Penn Astrophysics and Cosmology
Seminars
Talks are given on
topics of current interest, at a level that is accessible to all first-year graduate
students. This event is attended by all those interested in astrophysics and
cosmology, including undergraduate and graduate students, postdocs, and
faculty.
Academic Year 2011 - 2012
Spring 2012
DRL A6, Wednesdays at 2 PM,
except
for the dates of department colloquia
|
Date |
Speaker |
Host |
|
Jan 11 |
|
|
|
Jan 18 |
Jo Bovy (Institute for Advanced Study)http://www.cosmo.nyu.edu/~jb2777/ The phase-space structure of mono-abundance sub-populations of the
Milky Way disk Observations of the structure and kinematics of different stellar
populations in the Milky Way's disk provide a unique perspective on
disk formation and evolution. I will discuss how current and future
data sets that provide detailed kinematics and elemental abundances
beyond the Solar neighborhood lead to qualitatively new tests of
internal and external disk evolution models. In particular, I will
show recent results from a dissection into mono-abundance components
of the Galactic disk based on SDSS/SEGUE data. These results show
that
the individual components are simple, but exhibit very different
spatial structure, and they lend direct observational support for
inside-out formation models for galactic disks. |
Lidz |
|
Jan 25 |
Fergus Simpson (The University of Edinburgh) http://www.roe.ac.uk/ifa/people/frgs.html Testing the Laws of Gravity with the CFHT Lensing Survey |
Jain |
|
Feb 1 |
Megan Donahue (Michigan State University) http://www.pa.msu.edu/~donahue/ Baryons and Star Formation in the Cores of Clusters of Galaxies |
Devlin |
|
Feb 8 |
|
|
|
Feb 15 |
Donghui Jeong (Johns Hopkins University) http://www.pha.jhu.edu/~djeong/ Galaxy Power Spectrum on Large Scales: Scale Dependent Non-Gaussian bias and General Relativistic Effect In standard theory of large scale structure of the universe, the galaxy power spectrum on large scales is given by a simple linear rescaling of the underlying matter power spectrum.
The bias parameter, the proportionality constant of the rescaling, is also assumed to be constant on sufficiently large scales. This simple picture, however, does not work for general cases.
In this talk, I shall present two cases where we need to extend conventional linear bias model: when universe starts from non-Gaussianity initial condition and when considering near horizon scales.
Also, I shall show that understanding the galaxy power spectrum on large scales will enable us to test the physics of the early universe as well as a possible modification of general theory of relativity. |
Jain |
|
Feb 22 |
Albert Stebbins (Fermilab) http://home.fnal.gov/~stebbins/ WYSIWYG Space-Time: an observationally based, non-perturbative approach to learning about the space-time geometry of our universe. On macroscopic scales new forces are determined by measuring accelerations e.g. Newton and Kepler for gravity, or balancing known with unknown forces in a static configuration. Dark energy is a putative gravitationally repulsive substance which permeates our universe, yet the evidence for it involves neither technique, but is rather a mix of observations and assumptions about the geometry of space-time and initial conditions. In fact much of cosmology is done this way. Here I examine what one can learn about space-time geometry purely by observations from a single vantage point of distant objects and their motions and, in particular, not assuming the cosmological principle. A formalism is developed whereby all of space-time geometry is expressed in terms of observables. Some new and interesting formulae are derived and a possible future path for dark energy studies is given. |
Trodden/Lidz |
|
Feb 29 |
Kendrick Smith Constraining the physics of inflation The observational search for non-Gaussian statistics in the initial
conditions
of the universe is a powerful, multifaceted probe of the physics of
inflation.
In this talk I will outline the theory, describe different ideas for
constraining
primordial non-Gaussianity from observations, and present results
from
WMAP data. |
Lidz |
|
Mar 7 |
No
seminar: Spring Break |
|
|
Mar 14 |
Department Colloquium Rittenhouse Lecture: Richard Ellis |
|
|
Mar 21 |
James Kasting (Penn State University) http://www3.geosc.psu.edu/~jfk4/PersonalPage/Kasting.htm Is the Earth Rare?
