Upcoming and Previous Seminars (Past months or Previous years)

Note that if the talk's pdf or ppt is available after the talk, you can get it by clicking on the talk title.

Physics/Astronomy C290C Cosmology and Cosmology-BCCP Seminar
The Physics/Astronomy C290C series consists of the Cosmology-BCCP LBNL-Physics-Astronomy Cosmology seminars held Tuesdays 1:10-2:00 pm in room 131 Campbell Hall. Because this room is hard to keep clean, please don't bring your lunch (this is a change).
Please contact Joanne Cohn to add to this list or to suggest speakers.

Speaker/Visitor Info is here.

BOSS and Nyx
(Image by C. Stark)

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

April 2016
Apr. 1 , Friday
12 pm (INPA), not 12:10 pm
Josh Dillon, UCB
LBL 50-5026 INPA room
It's Always Darkest Before the Cosmic Dawn: Results from First Generation 21 cm Interferometers and Lessons for the Next Generation
Realizing the promise of 21 cm cosmology to provide an exquisite probe of astrophysics and cosmology during the "Cosmic Dawn" and the epoch of reionization (EoR) has proven extremely challenging. We're looking for a small signal buried under foregrounds orders of magnitude brighter. We need large interferometers, precisely calibrated, producing mountains of data to to have any shot of seeing the signal. To confront this challenge, we need fast, robust, and rigorous statistical methods for turn that data in cosmologically interesting results. In this talk, I will survey the new statistical techniques we've developed and the progress we've made toward separating the 21 cm signal from foregrounds using current generation interferometers, the Precision Array for Probing the Epoch of Reionization (PAPER) and the Murchison Widefield Array (MWA). Then I will discuss how the progress we've made is now shaping the new Hydrogen Epoch of Reionization Array, a purpose-built interferometer designed not just to detect the EoR but to characterize its evolution, to push into the pre-reionization epoch, and to improve cosmological parameter constraints by eliminating the CMB's optical depth degeneracy.
Apr. 5, Tuesday
1:10 pm (Cosmology/BCCP)
Andrew Wetzel, Caltech/Carnegie
Campbell 131
Reconciling Dwarf Galaxies with LCDM Cosmology
Low-mass "dwarf" galaxies trace structure formation on the smallest cosmological scales and represent the most significant challenges to the cold dark matter (CDM) model. Because these faintest galaxies are (best) observed only within the Local Group of the Milky Way (MW) and Andromeda (M31), it is critical to understand and model their formation within the environment of a MW-mass host. I will introduce the Latte Project, a new suite of cosmological zoom-in baryonic simulations that model the formation of Milky Way-mass galaxies at parsec-scale resolution, using the FIRE (Feedback in Realistic Environments) model for star formation and stellar feedback. These simulations self-consistently resolve the satellite dwarf galaxy populations that forms around the Milky Way-mass hosts, including the relevant physics to model their stellar populations. I will present first results from Latte, emphasizing the impacts of (internal) stellar feedback and (external) environment on the star formation histories, stellar kinematics, and chemical enrichment histories of dwarf galaxies, addressing long-standing "missing satellites", "too-big-to-fail", and "core-cusp" problems of CDM cosmology.
Apr. 8 , Friday
12 pm (INPA), not 12:10 pm
Darcy Barron, UCB
LBL 50-5026 INPA room
CMB Polarization Measurements: Cutting the trail to CMB-S4
The CMB community started the planning stages for the "ultimate" ground-based CMB polarization experiment, CMB-S4, in 2013. Since then, the current generation of ground-based experiments has published several detections of B-mode polarization from gravitational lensing, demonstrating the techniques that will be expanded to characterize the signal across the sky. Deep searches for primordial B-mode polarization have shown the challenges in foreground contamination and control of systematics for reaching high sensitivity at large angular scales. The CMB community is currently working on defining the science goals and instrument requirements for CMB-S4. Meanwhile, the next generation of even more powerful CMB polarization experiments will soon begin to produce results. I will give an overview of the current state of the field, and the ongoing planning for CMB-S4.
Apr. 12, Tuesday
1:10 pm (Cosmology/BCCP)
Anthony Gonzalez, Florida
Campbell 131
Hunting for MaDCoWS: High Redshift Galaxy Clusters over the Full Extragalactic Sky
The Massive and Distant Clusters of WISE Survey (MaDCoWS) is a comprehensive program to detect and characterize the most massive galaxy clusters at z~1 over the full extragalactic sky. I will give an overview of the survey and present recent results within the PanSTARRS footprint from our ongoing follow-up programs, including confirmation of the second most massive galaxy cluster known at z>1. I will discuss our Spitzer program to characterize the MaDCoWS cluster population, the complementarity of MaDCoWS with other ongoing high-redshift cluster searches, and finally prospects for extending the reach of wide-area infrared cluster searches out to z~2.
Apr. 15, Friday
12 pm (INPA), not 12:10 pm
Irina Zhuravleva, Stanford
LBL 50-5026 INPA room
Microphysics of Galaxy Clusters: Turbulent Heating in Radio-mode AGN Feedback
Cores of relaxed galaxy clusters are often disturbed by AGN activity as revealed by deep Chandra observations. Such perturbations reflect density and temperature fluctuations in the hot X-ray gas induced by shocks, subsonic gas motions, bubbles of relativistic plasma, etc. In my talk I will address the questions on the nature and energetics of the AGN-driven perturbations in the brightest nearby galaxy clusters, which were deeply observed by Chandra. I will present turbulence measurements and show that the heating rate due to dissipation of turbulence is sufficient to balance the radiative cooling locally at each radius within the cores, suggesting that turbulencemight be the key element in resolving the gas cooling problem in cluster cores and other X-ray gas-rich systems. The results are based on the auto- and cross-spectra analysis of emissivity fluctuations in soft and hard X-ray bands over a broad range of spatial scales, down to microphysical scales.
Apr. 18, Monday
12:10 pm (TAC)
Desika Narayanan, Haverford College
Campbell 131
ISM Theory in the Era of ALMA
With ALMA entering full-scale operations, the number of CO, [CII] and dust continuum detections of galaxies both near and far are rising exponentially. In this talk, I will utilize a combination of hydrodynamic simulations, chemical equilibrium and thermal equilibrium models to challenge pre-conceived notions of what these lines trace, and discuss how we can use information from ALMA over the next decade to understand high-redshift galaxy evolution.
Apr. 19, Tuesday
1:10 pm (Cosmology/BCCP)
Nikhil Padmanabhan, Yale
Campbell 131
“Revisiting large scale structure analysis techniques in the DESI era”
Galaxy redshift surveys are powerful cosmological probes, and the next generations of these surveys, including DESI, Euclid and WFIRST, forecast sub-percent statistical errors on the expansion and growth rate of the Universe. I’ll aim to explore some of the analysis challenges that these surveys present, and possible approaches to address these. I’ll focus on two specific problems. The first of these introduces a redshift weighting, optimized to measure the expansion history without resorting to binning in redshift. The second is estimating covariance matrices, where I’ll discuss a few approaches that can help alleviate the difficulties in estimating covariance matrices via Monte Carlo techniques.
Apr. 22, Friday
12 pm (INPA), not 12:10 pm
Peter Behroozi, UCB
LBL 50-5026 INPA room
Linking Halo Assembly with Galaxy Star Formation Rates
We summarize observational evidence for a connection between halo assembly rates and galaxy star formation rates, and discuss preliminary results from the next generation of self-consistent galaxy—halo matching models that incorporate these connections.
Apr. 26, Tuesday
1:10 pm (Cosmology/BCCP)
K. Decker French, Arizona
Campbell 131
Post-Starburst Galaxies: Tracers of Galaxy Evolution and the Unlikely Hosts of Tidal Disruption Events
Post-starburst galaxies are in transition between star-forming galaxies and early-types, and represent a clear path for galaxies to transform from star-forming to quiescence. Many show signs of a recent galaxy-galaxy merger and a newly-evolved stellar bulge, and most have LINER-like emission, which may indicate low luminosity AGN activity. Thus, the study of this short-lived phase of galaxy evolution can address the connections among mergers, star formation history, and the evolution of the nucleus as a galaxy evolves onto the red sequence. Surprisingly, we have discovered that many these galaxies, which are not currently forming stars, have significant reservoirs of molecular gas, which may fuel the central, supermassive black hole or later star formation episodes. We have also found that post-starburst galaxies host a disproportionate number of Tidal Disruption Events, in which a star is accreted onto the black hole. The recent starburst in these galaxies allows us to put strong constraints on the details of their recent star formation histories, and to place them on a timeline post-burst. I will discuss these results and other new work detailing how their stellar populations, gas content, and black hole properties evolve.
Apr. 29 , Friday
12 pm (INPA), not 12:10 pm
Marc Davis, UCB
LBL 50-5026 INPA room
"How cosmology has changed in 40 years: CfA1 and DEFW as examples of ancient redshift surveys and simulations”
This is a review of some of my ancient work, first published in 1979 and 1983, that made us aware of Large-Scale-Structure of the Universe. I also review the equipment used in the redshift survey. The abstract of the paper announcing the redshift survey states: "The space distribution of galaxies is frothy and characterized by large filamentary superclusters of up to 60 Mpc, corresponding to large holes devoid of galaxies.” Prior to this, the astronomical community had no idea of large-scale structure. Since the distribution looked unlike anything that anyone had produced, I felt it was most important to study the LSS by means of nbody simulations. Thus was born the DEFW. In simulations of size 32^3 particles (run on a Digital Equipment machine that fully occupied an air-conditioned room) we were able to show that massive neutrinos could not be the dark matter, but that CDM was a good candidate. We go so far as to introduce “biasing” in the galaxy distribution: "Finally, a situation in which galaxy formation is suppressed except in sufficiently dense regions is modelled which leads to models which can agree with observation quite well even for omega equal to one.” The data showed that an unbiased open CDM or a lambda–CDM was the best description, but there was no data to favor one model or another. This period of discovery was tremendous fun!

