April 2014:
Apr. 1, Tuesday
1:10 pm (Cosmology/BCCP)
Joe Hennawi, MPIA
Hearst Field Annex B-1
"Probing the Circumgalactic Medium in Absorption and Emission"
I will argue that observations of the diffuse gas in the outskirts of galaxies, the so called circumgalactic medium, are essential for constraining the 'initial conditions' for galaxy formation. Such observations provide a fruitful comparison to theory, because hydrodynamics at moderate overdensities is much easier to simulate than molecule or star-formation. A novel technique will be introduced, whereby a foreground quasar (and massive galaxy) can be studied in absorption against a background quasar, resolving scales as small as 30kpc. This experiment reveals a rich absorption spectrum which contains a wealth of information about the physical conditions of diffuse gas around massive proto-galaxies. I will summarize the implications of these new measurements in the context of galaxy formation models, and also discuss a sensitive search for emission from the same gas we study in absorption.
Apr. 3, Thursday
4:10 pm (Astronomy Colloquium)
Richard Ellis, Caltech
1 LeConte Hall
"Observations of Star Forming Galaxies in the Heart of the Reionization Era"
Deep exposures with the Hubble Space Telescope (HST) have provided the primary evidence that star-forming galaxies were present in the first billion years of cosmic history. Sometime during this early period the intergalactic medium transitioned from a neutral gas to one that is fully ionized. How did this `cosmic reionization' occur and were star-forming galaxies responsible? The electron scattering optical depth inferred from cosmic microwave background observations suggests that reionization occurred sometime in the redshift interval z=20 to z=6 so probing the abundance, luminosity distribution and spectral properties of galaxies during this uncharted period holds the key to addressing these fundamental questions. Recent imaging with HST's Wide Field Camera 3 in conjunction with Spitzer photometry and Keck spectroscopy has provided important new insight into understanding when reionization occurred and the role of early galaxies in the process. I will review this progress and discuss the remaining challenges ahead of future facilities such as TMT and JWST.
Apr. 4, Friday
12:00 noon (INPA talk)
Yuji Chinone, Blake Sherwin, Aritoki Suzuki, UCB
LBL 50-5026
"POLARBEAR's CMB B-modes, Bolometers, and the Future"
The POLARBEAR cosmic microwave background experiment, led by Berkeley, published the first CMB-only detection of CMB B-mode polarization in December and the first measurement of the B-mode power spectrum three weeks ago, on small angular scales from gravitational lensing. A tag team of postdocs will describe the detector and hardware advances that made this possible, the results and their science implications, and future plans for detailed constraints on inflation, dark energy, and neutrino mass.
Apr. 8, Tuesday
1:10 pm (Cosmology/BCCP)
Jolyon Bloomfield, MIT
Hearst Field Annex B-1
"The State of Dark Energy Theory"
Recently, a number of models describing general theories of dark energy have been constructed. Five separate lines of inquiry employing very different techniques have now converged to approximately the same general description. I will present a general overview of the theory space of dark energy and modified gravity models, before describing how the different approaches aim to construct a general model. I will focus on two effective field theory approaches, but aim to give an overall picture of the present state of dark energy theory, and efforts being taking towards the comparison of theory with observations.
Apr. 15, Tuesday
1:10 pm (Cosmology/BCCP)
Shy Genel, CfA
Hearst Field Annex B-1
"The Illustris simulation: novel successes and remaining failures in modelling galaxy formation"
I will present first results from the Illustris simulation, which is a cosmological hydrodynamical simulation using 2*1820^3 resolution elements. The simulation follows thousands of massive galaxies down to z=0 inside a (100Mpc)^3 volume, resolving < ~kpc scales. It is run using the Arepo code to model gravity and hydrodynamics, as well as cooling, stellar population evolution, and various feedback processes. I will discuss a broad range of observables at z= 0 ->5 that Illustris matches reasonably well (and not particularly tuned for), including galaxy masses, morphologies, and spatial distributions. I will also present points of failure that can guide us how to further improve our models.
