Upcoming and Previous Seminars (Past months or Previous years)

May 1, Monday
12:10 pm (TAC)
Aurelian Hees, UCLA
Campbell 131
Searches for extensions to General Relativity: from the Solar System to our Galactic Center
In this talk, we will review the basic principles of General Relativity and give motivations to search for alternative theories of gravitation. Then, we will review some of the very recent tests of the gravitation theory performed in the Solar System insisting on their implications. We will also discuss how the monitoring of short-period stars orbiting the supermassive black hole in our Galactic Center can be used to test General Relativity. Recent results in the fifth force formalism will be presented and plans to measure relativistic effects during the closest approach of the star S0-2 in 2018 will also be developed.

May 4, Thursday
4 pm (RPM)
Manoj Kaplinghat, Irvine
LBL 50-5132
“The self-interacting dark matter paradigm: motivations and tests”
I will describe how a simple model where dark matter has large elastic self-interactions (cross section over mass of order barns per GeV) can fully explain the observed diversity of all galactic rotation curves. I will summarize the constraints imposed on model building by observations of clusters of galaxies and end with an outline of tests of this paradigm.

May 22, Monday
12:10 pm (TAC)
Dylan Nelson, Garching
Campbell 131
The next generation of cosmological hydrodynamical simulations: Introducing IllustrisTNG
I will introduce the new IllustrisTNG project, a next generation of cosmological magneto-hydrodynamical simulations. The first, "TNG100", realizes a 100 Mpc volume and is a close analog to the original Illustris simulation. The second simulation, "TNG300", includes 2500^3 resolution elements in a 300 Mpc box, a volume more than twenty times larger hosting 280 massive clusters above 10^14 Msun and more than 12,000 Milky Way mass galaxies. Both simulations are run using the new TNG model for galaxy formation physics, developed in the moving-mesh code Arepo, incorporating several physical and numerical improvements, including a full treatment of cosmic magneto-hydrodynamics (MHD). I will first discuss the TNG model for galaxy formation, including the specific changes we made post-Illustris, and why, assessing the outcome of the new model on some benchmark runs. Leveraging the power of the new large-volume simulations, I will then show early results on the bimodal galaxy optical color distribution at z=0. Accounting for the attenuation of stellar light by dust, we compare the (g-r) colors of simulated galaxies to the observed distributions from SDSS, spanning 10^9 < Mstar/Msun <10^12. We find a striking improvement with respect to the original Illustris simulation, as well as excellent quantitative agreement with observations. I will discuss the relationships between the color of a galaxy and its SFR, gas content, and magnetic properties, among others. I will finish with some insights on the buildup of the color-mass plane, the role of the BH in quenching and color transition, and the formation of the red sequence in TNG.

May 25, Thursday
1:00 pm
Florian Kuhnel (KTH Royal Institute of Technology, Stockholm) Place: 50B-4205
Primordial Black Holes as Dark Matter
Abstract: Primordial black holes are black holes that may have formed in the early Universe. Their masses span potentially a range from as low as the Planck mass up to many orders of magnitude above the solar mass. Besides their conceptual importance regarding our understanding of quantum effects and gravity, they may provide the dark matter. In order to constrain this possibility, a proper understanding of their formation mechanism is crucial. In my talk, after a general introduction on primordial black holes, I will discuss recent investigations on this issue, including so-called critical collapse, non-sphericity and non-Gaussianity. Furthermore, I will discuss how to properly compare extended primordial black-hole mass spectra to observational constraints, such as those deriving from recent microlensing surveys.

May 26, Friday
12 pm (INPA)
Titouan Lazeyras, Garching
LBL 50-5132
Dark matter halo bias from separate universe simulations
The large-scale local bias parameters of dark matter halos are essential to describe the statistics of halos and galaxies on large scales, as well as for the halo model of the matter distribution. Using so-called separate universe simulations, we recently obtained precise measurements of the three leading bias parameters. For b2 and b3, these are the most precise measurements to date. We compare our results with bias parameters obtained from two and three points cross-correlation functions and with theoretical predictions from the excursion set peaks (ESP) model. Using the same set of simulations, we further investigate halo assembly bias, i.e. the dependence of the halo bias on properties other than the halo mass. We focus on four halo properties : halo concentration, spin, ellipticity and mass accretion rate. We measure assembly bias for b1 and nd good agree- ment with previous studies. Furthermore, we present results for assembly bias in b2 which are among the rst ones and most precise to date. To try and better understand the physical mechanisms behind assembly bias, we also look at the joint dependence of bias on two halo properties in addition to the mass.

June 1 , Thursday
4pm (RPM)
Florian Beutler, Portsmouth
LBL 50-5132
“On the reliability of Baryon Acoustic Oscillation (BAO) measurements”
In this talk I will discuss the reliability of the Baryon Acoustic Oscillation (BAO) signal in the distribution of galaxies. The solid theoretical understanding of this observable means that it represents one of only a few cosmological observables that are not yet dominated by systematic errors. This is one reason why BAO are one of the main science drivers for future galaxy surveys like DESI and Euclid. I will discuss my recent work on the relative velocity effect as one potential systematic for BAO. The relative velocity effect originates from the same physical effects which imprinted the BAO signal and therefore acts on the same scale. I will introduce this effect in detail, discuss how we can include it in our modeling and present current constraints from the Baryon Oscillation Spectroscopic Survey (BOSS).

Nov 14, Tuesday
1:10 pm (Cosmology/ BCCP)
Anze Slosar, BNL
Campbell 131

Sep. 14 , Thursday
4pm (RPM)
Cora Dvorkin, Harvard
LBL 50-5132

Past Months ( Previous Years )

Aug 29, Monday
12:10 pm (TAC)
Dan Whalen, ICG, Portsmouth
Campbell 131
Finding the First Cosmic Explosions
Primordial stars formed about 200 Myr after the Big Bang, ending the cosmic dark ages. They were the first great nucleosynthetic engines of the universe and may be the origins of the supermassive black holes (SMBHs) found in most massive galaxies today. In spite of their importance to the evolution of the early universe not much is known for certain about the properties of Pop III stars. But with the advent of JWST, Euclid, WFIRST and the ELTs it may soon be possible to directly observe their supernovae in the NIR and thus unambiguously constrain the properties of the first stars. I will present radiation hydrodynamical calculations of the light curves of the first SNe in the universe and discuss strategies for their detection. I will also describe how some high-z SNe may already have been found in surveys of galaxy cluster lenses such as CLASH and Frontier Fields. I will conclude my talk with new calculations of the evolution and collapse of supermassive primordial stars that constrain the masses of the first quasars at birth.

Aug 31, Wednesday
12 pm (INPA talk, noon, not 12:10)
Dan Whalen, ICG, Portsmouth
LBL 50-5026
How Supermassive Black Holes Form by z ~ 7
Over 100 quasars have now been discovered at z > 6, less than a Gyr after the Big Bang. The discovery of supermassive black holes (SMBHs) by this epoch posed severe challenges to current theories of structure formation because it is not known how objects so massive appeared by such early times. However, we have now developed numerical simulations that show that these quasars can form from direct collapse black holes at z ~ 20 if they are fed by strong, cold accretion streams, like those thought to fuel the rapid growth of some galaxies at later epochs. I will discuss these simulations and formation channels for DCBHs at high redshift. I will also discuss prospects for their detection in the NIR and at 21 cm by Euclid, JWST and the SKA.

Sep 6, Tuesday
1:10 pm (Cosmology/ BCCP)
Miguel Aragon-Calvo, Riverside
Campbell 131
A cosmic web model of galaxy formation and some adventures in data visualization
The cosmic web is the stage where galaxy formation and evolution occurs. However, current models of galaxy formation ignore the effect of cosmic environment beyond basic descriptors and rely on crude approximations that do not capture the complex interplay between galaxies and their environment. In this talk I will discuss the Cosmic Web Detachment (CWD) model recently proposed to describe the effect of cosmic environment on galaxy formation and evolution. The CWD model can naturally reproduce a range of galaxy properties and provides a framework to interpret observations in a truly cosmological context.
During the talk I will make use of innovative visualization techniques including stereo 3D , 3D printing and natural interaction and discuss how data visualization can be used as a driver for scientific discovery.

Sep 13, Tuesday
1:10 pm (Cosmology/ BCCP)
Andrea Petri, Columbia
Campbell 131
Cosmology with Weak Gravitational Lensing: the information beyond the Power Spectrum ,
also movies here and here
The LambdaCDM model of the Universe has been proven tremendously successful in explaining experimental data with only a few free parameters. While observations from a variety of sources (CMB, Supernovae IA, BAO, Large Scale Structure) have done an outstanding job in constraining the standard parameter space, the Dark Energy equation of state, w, remains essentially unconstrained. Weak Gravitational Lensing (WL) is a promising observational technique in this sense, because of its sensitivity to late universe physics, when Dark Energy dominates. Because of late time non-linearities, WL observables are not Gaussian distributed, and quadratic statistics such as Power Spectra likely miss some of the cosmological information contained in observations. Possible complementary statistics one could consider include higher order moments, peak counts and topological descriptors. I will review the fundamentals of WL, as well as the ray--tracing formalism on which our numerical simulations are based. I will also summarize our efforts in improving parameter constraints using a variety of higher order statistics, with both galaxy and CMB lensing data. I will also outiline some recent results on analytical prediction and origin of WL convergence peaks. To conclude, I will discuss some of the numerical subtleties that one must take into consideration when using higher order statistics to analyze WL data sets.

