Upcoming Seminars of possible interest to people in the Berkeley Cosmology Group 2004-2005


Physics/Astronomy C290C
The Physics/Astronomy C290C series consists of the LBNL-Physics-Astronomy Cosmology seminars held Tuesdays at 1:10 in room 544 Campbell Hall. (Feel free bring your lunch.)

Please contact Joanne Cohn to add to this list or to suggest speakers.

Note that there are also other talks which generally might be of interest, including

June 2005:

June 13-17 all day
LBL Cosmology Summer Visitor Program: Cosmology with the Ly-alpha Forest
Note: this will be mostly intensive discussion sessions, rather than formal talks.
July 2005:
August 2005:

Aug. 2 (Tuesday) 1:10 pm
Michele Cappellari, Leiden
544 Campbell Hall
tba

Aug. 3 (Wednesday) 1:10 pm
Eric Gawaiser,
544 Campbell Hall
tba

September 2005:

October 2005:

Oct. 11 (Tuesday) 1:10 pm
Raul Jimenez, U Penn
544 Campbell Hall
(ACT)
Past Months
May 2005:
May 2 (Monday) 12:10 pm (TAC seminar)
Tom Abel, Stanford
544 Campbell Hall
tba

May 3 All Day
Bay Area Friends of Cosmology Workshop: Cosmology from Astronomical objects
(Berkeley-Stanford-Santa Cruz) at Stanford/SLAC
KIPAC Institute, Redwood C/D conference room at SLAC
for info and to register, email Marusa Bradac AND Marina Shmakova

PROGRAM (preliminary)

May 10 (Tuesday) 1:10 pm
no talk 544 Campbell Hall
tba

May 17 (Tuesday) 1:10 pm
Andrey Kravtsov, U Chicago
544 Campbell Hall
"High-resolution cosmological simulations of galaxy clusters"
I will describe high-resolution self-consistent cosmological simulations of clusters forming in the concordance Cold Dark Matter model with vacuum energy. The simulations follow dissipationless dark matter and stars and dissipative gasdynamics components and include a number of physical processes critical to galaxy formation (e.g., radiative cooling, star formation, stellar feedback and metal enrichment). Adaptive Mesh Refinement is used to greatly increase the resolution in the high density regions. The resolution of the simulations is sufficiently high to resolve formation and evolution of cluster galaxies and their impact on cluster gas. We use these simulations to study the effects of galaxy formation on the global properties of clusters, such as the shape of cluster dark matter halo and its density profile, the baryon fractions, gas density and temperature profiles. I will present comparisons of simulations results with the recent X-ray Chandra, Sunyaev-Zeldovich, and optical observations of clusters with highlights of both successes and problems of the models.

May 24 (Tuesday) 1:10 pm
Roy Gal, UC Davis 544 Campbell Hall
"Galaxy clusters and large scale structure to z~1"
Galaxy clusters and superclusters provide laboratories for galaxy evolution in dense environments as well as constraints on structure formation and cosmology. Comparison of clusters and large-scale structure at low and high redshifts requires the production of well- understood samples at a range of epochs. At z<0.3, we have recently completed a cluster survey over the high-galactic latitude northern sky, with over 16,000 cluster candidates. I will also discuss an ongoing project to detect and study large scale structure around z>0.5 galaxy clusters, highlighting our first results on the Cl1604 supercluster at z~0.9.

May 31 (Tuesday) 1:10 pm
Nikhil Padmanabhan, Princeton
544 Campbell Hall
"Detecting Dark Matter Annihilation with CMB Polarization : Signatures and Experimental Prospects"
Dark matter (DM) annihilation during hydrogen recombination (z ~ 1000) will alter the recombination history of the Universe, and affect the observed CMB temperature and polarization fluctuations. Unlike other astrophysical probes of DM, this is free of the significant uncertainties in modelling galactic physics, and provides a method to detect and constrain the cosmological abundances of these particles. We parametrize the effect of DM annihilation as an injection of ionizing energy at a rate e_{dm}, and argue that this simple "on the spot'' modification is a good approximation to the complicated interaction of the annihilation products with the photon-electron plasma. Generic models of DM do not change the redshift of recombination, but change the residual ionization after recombination. This broadens the surface of last scattering, suppressing the temperature fluctuations and enhancing the polarization fluctuations. We use the temperature and polarization angular power spectra to measure these deviations from the standard recombination history, and therefore, indirectly probe DM annihilation.

April 2005:
Apr. 4 (Monday) 12:10 pm (TAC seminar)
Greg Bryan, Columbia
544 Campbell Hall
"Understanding the Formation and Evolution of X-ray Clusters"
The new X-ray observatories have unleashed an explosion of data about the hot gas in galaxy clusters, in the process overturning cherished theories and posing new puzzles, particularly about the impact of AGN on the thermal state of the cluster gas. I review what can be understood from observations, simple theory and high-resolution numerical simulations, showing show that in some areas -- such as the temperature profile at large radii -- the latest observational results are in surprisingly good agreement with theory. On the other hand, the impact of cooling and heating on the core, and on global scaling relations are still not perfectly well understood (although we have made considerable progress). I use new simulations to show that there are, in fact, two separate heating/cooling issues in galaxy clusters and the resolution of these issues may tell us something very important about high-redshift galaxy formation.
Apr. 5 (Tuesday) 1:10 pm
Andreas Berlind, NYU
544 Campbell Hall
"The Physics that Drives Galaxy Clustering"
Understanding the processes that drive galaxy clustering has always been one of the main goals of observational cosmology. In particular, the physical explanation for the approximately power-law shape of the galaxy two-point correlation function on small scales is still an open problem. The physics of galaxy formation, which almost certainly plays a role in determining how galaxies of different types and luminosities are clustered, is complicated and includes such poorly understood processes as gas cooling, star formation, and feedback. However, there is recent evidence that gravitational dynamics alone can explain the basic features of galaxy clustering. We investigate gravitational mechanisms such as the merger history of halos, and dynamical friction and tidal stripping of halos after they merge into larger systems, and we show how these mechanisms are largely responsible for shaping the observed clustering of galaxies.