May 2016
May 3, Tuesday
1:10 pm (Cosmology/BCCP)
Tessa Baker, Oxford/Penn
Campbell 131
Agnostic Approaches to Gravity
The past decade has witnessed an explosion in the number of alternative gravity theories in the literature. Unfortunately, progress in testing these theories against cosmological data and eliminating them has been much slower. This has left us uncertain which direction in the ‘theory landscape’ is most worthy of our attention. I’ll present a new, theoretically consistent parameterisation for testing gravity in a completely model-independent way. Such agnostic frameworks offer protection from the shifting fashions of particular modified gravity theories. I’ll show the current constraints on this parameterisation, and indicate the role of future surveys in improvements. I’ll also show a visualisation of how cosmological constraints fit in with the `big picture’ of gravity, which extends to the astrophysical, laboratory and strong-field regimes.
May 5, Thursday
4:00 pm (LBL RPM)
Giorgio Gratta, Stanford
LBL 50A-5132
“Probing Gravity – and Other Forces – at Extreme Scales”
he inverse square law of gravity has been empirically tested to various degrees for distances between < 0.1mm to 1AU. Outside this range very little is known and, yet, physics beyond the standard model may actually introduce new long-range forces that would be observed as anomalies in the 1/R^2 behavior of gravity. I will discuss some new experiments designed to substantially advance our knowledge in this area, at the two extremes of the distance range. While the long distance regime would involve a deep space mission, a new breed of experiments focusing on the micron regime is already taking data, not only on gravitational interactions.
May 10, Tuesday
1:10 pm (special BCCP talk)
Brice Menard,JHU
Campbell 131
De-projecting astronomical surveys
Observations of celestial objects are inherently a 2D mapping on the sphere but astrophysical studies usually require the knowledge of 3D positions. For most extragalactic sources, this estimation relies on photometric redshifts which require strong assumptions and can lead to catastrophic failures. In this talk I will show how it is possible to use clustering measurements to infer redshifts for any type of extragalactic sources. I will show how to turn this idea into a new tool for redshift estimation and show how accurate it is. I will then present applications of this "clustering-redshift" technique using various datasets at UV, optical, IR and radio wavelengths, and will show a number of surprises.
May 12, Thursday
4:00 pm (LBL RPM)
Bharat Ratra, KSU
LBL 50A-5132
“Dark Energy: Constant or Time Variable? (…and other open questions)”
Experiments and observations over the last two decades have persuaded cosmologists that (as yet undetected) dark energy is by far the main component of the energy budget of the universe. I review a few simple dark energy models and compare their predictions to observational data, to derive dark energy model-parameter constraints and to test consistency of different data sets. I conclude with a list of open cosmological questions.
May 17, Tuesday
1:10 pm (special BCCP talk)
Moritz Munchmeyer,IAP
Campbell 131
Searching for oscillations and massive particles with CMB data and futuristic 21cm experiments
In the first part of my talk I will show how Planck CMB data has constrained and can further constrain inflationary models with oscillations in the correlation functions. Such oscillations can be generated by a variety of mechanisms, and I will focus in particular on axion monodromy models. In the second part of my talk I give an overview of signatures from heavy particles m~H during inflation, which goes under the names "quasi single field inflation" and "cosmological collider physics". Many of these signatures can be tested only with a futuristic experiment targeting the 21cm signal from the dark ages. I will discuss what masses and couplings we could probe with such a hypothetical experiment, exploring what the best possible experiments would tell us about the highest energies probed by the primordial particle collider.
May 20, Friday
12 pm (INPA), not 12:10 pm
Nico Hamaus, USM/LMU Munich
LBL 50-5026 INPA room
Void Dynamics - Constraints on Cosmology and Gravity
The universe is mostly composed of large and relatively empty domains known as cosmic voids, whereas its matter content is predominantly distributed along their boundaries. The remaining material inside them, either dark or luminous matter, is attracted to these boundaries and causes voids to expand faster and to grow emptier over time. Using the distribution of galaxies centered on voids identified in the SDSS and adopting minimal assumptions on their statistical motion, we constrain the average matter content in the universe and the linear growth rate of structure at z = 0.57. These measurements are robust to a battery of consistency tests. They surpass (and are complementary to) existing constraints by unlocking cosmological information on smaller scales through an accurate model of nonlinear clustering and dynamics in void environments. As such, our analysis furnishes a powerful probe of deviations from GR in the low density regime which has largely remained untested so far.

Past Months ( Previous Years )