Sep 15, Thursday
4 pm (RPM)
Nick Kaiser, Hawaii
LBL 50-5132
The Physics of Gravitational Redshifts in Clusters of Galaxies
Wojtak, Hansen and Hjorth and others have measured the long-predicted gravitational redshift of light escaping from galaxy clusters using Sloan Digital Sky Survey data. The effect is very small, corresponding to a velocity shift of only ~10 km/s in clusters with internal random motions of order 600 km/s, but the result appears to be robust and is in good agreement with general relativity predictions and possibly in conflict with some alternative theories. It was soon realised that the interpretation of this measurement is more complex than initially thought as one needs to allow for the transverse Doppler (TD) redshift. In this talk I will describe how there are actually two more rather subtle and unexpected physical effects that need to be considered in interpreting these observations; there is a `light cone' effect that augments the TD shift, and there is a competing effect that reverses the sign of the transverse Doppler effect so that we actually observe a transverse Doppler blue-shift. I will discuss how these observations constrain gravitation theory, and along the way discuss some issues concerning the interpretation of astronomical redshifts in a broader context.

Sep 15, Thursday
4:10 pm (Astronomy Colloquium)
Freeke van de Voort, UCB and Taiwan
1 Le Conte
Cosmic gas flows: the key to understanding galaxy formation
The evolution of galaxies is critically linked to the gas flows in and the assembly history of their surrounding haloes. Although observationally gas is harder to detect than stars, it lies at the heart of our understanding of galaxy formation. The circumgalactic medium provides the gas reservoir to fuel star formation in galaxies, but galaxies do not just grow passively. Strong outflows driven by supernovae and supermassive black holes heat and enrich the galaxy's environment, thus completely changing its evolution. And it doesn't end there: galaxies can also grow through merging and they can be stripped of their gas and stars when they become satellites. I will discuss results from cosmological, hydrodynamical simulations and focus on the interaction of galactic feedback and gas accretion, their effect on the growth of galaxies, and on ways to probe this baryonic cycle observationally.

Sep 16, Friday
12 pm (INPA talk, noon, not 12:10)
Nick Kaiser, Hawaii
LBNL 50-5132
The Effect of Gravitational Lensing on Cosmological Parameter Estimation
A very long standing question in cosmology is whether gravitational lensing biases the distance-redshift relation D(z) or the mean flux density of sources. Interest in this has been rekindled by recent results in 2nd order relativistic perturbation theory which, if correct, would have profound implications for cosmological parameter estimation from both SN1a and the CMB. In this talk I shall first review the somewhat confusing history of the subject, going back to the early '60s and including both Weinberg's 1976 argument that there should be no effect on grounds of flux conservation and the general relativistic "focusing theorem" of the '80s that foreshadows the more recent results. I then show how the claimed subtle relativistic effects actually result from confusion between different types of averaging (specifically between averaging over sources and averaging over directions on the sky). I also show that while Weinberg's argument conceals a hidden loop-hole, in that he assumes that the area of a surface of constant redshifts is unaffected by lensing, the error incurred is only a one part in a million effect. This result validates conventional methods for analysis of the CMB and shows that, counter to claims in the literature, the focusing theorem does not in fact reveal an intrinsic tendency for structure to cause focusing of light rays.

Sep 19, Monday
12:10 pm (TAC)
Sarah Wellons, Harvard/CfA
Campbell 131
The diverse progenitors and descendants of (compact elliptical) galaxies in cosmological simulations
bservations of the high-redshift universe have revealed a population of galaxies which are already very massive (~10^11 Msun at z=2) and have typical sizes of < 2 kpc, much smaller than their counterparts in the local universe. How such dense, massive galaxies form, and why they appear to be less common at low redshift, have been questions of interest for both theorists and observers. I will discuss these questions in the context of the Illustris simulation, a hydrodynamical cosmological simulation in which tens of thousands of galaxies form, evolve, and interact with each other, situated within a cosmological context. I select a group of massive compact galaxies at z=2 in the simulation and trace them back and forth in time to discover both how they formed at high redshift, and what they evolve into at the present day. I find a variety of both progenitors (our compact galaxies form either via central starbursts generally brought on by mergers, or by racing out to the tip of the SF main sequence and forming very early) and descendants (many formerly-compact galaxies lurk at the core of a more massive galaxy today, others were consumed in mergers, and some evolve passively and undisturbed). Finally, I will discuss the implications of these results for observational methods of connecting galaxy populations across redshifts - in particular, the assumption of a constant cumulative comoving number density - and suggest an improvement to this method which takes the complexity and variety of galaxy evolutionary paths into account.

Sep 20, Tuesday
1:10 pm (Cosmology/ BCCP)
Hy Trac, CMU
Campbell 131
New Ways to Use Dynamical Measurements of Galaxy Clusters
Galaxy clusters contain large amounts of cold dark matter, hot ionized gas, and tens to hundreds of visible galaxies. The abundance of clusters as a function of mass and redshift can be used to probe the growth of structure and constrain cosmological parameters. Dynamical measurements probe the entire mass distribution, but standard analyses yield unwanted high mass errors. First we show that modern machine learning algorithms can improve mass measurements by more than a factor of two compared to using standard scaling relations. Support Distribution Machines are used to train and test on the entire distribution of galaxy velocities to maximally use available information. Second we show that cluster abundance can be quantified with the distribution of direct observables rather than inferred mass to avoid uncertainties in the mass-observable relation. A novel statistic called the velocity distribution function (VDF) is constructed by stacking the probability distribution of galaxy velocities for a select number of clusters in a given volume. The VDF can be measured directly and precisely, and produces unbiased constraints on cosmological parameters. Finally we discuss how our approaches can be generalized to multi-wavelength observations of gravitational lensing, SZ effect, and X-ray emissions.

Sep 27, Tuesday
1:10 pm (Cosmology/ BCCP)
Emmanuel Schaan, Princeton
Campbell 131
Understanding large-scale structure from the CMB
In this seminar, I will present two promising ways in which the cosmic microwave background (CMB) sheds light on critical uncertain physics and systematics of the large-scale structure.
Shear calibration with CMB lensing (arXiv:1607.01761): Realizing the full potential of upcoming weak lensing surveys requires an exquisite understanding of the errors in galaxy shape estimation. In particular, such errors lead to a multiplicative bias in the shear, degenerate with the matter density parameter and the amplitude of fluctuations. Its redshift-evolution can hide the true evolution of the growth of structure, which probes dark energy and possible modifications to general relativity. I will show that CMB lensing from a stage 4 experiment (CMB S4) can self-calibrate the shear for an LSST-like optical lensing experiment. This holds in the presence of photo-z errors and intrinsic alignment.
Evidence for the kinematic Sunyaev-Zel'dovich (kSZ) effect (arXiv:1510.06442); cluster energetics: Through the kSZ effect, the baryon momentum field is imprinted on the CMB. I will report significant evidence for the kSZ effect from ACTPol and peculiar velocities reconstructed from BOSS. I will present the prospects for constraining cluster gas profiles and energetics from the kSZ effect with SPT-3G, AdvACT and CMB S4. This will provide constraints for galaxy formation and feedback models.

Sep 29, Thursday
4:00 pm (Astronomy Colloquium)
Joop Schaye, Leiden
Le Conte
Simulating the formation of galaxies
The realism of hydrodynamical simulations of the formation and evolution of populations of galaxies has improved considerably in recent years. I will try to give some insight into the reasons behind this success, focusing in particular on the importance of subgrid models and the associated limitations. I will also present recent results from the cosmological EAGLE simulations as well as from other projects.

Oct 4, Tuesday
1:10 pm (Cosmology/ BCCP)
Irene Shivaei, Riverside
Campbell 131
A Multi-Wavelength Census of Star Formation and Dust in Galaxies at z ~ 2
Redshift of z ~ 2 is an important era in the history of the universe, as it contains the peak of star formation rate density and quasar activity. I will talk about the properties of galaxies during this era from two different, yet complementary, aspects: star formation and mass assembly, and galactic dust enrichment. In this study, I use a wealth of spectroscopic data obtained by the MOSDEF survey. I will introduce the MOSDEF survey, which is a multi-institutional project that uses the near-IR MOSFIRE spectrograph on the Keck I telescope to characterize the gaseous and stellar contents of ~ 1500 rest-frame optically selected galaxies at 1.37 < z < 3.80. Furthermore, I incorporate the mid- and far-IR data from the Spitzer and Herschel telescopes to obtain a complete census of obscured and unobscured star formation in galaxies. Specifically, I explore the star-formation rate and stellar mass relation at z ~ 2, using multi-wavelength star-formation rate tracers (UV, Hα, 24 micron, and far-IR). Moreover, I investigate, for the first time, the variation of the PAH emission at 7.7 micron, traced by Spitzer/MIPS 24 micron, in galaxies spanning a wide range in metallicity at z ~ 2. Our results have important implications for high-redshift studies that adopt 24 micron flux to derive total IR luminosity and star-formation rate.

