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 2010 - 2011
Spring 2011
DRL A6, Wednesdays at 2 PM,
except
for the dates of department colloquia
|
Date |
Speaker |
Host |
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Jan 12 |
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Jan 19 |
Cullen Blake (Princeton) http://www.astro.princeton.edu/~cblake/ Searching for Planets Orbiting Low-mass Stars The majority of stars
in the solar neighborhood are low-mass M dwarfs. However, these small stars
have largely been excluded from the Doppler surveys that have identified more
than 400 known extrasolar planets. Today, the precision of Doppler
measurements at optical wavelengths is approaching 1 m/s, but comparable
precision has not yet been demonstrated at the near infrared (NIR)
wavelengths where low-mass stars are brightest. Low-mass stars are attractive
targets for planet searches, particularly when searching for rocky,
Earth-like planets orbiting in the so-called Habitable Zones of their hosts.
I have developed a new technique for measuring the velocities of low-mass stars
in the NIR. This method uses
absorption features in Earth's atmosphere (telluric lines) as a velocity
reference. I will present the results of a five-year Doppler survey of L
dwarfs with the Keck telescope and describe two expanded follow-up surveys that
are currently underway. I will also describe the results of theoretical
calculations of the intrinsic limitations of using telluric lines for making
velocity measurements. Finally, I will describe a small spectrograph I am
building to study the motions of atmospheric water vapor lines and to explore
the potential for using small, robotic telescopes to detect planets. |
Bernstein |
|
Jan 26 |
Paul Demorest (NRAO) http://www.cv.nrao.edu/~pdemores/ Testing Fundamental Physics with Radio Pulsars Millisecond spin-period
radio pulsars provide us with unique astronomical “laboratories” for
exploring fundamental physics in a variety of ways -- from the physics of
matter at super-nuclear density, to experimental tests of gravity, to the
possible direct detection of gravitational radiation. In this talk, I will
describe two such experiments I am involved with: The North American
Nanohertz Observatory for Gravitational Waves (NANOGrav) aims to detect
nHz-frequency gravitational waves using an array of millisecond pulsars. I
will present up-to-date results from our current analysis of the first five
years of data, and discuss the prospects for future improvements. I will also describe our recent measurement
of a nearly two solar mass neutron star.
This measurement tests theories of neutron star composition via the
nuclear matter equation of state (EOS), and strongly constrains many proposed
EOS that involve “exotic” forms of matter. |
Aguirre |
|
Feb 2 |
Judd Bowman (ASU) http://loco.lab.asu.edu/ Data and Results! Redshifted 21 cm Cosmology Has
Begun The Murchison Widefield
Array (MWA) and the Experiment to Detect the Global EoR Signature (EDGES) are
designed to exploit different observable properties of the redshifted 21 cm
background to probe the epoch of reionization and earlier times. Both
instruments have recently passed important milestones and will soon open new
views of the early universe. In particular, for the first time ever, EDGES
has used observations of the redshifted 21 cm line to rule out very rapid
reionization histories between redshifts 6 and 13. I will report the latest
results from EDGES and the status of MWA development. |
Aguirre |
|
Feb 9 |
Department Colloquium Rittenhouse Lecture: David Charbonneau |
|
|
Feb 16 |
David Wake (Yale) http://www.astro.yale.edu/wake/Welcome.html Galaxy clustering in
the NEWFIRM Medium Band Survey: the stellar mass - dark matter halo mass
relation at 1 < z < 2 The NEWFIRM medium band survey is a novel deep imaging survey that
makes use of medium band filters in the IR to provide accurate photometric
redshifts for galaxies at z > 1.
I will present an overview of the survey along with clustering measurements
for mass limited galaxy samples at 1 < z
< 2 selected from the NMBS. These measurements show for the first time
that high redshift galaxies show mass dependent clustering much like galaxies
in the local universe. Using the halo model I will show how these galaxies
are related to the underlying dark matter distribution and how that
relationship has changed over the past 10 Gyrs. |
Sako |
|
Feb 23 |
Meg Schwamb (Yale) http://www.astro.yale.edu/mschwamb/Site/Home.html Beyond Sedna: Probing the Distant Solar System The discovery of Sedna
on a highly eccentric orbit beyond I have performed two
surveys to search for additional members of the Sedna population. In order to
find the largest and brightest Sedna-like bodies we have survey ~12,000
square degrees within ± 30 degrees of the ecliptic to a limiting R magnitude
of 21.3 using the QUEST camera on the 1.2-m Samuel Oschin Telescope. To
search for the fainter more common members of this distant class of solar
system bodies, I have performed an
ultra-deep survey using the Subaru Prime Focus Camera on the 8.2-m Subaru
telescope covering ~43 square degrees to a limiting R magnitude of ~25. I will present the results of these surveys
and will discuss the implications for a distant Sedna-like population beyond
the Kuiper belt and discuss future prospects for detecting and studying these
distant bodies, focusing in particular on the constraints we can place on the
embedded stellar cluster environment the early Sun may be have been born in,
where the location and distribution of Sedna-like orbits sculpted by multiple
stellar encounters is indicative of the birth cluster size. |
Lehner |
|
Mar 2 |
Jason Glenn ( Early Results from the
Herschel Space Observatory: Amazing
Images, Distant Galaxies, and Unprecedented Spectroscopy of the Cool (Warm!)
