop Schaye, Leiden
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Cosmological simulations of the formation of galaxies"
Cosmological hydro simulations can give unique insight into the formation and evolution of galaxies and their interplay with the intergalactic medium. They have realistic initial conditions, they can provide representative samples of galaxies that span a wide range of mass and environment, they can follow their evolution over time, and they can simultaneously model both the galaxies the intergalactic medium around them. The drawback of cosmological simulations is, however, their limited resolution and the importance of subgrid models. I will give an overview of the ingredients of the simulations and discuss recent developments, current issues and bottlenecks. I will then use the simulations to highlight the key role that self-regulation plays in the evolution of galaxies. Finally, I will demonstrate that the feedback processes that appear to be needed to match the observations have a dramatic impact on observational cosmology.
Dec 3, Tuesday
3:10 pm (GalForm)
Khee-Gan Lee, MPIA
Hearst Field Annex B-1
"Mapping the z~2 Cosmic Web with Lyman-alpha Forest Tomography"
I will discuss the technique of Lyman-alpha forest tomography, in which the Lyman-alpha forest absorption from an
extremely dense grid (>500 per sq deg) of faint background sources is used to make a fully 3D `tomographic'
map of large-scale structure at z~2. Using empirical luminosity functions of QSOs and LBGs,
I will show that at apparent depths of g~24, the background sources are transversely separated by only ~3 h-1 Mpc comoving
thus enabling mapping on that resolution. Using simulations, I will show that just S/N~4 per angstrom on g=24 background
sources is sufficient to generate maps with ~3 h-1 Mpc comoving resolution.
This requires just several hrs of integration on existing spectrographs on 8-10m telescopes, e.g. VLT-VIMOS and Keck-LRIS. I will introduce CLAPTRAP, a survey to map out 1 sq deg in the COSMOS field over a comoving volume of 106 h-3 Mpc3. The resulting maps can be used to study z~2 properties as a function of their large-scale environment, characterize
the topology of large-scale structure, and find galaxy protoclusters.
Dec. 12, Thursday
4:00 pm (LBL RPM)
Ashley Ross, Portsmouth
LBL 50A-5132
"Making Robust and Precise Physical Measurements Using Galaxy Surveys"
What is the nature of Dark Energy? Can we detect deviations from General Relativity (GR)?
What is the mass of the neutrino(s)? These fundamental questions can be addressed by analyzing the clustering
of galaxies and I will explain how using examples of measurements made using the SDSS-III Baryon Oscillation
Spectroscopic Survey (BOSS). I will describe the BOSS data, the methods we use to measure the clustering
of BOSS galaxies, and how our most recent clustering measurements have allowed us to measure the distance
to BOSS galaxies to within 1% precision. I will further describe some of the technical challenges and systematic
concerns in our analysis, and the methods and measurements we have used to ameliorate these concerns. I will
conclude with a discussion of the results that will be afforded by future surveys, such as DESI.
Dec 13, Friday
12 pm (INPA talk)
Amir Hajian, CITA
LBL-50-5026 (INPA Common Room)
"Exploring the microwave sky beyond CMB using cross correlations"
Past decade has been a golden era for precision cosmology. Cosmological surveys combined with Cosmic Microwave Background (CMB) provided us with valuable tools for studying the physics of the universe. Using a series of high-resolution and high-sensitivity CMB experiments, we have learned a great deal about the material content, shape and structure of the universe. These achievements have come about with the help of precise characterization of the statistical properties of the CMB fluctuations. In this talk, I will discuss the new astrophysical playground the current generation of the CMB experiments has opened up for us. I will describe how interesting information, beyond the traditional CMB power spectrum parameters, can be extracted from CMB data using cross correlations with the large scale structure surveys. I will present two recent results measuring thermal Sunya'ev Zeldovich effect and the Cosmic Infrared Background using cross correlations of CMB with X-ray and infrared data.
