Penn Astro-Cosmo Seminars

PENN Astrophysics Group: Seminars

People Research Seminars Journal Club Department

Seminars are Wednesdays 4:00pm in DRL A4.

Journal Club meets Fridays 1:00pm in DRL 4E19.
Departmental Colloquia every second Wednesday of each month 4:00pm in DRL A8.

2005-2006 Seminars

Ravi Sheth is running our seminar series this semester, so please email suggestions for speakers to him at shethrk_at_physics.upenn.edu.

January 11: Departmental Colloquium
January 13 (note this is a Friday!):
Rennan Barkana (Tel Aviv)
TBA
Host: Ravi K. Sheth
February 8: Departmental Colloquium
February 8: (*** 2:00pm in DRL A5 ***)
Joe Hennawi (Berkeley)
New Insights into Quasar Environments from Close Quasar Pairs
Modern spectroscopic quasar surveys are biased against discovering close sub-arcminute pairs of quasars due to the finite size of optical fibers in multi-objects spectrographs. However sub-arcminute separations project to proper distances < 300 kpc/h, which are extremely interesting scales for a variety of cosmological phenemona. I will discuss a sample of about 200 new sub-arcminute quasar pairs, discovered from an extensive follow up campaign to find companions around the Sloan Digital Sky Survey (SDSS) and 2dF Quasar Redshift Survey quasars. About half of these systems are physically associated binary quasars, which I use to present the first measurement of the small scale (10 kpc/h < R < 400 kpc/h) quasar correlation function. An effort to push these measurements to higher redshifts (z ~ 4) will also be discussed. With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasars environment in Ly-alpha absorption. We searched background quasar spectra obtained from Gemini, Keck, the MMT, and the SDSS to survey Lyman Limit systems and Damped Lyman Alpha systems in the vicinity of luminous foreground quasars. A sample of 28 of these extremely rare coincidences will be presented. If the foreground quasars have the same luminosities in the transverse direction, the implied ionizing photon fluxes are a factor of ~ 5-8000 times larger than the ambient UV background. I will discuss the manifold cosmological applications of these new systems: they provide new laboratories for studying flourescent Ly-alpha recombination radiation, constrain the environments, emission geometry, and radiative histories of quasars, and will shed light on the physical nature of the Lyman Limit systems and the Damped Lyman Alpha systems.
Host: Bhuvnesh Jain
February 10: (*** 1pm in DRL 4E19 ***)
Masao Sako (KIPAC/Stanford)
The Search for Cosmic Supernova Explosions with SDSS-II
The Sloan Digital Sky Survey II has started a massive supernova search, where 300 square degrees of the sky are scheduled for multi- band imaging on a cadence of two days during the fall seasons of 2005 - 2008. A unique large-format imaging camera array with a total of 120 million pixels is capable of recording 200 GB of data in a single night of observing, allowing efficient discoveries of supernova explosions out to z = 0.4, or about 1/3 of the way back to the Big Bang. The first-year campaign, which ended in December 2005, was a remarkable success and a total of 126 SN Ia in the redshift interval of 0.01 < z < 0.42 were spectroscopically confirmed in the 3-month period. Although our primary focus this year has been SN Ia cosmology, the survey has produced an enormous amount of data of other types of transient sources as well. I will present some early results from the first year of the survey and discuss future prospects.
Host: Raul Jimenez
February 13: (*** 4:00pm in DRL 3W2 ***)
Marla Geha (Carnegie)
The Baryon Content of Dwarf Galaxies
Dwarf galaxies range in optical luminosity from a few millionths to a few hundredths the luminosity of the Milky Way. As probes of cosmology and the processes of galaxy formation, dwarf galaxies may be uniquely useful and informative. I discuss a survey of nearby low mass dwarf galaxies selected from the Sloan Sky Survey. These data represent the largest homogeneous sample of dwarf galaxies fainter than Mr > -16 with well-measured HI and optical properties. I will explore how baryonic and dynamical mass are related to star formation rates, metallicity and environments at these faint luminosities.
Host: Licia Verde
February 15: (*** 4:00pm in DRL A4 ***)
Scott Gaudi (CfA)
Taking the Inventory of Extrasolar Planets with Microlensing