Oct 11, Tuesday
1:10 pm (Cosmology/ BCCP)
Derek Inman, CITA
Campbell 131
Non-linear neutrino effects in large scale structure
Detecting the cosmic neutrino background, either through observation or experiment, has proven to be a substantial challenge due to the very small neutrino mass. Typical cosmological studies rely on two point statistics and must distinguish small neutrino effects from much larger cold dark matter (CDM) and baryonic ones. Higher order statistics, in which generic CDM effects can be cancelled by design, are a promising avenue to improve constraints on neutrino properties. However, utilizing them requires an accurate understanding of neutrino co-evolution with the non-linear CDM. Surprisingly, the low neutrino mass makes this computation a significant numerical challenge. I will describe our N-body simulations that study this problem, including the TianNu simulation, which contains nearly three trillion particles. I will then describe three non-linear effects: the evolution of the neutrino power spectrum, the relative velocity dipole between neutrinos and cold dark matter, and differential neutrino condensation onto halos.

Oct 18, Tuesday
1:10 pm (Cosmology/ BCCP)
Chen He Heinrich, Chicago
Campbell 131
Complete Reionization Constraints from Planck 2015 Polarization
I will present a recent analysis of the Planck 2015 data that is complete in the reionization observables from large angle CMB polarization measurements using principal components. By allowing for an arbitrary ionization history, this technique tests the robustness of total optical depth inferences from the usual instantaneous reionization assumption. A reliable measurement of the total optical depth is important for the interpretation of many other cosmological parameters such as the dark energy and neutrino mass. We found that Planck 2015 data not only allow a high redshift z>15 component to the optical depth but prefer it at the 2σ level. This high redshift component contributes to a higher total optical depth than in the instantaneous reionization analysis, illustrating the need for a complete treatment of reionization observables. I will further demonstrate the power of the principal component method to efficiently constrain models given predictions of ionization history by applying our effective likelihood code.

Oct 20, Thursday
4 pm (RPM)
Marilena LoVerde, Stony Brook
LBL 50-5132
Neutrinos, Quintessence and Structure Formation in the Universe
The large-scale structure of our universe (the distribution of galaxies on very large-scales for instance) contains a wealth of information about the origin, evolution, and matter content of the universe. Extracting this information relies crucially on understanding how galaxies and other biased objects trace the large-scale matter distribution. In a universe such as our own, with both cold dark matter and massive neutrinos, or in alternative cosmologies with clustered quintessence, this problem is much more complicated. I will discuss new tools that my group has developed to study gravitational evolution in cosmologies with multiple fluids, the novel signatures we have identified including a new probe of neutrino mass, and the broader implications for models of large-scale structure.

Oct 21, Friday
12 pm (INPA talk, noon, not 12:10)
Enea Di Dio,
LBNL 50-5132
Relativistic effects on LSS: power spectrum and bispectrum
I will discuss the Large Scale Structure power spectrum and bispectrum in a relativistic framework. To first order, a relativistic description includes terms beyond the Kaiser approximation (Doppler effects and galaxy evolution), gravitational potentials and integrated terms (cosmic magnification, integrated Sachs-Wolfe and Shapiro time-delay). I will show how they can be isolated by correlating different probes, or by using the so-called multi-tracer technique. Through this technique future surveys may be able to detect some relativistic contributions. I will also discuss relativistic effects beyond linear theory, the relativistic bispectrum and how the lensing deflection angle smears out the BAO wiggles.

Oct 25, Tuesday
1:10 pm (Cosmology/ BCCP)
Alessandro Manzotti, Chicago
Campbell 131
Delensing CMB B-modes: results from SPT
A promising signature of cosmic inflation is the presence of a "B-mode" component in the polarization of the Cosmic Microwave Background (CMB) induced by primordial gravitational waves. For many inflation models, this B-mode signal is predicted to be at a level detectable in the near future. However current searches are limited by a "lensing B-mode" component that is produced by gravitationally lensing primordial E modes. In order to potentially detect the inflationary signal from B-mode measurements, lensing B modes must be characterized and removed in a process referred to as "delensing." This process has been studied extensively theoretically and with simulations, but has not been performed on polarization data. In this talk, we present the results of CMB B-mode delensing using polarization data from the South Pole Telescope polarimeter, SPTpol. Furthermore, using realistic simulations that include filtering and realistic CMB noise, we will show what is currently limiting the delensing efficiency and how it will rapidly improve in the near future.

Oct 27, Thursday
4 pm (Astronomy Colloquium)
Shirley Ho, LBL
1 Le Conte
Digging into the Large Scale Structure: Galaxies, Filaments and Neutral Hydrogen
Galaxy spectroscopic surveys provide the means to map out this cosmic large-scale structure in three dimensions, furnishing a cornerstone of observational cosmology. The information is given in the form of galaxy locations, and is typically condensed into a single function of scale, such as the galaxy correlation function or power-spectrum. However, galaxy correlation functions are not the only information those surveys provide. One of the most striking features of N-body simulations is the network of filaments into which dark matter particles arrange themselves. We however traditionally only use the information contained in the positions of the galaxies, and in some occasions, we look at other cosmic structures of the Universe such as voids.
In this colloquium, I explore the information beyond the galaxy positions in large sky surveys combining novel ideas with recent techniques in statistical methods and machine learning algorithms. In particular, we will investigate the following two topics: the "cosmic web" that are mostly ignored in any large scale structure analyses in the Universe and how it affects the surrounding galaxies; and Damped Lyman Alpha absorbers that are hidden within the observed quasar spectra, which dominates the neutral hydrogen budget after reionization.

Oct 28, Friday
**1 pm** (INPA talk), time change due to runaround
Samuel Flender, Argonne
LBNL 50-5132
The kinematic Sunyaev-Zel'dovich effect as a cosmology probe?
Future data from galaxy redshift surveys, combined with high-resolutions maps of the cosmic microwave background, will enable measurements of the pairwise kinematic Sunyaev-Zel'dovich (kSZ) signal with unprecedented statistical significance. This signal probes the matter-velocity correlation function, scaled by the average optical depth (tau) of the galaxy groups and clusters in the sample, and is thus of fundamental importance for cosmology. However, in order to translate pairwise kSZ measurements into cosmological constraints, external constraints on tau are necessary. In this talk I will present the current state of kSZ measurements, including a recent measurement by SPT and DES, insights from simulations, as well as recent progress in modeling the tau profile of galaxy clusters.

Nov 1, Tuesday
1:10 pm (Cosmology/ BCCP)
Alison Strom, Caltech
Campbell 131
"Star-formation history and chemical enrichment in the early Universe: clues from the rest-UV and rest-optical spectra of high-redshift galaxies"
Galaxies at the peak of cosmic star formation (z~2-3) exhibit significantly higher star formation rates and gas fractions at fixed stellar mass than nearby galaxies. These z~2-3 galaxies are also distinct in terms of their nebular spectra, reflecting important differences not only in the physical conditions of their interstellar medium (e.g., electron density and gas-phase metallicity), but also in the details of their massive stellar populations, especially their ionizing radiation fields. Jointly observing galaxies' HII regions, at rest-UV and rest-optical wavelength, and massive stars, in the rest-UV bandpass, is central to constructing a framework for understanding the differences between z~2-3 and z~0 star-forming galaxies and for self-consistently explaining the trends observed in the high-redshift population. I will present results from the Keck Baryonic Structure Survey (KBSS), which uniquely combines observations of the rest-optical spectra of ~400 individual galaxies (obtained with Keck/MOSFIRE) with deep rest-UV spectroscopy of many of the same galaxies (obtained with Keck/LRIS). These measurements represent one of the most comprehensive spectroscopic studies of z~2-3 galaxies to date and, when compared with predictions from photoionization models, offer compelling evidence that high-redshift galaxies exhibit chemical abundance patterns distinct from local galaxies, likely as the result of systematic differences in their star-formation histories.