Dec 13, Friday
3:10 pm (SSL talk)
Daisuke Nagai, Yale
SSL Addition
"Galaxy Clusters in the Era of Precision Cosmology"
Galaxy clusters are the most recently formed cosmological objects in the universe, making them ideal for studying the interplay between cosmology and baryonic physics in structure formation. Understanding their formation and growth requires not only an understanding of the baryonic physics behind gas cooling, star and black hole formation, and feedback processes, but also the detailed dynamics of how gas accretes from the cosmic filaments onto the virialization regions in the outskirts of galaxy clusters throughout their lifetime. Recent X-ray and microwave observations have revealed detailed thermodynamic structure of the hot X-ray emitting plasma from their cores to the virial radii, making comparisons of baryonic component in simulations to observations a strong cosmological probe. In this talk, I will review recent progress in our understanding of cluster astrophysics and discuss future prospects, opportunities and challenges for the use of galaxy clusters as a precision cosmological probe.
Dec. 17, Tuesday
4:00 pm (LBL RPM)
Tijmen de Haan, McGill
LBL 50A-5132
"Cluster Cosmology with the South Pole Telescope"
The South Pole Telescope (SPT) performed a five-year survey from 2007 to 2011, mapping 2500 square degrees of the mm-wave sky with exquisite sensitivity and angular resolution. I will discuss the discovery of hundreds of new massive galaxy clusters through the Sunyaev-Zel'Dovich (SZ) effect. These clusters form a mass-limited, redshift independent sample with a well-understood selection function. Comparison to theoretical abundance yields strong cosmological constraints, limited only by the unknown scaling relation between the SZ effect and cluster mass. In order to improve our knowledge of cluster scaling relations, we have embarked on a multi-wavelength follow up campaign. I will describe the most recent results and show projections for SPT cluster cosmology in the near future.
January 2014:
Jan. 28, Tuesday
1:10 pm
Marcel van Daalen, Leiden
Hearst Field Annex B-1
Feb 2014:
Feb. 4, Tuesday
1:10 pm
Andrew Hearin, Fermilab
Hearst Field Annex B-1
March 2014:
Mar. 4, Tuesday
1:10 pm
Sam Skillman, Stanford/SLAC
Hearst Field Annex B-1
Mar. 11, Tuesday
1:10 pm
McCullen Sandora, Davis
Hearst Field Annex B-1
April 2014:
May 2014:
Past Months
(Previous years)
November 2013:
Nov 1, Friday
12 pm (INPA talk)
Andreu Font, LBL
LBL-50-5026 (INPA Common Room)
"Tracing Large Scale Structure with the Lyman alpha Forest"
The Baryon Oscillation Spectroscopic Survey (BOSS) uses the SDSS telescope to obtain spectra of 1.5 million galaxies to get very accurate measurements of the BAO scale at redshift z ~0.5. Roughly 20% of the fibers of the spectrograph, however, are pointing to high redshift quasars with the goal of detecting the BAO in the clustering of gas responsible for the Lyman alpha absorption present in the quasar spectra, known as the Lyman alpha forest.
Nov 5, Tuesday
1:10 pm (Cosmology-BCCP)
Jake Vanderplas, Washington
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Information Theory and the Design of Astronomical Surveys"
What can an unfair coin toss teach us about the measurement of dark energy? Can the principles used to create and crack wartime cyphers help us more accurately determine the distances to far-away galaxies? In this talk, I'll answer these questions, and talk about the surprising ways that information theory can inform the design of scientific experiments. I'll start with a brief introduction to the central concepts of information theory, and explain how we've used them to create a very general framework to quantitatively evaluate the effectiveness of various design aspects of astronomical surveys. As a case study, I'll focus on the photometric redshift problem, which is a vital component of many current and upcoming cosmological probes. Using this information theoretic framework, we give quantitative recommendations to guide the choice of optimal filter profiles and observing cadences for next-generation astronomical surveys.
Nov 7, Thursday
4:00 pm (LBL RPM)
Eva Silverstein, Stanford
LBL 50A-5132
"New Solutions with Accelerated Expansion in String Theory and Applications"
We present concrete solutions with accelerated expansion in string theory, requiring a small, tractable list of stress energy sources. We explain how this construction (and others in progress) evades previous no go theorems for simple accelerating solutions. Our solutions respect an approximate scaling symmetry and realize discrete sequences of values for the equation of state, including one with an accumulation point at w=-1 and another accumulating near w=-1/3 from below. In another class of models, a density of defects generates scaling solutions with accelerated expansion. We briefly discuss potential applications to dark energy phenomenology, and to holography for cosmology.