Apr. 15, Tuesday
3:40 pm (String seminar)
Eva Silverstein, Stanford/SLAC
402 Old Leconte
"Gravity waves and large-field inflation in string theory"
Apr. 22, Tuesday
1:10 pm (Cosmology/BCCP)
Leonardo Senatore, Stanford
Hearst Field Annex B-1
The Effective Field Theory of Large Scale Structures
After discussing briefly some implications for Inflation after BICEP2, I will focus on Large Scale Structures surveys, as they promise to be the next leading probe of cosmological information. It is therefore crucial to reliably predict their observables. The Effective Field Theory of Large Scale Structures (EFTofLSS) provides a manifestly convergent perturbation theory for the weakly non-linear regime of dark matter, where correlation functions are computed in an expansion of the wavenumber k of a mode over the wavenumber associated with the non-linear scale k_nl. Since most of the information is contained at high wavenumbers, it is necessary to compute higher order corrections to correlation functions. I will present the predictions of the EFTofLSS up to 2-loops. We find that it matches to percent accuracy the non-linear matter power spectrum up to k~0.6 h/Mpc, requiring just one unknown coupling constant that needs to be fit to observations. Given that Standard Perturbation Theory stops converging at k~0.1 h/Mpc, our results demonstrate the possibility of accessing a factor of order 200 more dark matter quasi-linear modes than naively expected. If the remaining observational challenges to accessing these modes can be addressed with similar success, our results show that there is tremendous potential for large scale structure surveys to explore the primordial universe.
Apr. 24, Thursday
4:10 pm (Astronomy Colloquium)
Lucio Mayer, ETH (note change in speaker)
1 LeConte Hall
Formation pathways for massive BH seeds and their subsequent evolution as massive black holes binaries in gas-rich galaxy mergers
The emergence of bright Quasars as early as z >~ 7 strongly
suggests the existence of a rapid pathway to form supermassive black holes.
Conventional models
based on the growth of light BH seeds from primordial Population III stars
have difficulties in explaining such a rapid assembly. As a result, models
in which massive BH seeds form by direct gas collapse in protogalaxies
have received significant attention in the last few years. In the most
common variants such models rely on fairly idealized thermodynamical
conditions of gas flows in protogalaxies, such as suppression of cooling
via dissociation of molecular hydrogen and metal-free gas in order
to suppress fragmentation. We have
recently developed a novel formation scenario that does not rely on
any of such restrictive conditions (Mayer et al. 2010, Nature, 466, 1082).
It is based on mergers between the most massive, already metal enriched protogalaxies at z < ~ 10, in which
gas inflows in excesse of 10^4 Mo/yr can arise in less than 10^5 yr following
the merger. The latter give rise to supermassive, gravitationally unstable
nuclear clouds with masses in excesse of 10^8 Mo. These are likely
precursors of massive BH seeds that could form after a short supermassive star
and/or a quasi-star phase. I will show new simulations which
confirm this scenario further using more sophisticated
radiative cooling , highligthing the role of gravitoturbulence
in achieving prominent inflows while minimizing the effect
of fragmentation and star formation in the nuclear gas.
Using the Millenium simulations
combined with the latest semi-analytical galaxy formation models with
black hole growth we compare our scenario with a Pop III-based scenario.
We find specific signatures of massive BH seeds formed by our direct collapse
in the clustering and morphology of the host galaxies at both high and
low redshift. Our model is so far the only one consistent with very recent
determinations of the accreting SMBH population in dropout galaxies at z~6-8.