Interstellar Medium in Nearby Galaxies The
Herschel Space Observatory is a 3.5-meter-diameter submillimeter telescope
that was launched in 2009. Its purpose
is to study the cool interstellar medium (ISM) in high-redshift galaxies
prodigiously forming stars and the ISM in our own Milky Way and nearby
galaxies. I will briefly describe
Herschel and the motivation for it and summarize some early high-redshift
galaxy results. I will focus on a statistical
fluctuation analysis that resolves into galaxies half of the cosmic
far-infrared background radiation and on spectroscopy that reveals
surprisingly warm molecular gas in nearby starburst galaxies. I will end with a mention of new detector
array technology that will help us identify some of the highest-redshift galaxies (5 < z < 10). |
Aguirre |
|
Mar 9 |
No
seminar: Spring Break |
|
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Mar 16 |
|
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Mar 23 |
Mike Cosmic Flows on Very Large Scales: A Challenge to
the ΛCDM Cosmology? In the gravitational
instability paradigm of structure formation, the motion of the Local Group
and the surrounding volume with respect to the Cosmic Microwave Background is
due to fluctuations in the dark matter distribution on scales larger than the
volume being studied, and so is one of the only probes of matter fluctuations
on very large scales. I will briefly discuss the wild history of this topic,
and focus on recent results (Watkins et al. 2009) which may pose a challenge
to the standard ΛCDM cosmology. |
Lidz |
|
Mar 30 |
Anze Slosar (Brookhaven National
Laboratory) http://www.slosar.com/aslosar/ The Lyman-alpha forest in three dimensions: measurements of large
scale flux correlations from BOSS 1st-year data The Lyman-alpha forest is a series of absorption
features in the spectra of distant quasars, blue-ward of the Lyman-alpha
emission line. These features arise as the light from the quasar is absorbed
by the intervening neutral hydrogen. This gives one-dimensional information
about the fluctuations in the neutral hydrogen density along the line of
sight to the quasar. When spectra of many quasars are combined, it allows one
to build a three-dimensional image of the fluctuations in the neutral
hydrogen density and thus infer the corresponding fluctuations in the matter
density. This makes the Lyman-alpha forest a unique probe of the distant
Universe, opening a novel window on understanding dark energy, dark matter,
neutrino properties and inflation. Using approximately 14,000 quasars from
the first year data, the BOSS experiment has detected, for the first time,
three-dimensional correlations in the Lyman-alpha forest fluctuations to
cosmological distances. The signal has the expected amplitude and
redshift-space distortions and we find no evidence for overwhelming
instrumental or astrophysical contamination. The BOSS experiment was
projected to measure the distance to the redshift of z=2.5 with better than
2% precision through detection of baryonic acoustic oscillations in the flux
fluctuations. The current results give these forecasts new credibility. |
Bernstein |
|
Apr 6 |
CANCELLED |
Trodden |
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Apr 13 |
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Apr 20 |
Andrew Zentner (Pitt) http://www.phyast.pitt.edu/~zentner/Andrew_Zentner_Web/Home.html New Perspectives on the Indirect Detection of
Dark Matter A program to identify
dark matter relies on direct detection of dark matter scattering in
low-background experiments, collider signatures, and indirect astrophysical signatures
of dark matter. In recent years,
several interesting new perspectives for indirect detection or astrophysical
constraints on dark matter have been developed. These include gamma-ray signatures from
dark matter annihilation in the Milky Way halo, neutrino signals from
annihilation in the Sun, and the potential effects of dark matter on stellar
structure. Meanwhile, the Fermi
Gamma-ray Space Telescope is achieving interesting constraints on dark matter
properties, particularly the dark matter self-annihilation cross
section. I will review contemporary
constraints and several new perspectives on the indirect detection of dark
matter. |
Jain |
|
Apr 27 |
Mark Wyman ( Massive gravitons and enhanced gravitational
lensing The mystery of dark
energy suggests that there is new gravitational physics at low energies and
on long length scales. On the other hand, low mass degrees of freedom in
gravity are strictly limited by observations within the solar system. A
compelling way to resolve this apparent contradiction is to add a
galilean-invariant scalar field to gravity. Called galileons, these scalars
have strong self interactions near overdensities, like the solar system, that
suppress their effects on the motion of massive particles. These non-linearities are weak on
cosmological scales, permitting new physics to operate. Extending Galilean
invariance to the coupling of galileons to stress-energy -- as was first done
in the case of massive gravity -- can have a surprising phenomenological
consequence: enhanced gravitational lensing.