Nov 8, Friday
12 pm (INPA talk)
Ixandra Achitouv, Munich
LBL-50-5026 (INPA Common Room)
"Abundance of halos and voids in the excursion set approach"
In this talk I'll review the formalism of the excursion set theory applied to a coherent volume definition and a diffusive drifting barrier. I will illustrate on the mass function that the barrier parameters can be measured in the initial condition and that the corresponding mass function is in good agreement with respect to N-body simulations for large class of cosmological scenario and redshift. I will also apply this formalism to voids formation criteria and discuss the consistency of assuming spherical evolution to model the abundance of voids measured in N-body simulations.
Nov 12, Tuesday
1:10 pm (Cosmology-BCCP)
Vinu Vikram, Penn
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Astrophysical Tests of Modified Gravity: Constraints from Nearby Universe"
In a wide class of gravity theories a scalar field couples
to matter and provides an attractive fifth force. Due to their
different self-gravity, stars
and gas may respond differently to the scalar force leading to several
observable deviations from standard
gravity. HI gas, red giant stars and main sequence stars can be
displaced relative to each
other, and the stellar disk can display warps or asymmetric rotation
curves aligned
with external potential gradients. I discuss some of these based on
observations of dwarf
galaxies. I also discuss results obtained from the study
of distances to dwarf galaxies based on cepheids and tip of the red
giant stars. The limits obtained from dwarf galaxies are not yet
competitive with the limits from cepheids and TRGBs, but can be
improved with better
data. This allows to probe regions of parameter
space that are inaccessible using other tests.
Nov 15, Friday
12 pm (INPA talk)
Anthony Pullen, JPL/Caltech
LBL-50-5026 (INPA Common Room)
"Large-Scale Structure: Big Surveys, Systematics, and Intensity Mapping"
Large-scale structure (LSS) surveys have produced powerful probes of various cosmological phenomena, including inflation, reionization, and the accelerated expansion epoch. Current and upcoming LSS surveys will allow us to answer several fundamental questions about our Universe, but systematic effects are of great concern to these missions. We present our latest results considering systematic effects in upcoming LSS surveys. We show that photometric calibration errors contaminate photometric surveys on large scales, which biases measurements of non-Gaussianity, and present methods to mitigate their effects. We also discuss the contamination of emission-line surveys and dark energy measurements by interlopers, as well as potential methods to remove the contaminating emission lines. Finally we discuss "intensity mapping", a new LSS survey strategy where we map fluctuations in the intensity signal from star-forming galaxies and the intergalactic medium in order to probe LSS and reionization.
Nov 19, Tuesday
1:10 pm (Cosmology-BCCP)
Colin Hill, Princeton
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"New Constraints on the Amplitude of Cosmic Density Fluctuations and Intracluster Gas from the Thermal SZ Signal Measured by Planck and ACT"
Galaxy clusters form from the rarest peaks in the initial matter distribution, and hence are a sensitive probe of the amplitude of density fluctuations (sigma_8), the amount of matter in the universe, and the growth rate of structure. Galaxy clusters have the potential to constrain dark energy and neutrino masses. However, cluster cosmology is currently limited by systematic uncertainties due to poorly understood intracluster gas physics. I will present new statistical approaches to understand clusters and improve their cosmological constraining power through the thermal Sunyaev-Zel'dovich (tSZ) effect. First, I will describe a forthcoming first detection of the cross-correlation of the tSZ signal reconstructed from Planck data with the large-scale matter distribution traced by the Planck CMB lensing potential. This statistic measures the thermal gas pressure in moderately massive groups and clusters (M ~ 10^13-10^14.5 M_sun), a mass scale well below that probed by direct cluster detections. Second, I will describe the first measurement of the PDF of the tSZ field using ACT 148 GHz maps. This measurement contains information from all (zero-lag) moments of the tSZ field, beyond simply the 2- or 3-point functions. It is a very sensitive probe of sigma_8 and may also provide a method with which to break the degeneracy between sigma_8 and uncertainties in the physics of the intracluster gas.