Nov 4, Friday
12 pm (INPA talk, noon, not 12:10)
Colin Hill,
LBNL 50-5132
New Information in Ancient Photons: Novel Approaches to CMB Secondary Anisotropies
Cosmic microwave background (CMB) experiments have recently entered a new era in which cosmological and astrophysical constraints derived from the secondary anisotropies (due to late-time effects) substantially improve upon those derived from the primary anisotropies alone. In this talk, I will discuss new approaches to extract information from these signals, placed in the broader context of component separation in CMB analysis. I will describe novel methods for studying the thermal Sunyaev-Zel'dovich (SZ) effect --- the inverse-Compton scattering of CMB photons off hot electrons --- using cross-correlations, stacking, and beyond-Gaussian statistics. I will present projections for thermal SZ extraction from Advanced ACT data based on a new component-separation pipeline, as well as new foreground-marginalized forecasts for the all-sky tSZ (and $\mu$) spectral distortion monopole from the proposed PIXIE satellite. I will then present a measurement of the kinematic SZ effect (due to electrons moving with a net bulk velocity along the line-of-sight) with Planck, WMAP, and WISE data using a novel estimator that does not require redshift estimates for individual tracers. This measurement yields the tightest kinematic SZ-derived constraint on the low-redshift baryon fraction to date. The result is consistent with constraints derived from the primary CMB and Big Bang nucleosynthesis, thus resolving the long-standing "missing baryon problem".

Nov 8, Tuesday
1:10 pm (Cosmology/ BCCP)
Michael Wilson, ROE
Campbell 131
Geometric and growth rate tests of gravity with the linearised galaxy distribution
This talk will first outline the consistency of the VIPERS PDR-2 census of the galaxy distribution at z=0.8 with the expansion and growth rate histories predicted by General Relativity and a Planck (2015) cosmology. These may be inferred from the observed anisotropy of the galaxy power spectrum, which is due to both the coherent infall of galaxies towards clusters (outflow from voids) and the assumption of an expansion history differing from the true one.
I will then present the results of including a simple density transform prior to the analysis; this tackles the root-cause of non-linearity by down-weighting the most massive structures and extends the validity of theoretical models. Moreover, this weighting would amplify signatures of modified gravity in ‘shielded’ models and represents a higher-order statistic, which contains information beyond that available to the power spectrum.
Finally, the final VIPERS data release will occur on Nov 18th (http://vipers.inaf.it). I will detail the pros, and cons, of the survey and describe the breadth of the accompanying clustering analyses.

Nov 15, Tuesday
1:10 pm (Cosmology/ BCCP)
Vanessa Boehm, Garching
Campbell 131
A new bias to CMB lensing measurements
Weak gravitational lensing distorts the cosmic microwave background in a characeristic way that carries valuable information about the growth of structure and the spatial geometry of the Universe. The rapidly improving precision of measurements of this effect also requires a corresponding increase in the accuracy of theoretical modeling. A commonly made approximation is to model the CMB lensing potential as a Gaussian random field. In the work presented, we drop this assumption and analytically quantify the influence of the non-Gaussianity of the lensing potential, arising from nonlinear structure formation, on CMB lensing measurements. In particular, we evaluate the impact of the nonzero bispectrum of large-scale structure on the standard estimator for the lensing potential power spectrum. The result is a new, so far ignored, bias term that adds to the estimator and should be accounted for in future experiments. After an introduction to CMB lensing and CMB lensing measurements, I will explain the origin and structure of the bias and discuss its significance in current and upcoming surveys. I will further show updates of the published results that 1) include an improved modeling of the bispectrum of large-scale structure and 2) account for contributions to the lensing potential bispectrum from post-Born corrections. Finally, I will show preliminary results of a verification of the analytically derived bias with simulations.

Nov 15, Tuesday
4 pm (RPM)
Emmanuel Schaan, Princeton
LBL 50-5132
“Non-linearities in the large-scale structure: noise and signal”
he primordial density perturbations seen in the cosmic microwave background have collapsed under gravity to form the large-scale structure we see in the universe today. This evolution is non-linear, and therefore introduces coupling between Fourier modes that would otherwise be independent. I will present two consequences of this non-linear coupling.
Halo sample variance (arXiv:1406.3330): Gaussian estimates for the errors in large-scale structure measurements exaggerate the scientific impact of these measurements. Non-linear evolution and finite volume effects are both significant sources of non-Gaussian covariance, which reduce the ability of power spectrum measurements to constrain cosmological parameters. I will present a joint likelihood for cluster counts, power spectrum and bispectrum, including the non-Gaussian covariances, and show that a joint analysis of these observables can reduce this “information loss”. In some cases, the resulting improvement on cosmological parameters is equivalent to doubling the survey area.
Lyman-alpha – CMB lensing bispectrum (arXiv:1607.03625): The Lyman-alpha forest seen in the spectra of quasars is a powerful tool for constraining warm dark matter models and the neutrino masses, as well as properties of the intergalactic medium. Its use as a cosmological probe relies on modeling the connection between neutral gas and dark matter. I will present the first detection of the correlation between the Lyman-alpha forest and the cosmic microwave background, using data from BOSS and Planck. This signal quantifies the non-linear response of the neutral hydrogen to a large-scale overdensity, and thus tests our understanding of the connection between neutral gas and the dark matter.

Nov 16, Wednesday
12 pm (scientific computing seminar)
Davide Martizzi, UCB
380 Soda Hall
Studying cosmic structure formation with computational methods.
In this talk I will show how the use of numerical simulations has greatly aided the study of cosmic structure formation: galaxies, groups of galaxies, galaxy clusters. I will provide motivation for the use of numerical methods in astrophysics and cosmology and describe state-of-the-art techniques used by numerical astrophysicists to solve challenging problems. Finally, I will discuss the key results achieved in the field of numerical cosmology, as well as the current physical and computational challenges that the numerical cosmology community is facing.

Nov 17, Thursday
4 pm (RPM)
Robert Kirshner, Moore Foundation
LBL 50-5132
“Doing WFIRST Science Now: Supernovae in the Infrared”
An infrared-capable 2.4m telescope is presently in orbit: the Hubble Space Telescope. This makes it possible to do rest-frame infrared observations of Type Ia supernovae. In the infrared, SN Ia are more nearly standard candles and there is less obscuration by dust. I will give a status report on RAISIN2, an HST program that tiptoes into the realm of WFIRST science today.

Nov 17, Thursday
4 pm (Astronomy Colloquium)
Michael Boylan-Kolchin, Austin
1 Le Conte
"Far-reaching Science with Near-field Cosmology"
The local Universe provides a unique and powerful way to explore galaxy formation and cosmological physics. Through measurements of the abundances, kinematics, and chemical composition of nearby systems that can be studied in exquisite detail, we can learn about the initial spectrum of cosmological density fluctuations, galaxy formation, dark matter physics, and processes at cosmic dawn that might otherwise remain unobservable. I will highlight some recent developments in this rapidly-changing discipline of “near-field cosmology”, with an emphasis on (1) the interplay between dark matter and baryons in the centers of dwarf galaxies, and (2) connections between the local Universe and high-redshift galaxies.

Nov 18, Friday
12 pm (INPA talk, noon, not 12:10)
Daniele Sorini, Heidelberg
LBL 50-5132
3D-IMS: Accurately Modeling the Lyman-alpha Forest in Collisionless Simulations
Cosmological hydrodynamic simulations can accurately predict the properties of the intergalactic medium (IGM), but only under the condition of retaining the high spatial resolution necessary to resolve density fluctuations in the IGM. This resolution constraint prohibits simulating large volumes, such as those probed by BOSS and future surveys, like DESI and 4MOST. To overcome this limitation, I present “3D Iteratively Matched Statistics” (3D-IMS), a novel method to accurately model the Lyman-alpha forest with collisionless N-body simulations, where the relevant density fluctuations are unresolved. I compare the results given by 3D-IMS with a reference high-resolution hydrodynamic simulation, demonstrating that 3D-IMS can reproduce the probability density function (PDF), line-of-sight and 3D power spectra of the Lyman-alpha forest with high accuracy. I also show that commonly used approximate methods to model such statistics from N-body simulations are not suitable when large volumes (>~100 cMpc) are needed. The 3D-IMS method could be used to improve our understanding about the 3D correlations of the Lyman-alpha flux measured from BOSS, and their relation with the thermal state of the IGM or other small scale physics. This could increase the accuracy of the estimate of the BAO scale.

Nov 22, Tuesday
1:10 pm (Cosmology/ BCCP)
no talk
Campbell 131

Nov 29, Tuesday
1:10 pm (Cosmology/ BCCP)
Luke Kelley, Harvard
Campbell 131
Massive Black Hole Binary Mergers and their Gravitational Waves
Gravitational Waves (GW) from stellar-mass BH binaries have recently been observed by LIGO, but GW from their supermassive counterparts have remained elusive. Recent upper limits from Pulsar Timing Arrays (PTA) have excluded significant portions of the predicted parameter space. Most previous studies, however, have assumed that most or all Massive Black Hole (MBH) Binaries merge effectively and quickly. I will present results derived—for the first time—from cosmological, hydrodynamic simulations with self-consistently coevolved populations of MBH. We perform post-processing simulations of the MBH merger process, using realistic galactic environments, including models of dynamical friction, stellar scattering, gas drag from a circumbinary disk, and GW emission—with no assumptions of merger fractions or timescales. We find that despite only the most massive systems merging effectively (and still on gigayear timescales), the GW Background is only just below current detection limits with PTA. Our models suggest that PTA should make detections within the next decade, and will provide information about MBH binary populations, environments, and even eccentricities. I’ll also briefly discuss prospects for observations of dual-AGN, and the possible importance of MBH triples in the merger process.