Apr. 6 (Wednesday) 12:10 pm
Ed Bertschinger, MIT
501 Campbell Hall
"Fokker-Planck evolution of cold dark matter"

Apr. 11 (Monday) 5:45 pm Oppenheimer Lecture
Martin Rees, Cambridge
Pimentel Hall
"Scanning Cosmic Horizons"
Cosmologists have made enormous progress towards answering some fundamental questions about our universe. They have discovered that the universe contains a surprising 'mix' of ingredients, traced the key stages of cosmic history right back to within a millisecond of a 'beginning', and can offer a long-range forecast for our universe. These advances, due mainly to new instruments and advanced technology, bring new questions into sharper focus which offer challenges for the coming decades. How did the first stars and galaxies form, at redshifts of 20 or more? What are the 'dark matter' and 'dark energy'? What are the key challenges on the interface between cosmology and microphysics? And is our 'observable universe' just a tiny - and perhaps atypical - fragment of physical reality?

Apr. 12 (Tuesday) 1:10 pm
Chris Blake,UBC
544 Campbell Hall
"A new measuring stick for cosmology"
The recent detection of "baryon oscillations" in the clustering pattern of the SDSS Luminous Red Galaxy sample was an important breakthrough in cosmology. I will discuss the background and significance of this discovery, and outline efforts to extend this cosmological ruler to higher redshifts via future spectroscopic and photometric redshift surveys. This technique should provide an accurate probe of dark energy free of major systematic error.

Apr. 14 (Thursday) 4:10 pm ( Astronomy Colloquium)
Felix Aharonian,MPI
1 LeConte Hall
"The Fascinating TeV Sky"
The recent exciting discoveries of TeV gamma sources with the High Energy Stereoscopy System (HESS) of imaging atmospheric Cherenkov telescopes elevated the status of the field (characterised in the past as an "astronomy with a few sources") to the level of truly observational discipline. I will highlight the recent HESS morphological and spectroscopic studies of several galactic and extragalactic source populations obtained with an energy flux sensitivity close to 10**(-13) erg/cm2 s and angular resolution of a few arc-minutes. I will discuss the astrophysical and cosmological implications of some of these discoveries. I also will briefly discuss possible future developments of the field in the context of current ideas concerning the ground-based gamma-ray detectors in the post-HESS era.

Apr. 19 (Tuesday) 1:10 pm
Sarah Bridle, UCL
544 Campbell Hall
Quantifying Dark Energy
I discuss the prospects for measuring the properties of dark energy. I suggest that tht concept of an effective equation of state will be useful and show how this may be written as a weighted average over the true, potentially varying, equation of state. I show and discuss this weighting function for upcoming supernova and cosmic shear surveys. Finally I discuss the prospects for the Square Kilometer Array, potentially the ultimate dark energy experiment currently under discussion.

Apr. 20 (Wednesday)
deadline for May 3 workshop at Stanford registration, below.

Apr. 26 (Tuesday) 1:10 pm
Jochen Weller, FNAL
544 Campbell Hall
"Constraining Dark Energy with X-ray Galaxy Clusters, Supernovae and the Cosmic Microwave Background"
We present new constraints on the evolution of dark energy from an analysis of Cosmic Microwave Background, supernova and X-ray galaxy cluster data. Our analysis employs a minimum of priors and exploits the complementary nature of these data sets. We examine a series of dark energy models with up to three free parameters: the current dark energy equation of state $w_{\rm 0}$, the early time equation of state $w_{\rm et}$ and the scale factor at transition, $a_{\rmt}$. We find no significant evidence for evolution in the dark energy equation of state parameter with redshift. Marginal hints of evolution in the supernovae data become less significant when the cluster constraints are also included in the analysis. The complementary nature of the ata sets leads to a tight constraint on the mean matter density, $\Omega_{\rm m}$ and alleviates a number of other parameter degeneracies, including that between the scalar spectral index $n_{\rm s}$, the physical baryon density $\Omega_{\rm b}h2$ and the optical depth $\tau$. This complementary nature also allows us to examine models in which we drop the prior on the curvature.
Mar 2005:

Mar. 1 (Tuesday) 1:10 pm
No talk (see Thursday)

March 3 (Thursday) 4:10 pm (Astronomy Colloquium)
Dan Eisenstein, Arizona
1 LeConte
"Dark Energy and Cosmic Sound"
I present galaxy clustering results from the Sloan Digital Sky Survey that reveal the signature of acoustic oscillations of the photon-baryon fluid in the first million years of the Universe. The scale of this feature can be computed and hence the detection in the galaxy clustering serves as a standard ruler, giving a geometric distance to a redshift of 0.35. I will discuss the implications of this measurement for the composition of the universe, including dark energy and spatial curvature, and the prospects for future redshift surveys to use the acoustic peak to map the expansion history of the universe.

Mar. 8 (Tuesday) 1:10 pm
Adam Lidz, CfA
544 Campbell Hall
"J, T, and Delta from the Lyman-alpha Forest"
I will discuss constraints from the Lyman-alpha forest on the redshift evolution of the photoionizing background, the thermal history of the intergalactic medium, and on matter clustering. I will present work in progress on examining the impact of HeII reionization on the HI Lyman-alpha forest, and critique some of the evidence in the literature for HeII reionization near z~3. Finally, I will illustrate the utility of using the flux probability distribution function in conjunction with the flux power spectrum to constrain the dark matter power spectrum.

Mar. 14 (Monday) 12:10 pm (TAC seminar)
Zoltan Haiman, Columbia
544 Campbell Hall
"How Did the Cosmic Dark Age End?"
In the currently favored cosmological paradigm, the first non-linear objects are small dark matter halos that formed at redshift z ~ 30. The pristine primordial gas in these halos can dissipate its energy by excitations of molecular hydrogen, and contract to high densities to form the first generation of stars and black holes. These objects subsequently evolve into the population of well-studied galaxies and quasars at redshift z<6. The first stars and black holes, however, can have a significant impact on the rest of the universe as soon as they appear, by photo-ionizing most of the baryons. The cosmic microwave background anisotropies (measured by the Wilkinson Microwave Anisotropy Probe), and the spectra of the most distant quasars (discovered in the Sloan Digital Sky Survey), have recently provided the first glimpses of the early ionization history of the universe. I will discuss plausible interpretations of these recent observations. In the next decade, new instruments should characterize the ionization history and tomography in detail, and allow us to infer the abundance, spectrum, and other properties of the first generation of astrophysical objects.

Mar. 15 (Tuesday) 1:10 pm
Dragan Huterer, KICP
544 Campbell Hall
"Is the large-scale microwave background cosmic?"
Recent measurements of the cosmic microwave background anisotropies by the WMAP experiment provide a unique window to the processes in the early universe. Tests of gaussianity and isotropy of the CMB are particularly important, as they may lead to evidence for exotic particle physics models processes in the early universe, or perhaps nontrivial topology. In the first part of the talk I present "multipole vectors", a new basis to represent the CMB anisotropy. I then consider large-scale anisotropies as measured by the WMAP experiment. While the measurements are generally in good agreement with the currently favored cosmological model, large-scale CMB anisotropies exhibit statistically significant and entirely unexpected correlations with directions defined by the Solar System. I discuss these findings and their relation to other widely discussed results inferred from the CMB.

Mar. 16 (Wednesday) 1:00 pm
Mark Ashdown, Cavendish Laboratory
50B-4205 at LBL
"Destriping: a fast, approximate map-making method for Planck"
The Planck mission will measure the CMB anisotropies over the whole sky with unprecedented sensitivity and angular resolution. The volume of data makes its analysis a computationally challenging feat, even for the basic operation of making maps from the time-ordered series of observations. A fast map-making method is essential if large numbers of Monte Carlo simulations are to be used to assess the impact of random and systematic errors on the scientific results. Destriping is a fast, approximate method of map-making attuned to Planck's observation strategy. I will show that destriping can be used to derive a simple model of the uncertainties in the resulting maps that will be useful in any further analyses of the data. I will describe a parallel implementation of the algorithm and show results from applying it to simulated Planck data. Last, I will show that destriping can be extended to allow deconvolution of asymmetric beams.

Mar. 22
spring break
no talk

Mar. 22 (Tuesday at LBL) 4:00 pm
Paolo Creminelli, Harvard University
70A-3377 at LBL
"Non-Gaussianities of Primordial Perturbations"
I will review the 3-point function of density perturbations in the Universe and will describe the theoretical predictions for this observable in different scenarios and the information we can derive about the early Universe from its size and shape dependence.

Mar. 29 (Tuesday) 1:10 pm
Jean-Baptiste Melin, UC Davis
544 Campbell Hall
"The Selection Function of Sunyaev-Zel'dovich Cluster Surveys"
Millimeter-wave galaxy cluster surveys will soon provide a high number of clusters detected through the Sunyaev-Zel'dovich (SZ) effect. In order to link the observed cluster counts to the underlying cosmological parameters, one needs the survey selection functions. In the first part of my talk, I will emphasize the importance of determining the SZ selection functions for cosmological purposes. In the second part, I will describe a method to estimate the selection functions and I will give some results for typical future experiments. In the last part, I will explore the consequences of the selection function properties for cosmological parameter determination.

Feb 2005:

Feb. 1 (Tuesday) 1:10 pm
John O'Meara, MIT
544 Campbell Hall
"Precision Cosmology from observations of the Lyman Alpha Forest"
The combination of multiple sightline, high quality, calibrated observations of the Lyman alpha forest at high redshift with cosmological simulations allows for increasingly more accurate constraints of cosmological and astrophysical parameters. In this talk, I discuss the measurement of a key statistic describing the z~2 Lyman alpha forest, the mean flux decrement, and the constraints this statistic places on a variety of cosmological parameters.

Feb. 3 (Thursday) 12:00 pm, INPA seminar
Alison Coil, UCB
Bldg. 50, room 5026 (the INPA common room)
"First Large-Scale Structure Results from the DEEP2 Galaxy Redshift Survey"
Feb. 7 (Monday) 12:10 pm (TAC seminar)
Scott Burles , MIT
544 Campbell Hall
"Opacity distributions in the Lyman-alpha forest"
I will present recent results on studies of the 1 and 2-point distributions of flux and opacity in the Lyman-alpha forest. I will describe the completed analysis of the SDSS data sets with constraints on the dark matter power specturm and the properties of the intergalactic medium. Follow-up studies with the Magellan telescopes are underway, including plans for much deeper spectroscopy with a new echellette spectrograph named MagE.

Feb. 8 (Tuesday) 1:10 pm
James Taylor, CalTech
544 Campbell Hall
"The Private Lives of Dark Matter Halos"
Dark matter halos are the most distinctive and most important component of CDM models, providing the dynamical environment within which baryons can cool and form visible galaxies. The abundance and clustering of halos, as measured indirectly via galaxy redshift surveys, cluster surveys or weak lensing studies, provides an important measure of the matter power spectrum and the average cosmological growth rate. The internal properties of dark matter halos may depend on more subtle features of cosmology, however, such as the scale invariance of the power spectrum, sudden changes in the equation of state of the universe, or the physics of the dark matter particle. Given recent observational progress, there will soon be direct measurements of the internal structure of large numbers of individual halos, with which to perform these next-generation cosmological tests. In this talk I will summarize my own work modeling the formation and internal structure of dark matter halos, and then discuss recent applications of my model to a combined weak + strong lensing study of clusters substructure, and to the spatial distribution of dwarf galaxies in the Local Group. I will also describe an ongoing project to model halo substructure down to the very small scales relevant in terrestrial experiments to detect the dark matter particle directly.