Weak lensing observations will be able to detect or constrain out this
effect, which is not well described by existing “model independent” tests of
GR. |
Khoury |
Information for Speakers
Parking:
http://www.business-services.upenn.edu/parking/visitor.html
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 2010
|
Date |
Speaker |
Host |
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Sep 8 |
|
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Sep 15 |
Marilena LoVerde (Institute for Advanced Study) http://www.sns.ias.edu/~marilena/ Lensing in the Lyman-alpha Forest In Lyman-alpha forest
measurements it is generally assumed that quasars are mere background light
sources that are uncorrelated with the forest. I will discuss how
gravitational lensing of the quasars violates this assumption. This effect
leads to a measurement bias, but more interestingly it provides a valuable
signal. This signal will be challenging to observe but would provide a direct
measure of how features in the Lyman-alpha forest trace the underlying mass
density field thereby testing the hypothesis that fluctuations in the forest
are driven by fluctuations in mass, rather than in the ionizing background,
helium reionization or winds. If time permits I will also discuss recent work
on stochastic local non-Gaussianity. |
Sheth |
|
Sep 22 |
Alex Szalay (Johns Hopkins) http://www.sdss.jhu.edu/~szalay/ Virtual and Real Galaxy Surveys |
Jain |
|
Sep 29 |
Justin Khoury ( Screening Dark Energy |
|
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Oct 6 |
Michael Busha ( The Magellanic Clouds in Simulations and Real
Life Using a combination of
high-resolution cosmological simulations and wide-field photometric observations,
we study the statistics of Magellanic Cloud magnitude objects inside of Milky
Way-like hosts. Starting with both the
spectroscopic and photometric samples from the SDSS, we are able to quantify
the likelihood for an isolated Milky Way-magnitude galaxy to host n bright
subhalos. We then turn to the recent
Bolshoi simulation to both interpret these results and constrain our galaxy
modeling. The Bolshoi simulation modeled
a comoving 250 Mpc/h with the ability to resolve objects down to 50 km/s. Using SubHalo Abundance Matching to assign
magnitudes to our simulated halos, we measure a subhalo distribution in
almost perfect agreement with our SDSS observations where only 10% of the
Milky Way-like objects host two or more SMC or brighter satellites. Finally, we can use the Bolshoi simulation
to place constraints on both the mass of the Milky Way and the dynamical
state of the Magellanic Clouds, where we find strong evidence that the
Magellanic were recently accreted onto the Milky Way. |
Sheth |
|
Oct 13 |
|
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Oct 20 |
Eiichiro Komatsu ( The 7-year WMAP
Observations: Cosmological Interpretation We have announced the results from 7 years of observations
of the Wilkinson Microwave Anisotropy Probe (WMAP) on January 26. In this talk
we will present the cosmological interpretation of the WMAP 7-year data,
including the detection of primordial helium, images of polarization of
microwave background around temperature peaks, and new limits on inflation
and properties of neutrinos. We also report a significant detection of the
Sunyaev-Zel'dovich effect and discuss implications for the gas pressure in
clusters of galaxies. |
Aguirre |
|
Oct 27 |
Dragan Huterer ( Primordial
non-Gaussianity and large-scale structure Standard
inflationary theory predicts that primordial fluctuations in the universe
were nearly Gaussian random, though some realistic models specifically
predict large non-Gaussianity. Therefore, searches for, and limits on,
primordial non-Gaussianity present some of the most fundamental observational
tests of inflation and the early universe. I first review the history of the
measurements of non-Gaussianity from the cosmic microwave background
anisotropies in the universe over the past two decades. I then present
results from recent (2008) work where effects of primordial non-Gaussianity
on the distribution of largest virialized objects was studied numerically and
analytically. We found that the bias of dark matter halos takes strong scale
dependence in non-Gaussian cosmological models. Therefore, measurements of scale dependence
of clustering of galaxies and other tracers can - and do - constrain
primordial non-Gaussianity about two orders of magnitude better than
previously thought possible using the large-scale structure. I will discuss
prospects for future constraints on non-Gaussianity using this method. |
Trodden |
|
Nov 3 |
TO BE RESCHEDULED
FOR A LATER DATE Tanmay Vachaspati (Case Western) http://www.phys.cwru.edu/faculty/?vachaspati Aharonov-Bohm
Radiation |
Kamien |
|
Nov 10 |
|
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Nov 17 |
Savvas M. Koushiappas ( The influence of structure formation on the
interpretation of dark matter experiments Cosmological
structure formation gives rise to a distribution of dark matter that is set
by the complex process of hierarchical assembly. Dark matter experiments are inextricably
linked to the details of this cosmological structure formation. I will
discuss current work on quantifying the effects of structure formation on the
interpretation of dark matter experiments. More specifically, I will focus on
small scale structure and how it influences the expected rates in direct,
indirect and energetic neutrino experiments. |
Trodden |
|
Nov 24 |
No seminar: Thanksgiving |
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Dec 8 |
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