Nov 19, Tuesday
3:10 pm (GalForm)
Kasper Borello Schmidt, UCSB
Hearst Field Annex B-1
"The Brightest of Reionizing Galaxies (BoRG) survey: The z~8 luminosity function and spectroscopic follow-up with MOSFIRE"
Nov 26, Tuesday
1:10 pm (Cosmology-BCCP)
tbd
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
tba
October 2013:
Oct 1, Tuesday
1:10 pm (Cosmology-BCCP)
Elisa Chisari, Princeton
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Intrinsic alignments: cosmology from the large scales & constraining the non-linear regime"
While intrinsic alignments are usually regarded as a contaminant of cosmic shear measurements, they encode cosmological information and information about the formation history of galaxies. In the first part of the talk, I will discuss the tidal alignment model, which has been shown to reproduce the intrinsic alignments of Luminous Red Galaxies on large scales. I will present prospects of using the intrinsic alignments of Luminous Red Galaxies as a probe of baryon acoustic oscillations and primordial non-gaussianity with ongoing and upcoming surveys. In the second part of the talk, I will focus on the alignment of galaxies in non-linear scales, within clusters of galaxies. I will discuss our ongoing effort to constrain the intrinsic alignment of cluster galaxies in the Sloan Digital Sky Survey "Stripe 82".
Oct 8, Tuesday
1:10 pm (Cosmology-BCCP)
Daniel Green, SLAC/Stanford
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Towards an analytic theory of large-scale structure"
I will discuss how perturbation theory can reliably predict dark matter correlation functions using the effective theory of large scale structure. I will explain how the perturbation theory is organize so that the results are manifestly convergent. I will emphasize the predictions for the two-loop matter power spectrum at z= 0. These results show one percent agreement with N-body simulations up to k = 0. 6 h Mpc^{-1}. Most significantly, the lack of agreement at higher k is also a prediction of the EFT of LSS.
Oct 11, Friday
2:00 pm (INPA talk-note special time)
Jeremy Sakstein, Cambridge
LBL Bldg. 50, room 5026 (the INPA common room)
"Astrophysical Tests of Gravity"
Screened theories of modified gravity such as chameleon models
have attracted a lot of attention over the last few years. They give rise
to order one fifth-forces on large scales whilst masquerading as General
Relativity in our own solar system. This leaves us with the problem of
searching for them observationally. In this talk, I will describe some
recent work over the past few years at using astrophysical tests to
constrain these theories. Unscreened stars situated in Dwarf galaxies in
voids can show novel effects compared with General Relativity. They are
brighter, hotter and they pulsate faster. By exploiting these new features,
we have been able to place the strongest constraints to date and there is
little room left for these theories to hide.
Oct 15, Tuesday
1:10 pm (Cosmology-BCCP)
Cora Dvorkin, IAS
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Probing Dark Matter with the CMB and Large-Scale Structure"
I
will show that dark matter annihilation around the time of recombination can lead to growing ionization perturbations that track the linear collapse of matter overdensities. This amplifies small scale cosmological perturbations to the free electron density by a significant amount compared to the usual acoustic oscillations. Electron density perturbations distort the CMB, inducing secondary non-gaussianity. I will explain the physical processes that give rise to a CMB bispectrum at recombination.
In the last part of the talk, I will consider the possibility of dark matter-baryon interactions. I will present results from a Markov Chain Monte Carlo likelihood analysis of CMB data from the Planck satellite and measurements of the Lyman-alpha forest from the Sloan Digital Sky Survey that probe the imprints of these interactions both at large and small scales.
Oct 16, Wednesday
5:00-6:30 pm Public Lecture
David Spergel, Princeton
Wheeler Hall, 315
"Cosmology after Planck": Raymond and Beverly Sackler Distinguished Lecture in Astronomy
What happened during the first moments of the Big Bang? What is the dark energy? What were the properties of the first stars? In this free public lecture, Spergel will discuss the role of ongoing and future cosmic microwave background (CMB) observations and describe how the combination of large-scale structure, supernova and CMB data can be used to address these key questions.