Apr. 29, Tuesday
1:10 pm (Cosmology/BCCP)
Charlie Conroy, UCSC
Hearst Field Annex B-1
"Extragalactic Archeology"
One of the primary avenues for understanding the formation and evolution of galaxies is through studying their stellar populations. A new generation of population synthesis tools that we have been developing are now capable of measuring an unprecedented amount of information from high quality spectra of galaxies. In this talk I will present results from an ongoing program aimed at measuring the stellar initial mass function, ages, and detailed elemental abundance patterns of early-type galaxies over the interval 0 < z < 1. Constraints on the abundances of the alpha, iron peak, and neutron capture elements offer the promise of reconstructing the detailed star formation histories of these now dormant galaxies. By measuring the evolution of these quantities through cosmic time we are gaining fresh insights into the assembly histories of galaxies. The techniques we are developing will enable `extragalactic chemical tagging' and, more generally, will open up the low resolution universe for detailed study.
May 2014:
May 20, Tuesday
4:00 pm (RPM)
Marc Postman, STScI
LBL 50A-5132
The Cluster Lensing and Supernova Survey with Hubble
The Cluster Lensing And Supernova survey with Hubble (CLASH) combines the gravitational lensing power of 25 massive clusters with the panchromatic imaging power of HST. It's four primary scientific objectives are 1) map, with unprecedented accuracy, the distribution of dark matter in galaxy clusters and place constraints on the nature of the dark matter, 2) detect Type Ia supernovae out to redshift z ~ 2, allowing us to test the constancy of dark energy's repulsive force over time and look for any evolutionary effects in the supernovae themselves, 3) detect and characterize some of the most distant galaxies yet discovered at z > 7 (when the Universe was younger than 800 million years old, and 4) study the internal structure and evolution of the galaxies in and behind these clusters. The survey was completed this past July after 3 years and 525 orbits of time. I will present the major highlights from this rich publicly available dataset.
Past Months
(Previous years)
March 2014:
Mar. 4, Tuesday
1:10 pm (Cosmology/BCCP)
Sam Skillman, Stanford/SLAC
Hearst Field Annex B-1
"Radio Emission in Galaxy Clusters: Insights from Cosmological Simulations"
Galaxy clusters are unique astrophysical laboratories that contain many thermal and non-thermal phenomena that demand a coordinated effort from theory, numerical simulations, and observations. After discussing a few of the major open questions in galaxy cluster formation and evolution, I'll present our recent work in attempting to model the non-thermal cosmic-ray population present in clusters. It is proposed that cosmic shocks that propagate through the intracluster medium form through the process of structure formation, and may be capable of accelerating charged particles through diffusive shock acceleration. These relativistic particles decay and radiate through a variety of mechanisms, and have observational signatures in radio, hard X-ray, and Gamma-ray wavelengths. Modelling these dynamics require a combination of cosmological hydrodynamics coupled with a model to follow the momentum-space distribution of cosmic ray electrons and protons. We have implemented such a model by combining Enzo, an Adaptive Mesh Refinement hydrodynamics + N-body particle-mesh gravity solver, with a numerical library for cosmic ray transport. I will end with a look to what future observatories in the radio, X-ray, and sub-mm may uncover and what new capabilities our simulations must have to understand fundamental physical processes present in galaxy clusters.
Mar. 11, Tuesday
1:10 pm (Cosmology/BCCP)
Andrey Kravtsov, Chicago
Hearst Field Annex B-1
"Order out of chaos: stellar masses and sizes of galaxies and their host dark matter halos"
Galaxy formation is a complex, hierarchical, highly non-linear
process, which involves gravitational collapse of dark matter and
baryons, supersonic, highly compressible and turbulent flows of gas,
cooling and heating of gas, star formation, and stellar feedback.
Nevertheless, despite the apparent complexity of these processes, galaxies
exhibit a number of striking regularities, such as tight correlations
between galaxy sizes and stellar masses and the mass and extent
of their parent halos dominated by dark matter. I will discuss our
current understanding of halo structure and physical motivation for
the definition of halo radius and mass. I will also summarize
the relations between stellar mass and halo mass and galaxy
sizes and halo virial radius. I will show that the latter relation is close
to linear, which indicates that sizes of galaxies of all types are set by specific
angular momentum induced by gravitational torques during galaxy formation.