Understanding planet formation requires a complete inventory of Galactic extrasolar planets, including gas giants, ice giants, terrestrial planets, and ejected planetary embryos. Microlensing is unique in that it is potentially sensitive to analogs of all the solar system planets except Mercury and Pluto, as well as to free floating planets, and so provides an excellent way of taking this inventory. I review the landscape of microlensing searches for extrasolar planets, beginning with an outline of the method itself, and continuing with a review of the results that have been obtained to date. Three planets have been detected with microlensing so far; I discuss what these detections have taught us about the frequency of terrestrial and giant planets. I then speculate on the expected returns of next-generation microlensing experiments both from the ground and from space, placing them in the context of future space-based planet-finding missions such as SIM PlanetQuest, Kepler, and TPF.
Host: Mariangela Bernardi
February 20: (*** 4:00pm in DRL 3W2 ***)
Andrew Connolly (Pittsburgh)
Discovery in the Era of Large Surveys: Unraveling the Universe
The development of the next generation of large survey telescopes will provide an unprecedented access to observations of the sky that span the local and distant universe. Given the size and quality of these data we have an opportunity to measure the subtle correlations between galaxy properties (luminosity, color, spectral type) that can be used to probe the impact of the energy content of the universe on the formation of the structures we see today. The challenge we face is how do we undertake such a study when the data sets amount to 100's of millions of sources each with hundreds or thousands of measured attributes. We need a new approach to astrophysics one that interfaces astrophysics with statistics and computer science. In this talk I will discuss techniques we have developed for analyzing large data sets that are being used to understand the energy density of the universe, to measure the correlations between physical and observable properties of galaxies and to identify unusual sources in large data sets (e.g. new classes of star and galaxies).
Host: Gary Bernstein
February 24: (*** 1pm in DRL 4E19 ***)
Jeffrey Newman (Berkeley)
From Fine Structure to Large-Scale Structure with the DEEP2 Galaxy Redshift Survey
The DEEP2 Galaxy Redshift Survey is the first project to study the distant Universe by obtaining a dataset comparable in size and nature to recent generations of local surveys. DEEP2 was designed to measure both the properties of galaxies at redshift z~1 and their distribution in space, making possible a number of unique tests of both galaxy evolution and cosmology. We have now observed nearly 50,000 galaxies using the DEIMOS spectrograph at Keck Observatory, most at redshift 0.7 < z < 1.4; the survey is more than 95% complete. In this talk, I will first provide an overview of the DEEP2 survey and the multiwavelength efforts now underway in one of the four DEEP2 fields, the "Extended Groth Strip". I will then describe tests for both temporal and spatial variation in the value of the fine structure constant which we have performed using DEEP2 data. Finally, I will discuss several lines of evidence from DEEP2 large-scale structure information indicating that galaxy groups are critical to the formation of typical early-type/red sequence galaxies seen today, and illustrate ways in which low-redshift surveys can help us to understand phenomena observed at z~1.
Host: Ravi K. Sheth
March 1: Departmental Colloquium
March 3: (*** 1pm in DRL 4E19 ***)
Beth Willman (NYU)
A Little Light, a Lot of Relevance: The Least Luminous Galaxies in the Universe
Nearly all known galaxies fainter than M_V = -10 are within the Local Group. These nearby dwarfs provide the unique opportunity to trace the detailed histories of individual galaxies. Despite their insignificant contribution to the total luminosity density of the Universe, the properties of these least luminous galaxies also hold special significance for our understanding of the impact of reionization on galaxy formation, the extent of metal-enrichment by Population III stars, and the efficiency of feedback due to star formation and supernovae. Moreover, the total number and spatial distribution of Local Group dwarf galaxies hold special significance for possible resolutions to the ``missing satellite'' problem with CDM models. To create a well-defined dwarf galaxy sample to the faintest possible limits, we have been conducting a uniform survey of SDSS I for nearby dwarf galaxies. I present the current status of this search, which has thus far resulted in the discovery of two new Milky Way companions: Willman 1 and the Ursa Major dwarf galaxy, the lowest luminosity galaxy yet known. The properties of these two objects raise the questions: What is the relationship between globular clusters and dwarf galaxies? and What is the lower limit of galaxy formation? I discuss the spatial distribution of satellite galaxies and the results of this search in a cosmological context.