September 2015:
Sep. 1, Tuesday
1:10 pm (Cosmology/BCCP)
Ai-Lei Sun, Princeton
Campbell 131A
Unveiling the link between supermassive black holes and galaxies
Feedback from Active galactic nuclei (AGN) has been proposed as an important quenching mechanism to suppress star formation in massive galaxies. We investigate the most direct form of AGN feedback - galactic outflows, in the most luminous AGN in the nearby universe. Using ALMA and Magellan observations to target molecular and ionized outflows, we find that luminous AGN can impact the dynamics and phase of the galactic medium, and confirm the complex multi-phase and multi-scaled nature of the feedback phenomenon. I end with a new imaging selection technique to find extended ionized outflows and characterize their frequency, size distribution, and luminosity dependence. This technique will open a new window for feedback studies in the era of large-scale optical imaging surveys like HSC and then LSST.
Sep. 8, Tuesday
1:10 pm (Cosmology/BCCP)
Marcel Schmittfull, UCB
Campbell 131A
"Large-Scale Structure beyond the Power Spectrum"
As recent and future galaxy surveys map the large-scale structure of the universe with unprecedented pace and precision, it is worthwhile to consider innovative data analysis methods beyond traditional Gaussian 2-point statistics to extract more cosmological information from those datasets. Such efforts are often plagued by substantially increased complexity of the analysis. Hoping to improve this, I will present simple, nearly optimal methods to measure 3-point statistics as easily as 2-point statistics, by cross-correlating the mass density with specific quadratic fields [arXiv:1411.6595]. Inspired by these results, I will argue that BAO reconstructions already combine 2-point statistics with certain 3- and 4-point functions automatically [arXiv:1508.06972]. I will present several new Eulerian and Lagrangian reconstruction algorithms and discuss their performance in simulations.
Sep. 14, Monday
12:10 pm (TAC)
Yuan Li, Michigan
Campbell 131
"Cooling, AGN Feedback and Star Formation in Simulated Cool-Core Galaxy Clusters"
The feedback from active galactic nuclei (AGNs) is widely considered to be the major heating source in cool-core galaxy clusters, preventing a classical cooling flow where the intra-cluster medium (ICM) cools at hundreds to a thousand solar masses per year. Numerical simulations with AGN feedback have successfully suppressed radiative cooling, but generally fail to reproduce the right amount of cold gas and the expected cyclical AGN activities. We perform adaptive mesh simulations using Enzo including both momentum-driven AGN feedback and star formation to study the interplay between cooling, AGN heating and star formation over 6.5 Gyr in an isolated cool-core cluster. Cold clumps first cool out of the ICM due to the non-linear perturbation driven by the AGN jets. These cold clumps feed both star formation and the supermassive black hole (SMBH), triggering an AGN outburst which increases the entropy of the ICM and reduces its cooling rate. Within 1-2 Gyr, star formation completely consumes the cold gas, leading to a brief shutoff of the AGN. The ICM quickly cools and develops multiphase gas again, followed by another cycle of star formation/AGN outburst. Within 6.5 Gyr, we observe three such cycles. The star formation rate (SFR) is correlated with the total amount of cold gas in the system. The average star formation rate is 40 solar masses per year. The black hole accretion rate shows a large scatter, but the average correlates well with the star formation rate.
Sep. 15, Tuesday
1:10 pm (Cosmology/BCCP)
Alexander Kaurov, Chicago
Campbell 131A
"Theoretical approaches for studying the epoch of reionization and Dark Matter annihilation"
We explore the properties of the intergalactic medium (IGM) during the epoch of reionization numerically. Our simulation models fully self-consistently all relevant physics, from radiative transfer to gas dynamics and star formation, in volumes of up to 40 co-moving Mpc, and with spatial resolution approaching 100 pc in physical units. The achieved resolution allows us to consider the IGM to be fully resolved. We propose a type of phase diagram which helps to visually analyze the ionization and recombination rates, and calculate the clumping factor.
We then test the analytical models of reionization and show how they relate to the numerical models. In particular we outline the weak points of the existing analytical models, and how they can be improved. Using our findings of the IGM properties in numerical simulations, we build an analytic model which closely mimics the numerical simulations and reproduces the neutral hydrogen power spectrum.
Lastly, we take a look at an exotic scenario of reionization, in which the Dark Matter annihilation has a significant impact on the global ionization fraction. We explore what constraints can be placed on Dark Matter from current and future observations of the epoch of reionization.
Sep. 15, Tuesday
3:10 pm
Sean Johnson, Chicago
501B Campbell
The integergalactic medium-galaxy connection: environment and AGN
Sep. 22, Tuesday
1:10 pm (Cosmology/BCCP)
Anson D'Aloisio, Washington
Campbell 131A
"Large opacity variations in the z~5.5 Lyman-alpha forest: implications for cosmic reionization"
When the first galaxies emerged, ~100 - 500 million years after the Big Bang, their starlight reionized and heated the intergalactic hydrogen that had existed since cosmological recombination. Much is currently unknown about this process, including what spatial structure it had, when it started and completed, and even which sources drove it. Recent observations of high-redshift quasars show large-scale spatial variations in the opacity of the z~5.5 intergalactic medium to Lyman-alpha photons. These spatial variations grow rapidly with redshift, far in excess of expectations from previous empirically motivated models. I will discuss possible explanations for the excess, as well as what they imply about the reionization process.
Sep. 24, Thursday
4:10 pm (Astronomy Colloquium)
Brant Robertson, UCSC 1 LeConte Hall
"New Constraints on Cosmic Reionization from Planck and Hubble Space Telescope"
Understanding cosmic reionization requires the identification and characterization of early sources of hydrogen-ionizing photons. The 2012 Hubble Ultra Deep Field (UDF12) campaign acquired the deepest blank-field infrared images with the Wide Field Camera 3 aboard Hubble Space Telescope and, for the first time, systematically explored the galaxy population deep into the era when cosmic microwave background (CMB) data indicate reionization was underway. High-redshift observations with HST including UDF12, CANDELS, and the Frontier Fields provide the best constraints to date on the abundance, luminosity distribution, and spectral properties of early star-forming galaxies. We synthesize results from these HST campaigns and the most recent constraints from Planck CMB observations to infer redshift-dependent ultraviolet luminosity densities, reionization histories, and the electron scattering optical depth evolution consistent with the available data. We review these results, and discuss future avenues for progress in understanding the epoch of reionization.
Sep. 25, Friday
12 pm (INPA), not 12:10 pm
Ashley Ross, OSU
LBL 50-5026 INPA room
"Robust and Precise Physical Measurements using Galaxy Surveys: Successes from BOSS and Lessons for the Future"
Galaxy surveys allow answers to fundamental questions such as: What is the nature of Dark Energy? Can we detect deviations from General Relativity (GR)? What is the mass of the neutrino(s)? 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 then discuss the early results from the Dark Energy Survey and the extended BOSS (eBOSS), both of which are in the early phases of data analysis/operation. I will conclude with a discussion of the results that will be afforded by future surveys, such as DESI.
Sep. 29, Tuesday
no 1:10 pm (Cosmology/BCCP) talk
cosmology talk up at LBL, 4 pm
Sep. 29, Tuesday
4:00 pm (LBL RPM)
Zachary Slepian, Harvard
LBL 50A-5132
"The Baryon-Dark Matter Relative Velocity and a New Approach to the 3-Point Correlation Function"
Due to their different behaviors before decoupling (z~1020), at high redshift (z~50) there is a relative velocity between baryons and dark matter that is coherent on very large scales. If this relative velocity couples to galaxies today, it can shift the BAO peak in the galaxy-galaxy 2-point correlation function. Such a shift would systematically bias the expansion history inferred using the BAO method. I will give a configuration space picture of the relative velocity and show that the 3-point correlation function can be used to remove this systematic bias from the BAO method. I will then present a reformulation of the 3PCF that:
  • permits computing the 3PCF in N^2 not N^3 time, N the number of objects
  • allows analytic calculation of a highly accurate covariance matrix
  • gives perturbation theory predictions in excellent agreement with both mock catalogs and data
Using this approach on ~700,000 galaxies in SDSS DR11 constrains linear and non-linear bias and demonstrates a ~2.5 sigma BAO feature in the 3PCF. I'll conclude with prospects for using this approach, and an analogous one for the anisotropic 2PCF, on DESI.