Feb. 10 (Thursday) 4:10 pm (Astronomy Colloquium)
Mateusz Ruszkowski , JILA
1 LeConte Hall
"Singing Black Holes and AGN Feedback in Clusters"
Recent X-ray observations reveal growing evidence for heating by active galactic nuclei (AGN) in clusters and groups of galaxies. AGN outflows play a crucial role in explaining the riddle of ``cooling flows'', the entropy excess problem in clusters, and may explain the cutoff in the galaxy luminosity function. I will discuss the effects of AGN on the intracluster medium in idealized clusters as well as in a cosmological simulation using the adaptive mesh refinement FLASH code. I will discuss the role of viscosity and conductivity on the dissipation of weak shocks generated by the AGN activity in a realistic galaxy cluster. I will present a simple semi-analytical model of AGN heating in clusters and discuss its consequences for quenching of ``cooling flows'' and the entropy excess problem. I will also present synthetic Chandra observations and show that the simulated buoyant bubbles inflated by the AGN, and the weak shocks associated with them, are detectable with the Chandra observatory.

Feb. 14 (Monday) 12:10 pm (TAC seminar)
David Weinberg, Ohio State
544 Campbell Hall
" What Do We Learn From Galaxy Clustering?"
We are now obtaining measurements of galaxy clustering in the local universe that are unprecedented in detail and precision, from the 2dF Galaxy Redshift Survey and the Sloan Digital Sky Survey. The principal obstacle to testing cosmological models against these measurements is the expectation that galaxies are, at least to some degree, biased tracers of the underlying mass distribution. I will discuss the problem of bias in the context of the halo occupation distribution (HOD), which characterizes the relation between galaxies and mass by the probability distribution P(N|M) that a halo of virial mass M contains N galaxies, together with prescriptions that specify the relative spatial and velocity distributions of galaxies and dark matter within halos. After presenting HOD predictions from hydrodynamic simulations and semi-analytic models of galaxy formation, I will show how different aspects of the HOD affect different statistical measures of galaxy clustering. Because the constraints from different statistics are complementary, it should be possible to determine the HOD empirically from 2dF and SDSS clustering measurements. I will describe some of the initial efforts at such empirical determinations, and I will discuss the prospects for breaking the degeneracies between galaxy bias and cosmological parameter values using data that are now becoming available.

Feb. 22 (Tuesday) 1:10 pm
Christy Tremonti, U. Arizona
544 Campbell Hall
"The Origin of the Mass-Metallicity Relation: Insights from the 50,000 Galaxies in the Sloan Digital Sky Survey"
We use imaging and spectroscopy from the Sloan Digital Sky Survey to study the relation between the stellar mass and gas-phase metallicity in star forming galaxies at z~0.1. We find a tight correlation extending over 3 orders of magnitude in stellar mass and a factor of 10 in metallicity. We use these results in conjunction with simple chemical evolution models to show that low mass galaxies preferentially lose metals via strong galactic winds.

Jan 2005:
Jan. 11 (Tuesday) 1:10 pm
Simon DeDeo, Princeton
544 Campbell Hall
"Particle Dark Energy"
I will explore some of the issues raised in my recent paper astro-ph/0411283. There I describe a new class of dark energy models based on particles that couple to a spontaneously Lorentz violating condensate. I will introduce some of the crucial physical concepts behind this idea, and connect them to larger questions in high energy physics. I will then describe a number of realistic cosmological scenarios in which these "dark energy particles" could lead to the present cosmological acceleration, and possibly to dark energy clustering and smoothing of small scale power.

Jan. 14 (Friday) 12 noon
Adam Bolton, MIT
INPA Journal club, LBL Bldg. 50, room 5026
'Strong Gravitational Lensing and Elliptical Galaxy Structure'

Jan. 18 (Tuesday) 12:00 pm, INPA seminar
Rachel Bean, Princeton
Bldg. 50, room 5026 (the INPA common room)
"Dark Insights from Light - Addressing Different Perspectives on Dark Energy"
The existence, and enigmatic nature, of Dark Energy is one of the biggest theoretical upsets of recent times. In this seminar we present work on alternative theoretical and phenomenological approaches to the Dark Energy problem, in particular the issue of whether dark energy is a matter or gravity-based phenomenon, and the ways in which such approaches have been constrained and guided by observation. We also discuss some of the exciting future approaches that could provide unprecedented insights into the fundamentals of Dark Energy.

Jan. 18 (Tuesday) 1:10 pm
Neal Dalal, IAS
544 Campbell Hall
"Strong Lensing in Lambda CDM"

Jan. 19 (Wednesday) 12:10 pm (Wednesday lunch)
Karen Masters, Cornell
501 Campbell Hall
"Galaxy Flows in and around the Local Supercluster"

In the local universe, deviations from Hubble flow can account for a significant fraction of a galaxy's recessional velocity. I will describe the use of simple flow models (which include infall onto spherical attractors) to correct for these motions. The relevance of such models will be discussed within the current picture of filamentary large scale structure. In addition I will present the SFI++, a new all-sky sample of galaxies with Tully-Fisher distances.

