UA/Smithsonian 6.5-m Telescope Takes Its First Wide-Field Picture

Sept. 25, 2000

MOUNT HOPKINS, Ariz. -- The University of Arizona/Smithsonian 6.5-meter MMTO telescope on Mount Hopkins, Ariz., took its first wide-field picture on Sept. 6, as monsoons waned in southern Arizona.

The MMTO took first visible light images in May and first infrared images in June. Astronomers say the best is yet to come.

UA astronomer Donald W. McCarthy and graduate students Joannah Hinz and Rose Finn used an infrared electronic camera they designed to photograph spiral galaxy NGC 7479 in the constellation Pegasus. UA Steward Observatory graduate student Craig Kulesa processed the image into GIF format, which is on the web at http://loke.as.arizona.edu/~ckulesa/binaries/7479-J.gif The original image, which is available in several formats, contains much more detailed information than can be contained in GIF.

Astronomy graduate student Phil Hinz combined two infrared images for a true color image that shows interesting structures at the very heart of the galaxy. It is online at http://olympus.as.arizona.edu/~mccarthy/logcolor.tif Stars in this image are more blurred as combining the colors produces a halo effect around the stars.

"These images demonstrate the potential of the new telescope to examine large areas of the sky with the excellent clarity provided by the stable atmosphere over the Mount Hopkins site," McCarthy said.

NGC 7479 is a so-called "grand design spiral" showing extensive spiral arms with newly formed stars and glowing clouds of gas. The galaxy is 100 million light-years from Earth and about the size of our own Milky Way Galaxy, approximately 100,000 light-years across.

However, NGC 7479's nucleus appears much more active, McCarthy said. In addition, a long bar-shaped structure and spiral arms that are not symmetrical are visible in its central region. These unusual features are attributed to the fact that NGC 7479 is cannibalizing another galaxy in a merger that began 5 million years ago.

Infrared light is much redder than the red light visible to the human eye. Observations in infrared light enable astronomers to penetrate the obscuring dust in the spiral arms to examine the full extent and structure of the galaxy.

The new image is very sharp, 0.80 arcsec, or the angular size of a dime seen from three miles away. That's 75 times sharper than the resolution of the human eye. If humans had eyes as sharp, people could read newspapers a half-mile away.

"The MMTO can produce images 8 times sharper than we obtained, once all subsystems are working and as the atmosphere improves later this fall," McCarthy said. The telescope mirror's cooling system has yet to be completely installed, and focus-control and motion-tracking subsystems will be fine tuned.Their NGC 7479 image is also affected by "atmospheric seeing" as they observed the galaxy when it was close to the horizon. It is further degraded by the effects of adding together several 30-to-60 second exposures, as individual exposures are sharper than their sum.

The cryogenically cooled infrared camera, PISCES, designed by McCarthy, Hinz, Finn and UA astronomy alumnus Jian Ge of the University of Pennsylvania provides a uniquely wide field-of-view for any infrared camera on a large telescope. It can be used on several telescopes in the Tucson area. The team worked closely with a local company, Infrared Laboratories Inc., in constructing PISCES. The camera is described in an article accepted for publication in the Publications of the Astronomical Society of the Pacific.

McCarthy's group was first to use the 6.5-m (21.3-foot diameter) telescope after the monsoon rain season in early September. However, the telescope had already been used for visible and infrared observations in May and June, using instruments with a much smaller field-of-view. First light images are at The MMT Observatory web site. First infrared images, taken by Steward Observatory's Phil HInz and Bill Hoffmann at 10 micron wavelengths, are on the web at http://fromage.as.arizona.edu/~phinz/MMT/june.htm

The MMTO's sibling in the southern hemisphere - Magellan 1 at Las Campanas, Chile - succeeded in taking its first light image on Sept. 15, 2000. For more on that story,released Friday, click on the Science & Research web page at UANews.org

The UA Mirror Lab spincast both the MMTO and Magellan 6.5-m mirrors of Ohara E6 borosilicate glass, then polished them using the UA innovative stressed-lap technique. For more on UA mirror making, visit theUA Mirror Lab web site.