Nov 30, Wednesday
12 pm (INPA talk, noon, not 12:10)
Wai Ling Kimmy Wu, UCB
LBNL 50-5132
Constraining Inflation with BICEP/Keck and SPT
Inflation generically predicts a background of stochastic gravitational waves. In the standard cosmological model LCDM, these primordial gravitational waves (PGW) are the only source to the odd-parity (curl) B-mode polarization on the Cosmic Microwave Background (CMB) at the epoch of recombination. Therefore, we can learn much about inflation by constraining or potentially detecting primordial gravitational waves. In this talk, I will present two frontiers that advance the search for primordial gravitational waves: instrumentation of BICEP3 and delensing with SPTpol. I will conclude with the future outlook of such search with CMB-S4. In the first part of the talk, I will discuss the design and performance of BICEP3 — the path-finder of BICEP/Keck program’s Stage-3 effort. The BICEP/Keck telescopes are small aperture (~0.5m) cryogenic refractors that focus on measuring the degree-angular scale feature of the PGW-generated B modes. BICEP3 has ~10x optical throughput compared to BICEP2 due to a larger field-of-view and aperture size. As a result, we adopt new designs in BICEP3 for thermal filtering, optical elements selection, and detector modules packing. We deployed BICEP3 in the Austral summer of 2014-2015 and upgraded the instrument after the first season of testing and observations. I will present the improvements of the noise levels due to this upgrade. The second part of my talk will focus on delensing SPTpol data. Gravitational lensing of primordial (curl-free) E modes generates B modes. These lensing B modes are a source of foreground contamination to detecting the PGW-generated B modes. We can characterize and reduce the lensing B-mode contribution through a technique called “delensing.” I will present results of a first demonstration of delensing on polarization data. In this work, we delens B-mode maps from multi-frequency SPTpol observations of a 100 deg^2 patch of sky by subtracting a lensing B template constructed from two components: SPTpol E-mode maps and a lensing potential map formed from a Herschel 500 μm map of the CIB. In addition, we build and use a suite of realistic simulations to study the current limitations and expected future improvements in delensing with implications for future experiments.

Dec 1, Thursday
4 pm (Astronomy Colloquium)
Alexie Leauthaud, Santa Cruz
1 Le Conte
Lensing is Low: Cosmology, Galaxy Formation, or New Physics?
A fundamental goal in observational cosmology is to understand the link between the luminous properties of galaxies and the dark matter halos in which they reside. Weak lensing, which relies simply on the laws of gravity, is a unique method that can be used to directly probe the dark matter components of galaxies. In this talk, I will present new high signal-to-noise weak lensing measurements for galaxies from the BOSS “CMASS" sample. By comparing this signal with predictions from mock catalogs trained to match observables including the stellar mass function and the projected and two dimensional clustering of BOSS galaxies, I will show that the clustering of CMASS, together with standard models of the galaxy-halo connection, robustly predicts a lensing signal that is 20-40\% larger than observed. I will discuss several effects that may explain this mis-match including, a low value of the amplitude of low redshift structure compared to Planck2015, assembly bias, the effects of baryons on the matter distribution, and the effects of massive neutrinos. Towards the end of this talk, I will show some early results from the new Hyper Suprime Cam (HSC) survey, an ambitious multi-wavelength (g,r,i,z,y) weak-lensing program to map out 1500 square degrees of the sky with the 8.2m Subaru Telescope to i∼26 mag.

Dec 2, Friday
12 pm (INPA talk, noon, not 12:10)
Sebastian Cantalupo, Zurich
LBNL 50-5132
Direct imaging of the Dark Universe with the help of supermassive black-holes and Integral Field Spectroscopy
Gravitational collapse during the Universe's first billion years transformed a nearly homogeneous matter distribution into a network of filaments - the Cosmic Web - where galaxies form and evolve. Because most of this material is too diffuse to form stars, its study has been mostly limited so far to one-dimensional absorption probes against background sources or to three-dimensional studies limited however by relatively poor spatial resolution. In this talk, I will show how deep narrow-band imaging on Keck and Integral Field Spectroscopy with VLT/MUSE around bright quasars is providing us a completely new window for the study of the high-redshift Universe. In particular, using quasars and bright galaxies as external “sources of illumination”, we are now finally able to directly map in Ly-alpha emission and at high spatial resolution the diffuse gas that traces the sites of early galaxy formation (“dark galaxies”), the circumgalactic medium, as well as intergalactic filaments extending up to several hundred of kpc around massive galaxies. I will discuss the importance of the new instrumentation such as MUSE (and the Keck Cosmic Web Imager in the next future) for the tremendous discoveries and advancements in the last few years in this new field and I will present our first attempts to advance in parallel our physical understanding of baryonic structure formation as traced by the intergalactic Ly-alpha emission.

Dec 6, Tuesday
1:10 pm (Cosmology/ BCCP)
Sukhdeep Singh, CMU
Campbell 131
Galaxy-Lensing Cross Correlations: Measurements and Applications
Weak lensing has emerged as an important cosmological probe for our understanding of dark matter and dark energy. Galaxy-lensing cross correlations map the matter distribution around galaxies and provide important information about matter correlations and the growth of large scale structure. I will present our measurements of galaxy-galaxy lensing and galaxy-CMB lensing cross correlations using SDSS-BOSS spectroscopic samples with SDSS galaxy lensing and Planck CMB lensing. I will also address some of the issues in covariance estimation for these measurements. When combined with galaxy clustering and RSD measurements, galaxy-lensing also provides strong constraints on the standard cosmological model. As applications of these measurements, I will discuss the constraints on EG parameter, cosmological parameters and the estimation of relative calibration uncertainties between galaxy shear and CMB lensing.

Dec 8, Thursday
4 pm (RPM)
Johanna Nagy, Case Western
LBL 50-5132
“Probing Inflation with SPIDER, a Balloon-Borne CMB Polarimeter”
The generation of a stochastic gravitational wave background is a key prediction of cosmological theories of inflation. At large angular scales, these gravitational waves imprint a “B-mode” polarization pattern in the Cosmic Microwave Background, providing a new window into the physics of the early universe and helping to constrain and distinguish between inflationary models. SPIDER is a balloon-borne telescope that has been uniquely optimized to search for the inflationary B-mode signature in the CMB. Over the course of two Antarctic flights, SPIDER will make polarization maps over 10% of the sky in three frequency bands with degree-scale angular resolution. After an overview of the instrument and science goals, preliminary results from SPIDER’s 2015 flight will be presented along with a summary of progress towards the second flight.

Dec 9, Friday
12 pm (INPA talk, noon, not 12:10)
Julian Munoz, JHU
LBNL 50-5132
Probing dark matter with radio surveys
A significant part of dark matter could be compact, in particular in the form of primordial black holes. I will review the signatures of primordial black holes, both in the form of gravitational-wave events and as gravitational lenses of fast radio bursts. Alternatively, a WIMP-y dark-matter component could interact with baryons to some level. I will explain how these interactions can cause heating of the baryons, becoming observable in the 21-cm line prior to the epoch of reionization.

Dec 13, Tuesday
4 pm (RPM)
ChangHoon Hahn, NYU
LBL 50-5132
“Fundamental Physics with Galaxy Clustering”
Galaxies’ connection to the cosmic web allows us to use them to trace the matter distribution in the Universe and make precise measurements of large scale structure. The next galaxy surveys (eBOSS and DESI) will expand the cosmic volumes probed with galaxies by an order of magnitude and provide unprecedented statistical power. The main challenges for realizing their full potential are methodological. I will present how the main challenges can be solved with robust treatment of systematics (e.g. fiber collisions), accurate probabilistic inference, and higher order statistics. By overcoming these challenges and unlocking the full potential of eBOSS and DESI, I will present how we can measure the growth of structure and total neutrino mass with unprecedented precision.

Jan 5, Thursday
4 pm (RPM)
Eleonora di Valentino, IAP
LBL 50-5132
“New Constraints on Extensions of the Standard Cosmological Model”
The Cosmic Microwave Background (CMB) temperature and polarization anisotropy measurements from the Planck mission have significantly improved previous constraints on the neutrino masses, as well as the bounds on extended models with massive sterile neutrino states or extra particles, as for example thermal axions. In this talk firstly I will show the recent constraints from cosmology for the thermal axion mass and the neutrino sector, by considering several combination of datasets and scenarios. In particular, I will show how the inclusion of additional low redshift priors is mandatory in order to sharpen the CMB neutrino bounds, and that we are close to test the neutrino mass hierarchy with existing cosmological probes. Secondly, I will discuss how these constraints can change by taking into account the possibility that the primordial power spectrum could assume a more general shape than the usual power law description. Finally, I will present cosmological constraints in a significantly extended scenario, varying up to 12 cosmological parameters simultaneously, by looking for a new concordance model that should solve at the same time all the current tensions between the Planck data and the new direct measurements of the Hubble constant by Riess et al. 2016 and the parameters from weak lensing surveys, such as CFHTLenS and KiDS-450.