Jan. 20 (Thursday) 4:10 pm (Astronomy Colloquium)
Lars Hernquist, Harvard
1 LeConte Hall
"Black Holes in Galaxy Mergers"

Jan. 28 (Friday) 12:10 pm (Journal Club)
Darren Croton, MPA
544 Campbell Hall
"The many lives of AGN: from super-massive black holes to host galaxy colours and luminosities"

I use a semi-analytic model of galaxy formation and the Millennium Run LCDM N-body simulation to explore the evolution of the galaxy population, including super-massive black hole growth, in a cosmological context. I focus on the effect that AGN feedback has on cooling flows in massive systems, and discuss the impact that such cooling suppression has on the final galaxy properties.

Jan. 31 (Monday) 4:30 pm (Physics Colloquium)
Larry Gladney U Penn
1 LeConte Hall
"Seeing Dark Energy"
Our current cosmological model is compelling and simple, but puzzling in that two-thirds of the universe seems to be composed of a new form of energy, termed dark energy, which reveals itself only through the accelerated expansion it causes. Although several promising methods exist for exploring dark energy, the best probe is likely to be through observation of Type Ia supernovae. This talk will examine two methods for measuring the light from these objects with space-borne telescopes and a comparison of their relative strengths and weaknesses. Due to the fundamental importance of understanding dark energy, defining the optimal mission for determining its nature may be among the most important astro/particle physics tasks of the next two decades.

Dec 2004:

Dec. 1 (Wednesday) 3:30 pm
Eric Linder, LBNL
LBL Bldg. 50, room 50B-4205 (note correction!!)
'The Darkness of the Universe'
The darkness of the night sky teaches us about the finite past of the universe. Dark energy may have lessons about the infinite future. I discuss dark energy cosmology from a high energy physics theory perspective, matched with a cosmological measurements view. The seminar is aimed to be accessible to graduate students and interested physicists and astronomers.

Dec. 3(Friday) 12 noon
Joanna Dunkley, Oxford
INPA Journal club, LBL Bldg. 50, room 5026
'Non-adiabatic models: CMB constraints using fast MCMC'
The simplest inflationary models predict purely adiabatic primordial density perturbations. I will present constraints from the CMB and LSS on models with a non-adiabatic contribution, allowing all combinations of isocurvature modes. We find models with high non-adiabatic contributions (up to 60% of the CMB power) to fit current data. I discuss how future data will help constrain the initial conditions. I will then describe the fast Markov Chain Monte Carlo techniques we developed to allow reliable parameter estimation, and discuss their application to diverse problems in cosmology and astronomy.

Dec. 7(Tuesday) 1:10 pm
no talk,
544 Campbell Hall
tba

Dec. 13-14(Monday-Tuesday)
Week of Texas at Stanford meeting
Many of the early universe and cosmology talks are Monday and Tuesday.

Nov 2004:

Nov 1 (Monday, Monday lunch) 12:10 pm
Rafael Bousso, UCB
501 Campbell Hall
"String theory and the cosmological constant"

Nov. 2 (Tuesday, INPA Journal Club) 12:00 P.M.
Tamara Davis, Australian National University
LBNL 50-5026
"Expanding Confusion:Horizons and entropy in an accelerating universe"
"The full extent and richness of [the hot big bang model of the expanding universe] is not as well understood as it ought to be, even among those making the most stimulating contributions to the flow of ideas." --Jim Peebles, Principles of Physical Cosmology
In the context of the new standard LambdaCDM cosmology I'll discuss several common misconceptions about the expansion of the universe, including confusions regarding the particle horizon, the event horizon and the `observable universe'. I will show how we can observe galaxies that have, and have always had, recession velocities greater than the speed of light and explain why this does not violate special relativity. I'll discuss the cosmological event horizon of a LambdaCDM universe and ask whether it possesses an entropy proportional to its area analogous to the entropy of a black hole.

Nov. 2 (Tuesday) 1:10 pm
Informal discussion of Galaxy-IGM interactions KITP meeting,
544 Campbell Hall
Taotao and Tzu-Ching

Nov 8 (Monday, Monday lunch) 12:10 pm
Iro Tasitsiomi, U Chicago
501 Campbell Hall
"From clusters to clustering: N(o)-body('s) stories"
My talk is about using high resolution state-of-the-art collisionless N-body simulations to study Hence, in the first part of the talk I will discuss the inner slopes (cusps) of our clusters, and try to reveal the detailed connection between the mass accretion history of a halo and its density profile. In the second part of the talk, I will discuss the modeling of galaxy-mass correlations using collisionless simulations. I will present comparisons of the results with the recent SDSS weak lensing galaxy-mass correlation measurements. I will discuss what simulations teach us about the information that can be extracted from galaxy-galaxy weak lensing on, e.g., the bias, the halo masses and density profiles, etc., as well as how they can be used to obtain a deeper insight into the interpretation of observations.

Nov 9 (Tuesday) 1:10 pm
Ryan Scranton, Pitt
544 Campbell Hall
"Late Integrated Sachs-Wolfe Effect: SDSS & Beyond"
This will be a talk in two parts. The first half will be an update of measurements of the cross-correlation between luminous red galaxies in the Sloan Digital Sky Survey and the cosmic microwave background temperature maps from the Wilkinson Microwave Anisotropy probe. These new measurements increase our survey area to 5000 square degrees, up from 3400. We find a detection at greater than 99% confidence when we combine measurements using multiple photometric redshift-selected slices and the signal is consistent with what we expect from a late, integrated Sachs-Wolfe signature. The second half of the talk will focus on the future possibilities of this sort of measurement. Specifically, it will address the ability of future galaxy and CMB surveys to jointly constrain the both equation of state and the clustering of dark energy.

Nov 10 (Wednesday) 12:10 pm (TAC seminar)
David Hogg, NYU
544 Campbell Hall
"Galaxy formation events observed in the Sloan Digital Sky Survey"
We can see new bulge-dominated galaxies being created in the local Universe, and they are being created at a rate that corresponds to about one percent of the galaxy population per billion years.

