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.

September 14: Departmental Colloquium
September 21:
Stefano Zibetti (Max-Planck)
Ultra deep photometry with large surveys: The image stacking approach
Large surveys, like the SDSS, are by design relatively shallow in terms of surface brightness (mu_r<25 mag/arcsec2) and magnitude (r<22) limits, and therefore appear to be of little or no use to study faint diffuse light or distant galaxies. The enormous statistical basis they provide, however, makes it possible to adopt image stacking methods in order to detect and characterize the average properties of this kind of sources. Successful attempts have been done on stellar haloes of disc galaxies, on the intracluster light (ICL), and, lately, on the galaxies associated to MgII absorbtion systems in high-z quasars. In this talk I will summarize some of these results and outline some forthcoming and future developments.

Host: Ravi K. Sheth
September 28:
Rachel Mandelbaum (Princeton)
Science results with SDSS weak lensing
The SDSS has proven to be an excellent dataset for exploring various problems in astrophysics and cosmology using weak lensing, with the highest lensing signal to noise to date and spectroscopic redshifts for lens galaxies, which simplifies theoretical interpretation by allowing us to compute signal as a function of transverse separation rather than angle. In this talk, I will describe our new Reglens reduction method that is used to measure galaxy shapes, discuss constraints on systematic errors, and describe several interesting science results that have resulted from it. Recently, we have placed constraints on dark matter halo ellipticity, and detected intrinsic ellipticity-density alignments that may be important contaminants of current and future weak lensing surveys. I will also describe ongoing work such as a measurement of the dark matter power spectrum using a combination of galaxy-shear cross- correlation and galaxy-galaxy autocorrelation techniques; a study of the relationship between stellar masses, luminosities, and dark matter halo masses as a function of morphology and local environment; and the determination of average halo profiles using the lensing signal around field galaxies.

Host: Ravi K. Sheth
October 5:
Kathryn Johnston (Wesleyan)
Stellar Halos and Satellite Systems in a Lambda CDM Universe
In the context of Lambda CDM, galaxies are thought to form hierarchically. In this talk I will examine the implications of this formation mechanism for the build up of stellar halos and their associated satellite systems. I will first compare typical halo vs satellite accretion times and radial distributions. I will go on to discuss the implications of these results for stellar populations in the halo vs the satellites as well as expectations for the level of substructure in the stellar halo's phase-space distribution.

Host: Ravi K. Sheth
October 12: Departmental Colloquium
October 19:
Scott Burles (MIT)
First results from the SDSS Lens + ACS (SLACS) survey
I'll present recent results from an ongoing survey (SLACS) for new strong gravitational lens systems selected from the SDSS. We implement a novel spectroscopic search technique to identify candidates, and use high resolution HST imaging plus ground-based IFU spectroscopy, to confirm multiply imaged background galaxies. With the survey approximately 1/3 complete, we have discovered the largest number of strongly lensed systems of any single survey, currently 25 out of 40 candidates. I'll present our analysis of the first sample of 15 lenses, which reveal that the lens galaxies lie well within the fundamental plane and all are consistent with a pure isothermal distribution for the total mass profile.

Host: Ravi K. Sheth
October 26:
Roman Scoccimarro (NYU)
New Insights into Structure Formation
I discuss recent progress on extending cosmological perturbation theory into the nonlinear regime. I also illustrate how one can turn nonlinear effects into our advantage to help us extract more information from galaxy surveys.

Host: Ravi K. Sheth
November 2:
Josh Frieman (Fermilab)
The Dark Energy Survey
This talk will provide an overview of the Dark Energy Survey (DES), a proposed multi-band, optical survey of 5000 sq. deg in the southern sky, that will use a new wide-field CCD camera to be built for the Blanco 4-m telescope at Cerro Telolo Inter-American Observatory (CTIO). Over its five-year mission, the DES will collect data on tens of thousands of galaxy clusters, roughly 300 million galaxies, and about 2000 Type Ia supernovae. The survey data will be used to measure the dark energy and dark matter densities and the dark energy equation of state through four independent methods: galaxy clusters (in concert with the South Pole Telescope Sunyaev-Zel'dovich survey), weak gravitational lensing tomography, galaxy angular clustering (baryon oscillations), and supernova distances. These methods are doubly complementary: they constrain different combinations of cosmological parameters and are subject to different systematic errors. The DES will therefore make a substantial and robust advance in the precision of dark energy measurements.

Host: Bhuvnesh Jain
November 9:
No seminar
November 16: Departmental Colloquium
November 18:
Andy Connolly (TBA)
"TBA"
Host: Ravi K. Sheth
November 23:
Thanksgiving
November 30:
Patrick McDonald (CITA)
Probing inflation, dark energy, etc. using the Lyman-alpha forest
The absorption in high redshift quasar spectra by neutral hydrogen in the intergalactic medium, called the Lyman-alpha forest (LyaF), provides a good probe of the density field of the Universe on scales of a few megaparsecs. I will discuss the theory and observations of the LyaF that allow us to constrain cosmology. The current best constraints on the power spectrum of the initial density perturbations generated in the early Universe are obtained by comparing the LyaF observed in thousands of quasar spectra from the Sloan Digital Sky Survey to the predictions of cosmological numerical simulations, and combining the result with the CMB constraints on much larger scales. These constraints should improve significantly in the near future. I will also discuss the possibility of probing dark energy by using a future large survey to detect baryon acoustic oscillations in the LyaF.

Host: Ravi K. Sheth
December 7: Departmental Colloquium
December 14:
Rosanne Di Stefano (CfA)
Mesolensing: Discovering Nearby Stellar Remnants and Low-Mass Dwarfs
Although they exist in large numbers, we know of only a few individual isolated neutron stars, and no isolated black holes. The known white dwarfs and low-mass dwarfs constitute only a small fraction of the nearby population. Fortunately, nearby planetary and stellar-mass objects have a high probability of producing detectable lensing signatures as they travel across distant dense stellar fields. In this talk I will describe the signatures of these "mesolenses" and explore the ways lensing can be used to study nearby dark and dim populations.

Host: Bhuvnesh Jain

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