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L. Haberzettl, D.J. Bomans, R.-J. Dettmar (AI Ruhr-University Bochum, Germany)
We present results from a study of the star formation history (SFH) of a sample of Low Surface Brightness (LSB) galaxies. The LSB sample resulted from a search around the HDF-S (field size: 0.8 deg2) using SExtractor in combination with a median filter technique (Haberzettl et al. 2003, subm. to A&A). For the selection of the LSB galaxy candidates we used color--color diagrams (U-B vs. B-R). From the color--color diagram LSB candidates were selected based on their different location in comparison to the High Surface Brightness (HSB) galaxy redshift tracks. With this method and a lower diameter limit of 10 arcsec we derived a sample of 7 LSB galaxies.
For this sample we derived spectral energy distributions (SEDs) from 3500 Åto 7000 Åusing ESO 3.6m telescope. The measured SEDs we compared to synthetic spectra extracted from the synthesis evolution model PEGASE (Rocca & Volmerange 1997). The synthetic spectra were derived assuming an exponential declining SFR (time of decline \tau = 1.4 Gyr). With the basic assumption that LSB galaxies mostly have low metallicities we were able to fit synthetic spectra in the range of 2 to 5 Gyr to the measured SEDs. Applying the same method to a sample of HSB galaxies results in an averaged stellar population of about 10 to 14 Gyr. Therefore LSB galaxies tend to show much younger averaged stellar populations. This implies that the major star formation event of LSB galaxies took place at a redshift of z ~ 0.2 to 0.4 while for HSB galaxies this tends to be at z ~ 2 to 4.
This work is founded by the DESY/BMBF grant 05 AE2PDA/8.
The author(s) of this abstract have provided an email address for comments about the abstract: lutz.haberzettl@astro.rub.de
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.