Astrophysics and Cosmology
Overview
The astrophysics group in the Department of Physics and Astronomy at Penn currently consists of six full time faculty, one lecturer, and a number of post-doctoral fellows, full-time staff, and graduate students (photos here). We are in the process of hiring more faculty and plan to continue expanding our group over the next several years.
The astro group at Penn has a very strong experimental and theoretical interests in cosmology. We are specially strong in cosmology, galaxy evolution and stellar populations. There is a vibrant collaboration with the string cosmology group at Penn. We also do research on numerical astrophysics. Our areas of research include Kuiper-Belt objects, dark matter search, dark matter halos, large scale structure, galaxy formation and evolution, the cosmic microwave background, and the development of new astronomical instrumentation and telescopes. Our research activities cover the full spectrum -- computations, instrumentation, observation, and theory. There are many exciting projects for students to join.
Theoretical Astrophysics and Cosmology
Bhuvnesh Jain, Ravi K. Sheth, Mark Trodden, Justin Khoury
- Dark Matter Halos and Weak Lensing
One of the best ways of studying dark matter is through weak gravitational lensing, which is the shearing and magnification of light we receive from distant galaxies. The effect is very subtle, typically less than a 1% stretch of the image, so very large numbers of g alaxies must be analyzed to detect the effect. We have measured the shapes of 2 million galaxies in 75 square degrees of CCD 4-meter telescope images, detecting the effect and measuring the fluctuations in dark matter to ~10% accuracy. With improved algorithms we will examine these data again, and turn to deeper data being gathered by the Deep Lens Survey (http://dls.bell-labs.com). Our research has focused on understanding how small fluctuations in the early Universe grew to form the large-scale structure observed today. We use theoretical modeling of weak lensing by large-scale structure for different cosmological models and are interested in the measurement of galaxy clustering parameters and their relation to the clustering of dark matter measured by lensing effects.
- Dark Energy
The group has a strong interest in dark energy. So far we have developed methods to measure the time evolution of dark energy and unveil its nature by using observations from the cosmic microwave background, the differential ages of galaxies and weak lensing. The Penn group is involved in The SuperNova/Acceleration probe (SNAP, http://snap.lbl.gov), a proposed 2-meter space telescope designed to measure supernova to redshift 1.7 with sufficient accuracy to measure the evolution of the mysterious dark energy that dominates he present Universe. With its billion-pixel visible/near-infrared imager, SNAP is also the ideal tool for measuring the mass distribution of the Universe with weak gravitational lensing. We are currently working with the SNAP collabo ration to optimize the SNAP design andmission by conducting extensive calculations of its capabilities for supernova and weak-lensing measurements.
- Theoretical and string cosmology
The astro group at Penn is unique in that it has very strong ties with the string cosmologists. We have a very dynamic collaboration to address fundamental questions in cosmology: how was the universe created? what is dark energy? some of the leading ideas in theoretical cosmology (e.g. the ekpirotic universe) were thought at Penn.
- Galaxy Formation and Evolution
Much work has been done at Penn to understand the evolution and formation of galaxies by analyzing the stellar populations in distant galaxies. We have developed stellar population models and unveil the star formation history of galaxies from the SDSS. We have also studied in detail the evolution of elliptical galaxies over the Hubble time from SDSS and other surveys. We continue our research on stellar populations of galaxies from SDSS, high-redshift surveys and ACT optical follow-up
- Large scale structure
The astro group at Penn is involved in studies of large scale structure (2dF and SDSS) to determine the bias other cosmological parameters of the universe. The group is also leading the use of the halo model in studies of large scale structure and analytical mass functions.
- Numerical simulations of star and planet formation
Numerical simulations of stars (and recently planets) are performed at Penn in collaboration with the group in Copenhagen (Aake Nordlund) and the group in San Diego (Paolo Padoan & Mike Norman).
Experimental and Observational Astrophysics & Cosmology
Mariangela Bernardi, Gary Bernstein, Mark Devlin, Masao Sako
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BLAST - Balloon-borne Large Aperture Telescope
BLAST: The "Balloon-borne Large-Aperture Sub-millimeter Telescope," flies from a Long Duration Balloon (LDB) platform and incorporates a 2-meter primary mirror with large-format bolometer arrays operating at 250, 350 and 500 microns. By providing the first sensitive large-area (~0.5-40 square degrees) submillimeter surveys at these wavelengths, BLAST will address some of the most important cosmological and Galactic questions regarding the formation and evolution of stars, galaxies and clusters.
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Penn Array (MUSTANG):
The University of Pennsylvania, in collaboration with the National Insitute of Standards and Technology, NASA's Goddard Space Flight Center, and the National Radio Astronomy Observatory, have built 3 millimeter array of 8x8 TES detectors for the GBT. The GBT will have a better sensitivity in this range than current telescopes. The 90 GHz array will be a user instrument and is suitable for many different observations.
Inaugural observations were made of a star-forming region in the Orion Nebula. - PAPPA:
PAPPA is a balloon-borne instrument to measure the polarization of the cosmic micorwave background at millimeter wavelengths. It will search for the signature of gravity waves excited in an inflationary epoch shortly after the Big Bang. PAPPA uses a "polarimeter-on-a-chip" to instantaneously measure the Stokes I, Q, and U parameters in each pixel of the array. PAPPA is a collaboration with the University of Pennsylvania and the National Institute of Standards and Technology.
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ACT - Atacama Cosmology Telescope
The Atacama Cosmology Telescope project aims to observe the microwave
sky in three frequency bands at high angular resolution and sensitivity over a substantial region of the sky. ACT is a custom-designed 6-meter off-axis Gregorian telescope built by AMEC Dynamic Structures. The ACT detectors are transition-edge-sensing superconducting bolometers, assembled into detector arrays and read out with SQUID multiplexers. ACT's Millimeter-Wave Bolometric Camera (MBAC) will consist of three 32x32 arrays of bolometers, with each bolometer approximately 1 square millimeter in size; each array corresponds to one of the three ACT frequency channels at 150 GHz, 220 GHz, and 270 GHz.