Deep Study Reveals Hundreds of Objects in the Sky That Emit X-Rays
Color X-ray image of the 2-million second Chandra Deep Field-North, the deepest X-ray exposure ever taken
A catalog of objects based on the deepest view ever of the X-ray sky has recently been announced by a team of astronomers led by Penn State Postdoctoral Scholars David Alexander and Franz Bauer and Associate Professor of Astronomy and Astrophysics Niel Brandt. The study, which contains nearly 600 sources of X-ray emissions, will appear in the August issue of the Astronomical Journal.
The observations were obtained with the Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray Observatory. Between October 1999 and February 2002 Chandra was pointed 20 different times, for a total of 23 days, at a region centered on the Hubble Deep Field-North, an area of the sky intensely studied with the Hubble Space Telescope. The ACIS instrument, which was built by a team lead by Gordon Garmire, Evan Pugh Professor of Astronomy and Astrophysics, captured X-rays from a field that covers an area on the sky equal to slightly more than half of that covered by the moon.
"We have been able to measure the faintest X-ray sources ever detected," says Alexander. "The catalog gives accurate positions, brightnesses, and some spectral information on hundreds of interesting objects, ranging from nearby galaxies to quasars billions of light years away." Franz Bauer adds, "This is a truly unprecedented view of the X-ray universe. The faintest X-ray sources we discovered are so faint, their signal is only about one X-ray photon in every four days."
The "2 Million Second Survey" was designed to complement the Hubble Deep Field-North Survey that was obtained with the Hubble Space Telescope in the mid-1990s. The Hubble survey provided a view of the optical universe by recording visible light, whereas the Chandra observations centered on high-energy radiation by recording X-rays. Brandt, the Chandra survey's principal investigator, noted that "The penetrating nature of X-rays permits us to examine exotic phenomena that may be hidden from view at visible wavelengths, just as hospital X-rays can probe regions that cannot be seen with a standard optical camera."
Nearly two dozen scientific papers based on the Chandra Survey already have been published. Combining the X-ray data with images taken at other wavelengths—including radio, millimeter, infrared, and optical—has provided insights on the evolution of galaxies, spectacular events of star formation, and accretion of matter onto supermassive black holes when the universe was less than a billion years old. "This survey will be a treasure trove for the entire astronomical community for years to come," notes Alexander.
Other Penn State astronomers who participated in this work are Patrick Broos, George Chartas, Donald Schneider, Leisa Townsley, and Cristian Vignali. Other survey team members are Ann Hornschemeier at Johns Hopkins University, Amy Barger at the University of Wisconsin, Len Cowie at the University of Hawaii, Mark Bautz at the Massachusetts Institute of Technology, and W.L.W. Sargent at the California Institute of Technology. This study was partially supported by grants from NASA and the National Science Foundation.
CONTACTS:
Niel Brandt: +1 814-865-3509, niel@astro.psu.edu
Franz Bauer: +1 814-863-7111, fbauer@astro.psu.edu
Dave Alexander: +44 1223 766659 (U.K.), dma@ast.cam.ac.uk
Barbara Kennedy (PIO): 814-863-4682, science@psu.edu