October 2015:
Oct. 2, Friday
12 pm (INPA), not 12:10 pm
Matteo Biagetti, Geneva
LBL 50-5026 INPA room
"Looking for Primordial non-Gaussianity in Large Scale Structure: a new insight from the peaks approach to halo clustering"
One of the challenges of modern cosmology is to discriminate among the many models of inflation which are able to predict a scale invariant spectrum as observed in the Cosmic Microwave Backround. One of the features which could help in this effort is non-Gaussianity, namely if the random seeds of the initial perturbations are to be described with higher than 2-point statistics. Non-Gaussianity in its simplest form is generally parametrized by a non-linearity parameter, fNL.
With the advent of large scale galaxy surveys, constraints on primordial non-Gaussianity are expected to reach order O(fNL) ~1. In order to fully exploit the potential of these future surveys, a deep theoretical understanding of the signatures imprinted by primordial non-Gaussianity on the large scale structure of the Universe is necessary. In this talk we will introduce the peak approach to halo clustering, which provides a framework to predict such signatures. We will show in detail how this prediction is calculated and compare it to other methods (such as the peak-background split ansatz).
Lastly, we will compare these different predictions to direct measurements of primordial non-Gaussianity in N body simulations and discuss the result.
Oct. 6, Tuesday
1:10 pm (Cosmology/BCCP)
Shadab Alam, CMU
Campbell 131A
"Testing Gravity using Galaxy Redshift Surveys and CMB"
The Redshift Space Distortions (RSD) in galaxy redshift surveys can probe the local dynamics at a given epoch of galaxy. I will discuss how redshift can help us learn the local dynamics and hence measure the nature of gravity at the epoch of the galaxy. I will show results from our recent analysis of SDSS-III high redshift sample (CMASS). I will then talk about combining similar RSD measurements from various other surveys to learn more about cosmology and modified gravity. I will show some of the current best constraints we have obtained for popular modified gravity models. I will end with a discussion on combining these measurements with CMB lensing in order to probe gravity to better precision and earlier time. I will also show the very first measurement of combining Planck CMB lensing and SDSS CMASS redshift space clustering.
Oct. 9, Friday
12 pm (INPA), not 12:10 pm
David Jones, JHU
LBL 50-5026 INPA room
Studying Host Galaxy Biases and Measuring w with Over 1,000 Photometrically Identified Type Ia Supernovae from Pan-STARRS
The Pan-STARRS medium deep survey observed over 5,000 supernova (SN) candidates across 70 square degrees of sky. Over the last two years, we have measured spectroscopic host galaxy redshifts for over 60% of these candidates, including over 1,000 cosmologically useful SNe Ia. In the context of these data, I discuss the effect host galaxy biases and core-collapse SN contamination will have on a precise measurement of the dark energy equation of state, w.
Oct. 13, Tuesday
1:10 pm (Cosmology/BCCP)
Yao-Yuan Mao, Stanford
Campbell 131A
How halo concentration impacts subhalo abundance and the galaxy-halo connection
The existence of dark matter substructures is one of the most distinct predictions of the cold dark matter model, and the relation between dark matter substructures and satellite galaxies is one of the most critical questions in galaxy formation. We address some aspects of these theoretical questions with new suites of cosmological simulations and zoom-in simulations of Milky Way-mass halos. In this talk, I will discuss how to model the abundance abundance function to account for its dependence on the halo formation history. I will also discuss how to parametrize and to constrain the concentration dependence in the galaxy-halo connection under the framework of abundance matching, and the implications of this new parameter.
Oct. 16, Friday
2 pm INPA (time change due to runaround)
Marco Raveri, SISSA
LBL 50-5026 INPA room
The Effective Field Theory approach to gravitation on cosmological scales
One of the major challenges in modern cosmology is to explain the phenomenon of cosmic acceleration. Thanks to the enormous amount of precise data that have been gathered and will be provided by cosmological surveys it will soon be possible to discriminate between competing models. I will discuss the relevance of the Effective Field Theory (EFT) approach in testing modified gravity and dark energy models that aim at solving the problem of cosmic acceleration. In particular I will briefly review the EFT construction and its implementation into the Einstein-Boltzmann solver EFTCAMB that is publicly available and can be used to test a wide range of models against cosmological observations. I will then comment on the theories that have been recently studied with this tool and the corresponding observational constraints.
Oct. 20, Tuesday
1:10 pm (Cosmology/BCCP)
Anthony Pullen, CMU
Campbell 131A
Constraining Gravity at the Largest Scales through CMB Lensing and Galaxy Velocities
We discuss recent work exploring the use of CMB lensing to probe E_G, the ratio between curvature and velocity perturbations. This quantity is distinct for various gravity models, breaking the degeneracy in current cosmological probes of gravity and dark energy. While the lensing signal within E_G has traditionally been probed with galaxy-galaxy lensing, galaxy-CMB lensing is a more robust lensing tracer that can probe E_G at higher redshifts with fewer astrophysical uncertainties. We present constraints to E_G using CMB data from Planck and galaxy data from the SDSS BOSS survey, which are consistent with general relativity (GR). We also show forecasts for future surveys, finding that upcoming photometric surveys combined with next-generation CMB surveys like Advanced ACTPol could produce < 1%-level constraints that could potentially rule out alternatives to GR.
Oct. 26, Monday
12:10 pm (TAC)
Coral Wheeler, Irvine
Campbell 131
"Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites"
If LCDM is correct, then all dark matter halos hosting galaxies are filled with abundant substructure down to very low mass scales (<< 10^9 Msun). Specifically, even the dark matter halos of Local Group field dwarfs should be filled with subhalos (~ 10^8 Msun), and thus are potential targets for hosting small (ultrafaint) galaxies. Here we make predictions for the existence of ultrafaint satellites of dwarf galaxies using the highest resolution cosmological dwarf simulations yet run (mgas~ 250 Msun). We simulate four dwarf halos (10^9 Msun < Mvir < 10^10 Msun) down to z=0 using the GIZMO (Hopkins 2014) code. We predict that ultrafaint galaxies (M* ~ 3,000 Msun) should exist as satellites around more massive dwarf galaxies (M* ~ 10^6 Msun) in the Local Group. These tiny satellites, as well as the two isolated ultrafaints, have uniformly ancient stellar population (> 10 Gyr) owing to reionization-related quenching. Our results suggest that Mhalo ~ 5 x10^9 Msun is a probable dividing line between halos hosting reionization "fossils" and those hosting dwarfs that can continue to form stars in isolation after reionization. Importantly, we show that the extended ~50 kpc regions around Local Group field dwarfs may provide efficient search locations for discovering new ultrafaint dwarf galaxies. If these tiny satellites are observed, this would provide evidence that dark matter substructure is truly hierarchical, as predicted in the standard paradigm.
Oct. 27, Tuesday
1:10 pm (Cosmology/BCCP)
Yi-Kuan Chiang, Austin
Campbell 131A
Galaxy Proto-clusters as an Interface Between Structure, Cluster, and Galaxy Formation
Proto-clusters, the ancestor large-scale structures of present-day galaxy clusters, are ideal laboratories to study dark matter assembly, cosmic baryon cycle, galaxy growth, and environmental impact on galaxy evolution. We extract LCDM predictions for the physical properties and observational signatures of galaxy proto-clusters as a function of time and cluster mass. I will talk about observation strategies and our ongoing efforts to search for and characterize z>~2 proto-clusters in photometric and spectroscopic galaxy surveys. I will discuss cluster progenitors in the context of cluster formation, galaxy evolution and cosmic star formation, highlighting their unique roles linking scales from large to small, and epochs form active star-formation to quenching.
Oct. 30, Friday
12 pm (INPA), not 12:10 pm
Nathalie Palanque-Delabrouille, Saclay
LBL 50-5026 INPA room
What Lyman-alpha surveys tell us about neutrinos
Although tiny, the signature that massive neutrinos leave on large-scale structures is today used as one of the most sensitive probes that can improve our knowledge on neutrino masses. After a brief introduction on the impact of neutrinos on the growth of structures, I will present constraints that were obtained recently using data from BOSS Lyman-alpha survey and from Planck, in combination with dedicated hydrodynamical simulations that reproduce the impact of neutrinos on the intergalactic medium. In a second part, I will show how Lyman-alpha data and minimal extension of the previous grid of hydrodynamical simulations can also lead to competitive limits on warm dark matter, whether in the form of a thermal relic particle or a sterile neutrino.