In their 2000 book, Rare Earth, Peter Ward and Don Brownlee argue that complex life (i.e., animal life) is rare, for a variety of reasons, some of which are based on the idea that habitable planets are themselves rare. Possible reasons for this include: 1) Plate tectonics (possibly necessary to stabilize planetary climates) is rare; 2) large moons (possibly necessary to stabilize planetary obliquities) are rare; 3) magnetic fields (possibly necessary to retain atmospheres) are rare; 4) the Sun is anomalously metal-rich; 5) Jupiter-sized outer planets (possibly necessary to protect the Earth from frequent large impacts) are rare. In my talk, I will review these Rare Earth arguments and show that most, or all, of them are less troubling than Ward and Brownlee supposed. That said, there could be other factors not discussed by these authors that could make habitable planets scarce. But this should not discourage us from building the types of large space telescopes required to actually answer this question. |
Bernstein |
|
Mar 28 |
Risa Wechsler (Stanford University) http://risa.stanford.edu/ The Galaxy-Halo Connection across Mass and Time Dark matter halos are the fundamental building blocks in the growth of
structure and they provide the framework for our modern understanding
of galaxy formation. I will discuss the current state of the art in
our understanding of the connection between galaxy properties and
their dark matter hosts over a range of masses and redshifts. In the
context of a given cosmological model, I will show how the galaxy-halo
relation can be tightly constrained at low redshift, and how it can be
used to infer the full star formation histories of galaxies. This
model for the co-evolution of galaxies and LCDM halos is in excellent
agreement with a wide range of data, including the evolution of the
stellar mass function, galaxy clustering statistics, and the
statistics of satellites around Milky Way mass hosts. I will discuss
applications to several issues in cosmology. The faintest dwarf
galaxies still present challenges to this picture, and may hold the
key to new insight into galaxy formation or the properties of dark
matter on small scales. |
Jain |
|
April 4 |
Gurtina Besla (Columbia University) https://www.cfa.harvard.edu/~gbesla/Site/Welcome.html The Role of Dwarf Galaxy Interactions in Shaping the Magellanic System and
Implications for Magellanic Irregulars and Dwarf Spheroidals I will present a new numerical model of the evolution of the Milky Way's
largest satellite galaxies, the Large and Small Magellanic Clouds (LMC/SMC),
in which their current internal structure and kinematics and large-scale gas
morphology are dictated by their mutual tidal interactions, rather than
interactions with the Milky Way. This picture is consistent with the recent
HST proper motions of the LMC (Kallivayalil et al. 2006) - using
cosmologically motivated models for the Milky Way, these new proper motions
imply that the Clouds have not made multiple passages about the Milky Way.
In particular, the LMC's peculiar off-center bar and one-armed spiral
morphology is a natural by-product of a recent direct collision with the
SMC. This scenario may shed light on the dynamical state of a class of
dwarf galaxies known as Magellanic Irregulars (de Vaucouleurs & Freeman
1972), which, like the LMC, are asymmetric spirals with off-center bars, but
are rarely associated with massive spirals.