Nov 15 (Monday, Monday lunch) 12:10 pm
Brian O'Shea, UCSD
501 Campbell Hall
"Formulation and feedback of massive primordial stars"
I will present results from extremely high resolution numerical simulations of the formation of massive Population III stars in a Lambda CDM cosmology. These simulations were done using the publicly available Enzo adaptive mesh cosmology code. In addition, I will discuss work that is currently in progress where we simulate radiative feedback from massive Population III stars and the apparent positive effect that this will have on the formation of a second generation of objects. If time permits I will also discuss chemical feedback from the first stars and the formation of the first star in a universe composed of warm dark matter.

Nov 16 (Tuesday) 1:10 pm
Beth Willman, NYU
544 Campbell Hall
"The observed and predicted Milky Way satellite population"
I discuss some general properties of the known population of Milky Way dwarf satellite galaxies in the context of CDM and the substructure problem. I describe a systematic survey of the SDSS for new Milky Way satellites and estimate the properties of two incredibly low surface brightness (iLSB) companions discovered in our analysis. I then evaluate the extent to which our results can improve our understanding of the substructure problem and place constraints on ultra-low mass galaxy formation.

Nov 17 (Wednesday) 12:10 pm (TAC seminar)
Hiranya Peiris, U Chicago
544 Campbell Hall
"Can We See Planck/Stringy Physics via the CMB?"
I will discuss the possibility that physics at the Planck or string scales modifies standard estimates of the inflationary perturbation spectrum. I will summarize the likely signatures of these modifications, and present a detailed investigation into the fundamental limits upon their detection by future high precision CMB experiments.

Nov 22 (Monday, Monday lunch) 12:10 pm
Alice Shapley, UCB
501 Campbell Hall
Discussion of the recent Ringberg meeting plus whatever else people have to report.

Nov. 22 ( Monday) 2:00 pm ( Ly-a reading group)
Tzu-Ching Chang, UCB
544 Campbell Hall

Nov. 23 (Tuesday) 1:10 pm
David Sand, Caltech
544 Campbell Hall
"A search for gravitationally-lensed arcs in the HST/WFPC2 Archive"
By carefully examining the images of 129 clusters in the Hubble Space Telescope Wide Field and Planetary Camera 2 data archive we have located 12 candidate radial arcs and 105 tangential arcs, each of whose length to width ratio exceeds 7. Keck spectroscopy of candidate radial arcs suggests that contamination of the radial arc sample from non-lensed objects occurs at about the 30\% level. With our catalog, we explore the practicality of using the number ratio of radial to tangential arcs as a statistical measure of the slope $\beta$ of the dark matter distribution in cluster cores (where $\rho_{DM}\propto r^{-\beta}$ at small radii). Although the arc statistics presented are consistent with a range of density profiles -- beta<1.5 depending on various assumptions, we show that the stellar mass of the brightest cluster galaxy is the major limitation. With additional data, this method may provide a reliable statistical constraint on the form of cluster dark matter profiles on $\lesssim$100 kpc scales.

Nov. 29 ( Monday) 2:00 pm ( Ly-a reading group)
Matteo Viel, IOA
544 Campbell Hall
" Quantitative Cosmology with the Lyman-alpha Forest "
In this talk I will focus on the cosmological significance of the Lyman-alpha forest at z>2. Starting from a sample of high resolution high signal to noise quasar spectra and a set of large box size hydro-dynamical simulations, I will constrain the dark matter power spectrum at scales not probed by any other observable. I will discuss the inferred values of sigma_8, the spectral index and the running of the spectral index derived from a combined analysis of the forest data and WMAP. Some implications for slow-roll inflationary models will also be presented together with a comparison with the recent results of the SDSS collaboration. Results in terms of neutrino masses and masses of wark dark matter particles will also be presented.

Nov 30 (Tuesday) 1:10 pm
Tesla Jeltema, Carnegie
544 Campbell Hall
"The Evolution of Structure in X-ray Clusters of Galaxies"
Using archival data from the Chandra X-ray Observatory, we quantify the evolution of cluster morphology with redshift. Clusters form and grow through mergers with other clusters and groups, and the amount of substructure in clusters in the present epoch and how quickly it evolves with redshift depend on the underlying cosmology. Our sample includes 40 X-ray selected, luminous clusters from the Chandra archive, and we quantify cluster morphology using the power ratio method (Buote & Tsai 1995). The power ratios are constructed from the moments of the X-ray surface brightness and are related to a cluster's dynamical state. We find that, as expected qualitatively from hierarchical models of structure formation, high-redshift clusters have more substructure and are dynamically more active than low-redshift clusters. Specifically, the clusters with z>0.5 have significantly higher average third and fourth order power ratios than the lower redshift clusters. Of the power ratios, P_3/P_0 is the most unambiguous indicator of an asymmetric cluster structure, and the difference in $P_3/P_0$ between the two samples remains significant even when the effects of noise and other systematics are considered. After correcting for noise, we find a slope and 90% confidence limits of 4.09+3.94-3.27x10-7 for redshift versus P_3/P_0. This observation of structure evolution indicates that dynamical state may be an important systematic effect in cluster studies seeking to constrain cosmology, and when calibrated against numerical simulations, structure evolution will itself provide interesting bounds on cosmological models.