Jan 10, Tuesday
1:10 pm (Cosmology/ BCCP)
Patrick Breysse, JHU
Campbell 131
High-Redshift Astrophysics Using Every Photon
Large galaxy surveys have dramatically improved our understanding of the complex processes which govern gas dynamics and star formation in the nearby universe. However, we know far less about the most distant galaxies, as existing high-redshift observations can only detect the very brightest sources. Intensity mapping surveys provide a promising tool to access this poorly-studied population. By observing emission lines with low angular resolution, these surveys can make use of every photon in a target line to study faint emitters which are inaccessible using traditional techniques. With upcoming carbon monoxide experiments in mind, I will demonstrate how an intensity map can be used to measure the luminosity function of a galaxy population, and in turn how these measurements will allow us to place robust constraints on the cosmic star formation history. I will then show how cross-correlating CO isotopologue lines will make it possible to study gas dynamics within the earliest galaxies in unprecedented detail.

Jan 10, Tuesday
4 pm (RPM)
Michael Wilson, Edinburgh
LBL 50-5026 (note room change)
“Extracting precision tests of gravity from the intricate pattern of galaxies”
Galaxy redshift surveys deliver increasingly precise tests of gravity on cosmological scales and shed light on the uncertain nature of Dark Energy. I will present the VIPERS (http://vipers.inaf.it) census of the galaxy distribution at redshift 0.8 and describe its consistency with the expansion history and rate of gravitational collapse predicted by General Relativity and a Planck (2015) cosmology. This is facilitated by the anisotropy of the observed clustering, which is sensitive to both the coherent infall of galaxies towards clusters and the assumption of an expansion history differing from the true one. I will then present the results of including a simple density transform prior to this conventional analysis, which suppresses the most massive structures and extends the validity of the simplest models. Moreover, this has been shown to amplify signatures of modified gravity in ‘shielded’ theories and contains information beyond that available to the power spectrum. To do so requires correcting for many systematics that are characteristic of high-redshift surveys. I will describe the properties common to VIPERS, eBOSS and DESI and the potential of a density-weighted analysis with these next-generation surveys.
Finally, tests of gravity have predominantly focused on the large-scale velocities of galaxies to date, but that of clusters is imprinted on the Cosmic Microwave Background by the kinetic Sunyaev-Zel’dovich effect. The Simons Observatory and CMB-S4 experiments represent ideal test-beds for exploring the latter. I will discuss this and other future avenues for revealing the properties of Dark Energy with large-scale structure.

Jan 11-13
BCCP Cosmology with Neutral Hydrogen Meeting
Note that the room has limited capacity--if you have not registered please make sure you do not displace someone who has.

Jan 17, Tuesday
1:10 pm (Cosmology/ BCCP)
Hongming Zhu, University of Chinese Academy of Sciences
Campbell 131
"Nonlinear Reconstruction"
We present a direct approach to non-parametrically reconstruct the linear density field from an observed nonlinear map. We solve for the unique displacement potential consistent with the nonlinear density and positive definite coordinate transformation using a multigrid algorithm. We show that we recover the linear initial conditions up to k ∼ 1 h/Mpc with minimal computational cost, potentially substantially expanding the BAO and RSD information content of dense large scale structure surveys, including for example SDSS main sample and 21cm intensity mapping. This reconstruction approach generalizes the linear displacement theory to fully nonlinear fields, which has significant implications for the probe of cosmic acceleration, tests of gravity, measurement of neutrino masses and etc.

Jan 18, Wednesday
2:30-3:00 pm (short group meeting talk)
Kaze Wong, Hong Kong/CMU
LBL 50-5026 (INPA room)
Advanced LIGO lensing rate predictions
Gravitational lensing phenomena are widespread in electromagnetic astrophysics, and in principle may also be uncovered with gravitational waves. We examine gravitational wave events lensed by elliptical galaxies in the limit of geometric optics, where we expect to see multiple signals from the same event with different arrival times and amplitudes. By using mass functions for compact binaries from population-synthesis simulations and a lensing probability calculated from Planck data, we estimate the rate of lensed signals in the Advanced LIGO era, and predict the possible effects on detection in LIGO.

Jan 19, Thursday
4 pm (RPM)
Kirit Karkare, Harvard
LBL 50-5132
“B-Mode Polarization Results from BICEP/Keck Array and Beam Systematics in Current and Next-Generation CMB Experiments”
The BICEP/Keck Array cosmic microwave background (CMB) polarization experiments located at the South Pole are a series of small-aperture refracting telescopes focused on the degree-scale B-mode signature of inflationary gravitational waves. I will present our latest results which have produced the most stringent constraints on the tensor-to-scalar ratio to date: sigma(r) = 0.024 and r < 0.09 from B-modes alone (r < 0.07 in combination with other datasets). These constraints will rapidly improve with upcoming measurements at the multiple frequencies needed to separate Galactic foregrounds from the CMB, and in combination with higher-resolution experiments to remove B-modes induced by gravitational lensing. I will provide an update on our expanded frequency coverage and plans for future receivers.
Next-generation CMB experiments with hundreds of thousands of detectors will require exquisite control of instrumental systematics. I will review key aspects of the BICEP/Keck instrument design which maximize polarization sensitivity and reduce systematics at large angular scales, including the ability to measure beams in the far field with high precision. Finally, I will discuss the prospects for dealing with temperature-to-polarization leakage in future experiments, and how the beams systematics levels we achieve with current instrument and analysis technology will scale with detector count.

Jan. 20, Friday
12 pm (INPA talk, noon, not 12:10)
Marcelo Alvarez, CITA
LBL 50-5132
Simulating Large Scale Structure Observables from Reionization to the Present
The next generation of large scale structure surveys will map out the universe in unprecedented detail. Transformative techniques in computational astrophysics are emerging as the optimal ways to extract information from these surveys, with realistic and routine full sky simulations finally within reach. I will describe a new pipeline for efficiently simulating high resolution maps of the sky from the radio to x-ray and from reionization to the present. I will conclude with what questions are likely to be answered in the next decade.

Jan 24, Tuesday
1:10 pm (Cosmology/ BCCP)
Mohammadjavad Vakili, NYU
Campbell 131
Hunting down systematics in modern galaxy surveys
With the next generation of wide field galaxy surveys, both spectroscopic and photometric, we expect to achieve unprecedented constraints on the expansion history of the universe and the growth of structure. Maximizing the flow of information from these rich datasets to constraints on our cosmological models requires accurate characterization of systematic uncertainties. First, we present a method for estimation of covariance matrices of galaxy clustering measurements with spectroscopic surveys. We show that our method enables us to generate accurate galaxy mocks needed for BAO and RSD analyses on nonlinear scales. Then, we present the main challenges in extracting cosmological information from lensing measurements of deep imaging surveys. We show that employing novel techniques in estimation of the point spread function can keep this major systematic under control. Finally, we discuss various approaches for improvement of the photometric redshifts for the imaging surveys. We demonstrate how the precision and accuracy of photometric redshifts can be greatly enhanced if we take advantage of combining different datasets.

Jan 31, Tuesday
1:10 pm (Cosmology/ BCCP)
Duncan Campbell, Yale
Campbell 131
Connecting Galaxies to Dark Matter Haloes in a Universe with Assembly Bias
The assembly history of a dark matter halo affects both its internal properties and the large-scale environment in which it resides, a phenomena called assembly bias. Over the last several years, observational evidence has emerged to suggest that galaxies may also be influenced by assembly bias, although the magnitude of the effect remains unknown. Nevertheless, it is possible that widely used empirical models that connect galaxies to their host dark matter halos based only on mass are too simplistic. I will discuss efforts to measure and model the galaxy-halo connection, accounting for the possibility that galaxy evolution is influenced by assembly bias. First, I will discuss the extent to which group catalogs can accurately infer the subtle influences of assembly bias. Second, I will show that sub-halo abundance matching (SHAM) models, which place galaxies in halos and sub-halos in N-body simulations by matching the abundances of the two, are unable to predict galaxy clustering and galaxy growth histories without including the effects of assembly bias or other significant modifications. Finally, I will discuss Halotools, an open source code project which was designed to facilitate the creation and analysis of the increasingly complex models that are becoming necessary to account for the growing number and statistical power of observations.

