Livermore Astronomers Discover Dwarf Galaxy Merging with Radio Galaxy, Cygnus A

May 28, 2003

Livermore Astronomers Discover Dwarf Galaxy Merging with Radio Galaxy, Cygnus A

NASHVILLE, Tenn. — An astrophysicist from the Lawrence Livermore National Laboratory today time will discuss the first detected signs of a merger in the powerful radio galaxy, Cygnus A.

Using adaptive optics imaging and spectroscopy on the 10-meter Keck II Telescope, Gabriela Canalizo of Livermore’s Institute of Geophysics and Planetary Science has discovered a dwarf galaxy in the central regions of Cygnus A, which may be the smoking gun of a merger event.

Canalizo will present “A Possible Merging Companion to Cygnus A,” at 10 a.m. CDT today in Nashville, Tenn. at the American Astronomical Society meeting.

Working with Claire Max of Livermore Laboratory and the Center for Adaptive Optics at UC Santa Cruz, David Whysong and Robert Antonucci of UC Santa Barbara’s Physics Department, and Scott Dahm of the Institute for Astronomy at the University of Hawaii, Canalizo has observed a bright core most likely consisting of older stars that appears to be merging with Cygnus A, a radio galaxy that is about 800 million light years away from our galaxy.

“We’re seeing the clearest images of the core of Cygnus A with unprecedented resolution and depth,” Canalizo said. “These images show a secondary point source relatively close to the radio nucleus of Cygnus A.”

Canalizo and her colleagues have concluded that the secondary point may be the dense, gas-stripped core of a low luminosity merging galaxy that has survived the merger with the giant elliptical host to Cygnus A.

Astrophysicists believe that mergers and collisions between galaxies trigger activity within the nucleus of radio galaxies. These nuclei are often quasars that are hidden yet are usually hundreds to thousands of times brighter than the galaxy itself. In the case of the merger with Cygnus A, the dwarf galaxy appears to have been stripped of most of its mass, and the encounter is the driving mechanism fueling the quasar powering Cygnus A.

“This is the first time that we have a clear sign that Cygnus A might be a merger,” Canalizo said. “Though the answer is not definitive, it’s very likely that this is a merger.”

Cygnus A is relatively close to our galaxy, exhibits extreme characteristics and has played a fundamental role in the study of virtually every aspect of powerful radio galaxies.

Using the adaptive optics system at Keck, Canalizo and her colleagues were able to view the activity near Cygnus A with unprecedented detail and resolution with minimal blurring from the Earth’s atmosphere. The adaptive optics system uses light from a relatively bright star, called a “guide star,” to measure atmospheric distortions and to correct for them.

Canalizo and her colleagues plan to conduct a second, deeper spectroscopic observation this summer. This observation should allow a more definitive determination of whether the secondary point source is, in fact, the core of a dwarf galaxy merging with Cygnus A.

For images, go to:

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