As a result of its collision with the LMC, the simulated SMC is left in a
highly disturbed state where its older stellar population does not display a
pronounced rotation curve, as observed. The SMC may thus represent an object
in transition from a dwarf Irregular galaxy to a dwarf Spheroidal. This
process is expected to occur ubiquitously in small groups of low mass
galaxies and may represent a generic mode of dwarf galaxy evolution that is
independent of proximity to a massive host. |
Lidz |
|
Apr 11 |
|
|
|
Apr 18 |
No Seminar |
|
|
Apr 25 |
No Seminar |
|
|
May 2 |
Subo Dong ( Exploring Extrasolar Planet Demography with Discoveries, Statistics,
and Dynamics Revolutionary advances in extrasolar planet discoveries have revealed
great diversity in the architecture of planet systems. I will discuss
recent progress we have made in finding planets with gravitational
microlensing. These microlensing planets allow us to measure planet
frequency beyond the "snow line" for the first time. NASA Kepler
mission has found thousands of planet candidates and hundreds of
multiple planet systems. We have developed a statistical framework in
analyzing the Kepler planet systems and determined their inclination
distribution. After planets are formed, dynamical processes may leave
strong imprints on the planet architecture, and in particular, hot
Jupiters may have migrated to their current locations on
highly-eccentric orbits. We show that the predictions of such "high-e"
mechanisms can be tested by Kepler, radial velocity and direct-imaging
surveys. |
Jain |
Information for Speakers
Parking:
http://cms.business-services.upenn.edu/parking/
Reimbursement: Travel reimbursement and
W-9 forms are required, along with original receipts. The forms can be downloaded here: http://www.sas.upenn.edu/fas/drlbas/drlforms.htm
Previous Speakers
Fall 2011
DRL A6, Wednesdays at 2 PM,
except
for the dates of department colloquia
|
Date |
Speaker |
Host |
|
Sep 14 |
|
|
|
Sep 21 |
Mark Vogelsberger (Harvard CfA) http://www.mark-vogelsberger.de/ Moving Mesh Cosmology I will present results from the first hydrodynamical simulations of
galaxy formation using the new moving mesh code AREPO and compare
the results with equivalent GADGET simulations based on the SPH
technique. Both codes use an identical Tree-PM gravity solver and
include
the same sub-resolution physics for the treatment of star formation,
but employ a completely different method to solve the inviscid Euler
equations.
This allows us to cleanly assess the impact of hydro-solver
uncertainties on the results of cosmological studies of galaxy
formation. I will also present
simulations of idealized test problems with increasing complexity to
demonstrate uncertainties in current cosmological hydrodynamics
simulations. |
Lidz |
|
Sep 28 |
Michael Blanton (NYU) http://cosmo.nyu.edu/mb144/ How Does Star Formation End in Galaxies? Understanding how star formation slows --- and sometimes
completely ends --- in galaxies is thus key to understanding
their history. I will discuss this problem from the point of view
of dwarf galaxies, which might form the simplest
possible systems with which to understand star-formation
in galaxies. Dwarf galaxies almost certainly have not
participated in the decline in star-formation that massive
galaxies have in the last eight billion years. However, they do
have a very low star-formation efficiency. The standard
picture for this low efficiency requires massive galactic
winds to be a standard feature of dwarf galaxies. I will
review the evidence for this picture, concluding that what
evidence exists is rather indirect. As part of this discussion,
I will show that the census of dwarf galaxies puts surprisingly
good constraints on models of warm dark matter. |
Jain |
|
Oct 5 |
Jeff Peterson 21-cm Intensity Mapping By making all-sky observations of 21-cm flux at redshifts near one, the large scale structure of the Universe can be mapped in three dimensions. This can be accomplished by studying specific intensity with resolution ~ 10 Mpc, rather than via the usual galaxy redshift survey. This new technique is called Intensity Mapping. A new type of radio telescope based on fixed cylinders has been proposed for these observations, and I will report the progress of the testing of a prototype cylinder telescope built in Pittsburgh. The primary goal of the program is to detail the expansion history, in order to constrain dark energy models. To accomplish this the telescope will have mapping speed about 1000 times faster than any current radio telescope. |
Bernstein |
|
Oct 12 |
|
|
|
Oct 19 |
Immanuel Buder CMB Polarization Results from the QUIET Experiment Inflationary cosmology postulates that the Universe underwent a period of
accelerated expansion in the first 10^{-30} s after the Big Bang.
Inflationary models are attractive because they solve outstanding problems
in cosmology: the origin of structure, the absence of monopoles, and the
horizon and flatness problems.
Although inflation is consistent with existing data, the fundamental physics
responsible for it is unknown.