November 2015:
Nov. 3, Tuesday
1:10 pm (Cosmology/BCCP)
Cristobal Sifon, Leiden
Campbell 131A
Subhalos in the real Universe: satellite galaxy-galaxy lensing
I present galaxy-galaxy lensing measurements of the total masses of satellite galaxies in galaxy groups and clusters, obtained by combining high-quality imaging data with large spectroscopic galaxy catalogs. I focus on the overlap between the Kilo-Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey and present preliminary results on massive clusters from the Canadian Cluster Comparison Project (CCCP). The high purity of the resulting satellite catalogs allow us to cleanly interpret the galaxy-galaxy lensing signal as coming from the subhalos that host these galaxies. I compare these results with predictions from numerical simulations and results for central galaxies, and discuss the potential of satellite galaxy-galaxy lensing measurements as probes of galaxy formation and cosmology.
Nov. 6, Friday
12 pm (INPA), not 12:10 pm
Francisco Villaescusa-Navarro, Trieste
LBL 50-5026 INPA room
Massive neutrino signatures on the large-scale structure of the Universe
Neutrinos are described as fundamental particles by the standard model of particle physics. The fact that neutrinos are massive, as demonstrated by neutrino oscillations experiments, point towards physics beyond the standard model. One of the most important questions in modern physics is: what are the neutrino masses? Current tightest constrain on the sum of the neutrino masses arise from cosmological observables. In order to extract the maximum information from current and future surveys, as well as to avoid introducing biases in the values of the cosmological parameters, it is of primordial importance to understand, both at the linear and at the fully non-linear order, the impact that massive neutrinos induce on the distribution of matter, halos and galaxies. In this talk I will present some of the effects neutrinos induce on the Universe large-scale structure, among then the clustering of matter, the clustering of dark matter halos, the abundance of halos, the abundance of voids, their impact on the BAO peak and their effects of the spatial distribution of neutral hydrogen in the post-reionization era.
Nov. 10, Tuesday
1:10 pm (Cosmology/BCCP)
Ashley Perko, Stanford
Campbell 131A
"Beyond the CMB: The Effective Field Theory of Large Scale Structure"
The next hope to constrain cosmological parameters observationally is in surveys of the large scale structure (LSS) of the universe. LSS has the potential to rival the CMB in cosmological constraints because the number of modes scales like the volume, but the nonlinear clustering due to gravity makes it more difficult to extract primordial parameters. In order to take full advantage of the constraining power of LSS, we must understand it in the quasi-nonlinear regime. The effective field theory (EFT) of LSS provides a consistent way to perturbatively predict the clustering of matter at large distances. In this talk, I will discuss the status of the EFT of LSS and present recent work describing the inclusion of baryons in the EFT approach, including comparisons to N-body simulations.
Nov. 12, Thursday
4:10 pm (Astronomy Colloquium)
Aaron Parsons, UCB
1 LeConte Hall
"21 cm Cosmology: The End of the Beginning"
Since it was first proposed nearly two decades ago, measuring 21cm emission from neutral hydrogen in our early universe has tantalized us as a powerful probe of both cosmology and astrophysics. While the science case for 21cm cosmology, particularly during the Epoch of Reionization, is well established, the technical path toward measuring this signal has been more problematic. PAPER has recently distanced itself from its competitors, applying major technical breakthroughs to set the first physically meaningful upper limits on 21cm emission during reionization, and improving those limits a year later to show the presence of significant early heating. Even as PAPER's final season is under analysis, we are re-tooling our array to become HERA. New, 14-m dishes are replacing PAPER's smaller elements, giving HERA the sensitivity to drive beyond the detection phase of 21cm cosmology, into the exciting era of data-driven modeling. The results will revolutionize our understanding of galaxy and star formation and even improve upon CMB cosmology.
Nov. 13, Friday
11 am (SSL Colloquium)
Adrian Lee, UCB
SSL, Addition conference room
The LiteBIRD Space Mission and the Search for Inflation at the Beginning of the Universe
Inflation is the leading theory to explain the first instant of the universe. The case for inflation is building, and now we may have the opportunity to observe the signature of gravitational waves from the inflation event embedded in the cosmic microwave background. If seen, these signals would confirm inflation, point to the correct model for inflation, and, given the high energies involved, teach us about fundamental physics such as quantum gravity and string theory.
I will describe the LiteBIRD cosmic microwave background space mission, which is currently in collaborative Phase A studies in both Japan and the U.S. LiteBIRD will use a 50 cm diameter telescope and a ~2000 detector focal plane cooled to 100 mK to probe degree and larger angular scales in polarization. It will measure the entire sky with ~2 microK*arcmin noise (150 GHz), and measure in 15 bands from 40 to 400 GHz to measure and subtract foregrounds. A rapidly spinning Half-Wave Plate will be used to rapidly "chop" between two polarization states. It will orbit at the second Lagrange point (L2).
Nov. 17, Tuesday
4:00 pm (RPM) **note time/location change**
Anna Patej, Harvard
"Distributions of Baryons from the Virial Radius of Galaxy Clusters to Large Scales"
I will discuss my recent work on the distributions of baryonic matter on various scales, from the gas and galaxies in galaxy clusters to the clustering of massive galaxies on large scales. Near the virial radius of galaxy clusters, long-standing analytical models of structure formation as well as recent simulations predict the existence of steep density jumps in the gas and dark matter profiles. I will describe a new method for deriving models for the gas distribution in galaxy clusters, which relies on a few basic assumptions -- including the existence of such density jumps -- and show a resulting profile for the gas that is in good agreement with X-ray observations of cluster interiors and simulations of the outskirts.
Since cluster member galaxies are expected to follow similar collisionless dynamics as the dark matter, the galaxy density profile should show a steep density jump as well. I will address the question of whether we can find evidence for a feature consistent with a density jump with current observations, and will additionally discuss avenues for probing the density jumps with future data sets.
Moving to larger scales where massive galaxies of different types are expected to roughly trace the same large-scale structure, I will present a test of this prediction by measuring the clustering of red and blue galaxies at z~0.6 using the CMASS sample of galaxies from DR12 of SDSS-III. The stochasticity between these two samples can be quantified via the correlation coefficient r, which can be constructed from two different statistics, both of which indicate that on intermediate scales (20 < R < 100 Mpc/h) there is low stochasticity between the two samples of galaxies.
Lastly, I will describe some ongoing and future observational efforts, focusing on my involvement with the DECam Legacy Survey (DECaLS), a pathfinder imaging survey for the upcoming Dark Energy Spectroscopic Instrument (DESI) galaxy redshift survey.
Nov. 20, Friday
12 pm (INPA), not 12:10 pm
Fabian Koehlinger, Leiden
LBL 50-5026 INPA room
"Cosmological constraints from weak lensing: present measurements and future challenges"
Weak lensing is a powerful tool for cosmological inference. In this talk I will discuss two major applications, cosmic shear and galaxy-galaxy lensing, in the context of recent studies carried out together with my collaborators. In the first part I will discuss a technique to directly extract the matter power spectrum in different redshift bins from weak lensing measurements. I will show results from an application to state-of-the-art CFHTLenS data and discuss the constraints on cosmological parameters and neutrino mass. In the second part of my talk I will focus on the potentials and challenges of future large weak lensing surveys such as Euclid for cosmological constraints derived from galaxy cluster counts. For that accurate and precise cluster masses are paramount. In this context, I will discuss the impact of various sources of bias on weak lensing cluster mass estimates.
Nov. 24, Tuesday
No talk

December 2015:
Dec. 1, Tuesday
1:10 pm (Cosmology/BCCP)
Ying Zu, CMU
Campbell 131A
"Constrain Galaxy Formation Physics from Large-Scale Structure Measurements and Weak Lensing"
Galaxy formation is one of the most intractable phenomena in astrophysics due to the enormous complexity and diversity in the assembly histories of individual galaxies. Modern galaxy surveys provide a unique avenue to understanding galaxy formation physics in a statistical context, through various large-scale structure measurements and the weak gravitational lensing of large numbers of galaxies. I will introduce a new probabilistic framework, called the "iHOD" model, which enables strong constraints on the stellar-to-halo mass relation and the underlying driver for the quenching of star formation in galaxies probed by the Sloan Digital Sky Survey. I will also highlight the advantages of the iHOD model by comparing it with traditional HOD and SHAM methods, as well as an age-matching model in which galaxy quenching depends on halo age at fixed stellar mass. Lastly I will discuss the prospect of extending the iHOD framework to constrain the curious effect of "galaxy assembly bias" using marked statistics.
Dec. 8, Tuesday
1:10 pm (Cosmology/BCCP)
No talk (reading period)

