Radio Images from the ATA

The ATA can operate as a radio camera to image distant sources of radio waves. Some of these sources are clouds of hot ionized gas surrounding newly formed massive stars or the blast of a supernova explosion marking a star’s death. Such radio sources emit radio waves over a broad range of frequencies and we can learn about the temperature and density of the gas by measuring its spectrum, the power at many frequencies. Other radio sources are clouds of cool hydrogen gas spread though a galaxy and between galaxies. Hydrogen atoms emit radio waves at a particular frequency, 1420 MHz. As the gas orbits around the center of its galaxy, its velocity with respect to the Earth is different at different positions in the galaxy. These velocity differences produce a Doppler shift, changing the frequency of the radio waves that we receive. By measuring this frequency shift at all positions across a galaxy, we can determine how the gas is moving in the galaxy. The ATA is well suited to these kinds of observations.

Images of Nearby Galaxies

M31

m31
Image credit: Allen Telescope Array/UC Berkeley

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Familiar optical of M31, Andromeda Galaxy.

The first image taken by the 42-antenna Allen Telescope Array depicts the atomic hydrogen in the Andromeda Galaxy (Messier 31 or M31), the nearest large spiral galaxy to the Milky Way. Unlike all other radio telescopes, the ATA can image large objects like M31 - its diameter is about five times the diameter of the full moon - all at once instead of piecemeal. The telescope's wide field of view makes it ideal for mapping the heavens in search of new radio sources."

The colors, from blue to white, represent the intensity of the radio emissions and thus the density of hydrogen. Because atomic hydrogen is the stuff from which stars are made, the large "hole" in the center of Andromeda indicates that the galaxy is near the end of its star formation history. In the background are radio galaxies powered by massive black holes that are billions of light years away from Earth.

M33

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Image credit: Allen Telescope Array/UC Berkeley

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Optical image of M33, Pinwheel Galaxy.
Image credit: T.A.Rector (NRAO/AUI/NSF and NOAO/AURA/NSF) and M.Hanna (NOAO/AURA/NSF)

One of the first images taken by the 42-antenna Allen Telescope Array shows the atomic hydrogen in the Pinwheel Galaxy (M33), situated in the constellation Triangulum. Unlike M31, the Pinwheel Galaxy shows no hole at the center and an almost constant distribution of gas nearly to its outer radius. The Pinwheel's nearest neighbor, the Andromeda Galaxy, is large enough to generate tides in the galaxy, which blow out faint puffs of hydrogen seen at the top and bottom of the image.

The ATA's large field of view is 17 times larger than that of the Very Large Array in New Mexico, making the ATA ideal for surveys, both for radio astronomy and SETI.