In addition, I will show that stellar surface density profiles of galaxies of
different morphological types at radii beyond half-mass radius have similar shape.
The stellar mass-halo mass relation is tight, but its shape is complex
and is determined by the complicated physics of star formation and feedback.
I will show that the current generation of galaxy formation simulations
is capable of reproducing the shape of this relation with reasonable set of
assumptions about feedback physics.
Mar 13, Thursday
4:10 pm (Astronomy Colloquium)
Feryal Ozel, Arizona
1 LeConte Hall
Mar. 18, Tuesday
1:10 pm (Cosmology/BCCP)
Danilo Marchesini, Tufts
Hearst Field Annex B-1
"New Insights into the Formation and Evolution of the Most Massive Galaxies"
In the past decade, our understanding of the galaxy population in the last 12 billion years of cosmic history (i.e., since z=4) has improved significantly, thanks to the increasing ability to construct representative snapshots (in time) from z=4 (when the universe was ~1.5 billion years old) to the local universe. I will summarize our current knowledge of the evolution of massive galaxies since z=4, with an emphasis on the recent results from the UltraVISTA survey. I will conclude by presenting new findings on the evolution since z=3 of the progenitors of local ultra-massive galaxies, challenging previously proposed pictures for the formation and evolution of massive elliptical galaxies.
Mar. 25, Tuesday
spring break-no talk
Feb 2014:
Feb. 3, Monday
12:10 pm (TAC)
Julie Hlavacek Larrondo, SLAC/Stanford
Hearst Field Annex B-1
"Rise of the titans, the biggest black holes in the Universe"
One of the most fascinating discoveries in modern astrophysics has been the realization that massive black holes can have a profound impact on their host galaxies. This impact appears mostly in the form of AGN feedback and during this talk, I will review the current status of this field while focusing on the most massive black holes in the Universe, those that lie at the centres of clusters of galaxies. I will address how AGN feedback evolves in such systems over the last 8 Gyrs, and discuss the implications of these results in terms of our understanding of black hole physics.
Feb. 4, Tuesday
1:10 pm (Cosmology/BCCP)
Andrew Hearin, Fermilab
Hearst Field Annex B-1
"The Dark Side of Galaxy Evolution"
n this talk, I discuss recent developments in our understanding of the galaxy-halo connection, with a particular focus on the co-evolution of galaxies and dark matter halos. I will discuss the newly introduced age matching technique and describe the wide variety of successes this model achieves with very few ingredients. Moreover, I will show how the success of this model has exposed fundamental degeneracies in traditional approaches to galaxy-halo modeling. I conclude by outlining a plan for the path forward to breaking these degeneracies, so that we may reap the benefits of deep and wide-field galaxy surveys to develop a complete picture of galaxy evolution and contribute to the precision cosmology program with galaxy clustering measurements.
Feb. 6, Thursday
12:40 pm (Astro Thursday Lunch)
includes 10-15 min talk from
Paul Shellard, Planck Non-Gaussianity and Inflation
Wheeler 210
Feb. 11, Tuesday
1:10 pm (Cosmology/BCCP)
McCullen Sandora, Davis
Hearst Field Annex B-1
"Spherical Cows in the Sky with Fab Four"
We explore spherically symmetric static solutions in a subclass of
unitary scalar-tensor theories of gravity, called the `Fab Four'
models. The weak field large distance solutions may be
phenomenologically viable, but only if the Gauss-Bonnet term is
negligible. Only in this limit will the Vainshtein mechanism work
consistently. Further, classical constraints and unitarity bounds
constrain the models quite tightly. Nevertheless, in the limits where
the range of individual terms at large scales is respectively Kinetic
Braiding, Horndeski, and Gauss-Bonnet, the horizon scale effects may
occur while the theory satisfies Solar system constraints and,
marginally, unitarity bounds. On the other hand, to bring the cutoff
down to below a millimeter constrains all the couplings scales such
that `Fab Fours' can't be heard outside of the Solar system.