Dec. 8, Tuesday
3:10 pm (Galform)
Kim Vy Tran, Texas A&M
501 Campbell
"ZFOURGE & ZFIRE: Galaxy Evolution Over 10 Billion Years"
ZFOURGE and ZFIRE are deep near-IR surveys that track how galaxies assemble over cosmic time. ZFOURGE identifies approximately 30,000 galaxies up to redshifts of z~7 using a custom set of medium-band near-IR filters that provide high precision photometric redshifts. ZFIRE selects galaxies from ZFOURGE for spectroscopic follow-up with Keck/MOSFIRE to measure how baryons cycle between stars, winds, and the Inter-Stellar Medium at z~2. Here I summarize our results that include stellar mass functions at 0.5 < z < 3, building a library of composite Spectral Energy Distributions, and ISM conditions of galaxies in clusters at z~2.
Dec 11, Friday
12 pm (INPA), not 12:10 pm
Douglas Scott, UBC
LBL 50-5026 INPA room
In the history of studying the Cosmic Microwave Background, the lowest-order moments were initially the most important. But now that the spherical harmonic modes of the CMB have been measured so precisely out to high multipoles, these first moments of the sky get very little attention. But let me try to point out some things you might not already know about the CMB monopole, dipole and quadrupole - as well as throwing in a discussion of how these moments behave for other cosmic backgrounds, such as the cosmic infrared background or even the neutrino background.
Dec. 15, Tuesday
1:10 pm (Cosmology/BCCP)
Benny Trakhtenbrot, Zurich
Campbell 131
"Tracing the origins of the relations between super-massive black holes and their host galaxies"
In the local Universe, super-massive black holes (SMBHs) are observed to be closely linked to their host galaxies. In this talk I will address the co-evolution of SMBHs and their hosts, from the local Universe, out to z~4. Several observational studies suggest that SMBH growth generally precedes that of the stellar population in the host. Among these, I will present new results from a Keck campaign, that establish this picture at z~3.5. In particular, some objects show extremely BH-to-host mass ratios, more than an order of magnitude higher than in the local Universe. A rich collection of multi-wavelength data demonstrates that SMBH-related feedback does *not* necessarily affect the host galaxies. I will argue that a comprehensive understanding of the interplay between SMBHs and galaxy evolution requires high-resolution sub-mm observations with ALMA, some of which we have already obtained.
Dec. 16, Wednesday
4:00 pm (LBL RPM)
Rachel Mandelbaum, CMU
LBL 50A-5132
“Recent Progress and Future Prospects for Weak Lensing Cosmology”
Measurements of weak gravitational lensing (coherent shape distortions of distant galaxies due to the lensing effect of mass between us and those galaxies) and are among the most promising ways to learn about the equation of state of dark energy, the theory of gravity on cosmological scales, and the connection between galaxies and the dark matter density field. In this talk, I will review the state of the field of weak lensing, including recent cosmological analysis and prospects with future surveys. I will then discuss some of the obstacles to robust weak lensing cosmology, such as the difficulty in estimating coherent galaxy shape distortions in real data, or in removing the effect of coherent galaxy shape alignments that arise due to (for example) large-scale tidal fields. After presenting recent progress on both of these sources of systematic uncertainty, I will conclude with future prospects for reducing them to below the statistical error and enabling robust cosmological constraints with future large surveys such as LSST, Euclid, and WFIRST.
Dec. 18, Friday
12:00 pm (INPA Seminar)
Ting Li, Texas A&M
LBL 50-5026
"Exploring Milky Way Halo Substructure with Large-Area Sky Surveys"
Over the last two decades, large-area photometric surveys have provided deep photometric catalogs of stars in the Milky Way. As a result, our understanding of the formation of the Galactic halo has evolved from a simple monolithic collapse model to a much more complex and dynamic structure. The stellar halo is now known to be inhabited by a variety of spatial and kinematic stellar substructures, ranging from stellar streams to dwarf galaxy satellites, all of which are predicted by hierarchical Lambda-CDM models of galaxy formation. In my talk, I will present the latest discoveries of the halo substructures found in the Dark Energy Survey (DES). I will also discuss the spectroscopic follow-up observations of the stellar debris candidates found in the Two Micron All Sky Survey and the dwarf galaxy candidates found in DES. These newly discovered features can provide a more complete census of our Galaxy's formation history.

January 2016:
Jan 14, Thursday
4 pm (RPM)
Franz Elsner, UCL
LBL 50-5032
"Parameter estimation in cosmology and the Planck likelihood"
The inference of cosmological parameters requires the construction of a likelihood function that acts as an interface between theory and observational data. Using the CMB experiment Planck as a worked example, I provide an overview of the challenges associated with the analysis of high-resolution, state of the art experiments. In particular, I will discuss the approximations necessary to make an analysis feasible in practice, the role of nuisance parameters, and tests used to assess the robustness of the results. Reviewing the most important cosmological implications of Planck, I will conclude with an outlook of what we can expect to learn from future experiments.
Jan 15, Friday
12 pm (INPA), not 12:10 pm
Marius Lungu, Penn
LBL 50-5026 INPA room
Mapping the Polarized Microwave Sky with ACTPol
ACTPol is a novel polarization-sensitive receiver for the Atacama Cosmology Telescope (ACT) designed to measure the Cosmic Microwave Background (CMB) anisotropies to high precision on a wide range of angular scales. The instrument features three optically-independent feedhorn-coupled transition-edge sensor (TES) bolometer arrays continuously cooled below 100 mK with the aid of a dilution refrigerator. The first two arrays, each composed of 512 single-frequency polarimeters sensitive to 150 GHz, were deployed sequentially during the 2013 and 2014 observing seasons. A third, 256-polarimeter dichroic array operating at both 90 and 150 GHz was added in early 2015. I will present an overview of the experiment and discuss some of the challenges associated with converting raw data into accurate, high-resolution maps of the CMB. I will also highlight some early scientific results and report on the status of ongoing analyses.
Jan 22, Friday
12 pm (INPA), not 12:10 pm
Florian Beutler, LBL
LBL 50-5026 INPA room
Cosmology with the Baryon Oscillation Spectroscopic Survey
I will present the most recent results from the SDSS-III BOSS-DR12 analysis. I will focus on the analysis of the power spectrum multipoles, which allows to constrain the growth of structure through redshift-space distortions. Such measurements can be used to test GR and measure the sum of the neutrino masses. Beside RSD we also constrain the geometry of the Universe through the Alcock-Paczynski effect and Baryon Acoustic Oscillations.
Jan. 26, Tuesday
1:10 pm (Cosmology/BCCP)
Reinhard Genzel, UCB and Max-Planck
Campbell 131
"Recent results on the properties of z~1-2 star forming galaxy population"
I will discuss recent results of the KMOS-3D and PHIBSS surveys relating to the properties of the massive star forming population at the peak of cosmic star formation activity. Topics will be the angular momentum distribution, rotation curves, baryon fraction, gas content and outflows.
Jan 29, Friday
12 pm (INPA), not 12:10 pm
Brandon Hensley, JPL
LBL 50-5026 INPA room
Dust Polarization in the Microwave: Challenges on the Quest for B-Modes
Polarized emission from Galactic dust has been established as a key foreground in the search for primordial B-modes. Although dust modeling efforts and observations are painting an ever clearer picture of polarized dust emission in the microwave, a number of critical uncertainties remain. First, I will argue that analysis of the latest full-sky Planck maps calls into question the interpretation of anomalous microwave emission as rotational emission from spinning PAHs, thereby opening the door to other mechanisms that may be substantially more polarized. Second, I will describe current efforts to construct a comprehensive model of dust polarization by synthesizing data from the ultraviolet to the radio, focusing on the implications for the frequency-dependence of the polarized dust emission. Finally, I will suggest observations that could mitigate key uncertainties in the dust physics and enable higher fidelity foreground modeling.

