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Dr. James Higdon’s Update from ALMA

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The Ataama Large Millimeter Array (ALMA) is an interferometer array operating at millimeter and sub-millimeter wavelengths. Located high in the Chilean Andes.

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HST color images of ring galaxies AM 0644-741 and Arp 147 currently being observed with ALMA. Right picture shows fresh carbon monoxide in the ring.

Galaxies – once considered to be isolated “Island Universes” – actually experience collisions and close passages with their neighbors. Such events can drastically change both a galaxy’s appearance and rate at which it forms new stars.

One of the rarest and most dramatic examples of this are ring galaxies, created when a neighbor galaxy passes through the center of a larger “target” galaxy. The collision causes gas and stars in the target galaxy to accumulate into dense rings that travel outward at high speed. A prime example is the galaxy named AM0644-741, shown imaged in visible light by the Hubble Space Telescope in the displayed figure (left). The ring’s blue color indicates that it is robustly forming stars. Georgia Southern Professors James & Sarah Higdon are studying how stars form out of the gas swept up in the rings, and if this is different from the way ordinary galaxies do it. Stars form in dense and cold clouds of molecular gas (mainly hydrogen), so to study star formation they must measure its quantity and distribution.

They were recently awarded observing time with the Atacama Large Millimeter Array (ALMA), a collection of 66 separate radio telescopes located on the high Atacama plains in Chile. These telescopes work together to produce sensitive high resolution images of light emitted by molecules in distant galaxies. The panel at right shows that cold molecular gas is heavily concentrated in AM0644-741’s ring. Together with other data James and Sarah hope to learn if stars form with greater efficiency or more rapidly in the rings of these objects. Their work shows that 130-million years ago, in the middle of the dinosaur’s reign on Earth, a neighboring galaxy crashed through the center of a normal spiral galaxy, creating the ring we now observe moving outward at 340,000 mph and forming stars roughly 10-times faster than our own Milky Way galaxy.

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