Oct 17, Thursday
4:10 pm (Astronomy Colloquium)
David Spergel, Princeton
2 LeConte Hall
"Cosmology After Planck"
Oct 18, Friday
12 pm (INPA talk)
Ely Kovetz, Austin
LBL-50-5026 (INPA Common Room)
"Cosmic Bandits: Exploration vs. Exploitation in Cosmological Surveys "
Various cosmological observations consist of prolonged integrations over small patches of sky. These include searches for B-modes in the CMB, the power spectrum of 21-cm fluctuations during the epoch of reionization and deep-field imaging by telescopes such as HST/JWST, among others. However, since these measurements are hindered by spatially-varying foreground noise, the observational sensitivity can be improved considerably by finding the region of sky cleanest of foregrounds. The best strategy thus involves a tradeoff between exploration (to find lower-foreground patches) and exploitation (through prolonged integration). But how to balance this tradeoff efficiently?
This problem is akin to the multi-armed bandit (MAB) problem in probability theory, wherein a gambler faces a series of slot machines with unknown winning odds and must develop a strategy to maximize his/her winnings with some finite number of pulls. While the optimal MAB strategy remains to be determined, a number of machine-learning algorithms have been developed in an effort to maximize the winnings. By constructing adaptive survey strategies based on heuristic methods to solve the MAB problem, we will demonstrate that ground-based B-mode experiments can substantially improve the upper bound on the tensor-to-scalar ratio. Implementations of MAB strategies elsewhere are focus of current work and some pertaining issues will be discussed.
Oct 22, Tuesday
1:10 pm (Cosmology-BCCP)
Nick Battaglia, CMU
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Cosmology with the Secondary Anisotropies in the Cosmic
Microwave Background"
Measurements of the primary anisotropies in the CMB have been the
backbone of modern precision cosmology. Recently, high resolution CMB
measurements from experiments, such as the Atacama Cosmology
Telescope, the South Pole Telescope, and the Planck satellite are
probing scales where the secondary anisotropies dominate over the
primary. I will focus on the secondary anisotropies caused by the
thermal and kinetic Sunyaev Zel'dovich effects. Our ability to obtain
cosmological information from these secondaries is limited by our
theoretical understanding of the baryons in the large-scale structure
between us and the primary CMB. I will present numerical simulations
that model these baryons and attempt to constrain various cosmological
parameters. Additionally, I will discuss the wealth of astrophysical
large-scale structure information (in particular galaxy cluster
astrophysics) that is interconnected with these secondaries.
Oct 22, Tuesday
3:10 pm (GalForm)
Anna Nierenberg, UCSB
HFA B1
"Bright and dark: satellite galaxies as a test of galaxy formation and the nature of dark matter"
I present our recent measurements of the spatial distribution and the cumulative luminosity function of satellites up to a thousand times fainter than their hosts, as a function of host stellar mass and morphology between redshifts 0.1 and 0.8, using imaging from the COSMOS fields and a rigorous statistical analysis. I will demonstrate how these measurements provide powerful new constraints for abundance matching and cosmological simulations in the context of both warm and cold dark matter, and how future measurements of faint satellite colors using CANDELS, will provide important distinguishing power between warm and cold dark matter models. In addition, I will present results from a complementary gravitational lens modeling project in which we use spatially resolved spectra obtained with OSIRIS at Keck to place new constraints on the subhalo mass function.
