The Antennae: Prototype for Colliding Galaxies

Compiled by: John E. Hibbard

      jhibbard@nrao.edu
      NRAO, 520 Edgemont Road,
      Charlottesville, VA 22903-2475,
      (434) 296-0227

Collaborator: Joshua E. Barnes

      barnes@ifa.hawaii.edu
      Institute for Astronomy, University of Hawai`i
      2680 Woodlawn Drive, Honolulu, HI 96820
      (808) 956-8138

HISTORY

• One of the earliest studied peculiar galaxies (Perrine 1922, Duncan 1923)

• Antennae first suggested as a collision between two spiral galaxies by Holmberg in 1940.

• First member of the "Toomre Sequence" (Toomre 1977): a suggestive sequence of peculiar galaxies which represented for the first time the idea that two Spiral galaxies could fall together under their mutual gravitational attraction, merge, and evolve into a different type of galaxy, an Elliptical galaxy. This is now known as the Toomre Merger Hypothesis, and has been repeatedly validated by theory.

• The Antennae is the FIRST and MOST NEARBY galaxy in the Toomre sequence, hence may represent our best chance for understanding merging galaxies.

• First model of the Antennae produced by Toomre & Toomre (1972). First self-consistent model produced by Barnes (1988). These models helped solidify the once controversial idea that galaxies can and do merge.

• Our new model is the first model which matches both the observed shape and motions of the Antennae tidal features in detail. It was made possible by sensitive, high resolution observations of the cold atomic gas using the National Science Foundations Very Large Array (VLA). Those data, published by Hibbard, van der Hulst, Barnes & Rich in the Astronomical Journal in 2001, reveal which parts of the Antennae are moving toward us, and which are moving away from us. We ran simulations, varying the geometry of the encounter and the viewing perspective, until we could match these observations.

WHY IMPORTANT TO ASTRONOMERS

• Merging galaxies can transform one type of galaxy (spiral) to a different type of galaxy (elliptical). The merging process is now believed play a role in the formation of most, if not all, large galaxies.

• Building models in the computers allows us to watch their evolution in real time, a process that takes hundreds of millions of years in the real universe.

ANTENNAE FACTS

• Aliases for the Antennae:
  • NGC 4038/4039 (New General Catalog objects 4038 and 4039; NGC 4038 is the source of the southern tail, while NGC 4039 is the source of the northern tail)
  • VV 245 (object 245 in Vorontsov-Vel'yaminov's Catalog of Interacting Galaxies)
  • Arp 244 (object 244 in Arp's Catalog of Peculiar Galaxies)
  • The Ring-Tailed galaxy

• Distance: somewhere between 14-25 Mpc from earth. Most commonly accepted distance is 19 Mpc (62 million light year away)

• Original galaxy types: probably an Sc (NGC 4038) and Sb (NGC 4039)

WEB RESOURCES

• Animation showing the encounter and evolution of the two galaxies making up the Antennae:   <http://www.ifa.hawaii.edu/~barnes/pressrel/antfacts/vid010.mpg>

• Animation showing the best match to the Antennae rotated about the vertical axis:   <http://www.cv.nrao.edu/~jhibbard/n4038/snap35k40rot.mpg>

• Graphic comparing VLA observations (purple) to computer model (green):   <http://www.cv.nrao.edu/~jhibbard/n4038/r35k40a_00d8.gif>

• Observations of the Antennae are available at:   <http://www.cv.nrao.edu/~jhibbard/n4038/n4038.html>

• More details on computer models of interacting galaxies are available at:   <http://www.ifa.hawaii.edu/~barnes/research/interaction_models/>

• Barnes & Hibbard's 1992 press release on a model of The Mice (NGC 4676), another well-known pair of interacting galaxies:   <http://www.ifa.hawaii.edu/~barnes/pressrel/mice/index.html>

Last modified: January 6, 2004
http://www.ifa.hawaii.edu/~barnes/pressrel/antfacts/index.html