Feb 7, Tuesday
1:10 pm (Cosmology/ BCCP)
Steve Finkelstein, Texas
Campbell 131
"Did Galaxies Reionize the Universe? (yes, probably)"
The study of the reionization of the intergalactic medium is a key probe of cosmology, as it encodes information regarding the onset of the first luminous sources (stars and galaxies). While it has been suspected that star-formation activity within galaxies was the dominant source of ionizing photons in this epoch, only over the past ~seven years have we been able to directly observe galaxies within the likely epoch of reionization (z > 6). I will briefly overview the progress that has been made in discovering galaxies into the epoch of reionization at 6 < z < 10, including results using gravitational lensing to probe systems intrinsically 100X fainter than those observed in the Hubble Ultra Deep Field. While armed with galaxy ultraviolet luminosity functions we are in excellent position to address the contribution of galaxies to reionization, this conversion requires a number of assumptions, most notably the escape fraction of ionizing photons. I will discuss a new model of reionization which uses theoretical escape fractions, finding that it is possible for galaxies to dominate reionization even with typical escape fractions of < 5%. Finally, I will discuss future observations which will better constrain both the time and spatial evolution of the reionization process.

Feb. 9, Thursday
4:10 pm (Astronomy Colloquium)
Nitya Kallivayalil, Virginia
1 Le Conte
Probing the Dark Halo of the Milky Way
The Local Group, the regime in which detailed star-by-star studies can be done, is becoming a major testbed for the cold dark matter-based model of the Universe. Critical to these tests is a better estimate of the total Milky Way halo mass. The most reliable means by which to constrain the properties of the Milky Way dark halo is through assessing the 6-D phase space distributions of tracers of its gravitational potential. This requires accurate proper motions (tangential velocities) in addition to generally known radial velocities for field stars, streams, and satellite galaxies widely distributed throughout the halo. In turn, these measurements allow us to investigate the past histories of these tracers, and thus the accretion history of the Milky Way. I will discuss some novel approaches we have been developing to obtain proper motions for a variety of tracers in the Milky Way halo, including streams, globular clusters, and satellite galaxies, to definitively constrain the Milky Way's dark halo mass, shape and distribution. These techniques involve space-based imagers (HST), wide-field ground-based imagers, as well as imagers equipped with adaptive optics systems. I will also discuss the future prospects for this work, and the trade-off between Gaia, space missions (JWST, WFIRST, EUCLID), and ELTs.

Feb 14, Tuesday
1:10 pm (Cosmology/ BCCP)
Richard Shaw, UBC
Campbell 131
Probing Dark Energy with the Canadian Hydrogen Intensity Mapping Experiment (CHIME)
CHIME will use Intensity Mapping of the 21cm line of neutral hydrogen to map large-scale structure between redshifts of 0.8 and 2.5. By measuring Baryon Acoustic Oscillations (BAO) we will place constraints on the dark energy equation of state as it begins to dominate the expansion of the Universe, particularly at redshifts poorly probed by current BAO surveys.
In this talk I will introduce CHIME, a transit radio interferometer designed specifically for this purpose. I will discuss the promise and pitfalls of Intensity Mapping and describe the new analysis techniques we have developed to confront the many challenges of such observations, in particular removal of astrophysical foregrounds which are six orders of magnitude larger than the 21cm signal. A smaller 40m x 37m pathfinder telescope is currently operating at the DRAO in Penticton, BC, and the full-sized 80m x 100m instrument will be completed this year. I will report on current progress, and the lessons already learned.

Feb 21, Tuesday
1:10 pm (Cosmology/ BCCP)
Elena Massara, UCB
Campbell 131
Neutrinos and voids in modern cosmology
Neutrino oscillation experiments have shown neutrinos to be massive, thus they participate to the matter content of the Universe and to its evolution. In this era of precision cosmology, the analysis of observational datasets must account for neutrinos, both because cosmology can put strong constraints on the sum of their masses, and because ignoring them can bias the estimation of other cosmological parameters. Having this in mind, I will discuss how to model the nonlinear matter power spectrum in a massive neutrino cosmology, using an extended version of the halo model. Second, since cosmic voids are expected to be good environments to characterise the neutrino-induced effect on the matter distribution, I will present the results from a numerical study of void properties that aims to identify these effects. Finally, I will discuss a model for describing the shape and evolution of void density profiles and void bias.

Feb 28, Tuesday
1:10 pm (Cosmology/ BCCP)
Jerome Gleyzes, JPL
Campbell 131
Consistency relations of the large scale structure and how to break them
Upcoming cosmological experiments intend to exploit the large scale structure of the Universe to get a better understanding of the observed cosmic acceleration. By measuring the power spectrum, one can constrain the equation of state of dark energy, and galaxy surveys promise great improvement over the current constraints. Galaxy surveys can also be used to gather cosmological information beyond cosmic acceleration. For example, one can derive consistency relations that can relate the bispectrum to the power spectrum for example. Those relations are very robust, as they rely on only two assumptions: the equivalence principle and the gaussianity of initial conditions. They are thus expected to hold within the standard cosmological model. On the other hand, their potential violation can be used to put bound on theories that predict deviations from one of those two assumptions, which is what I will explore in this talk.

Mar 3, Friday
12 pm (INPA)
Martina Gerbino, Nordita
LBL 50-5132
Three Neutrinos in Cosmology (to Say Nothing of Laboratory)
Neutrinos are the only standard model particles of unknown mass. Thus, measuring their mass is one of the leading goals in fundamental physics. Cosmology currently provides the tightest bounds on the sum of the neutrino masses and the possibility that next generation experiments can provide a detection looks promising. Then, further questions would have to be addressed, such as the neutrino hierarchy and the neutrino nature. In this talk, I will discuss the treasure trove of information about massive neutrinos that we can collect from different cosmological probes. I will stress the importance of extending our interest to laboratory searches, such as kinematic measurements and neutrino less double-beta decay experiments, for going beyond measuring the neutrino mass. Finally, I will choose a different angle and show how massive neutrino unknowns can affect the constraints on inflationary models.

Mar 7, Tuesday
1:10 pm (Cosmology/ BCCP)
CANCELLED
Campbell 131

Mar 14, Tuesday
1:10 pm (Cosmology/ BCCP)
Azadeh Moradiinezhad Dizgah, Harvard
Campbell 131
Primordial non-Gaussianity from large scale structure : prospects and challenges
Tighter constraints on primordial non-Gaussianity will significantly improve our understanding of the physics of the early universe and the origin of primordial fluctuations. High-precision data from large-scale structure surveys are our best hope to improve upon the constraints on primordial non-Gaussianiy coming from Cosmic Microwave Background observations. In the first part of this talk, I will discuss one of the theoretical challenges in modeling the observed bispectrum of the biased tracers on very large scales, namely the relativistic projection effects. I will describe the contamination to the bispectrum due to projection effects and how they should be accounted for. In the second part of the talk, I will discuss some preliminary results indicating the prospects of learning about physical properties of additional particles present during inflation (such as their mass and spin) through their signature on the power spectrum of the biased tracers.

Mar 17, Friday
12 pm (INPA talk, noon, not 12:10)
Jessie Muir, Michigan
LBL 50-5132
Unbiasing cosmology on the largest scales
One of the most exciting areas of research in cosmology is the effort to extract information about fundamental physics from observations of the universe on large scales. With the advent of increasingly large cosmological datasets (and correspondingly small statistical uncertainties), future progress in the field will fundamentally be determined by our ability to understand and account for systematic errors. In this talk, I’ll discuss two projects which further that ability: a study of how reliably we can separate primordial and late-time contributions to large-angle features of the the Cosmic Microwave Background (CMB) and the development of a blinding strategy to prevent experimenters’ bias from influencing the Dark Energy Survey’s cosmological analysis.

Mar 20, Monday
4:15 pm (Physics Colloquium)
Dan Green, UCB
1 Le Conte
nu Windows to the Early Universe
Cosmological observations give us some of the clearest views of the history of the universe and the laws that shaped it. Yet, despite the incredible progress, our view is still quite limited. The next generation of observations will break new ground in our sensitivity to earlier times in our thermal history. In this colloquium, I will review the status of our understanding of the early universe from current data. I will then highlight the measurement of cosmic neutrino background and the search for additional light relics of the hot big bang using current and future cosmological surveys. I will explain why these measurements are robust and how they are important as a probe of fundamental physics. I will discuss several targets that can be achieved from the CMB with the Simons Observatory and CMB Stage 4, and the potential for improvements from future galaxy surveys.

Mar 21, Tuesday
1:10 pm (Cosmology/ BCCP)
Julie Dumas, Vanderbilt
Campbell 131
Testing the Caustic Ring Dark Matter Halo Model Against Observations in the Milky Way
A prediction of axion dark matter models is they can form Bose-Einstein condensates and rigid caustic rings as a halo collapses in the non-linear regime. In this talk, I will present results from the first study of the caustic ring model for the Milky Way halo (Duffy & Sikivie 2008), focusing on observational consequences. I will describe the formalism for calculating the gravitational acceleration of a caustic ring halo. The caustic ring dark matter theory reproduces a roughly logarithmic halo, with large perturbations near the rings. I will show that this halo can reasonably match the known Galactic rotation curve. We explored the effects of dark matter caustic rings on dwarf galaxy tidal disruption with N-body simulations. N-body simulations of the Sagittarius (Sgr) dwarf galaxy in a caustic ring halo potential, with disk and bulge parameters that are tuned to match the Galactic rotation curve, match observations of the Sgr trailing tidal tails as far as 90 kpc from the Galactic center. Like the Navarro-Frenk-White (NFW) halo, they are, however, unable to match the leading tidal tail. None of the caustic, NFW, or triaxial logarithmic halos are able to simultaneously match observations of the leading and trailing arms of the Sagittarius stream. I will further show that simulations of dwarf galaxies that move through caustic rings are qualitatively similar to those moving in a logarithmic halo.