Cosmic Microwave Background (CMB) measurements promise to verify one of the
predictions of inflation: odd-parity polarization modes (B modes).
CMB B modes have not yet been detected.
I will describe the QUIET instrument, how it mitigates systematic
contamination, and results from the first season of observation at 43 GHz.
QUIET sets one of the best limits to date on inflationary B modes (r <
2.2).
Moreover the unique QUIET design leads to the lowest levels of systematic
contamination in the inflationary signal reported by any CMB polarization
experiment.
This suppression of systematic errors demonstrates the technology for a
next-generation experiment.
I will also report the status of analysis of the QUIET second-season 95-GHz
data. |
Devlin |
|
Oct 26 |
Daniel Grin (Institute for Advanced Study) Do baryons trace dark matter in the early universe? Compensated Isocurvature Perturbations and the Cosmic Microwave Background Measurements of cosmic microwave background (CMB) anisotropies constrain
isocurvature fluctuations between photons and non-relativistic particles to
be sub-dominant to adiabatic fluctuations. Perturbations in the relative
number densities of baryons and dark matter, however, are surprisingly
poorly constrained. In fact, baryon-density perturbations of fairly large
amplitude may exist if they are compensated by dark-matter perturbations, so
that the total density remains unchanged. These compensated isocurvature
perturbations (CIPs) leave no imprint on the CMB at observable scales, at
linear order in their amplitude. I will review the standard lore on
isocurvature, and motivate the consideration of CIPs. I will then consider a
variety of astrophysical probes of CIPs. I will then show that the
conventional wisdom on CIPs fails: CIPs do leave an imprint on the cosmic
microwave background, providing a new mode for B-mode generation. I will
show how the cosmic microwave background could be used to probe for
fluctuations between baryon and dark matter. I will conclude by considering
both some practical issues involved in CIP extraction from the data, and
horizons for future theoretical work on CIPs.
|
Jain |
|
Nov 2 |
Sylvain Veilleux (University of Maryland) **Seminar in A5** Galactic Winds and Their Cosmological Implications Galactic winds are the primary mechanism by which energy and metals are
recycled in galaxies and are deposited into the intergalactic medium.
New observations are revealing the ubiquity of this process,
particularly at high redshift. I will describe the physics behind these
winds, discuss the observational evidence for them in nearby star-forming
and active galaxies and in the high-redshift universe, and consider the
implications of energetic winds for the formation and evolution of
galaxies and the intergalactic medium. To inspire future research, I
will conclude with a set of observational and theoretical challenges.
|
Bernstein |
|
Nov 9 |
|
|
|
Nov 16 |
Aristotle Socrates Tidal Evolution of the Hot Jupiters The hot Jupiters are close-in extra-solar gas giant planets.
Their existence poses two
fundamental questions. Why are they so close to their host sun-like stars?
Why are their inferred radii
significantly larger than theoretical expectations? I will address the
first question by introducing
a framework that allows for a test of theories of migration that rely upon
tidal dissipation taking
place inside the planet. I propose that inflated radii are due to a subtle
effect known as thermal tides,
which render the hot Jupiters in a perpetual state of asynchronous spin.
Persistent tidal dissipation is then
responsible for heating the planet at great depth, leaving the planet's
equilibrium structure in a
perpetual state of inflation.
|
Lidz |
|
Nov 23 |
No seminar: Thanksgiving |
|
|
Nov 30 |
Marc Kamionkowski (Johns Hopkins University) The Cosmic Microwave Background: Beyond the Power Spectrum Virtually all the information we've obtained from
the cosmic microwave background (CMB) about cosmological
parameters and the early Universe comes from measurements of
the temperature power spectrum or, equivalently, the
temperature two-point correlation function. However, a variety
of higher-order correlations, and the polarization, may encode
a wealth of additional information on the early Universe, the
physics of cosmic acceleration, and the distribution of matter
at low redshifts. I will discuss some of these new signatures
as well as the physical scenarios that probe. |
Trodden |
|
Dec 7 |
|