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M. N. Fanelli (TCU), P. M. Marcum (TCU & NASA HQ), C. Mitchell (UNT)
Recently, we identified two extremely isolated early-type galaxies with unusually blue optical colors (Marcum etal, AJ 127, 3213), indicating current or recent massive star formation. Merger-induced star formation is the most likely mechanism for the odd photometric properties of these systems, yet, interestingly, they do not show the strong morphological scars (tidal tails, shells) generally attributed to merger activity. We concluded that these systems are late stage mergers, in which those morphological scars have largely dissipated, but photometric anomalies remain.
In a separate investigation, we are exploring the properties of a large sample of luminous blue compact galaxies (Fanelli etal, 2004), many of which exhibit blue colors and an elliptical-like morphology. While the luminous blue compacts exist in a variety of environments, both samples may represent the same phenomena – the assembly of a spheroidal stellar system from the merger of multiple smaller gas-rich systems.
To further explore the evolutionary paths which lead to isolated early-type galaxies, we are “mining” the Sloan Digital Sky Survey for anomalously blue ellipticals. These systems exhibit blue colors within the Sloan bands, and also show radial light profiles largely consistent with an r(1/4) law. We will present and describe representative objects. The importance of identifying local universe analogues to distant young galaxies comes from the ability to explore these systems at many wavelengths with excellent spatial and spectral resolution, in contrast to high-redshift systems. The latter are faint and subtend a few arcseconds, requiring substantial integration times with 4-10m class telescopes. This research was supported by NASA ADP grant NNG05GC53G, and the Texas Advanced Research Program.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.