The Tadpole -OR- The Chainsaw ?

In 2001, Westerbork observations of the disturbed galaxy named VV-29 (alias Arp-188, UGC-10214) showed that there is second smaller galaxy (named VV-29c) that appears behind the western side of the main body of the distorted galaxy. Through its gravitational forces during a close orbital encounter, this second galaxy appears to have been responsible for raising the long `tail of the tadpole' that extends outward from VV-29.

VV-29 received wide press coverage during May 2002, when it appeared on the front pages of major newspapers to announce the commissioning of the Hubble Space Telescope's Advanced Camera. The galaxy was featured as the May 2, 2002 Astronomy Picture of the Day. The bright, blue-ish center of the new galaxy VV-29c can be seen through the double spiral arms of VV-29.

The mosaic of images below compares the HST image with two other diagnostic images: one comes from the Westerbork Radio Synthesis Telescope, and the second from the 2.5m Isaac Newton optical telescope in La Palma. The images are oriented with north upward and east to the left.

The color radio image records the emission from the galaxy in the 21cm line of neutral hydrogen, indicating both the extent of the hydrogen gas and its velocity along the line of sight to the observer (using the Doppler effect). The blue end of the spectrum indicates the regions in the galaxy that are approaching us, while the red regions of the `velocity field' indicate recession. The WSRT observations revealed the second galaxy VV29c through its velocity offset, which you can see as the red background object that is viewed through the artificial perforation in the velocity field on the right side of the galaxy.

The very deep Isaac Newton Telescope image has also been heavily smoothed to bring out the faintest diffuse light levels. This reveals additional structures not seen in the HST image: a faint counter-arm to the right, and a vertical spur on the left side of the main body of the galaxy.

GALAXY NAMES: Galaxies acquire names when their coordinates in the sky are measured and they are listed in catalogs for subsequent study by astronomers. For example, the interesting system pictured above has a large number of `aliases', which result from its listing in several popular catalogs. The first catalog to list it was the Vorontsov-Velyaminov "Atlas and Catalog of Interacting Galaxies", published in 1959. This galaxy was the 29th object listed in the catalog. In fact, Vorontsov-Velyaminov actually split the galaxy into two parts: VV-29a, the main body of the galaxy, and VV-29b, the tidal tail that extends to the east (left) in the pictures. When the third galaxy was discovered in the WSRT data, the observing team (Briggs, Moller, Higdon, Trentham, Ramirez-Ruiz) decided to continue this convention by naming the new galaxy VV-29c.

VV-29 has other names, which result from its appearance in many catalogs: Arp-188 (in Arp's "Atlas of Peculiar Galaxies," 1966), CGCG275-023 (in Zwicky's "Catalogue of Galaxies and of Clusters of Galaxies," 1966), UGC10214 (in Nilson's "Uppsala General Catalogue of Galaxies," 1973).

When VV-29 had its 15 minutes of fame in May 2002, it appeared under the name "The Tadpole Galaxy," but based on the images above, we will always think of it as "The CHAINSAW"!

PUBLISHED PAPER: 2001, A&A, 380, 418 (Briggs, Moller, Higdon, Trentham, Ramirez-Ruiz). "Did VV 29 collide with a dark Dark-Matter halo?"

Last modified on: September 6, 2002
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