Oct 22, Tuesday
4:00 pm (LBL RPM)
Marcel Schmittfull, UCB
LBL 50A-5132
"Large-scale structure bispectrum with modal methods, and Joint analysis of CMB temperature and lensing-reconstruction power spectra"
(70 Mb file)
The talk will be split in two independent parts:
First, I will present the implementation of a fast estimator for the full bispectrum of a three-dimensional particle distribution relying on a separable modal expansion of the bispectrum. The computational cost of accurate bispectrum estimation is negligible relative to the time required to run N-body simulations, so the isotropic bispectrum can be used as a standard diagnostic whenever the power spectrum is evaluated in simulations. As an application we measure the evolution of gravitational and primordial dark matter bispectra in N-body simulations with Gaussian and non-Gaussian initial conditions. The triangle dependence of the measured bispectra is compressed to about 50 coefficients, which is useful to confront theory with simulations and to treat correlations present in real data. In the nonlinear regime with k < 2h/Mpc we find an excellent correlation between the measured dark matter bispectrum and a simple model based on a "constant" bispectrum plus a (nonlinear) tree-level gravitational bispectrum. In the same range for non-Gaussian simulations, we find an excellent correlation between the measured additional bispectrum and a constant model plus a (nonlinear) tree-level primordial bispectrum. We demonstrate that the constant contribution to the non-Gaussian bispectrum can be understood as a time-shift of the constant mode in the gravitational bispectrum, which is motivated by the halo model. I will also discuss modal methods to efficiently create general non-Gaussian N-body initial conditions for arbitrary primordial bispectra and a wide class of trispectra.
In the second part of my talk I will address potential issues when using CMB lensing reconstructions for cosmological parameter estimation. Gravitational lensing provides a significant source of cosmological information in modern CMB parameter analyses. It is measured in both the power spectrum and trispectrum of the temperature fluctuations. These observables are often treated as independent, although as they are both determined from the same map this is impossible. We perform a rigorous analysis of the covariance between lensing power spectrum and trispectrum analyses. We find two dominant contributions coming from: (i) correlations between the disconnected noise bias in the trispectrum measurement and sample variance in the temperature power spectrum; and (ii) sample variance of the lenses themselves. The former is naturally removed when the dominant N0 Gaussian bias in the reconstructed deflection spectrum is dealt with via a partially data-dependent correction, as advocated elsewhere for other reasons. The remaining lens-cosmic-variance contribution is easily modeled but can safely be ignored for a Planck-like experiment, justifying treating the two observable spectra as independent. We also test simple likelihood approximations for the deflection power spectrum, finding that a Gaussian with a parameter-independent covariance performs well. The Planck lensing likelihood is based on the results obtained in this work."
Oct 25, Friday
12 pm (INPA talk)
Jeff Newman, Pittsburgh
LBL-50-5026 (INPA Common Room)
"Exploring the Third Dimension: Why Imaging Dark Energy experiments need DESI"
This talk will explore a number of applications of wide-area spectroscopic surveys, such as those DESI will provide, to solving key problems for imaging dark energy experiments. First, I will discuss the problem of photometric redshifts (a.k.a. photo-z's): i.e., estimates of the redshifts of objects based only on flux information obtained through broad filters. Higher-quality, lower-scatter photo-z's will result in smaller random errors on cosmological parameters; while systematic errors in photometric redshift estimates, if not constrained, may dominate all other uncertainties from these experiments. In this talk, I will describe the key challenges for training and calibrating photometric redshift algorithms in the next two decades, and describe how DESI can help us address these challenges. Second, I will discuss the contributions the DESI instrument can make to LSST supernova studies by measuring spectroscopic redshifts for large samples of supernova hosts, which would require comparatively modest time allocations. Finally, I will describe the new LSST Dark Energy Science Collaboration and how each of us can get involved now in preparing for this extraordinarily rich dataset.
Oct 29, Tuesday
1:10 pm (Cosmology-BCCP)
Michael Kopp, LMU
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Beyond single-streaming dark matter with the Schroedinger method"
We extend a method originally proposed by Widrow and Kaiser (1993, ApJ 416) as an alternative to cosmological N-body simulations of dark matter, to cosmological perturbation theory. This so called Schroedinger method makes use of a mathematical mapping between the Schroedinger-Poisson and Vlasov-Poisson equations to obtain an approximate phase space distribution function, which thereby models self-gravitating multi-streaming collisionless dark matter. We find that the resulting hierarchy of moments is truncated automatically, similar to the case of the single streaming dust fluid. The first two moments - the continuity and an Euler-type equation - therefore encode multi-streaming phenomena, while being at the same time not much more complicated than the corresponding equations of a dust fluid.
