PENN Astrophysics Group: Research
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Overview of the Penn Astrophysics Group
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 component in cosmology. We are specially strong in cosmology, galaxy evolution and stellar populations. There is a vibrant collaboration with the string cosmology group of which Penn is one of the world leaders. We also do research on numerical astrophysics and star and planet formation and searches. 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
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.
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 the 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.
The astro group at Penn is unique since it has very strong ties with the string cosmologist. 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.
The astro group at Penn is involved in studies of large scale structure (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.
Experimental and Observational Astrophysics and Cosmology
Penn is one of the three leading instititutions (with Princeton and Rutgers) on the Atacama Cosmology Telescope. ACT is a 6m telescope to start operations in the atacama desert in 2006 and that will produce an exquisite map of the CMB at angular resolutions of 1'. The ACT project has three frequency bands strategically posed to detect the SZ effect from galaxy clusters. In addittion, ACT has an optical follow-up program to obtain redshifts to galaxies in this clusters and to obtain weak lensing maps to determine the dark matter mass in the cluster.
Penn is the lead institution in a large international collaboration which makes up BLAST. The design of BLAST incorporates a 2.0~m mirror that will be replaced with a 2.5~m mirror in the 4th and 5th years of the project. The telescope will operate on a Long Duration Balloon (LDB) platform with large format bolometer arrays at 250, 350, and 500 microns. BLAST will address some of the most important galactic and cosmological questions regarding the formation and evolution of stars, galaxies and clusters. It will conduct large-area sensitive galactic and extragalactic surveys which will: (i) identify large numbers of distant high-redshift galaxies; (ii) measure cold pre-stellar sources associated with the earliest stages of star and planet formation; (iii) make high-resolution maps of diffuse galactic emission from low to high galactic latitudes.
The PBA is a direct result of CMB receiver development efforts. The receiver originally built for MAT will be outfitted for 3 millimeter observations on the Green Bank Telescope (GBT) in West Virginia. A feasibility study of the implementation of this work has been completed in collaboration with NRAO. The science potential of a 3 millimeter array on a 100~m dish is astounding, ranging from actually mapping SZ clusters to searching for planetary disks in star-forming regions in the Galaxy. The array is scheduled to be on the GBT in late 2004.
Nearly 1000 small bodies have been discovered orbting beyondNeptune, 30 to 50 AU from the Sun. These Kuiper Belt Objects (KBOs) are remnant ice and rock chunks from theformation of our Solar System which have survived 5 billion years to the present day. We will use the new Advanced Camera for Surveys aboard the Hubble Space Telescope to search for KBOs as small as 15 km in diameter. The results of this survey will help unravel the history of our Solar System. These planetesimals are too small to be o bserved around other stars with any technology of the foreseeable future, so the Kuiper Belt represents our best chance to learnabout this step toward planet formation.
The Taiwanese-American Occultation Survey (TAOS), is performing a census of small bodies (> 2 km) in the Kuiper Belt (the region just outside the orbit of Neptune, from which most short period comets are believed to come).