February 2016
Feb. 2, Tuesday
1:10 pm (Cosmology/BCCP)
Daniel Green, CITA/Berkeley
Campbell 131
ν Physics in the CMB
I will describe the measurement of the cosmic neutrino background using the CMB and the implications for beyond the Standard Model physics. I will explain the importance of a CMB Stage IV experiment for these goals.
Feb. 5, Friday
12 pm (INPA), not 12:10 pm
Daniel Gruen, SLAC
LBL 50-5026 INPA room
The Dark Energy Survey: Status and new gravitational lensing results
The Dark Energy Survey is in the process of imaging 5000 sq. deg. of the southern sky in five broad-band filters. Its primary purpose is to constrain cosmology and the physics of dark energy using weak gravitational lensing, galaxy clusters, baryonic acoustic oscillations, and supernova distance measurements. I will give an overview of the recently released early results on the Science Verification data set and upcoming work on the main survey data, with a focus on weak gravitational lensing and the newly developed statistics of galaxy troughs.
Feb. 9, Tuesday
1:10 pm (Cosmology/BCCP)
Laura Sales, Riverside
Campbell 131
Dwarf galaxies and their satellites as extreme probes of LCDM
Dwarf galaxies are extremely diverse in their morphology, from rotationally-supported star-forming disks to gas-free spheroidal stellar systems with no star-formation and negligible rotation. We use cosmological hydrodynamical simulations to show that environment plays a significant role on the assembly history, star formation and globular cluster population of dwarfs, solving a long-standing issue on the origin of dwarf ellipticals in galaxy clusters. But as observations push deeper into fainter and fainter galaxies, the theoretical predictions become most extreme. LCDM galaxy formation models make two clear predictions: i) galaxy formation should become increasingly inefficient in lower mass halos, implying that dwarfs are only able to collect a few percent of their baryonic content, and (ii) dwarfs, like any galaxy, should be surrounded by a wealth of dark-matter substructure, implying that faint satellites of dwarfs should be common. I will use cosmological simulations to address these predictions and to compare them with available observational constraints, such as the Baryonic Tully-Fisher relation and the inventory of dwarfs in the Local Volume. The recent detection by the DES survey of several dwarfs potentially associated with the Magellanic Clouds is an exciting discovery that confirms that the hierarchical nature of galaxy formation extends down to the faintest limits probed, just as predicted by LCDM. On the other hand, the extreme baryon content of some isolated dwarfs presents a newly recognized challenge to the paradigm that still awaits resolution.
Feb. 10, Wednesday
12 pm (BOSS lunch talk)
Nic Ross, ROE
LBL 50-4205
“The Curious Case of the Disappearing (and Appearing) Quasars”
Feb. 11, Thursday
4 pm (RPM)
Neal Dalal, UIUC
LBL 50-5032
"Detecting Dark Matter Substructure Using ALMA"
Dark matter halos surrounding galaxies are expected to contain copious substructure, in the form of gravitationally bound subhalos. Local Group observations suggest that our Galaxy has a deficit of substructure (the Missing Satellites Problem), possibly indicating new physics in the dark sector. I will describe how gravitational lensing may be used to measure the amount of dark substructure that exists in typical galaxy halos. In particular, I will explain how observations by the newly commissioned ALMA observatory of dusty galaxies from CMB surveys can probe halo substructure. I will show first results from our ALMA Cycle 2 observations, and argue that ALMA should be able to answer the Missing Satellites Problem in upcoming years.
Feb. 16, Tuesday
1:10 pm (Cosmology/BCCP)
Joe Hennawi, MPIA
Campbell 131
First Measurement of the Small Scale Structure of the Intergalactic Medium
There is no such thing as empty space. Indeed, the most barren regions of the universe are the vast expanses between the galaxies, known as the intergalactic medium (IGM). Averaging just one lonely atom per cubic meter, this primordial gas left over from the Big Bang encodes fundamental information about our universe's history. About half a million years after the Big Bang, the plasma of primordial baryons recombined to form the first neutral atoms, releasing the cosmic microwave background and initiating the cosmic 'dark ages'. During this period primordial gas expanded and cooled to very low temperatures T~ 20 K, until the stars and black holes in the first galaxies emitted enough ionizing photons to reionize and reheat the universe. The thermal state of gas in the IGM is a relic of these reionization phase transitions, which can be measured via optical observations of bright distant quasars at cosmological lookback times of a few gigayears. On Mpc length scales, gas in the intergalactic medium traces density fluctuations in the underlying and gravitationally dominant dark matter, but on smaller scales of hundreds of kpc, fluctuations are suppressed because the ~10^4 Kelvin gas is pressure supported against gravity, analogous to the classical Jeans argument. This Jeans pressure smoothing scale thus quantifies the small scale structure of the IGM and provides a record of cosmic reionization and thermal evolution. Recently we have shown that it is possible to directly measure this scale by characterizing the coherence of correlated intergalactic absorption lines in the spectra of pairs of quasars, at small angular separation on the sky. I will describe a statistical method which quantifies correlated absorption in quasar spectra, which is highly sensitive to the pressure smoothing scale, and present its first-ever measurement with data collected from the Keck telescopes. Our preliminary results suggest that the pressure smoothing scale is smaller than expected from the standard models of reionization and the thermal evolution of the IGM.
Feb. 19, Friday
12 pm (INPA), not 12:10 pm
Elisabeth Krause, Stanford
LBL 50-5026 INPA room
Activities in the LSST DESC Theory & Joint Probes Working Group
Last fall the Dark Energy Science Collaboration (DESC) wrote a Science Roadmap (SRM) detailing the key projects and deliverables required to have the DESC analysis pipeline in place to undertake a cosmology analysis of LSST year 1 data. I will provide an overview and user guide to the SRM to make this document more accessible. I will then give a broad introduction to the different lines of research developed in the Theory and Joint Probes working group within DESC, and highlight near term projects which aim to optimize the constraining power of systematics limited analyses.
Feb. 23, Tuesday
1:10 pm (Cosmology/BCCP)
Andrew Hearin, Yale
Campbell 131
Modeling Galaxies in the Era of Precision Cosmology: An open source approach with Halotools
In this talk, I will review how models of the galaxy-halo connection can provide constraints on cosmology and insight into galaxy formation physics. Theoretical predictions in conventional formulations of these models are plagued by persistent systematic errors, for example due to uncertainty associated with "assembly bias". As galaxy surveys continue to provide ever more precise information on large-scale structure measurements, these theory-level systematics will place a ceiling on the reliability of the conclusions that can be drawn from traditional galaxy-halo techniques. In this talk, I'll describe how the open source Halotools package provides an object-oriented python framework designed to help remedy assembly bias and other systematics associated with nonlinearities in structure formation. Halotools is analogous to Boltzmann codes such as CMBFAST, CAMB and CLASS, but instead provides an optimized pipeline for populating mock galaxy catalogs into both low- and high-resolution simulations. I will conclude by describing how Halotools can be used to provide robust constraints on galaxy formation and help prepare the field of cosmology for the arrival of Stage IV dark energy experiments.
Feb. 23, Tuesday
4 pm (RPM)
Andreu Font, LBL
LBL 50-5032
"Studying the Expansion of the Universe with quasar spectra"
After six years of observations, the Baryon Oscillation Spectroscopic Survey (BOSS) ended last year, and all its data is already public (SDSS Data Release 12). During these years, it has used the SDSS telescope to obtain spectra of 1.5 million galaxies to get very accurate measurements of the Baryon Acoustic Oscillations (BAO) scale at redshift z ~0.5. At the same time, BOSS observed over 184 000 high redshift quasars (z>2.15) with the goal of detecting the BAO feature in the clustering of the intergalactic medium, using a technique known as the Lyman alpha forest (LyaF). In this talk, I will overview several results from the LyaF working group in BOSS, including the measurement of BAO at z=2.4 both from the auto-correlation of the LyaF (Delubac et al. 2015) and from its cross-correlation with quasars (Font-Ribera et al. 2014). From the combination of these studies, we are able to measure the expansion rate of the Universe 11 billion years ago with a 2% uncertainty.
Feb. 24, Wednesday
2 pm (Particle seminar)
Jeremiah Ostriker, Princeton
LBL 50-5132
"Dark Matter: Very Light Particles Have the Right Properties to Explain Small Scale Structure and Delayed Galaxy formation"
The standard LCDM paradigm has been phenomenally successful on many fronts. In particular, all predictions with respect to the overall cosmology and structure on large scales have proven accurate. But on small scales - kilo parsecs and less – the hierarchical model has been neither confirmed nor refuted. For example, dark matter cusps are predicted, but observations do not strongly confirm the predictions. With L, Hui, S. Tremaine, and E. Witten an exploration is under way concerning the possibility that very light axions provide the bulk of the dark matter. This choice, sometimes labeled the Fuzzy Dark Matter (“FDM”) hypothesis, would strongly smooth out small scale structure due to standard quantum effects and in addition would strongly suppress early formation of low mass halos and small galaxies. Thus predictions for “first light” provide strong tests of this cosmological model. In it the peak formation epoch of low mass halos (eg 10^8 Msolar) and the corresponding galaxies is later than in the standard LCDM model.

