Astronomers itch to detect the very faint galaxies that were created close to the beginning of the universe. Now a panoramic infrared camera, one with the largest field of view for a large telescope, has been installed on the Palomar Observatory's Hale 200-inch telescope. This much-awaited instrument promises to yield many new insights for deep-space astronomy.
The Palomar Observatory, which is owned and operated by the California Institute of Technology, has a long tradition as a pioneer in infrared astronomy, using both ground and space-based telescopes. The unique feature of the new camera is a $350,000 sensor manufactured by Rockwell Scientific in Camarillo, California. The sensor rests inside a camera that has been provided by Cornell University as part of their collaborative program with Caltech at Palomar. Caltech's contribution—the infrared sensor—was made possible by a $1 million gift generously provided by Sam and Lynda Oschin for the upgrading of instruments at Palomar.
The new camera is one of many efforts over the years to keep the Palomar telescopes modernized and relevant. It's one of the reasons that scientific research at Palomar has been remarkably productive since the observatory's debut in 1948. Just this month, for example, on October 4, Caltech astronomer Derek Fox detected the afterglow of a gamma-ray burst just nine minutes after the explosion. Then, three days later, astronomers announced the discovery of a spherical body orbiting in the outer reaches of the solar system. Both discoveries were made using Palomar's 48-inch Oschin telescope.
The Hale telescope's newly commissioned digital camera, whose format is 2048 x 2048 pixels, will bring unprecedented speed to surveying the heavens for near and distant objects that emit radiation primarily in the infrared spectral regions. It replaces the observatory's current infrared camera, which had a format of only 256 x 256. This gives the 200-inch Hale "a truly extraordinary leap in capability—a factor of 64 increase in survey speed at a single stroke," says Caltech's Richard Ellis, the director of Caltech optical observatories and the Steele Family Professor of Astronomy.
Infrared radiation is not visible to the human eye but offers key diagnostic features for astronomers. As the universe expands, distant galaxies are moving away from us. Accordingly, much of the visible light they emit is "redshifted" into the infrared part of the spectrum by the time it reaches astronomers' telescopes. That's why a survey capability for locating faint infrared sources is so important to astronomers. Once astronomers have charted the locations of the most distant galaxies with such infrared surveys, those galaxies are scrutinized in more detail with the 10-meter Keck telescope in Hawaii, says Ellis. (The Keck Observatory is jointly operated by Caltech, the University of California, and NASA.)
Closer to Earth, the camera will be equally valuable to astronomers interested in probing solar system sources beyond the orbit of Pluto, as well as the poorly understood brown dwarfs. The latter are objects sized somewhere between a giant planet and a star that, due to their low mass and coolness (2,000 degrees or less), are difficult to detect except at infrared frequencies.
Each pixel of Rockwell's camera has a surface layer composed of mercury, cadmium, and telluride, the compound used for infrared sensing. Another key element of the camera is its complementary metal oxide semiconductor (CMOS), which precisely reads the infrared light from each pixel and converts it to a usable signal. Electronics developed jointly by Caltech and Cornell staff downloads this signal and assembles a digital image on a computer.
For several months, Roger Smith, head of detector development at Caltech, and colleagues, had the use of a so-called "engineering-grade" camera to "play with," as Ellis puts it. That allowed the Caltech engineers to ensure it worked properly, to tune up the voltages, and to practice its proper installation. Then, last month, with some trepidation, they successfully installed the delicate and expensive science-grade version in the camera system built by Cornell.
Using the 200-inch Hale, the "first light" images were taken by Ellis; Smith; Keith Taylor, the associate director for development of the Caltech Optical Observatories; and colleagues from Cornell led by Professor Steve Eikenberry. The images, reduced by Caltech grad student Kevin Bundy and Chris Conselice, a postdoctoral scholar, demonstrate the dramatic leap in imaging capability: with the new camera, a single exposure of NGC 891 (a nearby star-forming spiral galaxy) is all that's needed to capture an entire galaxy. That contrasts with the previous camera, where a sequence of dozens of independent exposures would have been necessary to achieve the same goal. In the coming weeks, a series of Caltech, JPL, and Cornell observers will be putting the new instrument through its paces.
When Palomar Observatory was dedicated in the summer of 1948, the Caltech facility instantly became the preeminent astronomical observatory in the world. For decades, its 200-inch telescope, named after famed astronomer George Ellery Hale, maintained its distinction as the world's leading astronomical instrument. Now, the addition of the jointly produced Cornell-Caltech camera funded in part by Sam and Lynda Oschin, says Ellis, "demonstrates Caltech's commitment to giving a new lease on life to the 200-inch through innovative state-of-the-art instruments."
Note to Editors: A photo of NGC 891 is attached. Photo Caption: "First light" image of the edge-on spiral galaxy, NGC 891 taken through a filter transmitting at 2.4 microns. The small square indicates the field of view of the previously-available Palomar infrared camera.
