Tidal dwarfs in the M81 group: the second generation?

We present a quantitative star formation history derivationof the foursuspected tidal dwarf galaxies in the M 81 group: Holmberg IX, BK3N,Arp-loop (A0952+69) and Garland using HST/WFPC2 images of these galaxies.We construct a library of synthetic Colour-Magnitude Diagrams(CMDs) based on theoretical isochrones and data-derived determinations ofphotometric errors. These synthetic CMDs were combined linearly andχ 2 -compared to observed photometry. All the galaxies show continuous star formation between about 20 and 200 Myr ago with star formation rates between 7.5⋅10 -3 M ⊙ /yrand 7.67⋅10 -4 M ⊙ /yr. The metallicity of the detected stars is spanning rather a wide range, being lower than solar abundance. We suppose, that all the galaxies were formed out of materialfrom metal-poor outer part of the giant spiral galaxy M81after tidal interaction about 200 Myr ago.However, this suggestion requires significantly more deep color-magnitudediagrams to be sure with the scenario of the galaxy evolution.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41996/1/10509_2004_Article_5125553.pd