Oct 2004:

Oct. 5 (Tuesday) 1:10 pm
Daisuke Nagai, Chicago
544 Campbell Hall
"Simulating the Formation of Galaxy Clusters"
I will present high-resolution Adaptive Mesh Refinement (AMR) N-body+gasdynamics simulations of galaxy clusters forming in the LCDM universe. The simulations include various physical processes critical to galaxy formation (e.g., gas cooling, star formation and stellar feedback). The simulations thus follow the evolution of galaxies in dense cluster environment and its complex interaction with ambient cluster gas. I will discuss the radial distribution and scaling relations of galaxies in LCDM clusters and show that they are reasonably consistent with observations. Simulating realistic galaxy cluster, however, still remains a challenge. I will show that gas cooling and star formation play an important role in shaping the properties of galaxy clusters such as the distribution of mass, dark matter, entropy and temperature of intracluster gas. But, the magnitude of these effects is likely overestimated because the current simulations suffer from the "overcooling" problem : a much larger fraction of gas is found in the cold phase than is observed in real clusters. These results indicate that an additional heating is necessary to reproduce the observed properties of galaxy clusters. I will discuss energy injection from active galactic nuclei (AGN) as a possible missing heating source in the current cluster formation model.

Oct. 11 (Monday) 2:30 pm, Particle Theory seminar
Jonathan Feng , UCI
Oppenheimer room, Birge Hall
"SuperWIMP dark matter"

Oct. 11 (Monday) 3:10 pm, RAL seminar
Miguel Morales , MIT
544 Campbell Hall
"Observing the Epoch of Reionization with Wide-Field Radio Measurements"
The Epoch of Reionization (EOR) marks a fundamental phase change in the universe and the emergence of the first luminous objects. The high optical depth of the neutral hydrogen Lyman lines makes it very difficult to observe objects with optical instrumentation before reionization is complete, and consequently this epoch has become known as the "cosmic dark ages." However, radio observations of the highly redshifted 21 cm line of neutral hydrogen offer the opportunity to observe the neutral hydrogen, the formation of structure, and the emergence of the first stars and quasars. Consequently, long wavelength radio observations have become one of the most exciting new areas of experimental cosmology. Drawing on the results of the international EOR Workshop held this summer, I will discuss the observational signatures and the theoretical and experimental challenges facing these observations. I will also introduce the Mileura Wide-field Array Demonstrator, the US-Australian low frequency observatory which promises to be the premier EOR instrument when it comes on line in early 2007.

Oct. 12 (Tuesday) 1:10 pm
Erin Sheldon, Chicago
544 Campbell Hall
"Weak Lensing Measurements of Galaxies and Clusters of Galaxies in the SDSS"
I will present measurements of weak gravitational lensing by galaxies and clusters of galaxies in the Sloan Digital Sky Survey (SDSS). We have assembled samples of a few hundred thousand galaxies and clusters of galaxies from the SDSS. We find that the mass distribution around galaxies is a strong function of the galaxy color, luminosity, and velocity dispersion. We find that the shape of the inferred galaxy-mass cross correlation function for L* galaxies is consistent with the autocorrelation function on 0.2-8 Mpc scales, implying simple bias over these scales. We detect significant deviations from a power law at higher luminosities. Furthermore, under reasonable assumptions about bias, these results place a strong constraint on Omega_m with no other assumptions. For clusters, the shape of the density profile and the virial mass correlate strongly with the number of luminous red galaxies in the cluster. These profiles are also found to differ significantly from a power law, and are consistent with the standard NFW profile. I will discuss the results of modeling these measurements in N-body simulations.
Finally, I will briefly discuss the upcoming Dark Energy Survey, designed as an optical followup mission for clusters found in the South Pole Telescope cluster survey. If systematics can be controlled, weak lensing will provide a good independent calibration of the mean mass-richness relation. In addition, strong constraints will be placed on cosmology using lensing alone through cosmic-shear and cluster lensing.

Oct. 13 (Wednesday) 12:10 pm (TAC seminar)
Ben Chandran, Iowa
544 Campbell Hall
"Galaxy clusters and the cooling flow problem"
Heating of intracluster plasma holds the key to two of the central problems in the study of galaxy clusters. The first is the cooling-flow problem, which amounts to explaining the observation that very little intracluster plasma cools to temperatures below one-third of the average cluster temperature, despite the fact that the radiative cooling time in the centers of many clusters is much less than a cluster's age. The second is the more general problem of cluster formation. Numerical simulations of cluster formation show that some heat source in addition to supernovae is essential to explaining observed plasma density and temperature profiles and cluster star-formation histories. In this talk I will discuss recent work on two of the most important heating mechanisms: thermal conduction and heating by a central AGN.

Oct. 14 (Thursday) 4:10 pm (Astronomy Colloquium)
Tony Readhead, CalTech
2 LeConte
"Cosmic Background Imager"
The combination of the Cosmic Background Imager (CBI) two-year (2000+2001) total intensity observations with the first year WMAP observations leads to significantly refined estimates of basic cosmological parameters, and provides a stringent test of the scale invariance of the primordial spectrum. The CBI polarization observations from ~300 nights of observations provide a highly significant detection of polarized emission from the microwave background on the scale of the seeds of galaxy clusters, and show that the polarization spectrum is "out of step" with the total intensity spectrum, as expected for acoustic waves. The next generation of coherent detectors - large arrays of MMIC receivers - is being developed for deployment on the CBI in late 2005 and these developments will also be discussed.

Oct. 19 (Tuesday)
no talk scheduled.

