September 2016
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
October 2016
Oct 4, Tuesday
1:10 pm (Cosmology/ BCCP)
Irene Shivaei, Riverside
Campbell 131
Oct 11, Tuesday
1:10 pm (Cosmology/ BCCP)
Derek Inman, CITA
Campbell 131
Oct 18, Tuesday
1:10 pm (Cosmology/ BCCP)
Chen He Heinrich, Chicago
Campbell 131
Oct 21, Friday
12 pm (INPA talk, noon, not 12:10)
Enea Di Dio,
LBNL 50-5132
Oct 25, Tuesday
1:10 pm (Cosmology/ BCCP)
Alessandro Manzotti, Chicago
Campbell 131
Oct 27, Thursday
4 pm (Astronomy Colloquium)
Shirley Ho, LBL
Le Conte
Oct 28, Friday
12 pm (INPA talk, noon, not 12:10)
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.
November 2016
Nov 1, Tuesday
1:10 pm (Cosmology/ BCCP)
Alison Strom, Caltech
Campbell 131
Nov 4, Friday
12 pm (INPA talk, noon, not 12:10)
Colin Hill,
LBNL 50-5132
Nov 8, Tuesday
1:10 pm (Cosmology/ BCCP)
Michael Wilson, ROE
Campbell 131
Nov 15, Tuesday
1:10 pm (Cosmology/ BCCP)
Vanessa Boehm, Garching
Campbell 131
Nov 17, Thursday
4 pm (Astronomy Colloquium)
Michael Boylan-Kolchin, Austin
Le Conte
Nov 18, Friday
12 pm (INPA talk, noon, not 12:10)
Daniele Sorini, Heidelberg
LBL 50-5132
Nov 22, Tuesday
1:10 pm (Cosmology/ BCCP)
,
Campbell 131
Nov 29, Tuesday
1:10 pm (Cosmology/ BCCP)
Luke Kelley, Harvard
Campbell 131
December 2016
Dec 1, Thursday
4 pm (Astronomy Colloquium)
Alexie Leauthaud, Santa Cruz
Le Conte
Dec 2, Friday
12 pm (INPA talk, noon, not 12:10)
Sebastian Cantalupo,
LBNL 50-5132
Dec 6, Tuesday
1:10 pm (Cosmology/ BCCP)
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Campbell 131
Dec 9, Friday
12 pm (INPA talk, noon, not 12:10)
Julian Munoz,
LBNL 50-5132
Past Months
(
Previous Years
)
August 2016
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.
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