From Globular Clusters to Tidal Dwarfs: Structure Formation in Tidal Tails

Karen Knierman (Penn State), Sally Hunsberger (Lowell), Sarah Gallagher, Jane Charlton (Penn State), Bradley Whitmore (STScI), John Hibbard (NRAO), Arunav Kundu (Virginia), Dennis Zaritsky (Arizona)


This slideshow presents our poster from the 2000 winter meeting of the AAS.

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Abstract

Galaxy interactions trigger star formation in tidal debris. How does this star formation depend on the local and global physical conditions? Using WFPC2/HST images, we investigate the range of structure within tidal tails of four classic ``Toomre Sequence'' mergers: NGC 4038/9 (``Antennae''), NGC 7252 (``Atoms for Peace''), NGC 3921, and NGC 3256. These tails contain a variety of stellar associations with sizes from globular clusters up to dwarf Irregulars. We explore whether there is a continuum between the two extremes. Our eight fields sample seven tidal tails at a variety of stages in the evolutionary sequence. Some of these tails are rich in HI while others are HI poor. Large tidal dwarfs are embedded in three of the tails.

Using V and I WFPC2 images, we measure luminosities and colors of substructures within the tidal tails. The properties of globular cluster candidates in the tails will be contrasted with those of the hundreds of young clusters in the central regions of these mergers. We address whether globular clusters form and survive in the tidal tails and whether tidal dwarfs are composed of only young stars. By comparing the properties of structures in the tails of the four mergers with different ages, we examine systematic evolution of structure along the evolutionary sequence and as a function of HI content.

We acknowledge support from NASA through STScI, and from NSF for an REU supplement for Karen Knierman.

Preview of Slideshow:

Intro about each pair with WFPC2/HST fov overlayed WFPC2/HST images with point sources indicated WFPC2/HST images with extended sources indicated Tidal Dwarf closeup CMD and conclusions for each

NGC 4038/9 Southern Tail

NGC 3256 Western Tail

NGC 3256 Eastern Tail

NGC 3921 Southern Tail

NGC 7252 Western Tail

NGC 7252 Eastern Tail


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