We derive Lagrangian and Eulerian perturbation theory kernels up to third order and test them against N-body simulations and the standard perturbation theory kernels by examining the two-point correlation function of dark matter halos both within the N-body simulation and using Convolution Lagrangian Perturbation Theory, proposed by Carlson et al. (2012, MNRAS 429).
September 2013:
Sep 3, Tuesday
1:10 pm (Cosmology-BCCP)
Nuala McCullagh, JHU
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Modeling the Nonlinear and Redshift-space Behavior of Baryon Acoustic Oscillations"
In order to accurately constrain cosmological parameters using Baryon Acoustic Oscillations (BAO), we must model the effects of nonlinearity and redshift-space distortions on the location and shape of the acoustic peak. I will present a method of calculating the nonlinear correlation function in configuration space using the Zel'dovich Approximation. I will show that working in configuration space can simplify the higher-order terms in perturbation theory, and that the result can be straightforwardly extended to redshift-space. This configuration-space model of the nonlinear correlation function can also be used to understand the effects of local density transformations on the BAO peak location.
Sep 10, Tuesday
1:10 pm (Cosmology-BCCP)
Elisabeth Krause, Penn
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Combining Probes of Large-Scale Structure in the Precision Cosmology Era"
The ongoing Dark Energy Survey and other upcoming large-scale structure surveys aim to determine the composition of the Universe and the nature of dark energy by mapping the spatial distribution and shapes of hundreds of millions of galaxies. These data sets will enable precision measurements of various observables of large-scale structure, such as weak lensing, galaxy clustering, and the abundance of galaxy clusters. These observables probe different aspects of cosmic structure formation, and combining them improves constraints on cosmology significantly. In this talk I will introduce the analysis framework for the joint analysis of probes of large-scale structure currently under development for the Dark Energy Survey. In particular, I will discuss systematic uncertainties and cross-correlations of observables in detail, and outline extensions of these methods to future data sets.
Sep 17, Tuesday
1:10 pm (Cosmology-BCCP)
Matthias Steinmetz, Potsdam
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"The Wobbly Galaxy: kinematics north and south with RAVE"
he RAVE survey is the largest systematic spectroscopic survey of the Milky Way performed to date. Almost 600 000 spectra for nearly 500 000 stars have been taken. At a resolution of R=7500 in the CA triplet region, RAVE spectra allow to measure radial velocities, stellar parameters, abundances of several chemical elements, and, combined with photometric information, fairly precise distances.
Combined with proper motions, the RAVE survey can be used to study in detail stellar kinematics in the extended solar neighbourhood (solar suburb). We examine the mean velocity components in 3D between an R of 6 and 10 kpc and a Z of -2 to 2 kpc, concentrating on North-South differences. We confirm the recently discovered gradient in mean Galactocentric radial velocity, VR, finding that the gradient is more marked below the plane, with a Z gradient also present. The vertical velocity, VZ, also shows clear structure, with indications of a rarefaction-compression pattern, suggestive of wave-like behaviour. The complex three-dimensional structure of velocity space presents challenges for future modelling of the Galactic disk, with the Galactic bar, spiral arms and excitation of wave-like structures all probably playing a role.
Sep 24, Tuesday
1:10 pm (Cosmology-BCCP)
Alex Mendez, UCSD
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Star Formation Quenching and AGN in Galaxies"
I will discuss two observational projects related to galaxy and active galactic nuclei (AGN) evolution at z < 1. First I will present a statistical study of the morphologies of galaxies in which star formation is being shut down or quenched; this has implications for how red, elliptical galaxies are formed. I will discuss the physical processes behind star formation quenching from the morphological transformations that galaxies undergo during this process. Then I will focus on multi-wavelength AGN selection methods and tie together disparate results in the literature. Several IR-AGN selection methods have been developed using Spitzer/IRAC data in order to supplement traditional X-ray AGN selection; I will characterize the uniqueness and complementarity of these methods as a function of both IR and X-ray depth. I will use data from the PRIsm MUlti-object Survey (PRIMUS) to compare the efficiency of IR and X-ray AGN selection and discuss the properties of the AGN and host galaxy populations of each. Finally, I will briefly mention ongoing work to compare the clustering of observed IR and X-ray AGN samples relative to stellar mass-matched galaxy samples.
