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:

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 Kohlinger, Leiden
LBL 50-5026 INPA room

Nov. 24, Tuesday
1:10 pm (Cosmology/BCCP)
Campbell 131A

December 2015:
Dec. 1, Tuesday
1:10 pm (Cosmology/BCCP)
Ying Zu, CMU
Campbell 131A

March 2016
Mar. 8, Tuesday
1:10 pm (Cosmology/BCCP)
Tessa Baker, Oxford/Penn
Campbell 131A

Past Months ( Previous Years )

  Privacy & Security Notice, etc.   Contact   Updated January 2008