Host: Mark Devlin
March 8:
Spring Break
March 15:
Fernando Atrio-Barandela (Salamanca)
The effect of the Intergalactic medium on the CMB temperature anisotropies
If a large fraction of baryons at low redshifts are in the form of a Warm Hot Intergalactic Medium, they could generate measurable CMB temperature anisotropies. We assume the non-linear baryonic density contrast is well described by a log-normal distribution. For model parameters in agreement with observations, the largest IGM contribution corresponds to scales l about 2000. The amplitude is rather uncertain and could be comparable to the contribution of galaxy clusters. The actual value is strongly dependent on the gas polytropic index gamma and the amplitude of the matter power spectrum sigma8.
Host: Ravi K. Sheth
March 22:
Rob Thacker (Queens)
From First Objects to Quasars: Some Recent Results in Numerical Cosmology
I shall review results from two ongoing projects. The first project, conducted in collaboration with Scannapieco (UCSB), examines the impact of a hydrodynamic outflow model for quasars within a simulation of a cosmological volume. The large dynamic range of our simulation enables us to calculate both correlation and luminosity functions for the quasar and AGN distributions in addition to more frequently predicted statistics such as the Lx-T relation of clusters. The results from this work highlight some unexpected differences in the treatment of physics in semi-analytic models versus simulations and call into question some of the underlying assumptions of semi-analytic models. The second project I shall discuss reexamines the effect of finite box size on simulations with k^\sim3 power spectra, which is particularly important for simulations of first object formation.
Host: Ravi K. Sheth
March 29:
Lam Hui (Columbia)
Stealing Einstein's Blunder(s) - Aspects of Dark Energy Measurements
I will discuss how correlated luminosity distance fluctuations, from peculiar flows, lensing and so on, might impact dark energy measurments from supernovae Ia. I will also discuss the issue of distinguishing dark energy from modifications of general relativity.
Host: Bhuvnesh Jain
April 5: Departmental Colloquium
April 12:
Derek Richardson (Maryland)
Binary Minor Planets
Since the discovery of the first binary minor planet in 1993 (not counting Pluto/Charon!), over 70 examples of asteroids and transneptunian objects with orbiting companions have been found, including one triple asteroid system. I will review the observations and theories about these objects, with an emphasis on understanding the formation of near-Earth asteroid binaries via tidal disruption of fragile asteroids.
Host: Ravi K. Sheth
April 14:
Jim Bartlett (Paris)
Cosmology with galaxy clusters and the SZ effects
Host: Ravi K. Sheth
April 19:
Mauro Giavalisco (STScI)
Star Formation at High Redshift
Recently, galaxies at high redshifts have been the targets of extensive, coordinated programs of observations from NASA's Great Observatories, as well as from the major ground--based telescopes. The sensitivity and angular resolution of Hubble and the wavelength coverage of Spitzer are allowing us, for the first time, to compare properties of galaxies observed as far back in the past as ~93% of the age of the universe with those of systems observed at much later times in the cosmic evolution. I will show results from these studies that are relevant to understand key features of galaxy evolution and to test some of our general ideas on how galaxies form and evolve. I will focus, in particular, on the morphology and spatial clustering of galaxies at redshifts z>2 and discuss their implications about the physics of star formation in these systems.
Host: Ravi K. Sheth
May 3: Departmental Colloquium

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Past seminars: Fall 2000, Spring/Fall 2001, Spring 2002, Fall 2002. Spring 2003. Fall 2005.