March 2016
Mar. 1, Tuesday
1:10 pm (Cosmology/BCCP)
Gil Holder, McGill
Campbell 131
"Mapping missing matter with the South Pole Telescope and other mm/submm-wave telescopes"
There are issues of dark or missing matter on scales ranging over 12 orders of magnitude that can be addressed with CMB experiments.
On cosmological scales, we can make mass maps using lensing of the CMB. I'll show recent results from the South Pole Telescope using these mass maps to investigate the connection between dark matter and galaxies in the Dark Energy Survey.
On galaxy scales, these CMB maps (and other mm/submm wave maps) are very effective at discovering star-forming galaxies that are strongly gravitationally lensed. Follow-up with ALMA has allowed us to use these lenses to search for dwarf-galaxy scale substructure in the galaxy that is doing the lensing. I'll show our recent detection of a 10^9 solar mass object using this method.
On solar system scales, CMB experiments are now sensitive enough over a wide enough area that it should be possible to detect planets and dwarf planets in the outer solar system using their thermal radiation.
Mar. 3, Thursday
4:00 pm (LBL RPM)
Julien Guy, LPNHE
LBL 50A-5132
"The Prospects and Challenges of the Dark Energy Spectroscopic Instrument"
I will present the prospects of DESI for the measurement of Dark Energy in light of a decade of efforts to unveil its nature, from the discovery of cosmic acceleration with type Ia supernovae, to the most recent results with supernovae and baryon acoustic oscillations (BAO).
DESI will map cosmic expansion up to redshifts of 3, anchoring distances at low redshift to the era of past deceleration with an order of magnitude gain in precision compared to current surveys. DESI data will offer a stringent test of the standard model of cosmology, with important possibilities for discovery.
The project, however, is not free from experimental challenges. I will review the analysis efforts needed to extract the whole potential of the BAO probe, from the optimization and calibration of the efficiency of the redshift survey, to the characterization of the instrumental noise in the Lyman-alpha forests.
Mar. 4, Friday
12 pm (INPA), not 12:10 pm
Michelle Lochner, UCL
LBL 50-5026 INPA room
Photometric Supernova Classification With Machine Learning
The automated classification of photometric supernovae has become an active field in recent years in light of current and upcoming imaging surveys, including the Dark Energy Survey (DES) and the Large Synoptic Telescope (LSST). Spectroscopic confirmation of type will be impossible for all supernovae discovered with these surveys, making photometric classification an important step for both cosmology and core-collapse studies. With this in mind, we develop a multi-faceted classification pipeline, investigating the use of machine learning algorithms combined with existing and novel methods of extracting features from light curves. In this talk, I will provide an overview of the methods used and discuss the results from applying the pipeline simulated supernova data. I will also discuss the effect of representativeness of training set and show that accurate classification is possible without redshift information.
Mar. 7-8, Monday-Tuesday
CMB S4 workshop
Mar. 7, Monday
4:15 pm (Physics colloquium)
Steve Furlanetto, UCLA
1 LeConte
"New Insights into Cosmic Reionization"
The epoch of reionization, when intergalactic hydrogen is ionized by photons from stars or other luminous sources, is one of the frontiers of observational cosmology, the landmark event where structure formation touched every baryon in the Universe. I will describe recent advances toward understanding its end phases, including the observed galaxy populations and the intergalactic medium just after reionization completes, and recent improvements in our understanding of reionization as a phase transition.
Mar. 8, Tuesday
1:10 pm (Cosmology/BCCP)
Ryan Hickox, Dartmouth
Campbell 131
"The Hidden Monsters: Obscured AGN in the era of NuSTAR and WISE"
The study of powerful, highly obscured accreting black holes has recently seen dramatic advances with hard X-ray observations from NuSTAR and mid-infrared data from WISE. These "hidden" obscured quasars were for a long time elusive, but we can now identify millions of these objects across most the sky, and characterize the nature of their obscuration and their role in the formation of galaxies. I will describe a few recent efforts to characterize the star formation rates, dark matter halo masses, and level of obscuration in these "hidden" AGN, and present evidence that (at least some) powerful obscured quasars represent an evolutionary phase in the evolution of their host galaxies, as predicted by models of galaxy formation.
Mar. 10, Thursday
4:00 pm (RPM)
Shirley Ho, CMU
LBL 50A-5132
"Joining Forces Against the Dark Universe: From the Cosmic Microwave Background to Large Scale Structure"
Despite tremendous recent progress, gaps remain in our knowledge of our understanding of the Universe. We have not yet pinned down the properties of dark energy, nor have we confirmed Einstein’s theory of Gravity at the largest scales.Current and upcoming large sky surveys of the Cosmic Microwave Background (CMB), Large Scale Structure (LSS) in galaxies, quasars and the Lyman-alpha forest present us with the best opportunity to understand properties of the Universe.
I will first review recent cosmology results from the CMB and LSS, concentrating on BOSS results using Baryon Acoustic Oscillations and Redshift Space Distortions. I will then introduce novel cosmological probes which combine CMB with LSS directly. These novel probes will open new windows into the momentum field of the Universe and Gravity at the largest scales. I will finally put these into the context of upcoming surveys such as Dark Energy Spectroscopic Instrument (DESI), Wide Field Infrared Survey Telescope (WFIRST) and CMB S4.
Mar. 11, Friday
12 pm (INPA), not 12:10 pm
Rachel Bean, Cornell
LBL 50-5026 INPA room
Next Generation Cosmological Constraints on the Dark Sector and Gravity
A rich portfolio of upcoming complementary cosmological experiments will be producing data in the next 5-10 years. We discuss ways in which these can be used in combination to extract insights into the properties of the dark sector (dark matter, neutrinos and dark energy) and gravity on cosmic scales and mitigate pernicious astrophysical systematics.
Mar. 15, Tuesday
1:10 pm (Cosmology/BCCP)
Anastasia Fialkov, Harvard
Campbell 131
The Missing Pages of Cosmic History
The first 400 Myr of cosmic history are extremely challenging to model and observe, but at the same time are also deeply important to understand since some of the crucial events in cosmic history, such as the formation of the very first stars, took place in that time window. Perhaps the most promising way to fill in the missing pages of cosmic history is by detecting the 21-cm signal of neutral hydrogen emitted by the intergalactic medium. This signal is predicted to be observable by the upcoming generation of radio telescopes, and, being correlated to the radiation emitted by stars and quasars, it can tell us a great deal about the epoch of Reionization and Cosmic Dawn. In this talk I will discuss theoretical modeling of the 21-cm signal, expand on its properties, and outline what can be learned from this signal about the early Universe, focusing on the nature of the first heating sources.
Mar. 18, Friday
12 pm (INPA), not 12:10 pm
Francisco Kitaura, Potsdam
LBL 50-5026 INPA room
"Signatures of the primordial Universe from its emptiness"
Sound waves from the primordial fluctuations of the Universe imprinted in the large-scale structure, called baryon acoustic oscillations (BAOs), can be used as standard rulers to measure the scale of the Universe. These oscillations have already been detected in the CMB, the distribution of galaxies, and the Lyman alpha forest. We propose to measure BAOs from the troughs (minima) of the density field. We estimate the troughs from the empty circumspheres centres constrained by tetrahedra of galaxies using Delaunay triangulation. Our theoretical models based on an unprecedented large set of 1,000 detailed simulated void catalogues are remarkably well confirmed by observational data. To the generation of such catalogues we have used improved perturbation theory and bias schemes, including halo and stellar mass reconstruction considering nonlinear, nonlocal and stochastic bias components. We use the largest recently publicly available sample of Luminous Red Galaxies from SDSS-III BOSS to unveil for the first time a >3 sigma BAO detection from voids in observations. I will discuss the potential of this technique to obtain improved measures of the BAO in future surveys such as eBOSS, DESI, JPAS, LSST, 4MOST, or EUCLID.
Mar. 22, Tuesday
No talk, spring break

Mar. 28, Monday
12:10 pm (TAC)
Nicholas Battaglia, Princeton
Campbell 131
Constraints on halo energetics from combined Sunyaev-Zel'dovich measurements
Both feedback and non-thermal processes play important roles in the thermodynamic and star-formation properties of the intracluster medium (ICM). Recently, there have been exciting detections of the kinetic Sunyaez-Zel'dovich (SZ) from galaxy clusters. These measurements and future ones provide a new window into the thermodynamic properties of the ICM. I will show how we propose to constrain the average feedback and non-thermal pressure support by combining thermal SZ and kinetic SZ measurements. These constraints will further inform the sub-grid feedback models used in galaxy formation simulations.
Mar. 29, Tuesday
1:10 pm (Cosmology/BCCP)
Campbell 131

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