Sep 27, Friday
12:00 pm (INPA talk)
Paul M. Sutter, Paris
LBL Bldg. 50, room 5026 (the INPA common room)
"Cosmology and astrophysics with cosmic voids"
Voids are the large, underdense regions in the cosmic web.
While they are obviously useful cosmological probes, due to their
intimate connection to the growth of structure, they are also
interesting places to study astrophysics such as neutrino mass and
primordial magnetic fields. I will present the latest work to identify
voids in galaxy redshift surveys, how they connect to underdensities
in dark matter, and the first results in exploiting their properties
(sizes, shapes, interior contents) for scientific gain.
Aug 2013:
Aug 9, Friday
12:00 pm (INPA talk)
Julien Guy, Paris
LBL Bldg. 50, room 5026 (the INPA common room)
Improved cosmological constraints from the joint analysis of the
SDSS and SNLS Type Ia supernova samples
I will present recent progress in the measurement of cosmological
parameters with type Ia supernovae which result mainly from a
significant improvement in the photometric calibration of the SNLS
and SDSS surveys.
The high supernova statistics gathered recently, combined with a
sub-percent accuracy in the relative flux calibration, allows us to
map the variations of the luminosity distance as a function of z with
a relative precision of about 3% in logarithmic redshift bins
delta_z/z = 0.5 between to z = 0.02 and z = 0.7. This approach is,
today, the most sensitive probe of Dark Energy. Combining with the
recent CMB measurement from Planck, we obtain an accuracy better than
6% on the equation of state parameter w.
Aug. 13, Tuesday
1:10 pm (Cosmology-BCCP)
Yu Feng, CMU
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Modeling quasars at two extremes"
In this talk we look at the modeling of quasars with simulations: (i)
how they form, grow and interact with the host; and (ii) how they
cluster with the matter (esp. Lyman alpha forest). Both topics are of
great interest in cosmology, yet different scales require different
approximations and treatments. For the first, we simulate super massive
black-holes under thermal feedback model in SPH cosmological simulations
and re-simulations with zoomed initial conditions (~ hundred Mpc/h box).
For the second, we mock quasar clustering with Lyman alpha forest with
linear theory on a nested mesh(~ ten Gpc/h box).
Aug. 20, Tuesday
1:10 pm (Cosmology-BCCP)
Nathan Whitehorn, UW-Madison
Hearst Field Annex, B1 (also videoconferenced to 50-5026)
"Evidence for High-Energy Astrophysical Neutrinos at IceCube"
The origin of high-energy cosmic rays is one of the most persistent mysteries in
physics. Neutrinos, as neutral tracers of hadronic acceleration, may offer a new and unique window into this problem and others in high-energy astrophysics.
I will discuss recent results from the antarctic IceCube neutrino observatory, showing the first evidence for a population of extremely high energy nuetrinos (100+TeV) that cannot easily be explained by processes uccurring in cosmic ray showers in the Earth's atmosphere and may be the first evidence for a population of high-energy neutrinos of extraterrestrial origin.
Aug 30, Friday
12:00 pm (INPA talk)
David Harvey, ROE
LBL Bldg. 50, room 5026 (the INPA common room)
'On measuring the cross-section of dark matter using substructure infall into galaxy clusters'
Recent studies of galaxy clusters has provided loose evidence for the existence of self interacting dark matter. These measurements on single cluster environments and major mergers have suffered from assumptions on the time of in-fall, orientation of impact and line of sight projections. In this talk, I will present a unique method to measure the interaction cross-section of dark matter using an ensemble of galaxy clusters, which is independent of all these factors. Using hydrodynamical simulations, I will show that one should be able to constrain the cross-section to extremely high accuracy using only 40 clusters, a typical sample size one would expect from the Hubble archive. I will finish by commenting on how one would be able to extend this theory to missions such as Euclid and LSST.
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