Oct. 27 (Wednesday) 12:10 pm (TAC seminar)
Volker Springel, MPA
544 Campbell Hall
"The universe in a supercomputer: Following the formation of galaxies and the first quasars"

Sep 2004:

Sep 1 (Wednesday) 12:10 pm (TAC seminar)
Evan Scannapieco, KITP
501 Campbell Hall
"Quasar feedback in structure formation"
Quasar outflows, in the form of broad-absorption line winds and radio jets, are likely to have left an indelible cosmological imprint. As material from the centers of galaxies made its way into the intergalactic medium (IGM), it impacted structures on many scales, much as supernovae impact structures on many scales within the interstellar medium. I will outline several observational features that are likely to have been caused by these interactions. As large regions of the IGM are shocked heated above a critical entropy of 100 keV cm^2, cooling becomes impossible within them, regardless of further changes in density. On quasar scales, this results in the observed fall-off in number densities below z = 2. On galaxy scales, quasar heating fixes the turn-over scale in the galaxy luminosity function (L_*) as the nonlinear scale at the redshift of strong feedback. The galaxy luminosity function then remains largely fixed after this epoch, consistent with recent observations and in contrast to the strong evolution predicted in more standard galaxy-formation models. Finally, strong quasar feedback explains why the intracluster medium is observed to have been pre-heated to entropy levels just above the minimum excess that would not have been erased by cooling.

Sep. 7 (Tuesday) 1:10 pm
Ruediger Kneissl, Cambridge
544 Campbell Hall
"Sunyaev-Zel'dovich Cluster Surveys and Cosmology"
In later cosmic times when the dark energy begins to dominate the evolution of the universe, clusters of galaxies probe key cosmological parameters through their number density evolution, their distribution embedded in the large-scale structure and their internal properties. Cluster surveys via the SZ effect promise large samples, efficiently selected by the integrated pressure and unbiased in redshift, and are therefore ideal to learn about the thermal history of the cluster gas and to apply clusters to cosmology. I will discuss prospects and challenges for this method to work in practice, with examples taken from two different experiments, Planck and AMI, and present some recent results from SZ observations of nearby clusters with the VSA.

Sept. 10 (Friday) 9:30 am-5 pm
1st Annual Berkeley-Davis Day
544 Campbell Hall
This is an opportunity for research groups in cosmology, astrophysics, and fundamental physics at Berkeley (campus and LBL) and Davis to mingle and interact. About a dozen Davisites will be visiting. The morning will involve informal discussion and the afternoon will see talks exclusively by student members of the institutions.
Students are especially encouraged to attend. If any student wishes to present a research topic, please contact Chris Vale cvale@astron.berkeley.edu asap. For further questions, contact Chris on campus or Eric Linder evlinder@lbl.gov at LBL.

Sep 22 (Wednesday) 12:10 pm (TAC seminar)
Marc Kamionkowski, CalTech
544 Campbell Hall
"Halo Merger Rates"

Sept. 23 (Thursday) 1:10 pm
Ue-Li Pen, CITA
544 Campbell Hall
"PAST: science at the epoch of reionization"
I will describe the current status of the Primeval Anisotropy Telescope in Xinjiang, China. Its primary science goal is to measure structure in the 21cm emission at redshifts 6-20. In addition to measuring the ionization history and first light in the universe, these structures can serve as a source screen for gravitational lensing, to measure dark matter, dark energy, and reduce the cosmic variance of the CMB.

Sep. 28 (Tuesday) 1:10 pm
Steve Myers, NRAO
544 Campbell Hall
"The Angular Power Spectrum of CMB Polarization: New Results from the Cosmic Background Imager (CBI)"
Measurement of the angular power spectrum of polarization of the cosmic microwave background (CMB) radiation is one of the key tests of the "standard cosmological model". I will describe the recently announced new results from the Cosmic Background Imager (CBI) project, which is a 13-element interferometer dedicated to CMB observations located at a high-altitude site in the Chilean Andes. The CBI has measured the power spectrum of the predominant "E-mode" polarization, and found its amplitude and shape to be consistent with the predictions of the standard models in concordance with other observations (such as the previous results of WMAP, CBI, and ACBAR). For example, the signature peaks due to acoustic resonances driven by the primordial density and velocity fields at last scattering are seen to be one-half cycle out of phase with those seen in the CMB temperature power spectrum, in accordance with prediction. I will put these new results in context with other recently reported results from DASI and CAPMAP, and give prospects for future CMB polarization observations.

Sep 29 (Wednesday) 12:10 pm (TAC seminar)
James Bullock, UC Irvine
544 Campbell Hall
The Milky Way as a Laboratory for Cosmology
I will discuss how High-Velocity Clouds and evidence for substructure in the Milky Way stellar halo may be used as a probe for important aspects of galaxy formation and similarly test whether structure formation is indeed hierarchical on small scales.
Aug 2004:

Aug 2-13, LBNL
Weak Lensing LBL summer visitor program

Aug 13 (Friday) 4:00 pm
Mark Trodden , Syracuse
LBL, Building 50B, room 4205
"Is Cosmic Acceleration Telling Us Something about Gravity?"

Aug. 30 (Monday) 3:10 pm
Wayne Hu, U Chicago
544 Campbell Hall
"Dark energy probes in light of the CMB"

Aug. 31 (Tuesday) 1:10 pm
Kev Abazajian, LANL
544 Campbell Hall
"All-Scale Galaxy Clustering and Cosmology"
Over the last several years, halo occupation models of galaxy bias have led tosubstantial progress in characterizing the relation between the distributions of galaxies and dark matter. Gravitational clustering of the dark matter determines the population of virialized dark matter halos, with essentially nodependence on the more complex physics of the sub-dominant baryon component. Galaxy formation physics determines the halo occupation distribution (HOD) of galaxies within dark matter halos. Since cosmological uncertainties are growing progressively smaller, the galaxy HOD can be disentangled from the uncertainties in the cosmological distribution of dark matter, and galaxy clustering statistics at all scales can be used to determine the underlying HOD and cosmology. This has been applied to galaxy subsamples in the SDSS and may be used to quantify evolution of galaxy populations as well as cosmological quantities with high-redshift galaxy clustering statistics, such as those measured by DEEP.

Past Cosmology Seminars in 2003-2004 Academic Year

Past Cosmology Seminars in 2002-2003 Academic Year

Past Cosmology Seminars in 2001-2002 Academic Year


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