Press Release

Radio Galaxy at a Distance of 9.2 Billion Light Years

September 16, 1999

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Object Name: Radio galaxy B3 0731+438
Telescope: Subaru Telescope / Cassegrain Focus
Instrument: CISCO
Filter: N225 (2.25micron), K'(2.13micron)
Color: Blue (K'), Green (K'+N225), Red (N225)
Date: UT1999 February 28
Exposure: 48 min (N225), 32 min (K')
Field of View: 8.4 x 12.1 arcsecs (right figure)
Orientation: North up, east left
Position: RA(J2000.0)=7h35m22s, Dec(J2000.0)=+43d44m (Lynx)
A radio galaxy is a galaxy that emits strong radio waves. These waves are powered by an active galactic nucleus (AGN) at its center, which is generally believed to be a black hole whose mass is more than one million times that of the Sun. The AGN is powered by the gravitational energy released as the surrounding gas falls into the black hole.

The radio galaxy B3 0731+438 is about 9.2 billion light years away from the Earth. Two high speed jets flow in opposite directions from the AGN at a few thousand km/sec. These jets flow through holes in the gas and dust which surround the AGN and prevent us from observing it directly. Strong ultraviolet radiation from the AGN can escape through these holes and illuminate the surrounding hydrogen gas, seen here with CISCO attached to the Subaru Telescope for the first time. The "X"-shaped structure may be caused by the jets pushing aside the gas and forming two conical cavities.

This observation with the Subaru telescope is the first time that such a structure has been seen in a distant radio galaxy. It is expected that observations such as this will become important as we try to understand the nature of AGNs and the birth of radio galaxies.

The expansion of the Universe means distant radio galaxies such as B3 0731+438 are moving rapidly away from us. The hydrogen line at 6563 Angstroms is redshifted to 22,500 Angstroms (2.25 microns) by the
Doppler effect when it reaches the Earth. The hydrogen emission was observed with a 2.25 micron narrow filter, and the continuum emission with a 2.13 micron wide filter. Combining the two images, the hydrogen gas from the radio galaxy appears orange while galaxies and stars appear as white spots.

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