Mar 22, Wed
12 pm (BOSS/DESI lunch)
Jose Onorbe, Heidelberg
Direct Constraints of HI Cosmic Reionization from Lyman-alpha observations at z ~ 5-6

Mar 28, Tuesday
1:10 pm (Cosmology/ BCCP)
Spring break, no talk

Apr 3, Monday
12:10 pm (TAC)
John Wise, Georgia Tech
Campbell 131
The First Stars and Galaxies in the Universe
Cosmic structure forms hierarchically through smooth accretion and dark matter halo mergers. As a consequence, all galaxies are the product of the dozens of mergers over billions of years. However, one can ask, "What were the first stars and galaxies in the universe?" I will review the current state-of-the-art simulations of early galaxy formation, starting with the formation of the first stars, which are initially devoid of metals and are suggested to have a characteristic mass of tens of solar masses. I will then present results from a suite of cosmological radiation hydrodynamics simulations that focus on the transition from the first stars to the first galaxies. Each simulation captures the radiative and chemical feedback from 10,000 first stars, leading to the formation of a 10^8 solar mass galaxy only 500 million years after the Big Bang, which is detectable with the upcoming James Webb Space Telescope. We have found that the galaxy luminosity function flattens at UV magnitudes above -14 due to feedback effects, and I will present theoretical predictions for their photometry and effects from dust extinction. I will also demonstrate that these faintest galaxies are the primary driver of the reionization of the universe, only to be suppressed by photo-heating at later times, perhaps evolving into a subset of dwarf galaxies in the local universe.

Apr 4, Tuesday
1:10 pm (Cosmology/ BCCP)
Azadeh Fattahi, Victoria
Campbell 131
APOSTLE Local Group simulations: why bother with faint galaxies?
Despite its success in explaining the large scale structure of the Universe, the standard model of cosmology (LCDM) has faced a number of problems in explaining the properties of dwarf galaxies. Detailed studies of these intrinsically faint objects are only possible in the Local Universe. The Local Group of galaxies therefore serves as a laboratory for studying galaxy formation scenarios and for testing predictions of cosmological models. I will introduce the APOSTLE project, a suite of high resolution hydrodynamical simulations of Local Group-like regions within the LCDM framework, and explain how the small scale problems” of LCDM are resolved or persist in this model. I will particularly focus on the too-big-to-fail problem for MW satellites and its solution within LCDM and without requiring dwarf galaxies to have “cores” in their dark matter density profiles. I will extend the discussion to Andromeda satellites. Is there any too-big-to-fail problem in this system?

Apr 11, Tuesday
1:10 pm (Cosmology/ BCCP)
Lluis Mas , Norway/UCSB
Campbell 131
Small-scale Intensity Mapping: Extended Halos as a Probe of the Faintest Galaxies and Reionization Physics.
A fundamental question concerning the epoch of cosmic reionization (EoR) is the amount of ionizing photons contributed by primeval galaxies, which is at present dominated by two major unknowns, namely: (i) the contribution of galaxies to reionization depends significantly on the ability of their ionizing radiation to escape the galaxy and its circumgalactic medium (CGM) and ionize the more distant intergalactic medium (IGM). However,the escape fraction of ionizing photons is impossible to measure directly at z > 4. (ii) The presence of a large population of faint (currently unobservable) galaxies which might contribute significantly to the total ionizing photon budget is unclear.
I will present and discuss future observations of diffuse Ha and continuum emission around star-forming galaxies with JWST as a new method two address the two above problems. I will demonstrate how these observations can also constrain star formation in the halo of star-forming galaxies when applied to lower redshift, and how the comparison between the Lya, Ha and continuum surface brightness profiles in this case will disentangle the possible mechanisms that give rise to the presence of Lya halos nearly ubiquitously observed around galaxies at z ~2-5.

Apr 12, Wednesday
12:10 Galform
Lluis Mas , Norway/UCSB
Campbell 501b
Metal abundances in DLAs and star formation in the IGM
DLAs constitute an important reservoir of gas for star formation. Using spectra from SDSS/BOSS DR12, we calculate the mean DLA metal-line absorption spectrum by averaging over ~ 27000 systems, which allows for the detection of faint metal absorption lines, several of them within the Lyman alpha forest. Our derived metallicities are consistent with those of metal-poor halo stars, but we also observe CI and CII] absorption lines, which can be used as tracers of star formation. Motivated by the possible scenario where star formation can occur far from bright detected galaxies, we conduct studies of cross-correlations of faint CIV absorption doublets with the Lya forest, and compare the bias of the carbon with that of galaxies.

Apr 14, Friday
12 pm (INPA)
Samuel Flender, Argonne
LBL 50-5132
Cosmology and the Sunyaev-Zel’dovich sky: Observations and simulations
The Sunyaev-Zel’dovich (SZ) effect is an important observational signature of galaxy clusters, the largest objects in the Universe today. In particular, the pairwise kinematic SZ signal probes the matter-velocity correlation function, scaled by the average optical depth of galaxy clusters, and is thus an interesting probe both from a cosmological and astrophysical point of view. In this talk, I will give an overview about our current cosmological understanding, highlighting the role of the SZ effect. I will present the current landscape of kinematic SZ measurements, including a recent measurement by the South Pole Telescope collaboration and the Dark Energy Survey collaboration, as well as insights from new, state-of-the-art simulations, and recent progress in the modeling of gas profiles of galaxy clusters.

Apr 18, Tuesday
1:10 pm (Cosmology/ BCCP)
Yashar Hezaveh, Stanford
Campbell 131
Measuring the mass function of dark matter subhalos with ALMA observations of gravitationally lensed dusty galaxies
The number of observed dwarf satellites of the Milky Way is about three orders of magnitude lower than what cold dark matter (CDM) simulations predict, an issue that is referred to as the "Missing Satellite Problem". In this talk, I will discuss how in strong lensing systems we can detect low-mass dark matter subhalos in the lens galaxies by measuring the gravitationally-induced distortions that subhalos induce in the lensed images of background sources. Measuring the abundance of dark matter subhalos with strong lensing allows us to determine their mass function and to compare it with the predictions of CDM and other dark matter models. I will present our first detection of a subhalo using ALMA data and show how we can place constraints on the abundance of subhalos down to ~2e7 M_{\odot} with these observations. I will also give a brief overview of our ongoing observational campaign to place stronger constraints at lower masses.

Apr 25, Tuesday
1:10 pm (Cosmology/ BCCP)
Rychard Bouwens, Leiden
Campbell 131
Extremely Low-Luminosity Galaxies in the Early Universe: New Horizons for Hubble, Spitzer, and the James Webb
By combining the power of gravitational lensing magnification from massive galaxy clusters with long exposures from the Hubble and Spitzer Space Telescopes, the Hubble Frontier Fields initiative allows us to look fainter into the universe than ever before. In so doing, the campaign provides us with our first-ever direct probe into the prevalence of extremely low luminosity galaxies in the early universe, while simultaneously providing us with a high spatial resolution view of the same galaxies. Interestingly enough, not only does this new high resolution view suggest that many ultra-faint galaxies have sizes similar to that of super star clusters, i.e., 30-150 parsecs, but also this same view is essential to obtaining a systematics-free answer to the prevalence of these same galaxies and their ionizing emissivities. The purpose of my presentation is to describe not only the sizes, structure, and other properties the community is discovering for extremely low luminosity galaxies (100-1000 times fainter than L*), but also current efforts to probe the galaxy luminosity function into the same regime.

Apr 27, Thursday
4 pm (Astronomy Colloquium)
Rychard Bouwens, Leiden
Le Conte
Young Galaxies Forming in the High-Redshift Universe
Over the last few years, enormous progress has been made in studying galaxies in the first two billion years thanks to the incredible capabilities of the Hubble and Spitzer Space Telescopes. Already, more than 1500 probable galaxies are known at redshifts above z~6, and now the current frontier is at z~9-10, with 50 plausible galaxy identifications to date, and a spectroscopic redshift measurement to z=11.1. Noteworthy advances are also being made in characterizing the physical properties of these distant galaxies, with probes of the nebular emission lines and specific star formation rates to z~8.5 and new constraints on dust-enshrouded star formation at z>~2 from ALMA. One area where there has been particularly exciting activity is in the study of ultra-faint galaxies in the early universe with the Hubble Frontier Fields (HFF) program, combining the power of long exposures with Hubble and Spitzer with gravitational lensing by massive galaxy clusters. In this colloquium, I survey these and other highlights of current research on high redshift galaxies, while looking forward to future work with JWST.

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