Feb. 14, Friday
12:00 pm (INPA)
Donough Regan, Sussex
LBL 50-5026 (INPA room)
What CMB non-Gaussianity tells us about Effective Field Theories of Inflation
The Lagrangian of the effective field theory of single field inflation has only a finite number of operators, with each giving a specific bispectrum shape. Decomposing into partial waves, a likelihood function is constructed. This is then used to constrain up to four linearly independent combinations of the coefficients. A Bayesian comparison test is carried out with results suggesting that models with two or more free parameters are disfavoured by the data.
Feb. 18, Tuesday
1:10 pm (Cosmology/BCCP)
Karen Gibson, CWRU
(LUX)
Feb. 25, Tuesday
1:10 pm (Cosmology/BCCP)
Carlos Cunha, KIPAC/SLAC
Hearst Field Annex B-1
"Photometric Redshifts: the long road ahead"
Uncertainties in photometric redshifts are one of the key systematics for existing and up-coming large, optical+NIR, surveys such as DES, HSC and LSST. I will review the basics of photo-zs, go over existing plans for obtaining spectroscopic follow-up and present my view of what the next steps of the field should be if we hope to end up with trustworthy cosmological constraints from future surveys.
Feb. 27, Thursday
4:10 pm (Astronomy Colloquium)
Michael Cooper, UCI
1 LeConte Hall
"Expanding the Low-Mass Galaxy Frontier"
While modern models of galaxy evolution have made significant strides in explaining the observed properties of massive galaxies over cosmic time, recent observational results have illustrated a fundamental problem with the ability of these same models to predict the evolution of low-mass systems. In particular, simulations of galaxy evolution tend to overpredict the number of passive (or "quenched") low-mass satellite galaxies at low and intermediate redshift. Using data from the SDSS, I will present recent work to constrain the quenching of satellite galaxies in the local Universe, with a focus on identifying the host and satellite properties critical to the cessation of star formation at low stellar masses. This analysis, when combined with observations of the Local Group, points towards a characteristic mass scale for satellite quenching as well as strong limits to our understanding of dwarf galaxies. As time permits, I will present ongoing efforts to expand our knowledge of this low-mass galaxy frontier.
January 2014:
Jan. 21, Tuesday
1:10 pm (Cosmology/BCCP)
Jeff Filippini, Caltech
Hearst Field Annex B-1
"Casting a cold eye on the dark universe"
Decades of work by countless astrophysicists have built a quantitative understanding of the composition, history, and fundamental laws of our cosmos. Despite these successes major mysteries remain, among them the nature of the dark matter in our universe and the physics behind the inflationary epoch at its beginning. These and other mysteries suggest new fundamental physics waiting to be discovered. I will describe two efforts to probe such fundamental mysteries with novel low-temperature instrumentation. The first is the quest to directly detect the interactions of dark matter in detectors deep beneath the earth's surface, in particular those of the Cryogenic Dark Matter Search (CDMS). The second is a suite of instruments to observe the imprint of cosmic inflation on the polarization of the cosmic microwave background from vantage points on (BICEP2, Keck) and far above (SPIDER) the Antarctic ice. Each of these instruments employs novel sub-Kelvin detectors to achieve the exquisite sensitivity and control of systematic errors needed to push forward the frontiers of these and future endeavors.
