Universe Today : It’s a Bird! It’s Tinker Bell! It’sThree Galaxies!

Written by Nancy Atkinson

There once was a galaxy known as ESO 593-IG 008. It was thought to be a relatively mild-mannered galaxy, even though scientists believed it was a collision of two different galaxies; one a barred spiral and the other an irregular galaxy. But now, an international team of astronomers has discovered that it actually is a stunning rare case of three interacting galaxies, with the third galaxy forming stars at a frantic rate.

Using adaptive optics on the European Southern Observatory’s (ESO) Very Large Telescope (VLT), astronomers were able to see through the all-pervasive dust clouds of the object that has been dubbed as “The Bird“ because of its resemblance to a winged creature. With the adaptive optics of what’s called the NACO instrument, very fine details were able to be resolved.

"Examples of mergers of three galaxies of roughly similar sizes are rare," says Petri Väisänen, lead author of the paper which will appear in the journal of the Royal Astronomical Society. "Only the near-infrared VLT observations made it possible to identify the triple merger nature of the system in this case."

NACO is the combination of NAOS - Nasmyth Adaptive Optics System that is equipped with both visible and infrared sensors, and CONICA, a Near-Infrared Imager and Spectrograph.

Looking like a bird or a cosmic Tinker Bell, the NACO images show two unmistakable galaxies that form the body and wings of “The Bird.” Astronomers were surprised with the new images that identify a third, clearly separate component that forms the head. This irregular, yet fairly massive galaxy is forming stars violently, at a rate of nearly 200 solar masses per year. It appears to be the major source of infrared luminosity in the system, even though it is the smallest of the three galaxies. The other two galaxies appear to be at a quieter stage of their interaction-induced star formation history. The object is 650 million light years distant but it is quite large with the ‘wings’ alone extending more than 100,000 light-years, or the size of our own Milky Way.

Subsequent optical spectroscopy with the new Southern African Large Telescope, and archive mid-infrared data from the NASA Spitzer space observatory, confirmed the separate nature of the 'head', but also added further surprises. The 'head' and major parts of the 'Bird' are moving apart at more than 400 km/s (1.4 million km/h!). Observing such high velocities is very rare in merging galaxies.

"The Bird" belongs to the prestigious family of luminous infrared galaxies, with an infrared luminosity nearly one thousand billion times that of the Sun. This family of galaxies has long been thought to signpost important events in galaxy evolution, such as mergers of galaxies, which in turn trigger bursts of star formation, and may eventually lead to the formation of a single elliptical galaxy.

The galaxy is also designated as IRAS 19115-2124. The ESO is more formally known as the European Organization for Astronomical Research in the Southern Hemisphere.

Original News Source: ESO Press Release: