The star cluster population in the tidal tails of NGC 6872

¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching b. München, Germany e-mail: bastian@astro.uu.nl
² Astronomical Institute, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
³ Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
⁴ Gemini Observatory, c/o AURA, Casilla 603, La Serena, Chile
⁵ Universidad de La Laguna, Av. Astrofisico Francisco Sanchez sn, 38206, La Laguna, Tenerife, Spain

Received: 18 October 2004
Accepted: 3 February 2005

Abstract

We present a photometric analysis of the rich star cluster population in the tidal tails of NGC 6872. We find star clusters with ages between 1-100 Myr distributed in the tidal tails, while the tails themselves have an age of less than 150 Myr. Most of the young massive () clusters are found in the outer regions of the galactic disk or the tidal tails. The mass distribution of the cluster population can be well described by a power-law of the form , where , in very good agreement with other young cluster populations found in a variety of different environments. We estimate the star formation rate for three separate regions of the galaxy, and find that the eastern tail is forming stars at ~2 times the rate of the western tail and ~5 times the rate of the main body of the galaxy. By comparing our observations with published N-body models of the fate of material in tidal tails in a galaxy cluster potential, we see that many of these young clusters will be lost into the intergalactic medium. We speculate that this mechanism may also be at work in larger galaxy clusters such as Fornax, and suggest that the so-called ultra-compact dwarf galaxies could be the most massive star clusters that have formed in the tidal tails of an ancient galactic merger.