Jan. 23, Thursday
4:10 pm (Astronomy Colloquium)
Claude-Andre Faucher-Giguere, Berkeley/Northwestern
1 LeConte Hall
"Feedback-regulated star formation on galactic and cosmological scales"
A central problem in galaxy formation is to understand why star formation is so inefficient. Within individual galaxies, gas is converted into stars at a rate two orders of magnitude slower than unimpeded gravitational collapse predicts, a fact embodied in the low normalization of the observed Kennicutt-Schmidt (K-S) relationship between star formation rate surface density and gas surface density. Star formation in galaxies is also globally inefficient in the sense that the stellar mass in dark matter halos is a small fraction of the universal baryon fraction. I will show that these two facts can be explained by the self-regulation of star formation by feedback from massive stars. Within galaxies, stellar feedback drives turbulence that supports the interstellar medium against collapse and the K-S law is set by the low strength of gravity relative to stellar feedback. The energy input from the same stellar feedback processes drive powerful galactic outflows that remove most of the gas accreted from the intergalactic medium before it has time to turn into stars. Using cosmological hydrodynamical simulations from our FIRE project ("Feedback In Realistic Environments"), I will show that gas removal by star formation-driven galactic winds successfully explains the observed galaxy stellar mass function, at least for galaxies less massive than the Milky Way, and discuss the observational signatures of circum-galactic gas flows. Feedback from massive black holes may be required to explain the quenching of galaxies much more massive than the Milky Way.
Jan. 27, Monday
12:10 pm (TAC seminar)
Evan Scannapieco, ASU and UCB
Hearst Field Annex B-1
"Feedback and Turbulence in Galaxy Formation"
Feedback and turbulence play a key role in galaxy formation, impacting issues ranging from the evolution of the galaxy luminosity function, to the establishment of the galaxy mass-metallicity relation, to the transition of Population III to modern-day star formation. I will review ongoing efforts by my group to better understand these processes, focusing on three topics: (i) the use of subgrid-scale turbulence modeling to simulate supernova-driven outflows from starbursting galaxies and predict their observational properties; (ii) the use of direct numerical modeling to study the turbulent mixing of metals into supersonic, magnetized, and metal-free media; (iii) the use of cosmic microwave background observations to constrain feedback from active galactic nuclei.
Jan. 28, Tuesday
1:10 pm (Cosmology/BCCP)
Marcel van Daalen, Leiden
Hearst Field Annex B-1
"The effects of galaxy formation on clustering"
The observed clustering of both galaxies and matter provide important constraints on both cosmology and models of galaxy formation. Even though the dissipation, and more importantly the feedback processes associated with galaxy formation are thought to affect the distribution of matter, essentially all models used to predict clustering data are based on dark matter only simulations. Using hydrodynamical simulations, I will show how galaxy formation affects different measures of clustering, on a wide range of scales. I will demonstrate that the changes due to the inclusion of baryons are larger in magnitude, affect a wider range of scales and may even have a different sign than what is often assumed. I will also discuss how these changes in clustering relative to the dark matter only scenario arise, how they affect our ability to determine cosmological parameters, and how we may be able to account for them.
Jan. 31, Friday
12:00 pm (INPA)
Francisco Prada, Instituto de Fisica Teorica UAM/CSIC, Madrid
LBL 50-5026 (INPA room)
"Hunting down the acoustic scale after the cosmic high noon"
The discovery of cosmic acceleration has motivated the development of large experiments that aim to measure the expansion history of the universe and growth of structure with high precision at the 0.1-1% level. Ongoing and future galaxy, QSO and Ly-alpha surveys rely on the Baryon Acoustic Oscillation (BAO) technique which has undergone an enormous progress since the BAO feature was detected for the first time in the SDSS-II and 2dFGRS galaxy clustering. With the completion of BOSS in 2014, the current results for the galaxy survey predicts an improvement of 1% precision, which will be superseded by new experiments such as DESI and Euclid. Both surveys aim to measure the BAO scale to the sub-percent level over a wide redshift range 0.5 < z < 3.5, thus, providing unprecedented constraints on the dark energy equation of state. The new generation dark energy experiments also impose severe challenges on understanding any possible systematic shifts in the BAO signature due to nonlinear gravitational growth and scale-dependent bias to a high precision better than the measured statistical uncertainties. I'll present the new suite of BigMultiDark Planck simulations with large volume and high enough resolution to resolve the distinct and subhalo dark matter halo population that host typical BOSS galaxies. This allows for the first time to have a precise measurement of the halo BAO shifts and damping, and scale-dependent bias; which result very relevant for the interpretation of current and future galaxy surveys.
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.
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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