Chemistry and Physics Faculty Proceedings, Presentations, Speeches, Lectures

Properties of Flat Disk Galaxies

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Sun, Solar System, Stars, Interstellar Matter, Galaxy, Extragalactic Systems, Cosmology, Instruments / Supplement: Short Contribution of the Annual Scientific Meeting of the Astronomische Gesellschaft in Freiburg, September 15-20, 2003

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Motivation: Flat (or superthin) galaxies are edge-on galaxies with axial ratios bigger than a/b = 6. This type of systems can be described with an extended thin stellar disk of blue color embedded in a redder thick stellar extension (Dalcanton and Bernstein 2002). Nevertheless, no distinct bulge component is detected in flat galaxies (Matthews et al. 1999a). According to their other unique properties (e. g., Matthews et al. 1999b) such as low optical stellar densities and low star formation rates, high neutral gas content and low metallicities, it is presumed that they present the edge-on counterpart of late-type spiral galaxies (Scd-Sdm) with low surface brightness. These late-type spiral systems have luminosities below those of normal spirals of the same morphological Hubble class (Matthews and Gallagher 1997). The rotation curves of flat galaxies are solid-body like, slowly rising (Karachentsev and Xu 1991) and therefore they exhibit typical features of dwarf and irregular galaxies. These global characteristics of flat galaxies lead to the assumption that they are “underevolved” systems in the sense of dynamical and age evolution.

The Sample: A collection of flat galaxies is presented in the Flat Galaxy Catalogue (Karachentsev et al. 1993, hereafter FGC) and in the Revised Flat Galaxy Catalogue (Karachentsev et al. 1999, hereafter RFGC). While the objects of the FGC (and in extension the RFGC) are found from a visual inspection of photographic survey plates we are using the Sloan Digital Sky Survey (SDSS) to recover these galaxies. The SDSS is a photometric and spectroscopic database (Stoughton et al. 2002) that allows us to study the statistical properties of these systems in greater detail and gives us the possibility to extend their census to fainter magnitudes.

Results and Discussion: We present first results from our survey with the SDSS and we demonstrate the frequency of flat galaxies in these data. Our measurements show that flat galaxies are a common galaxy type in the nearby universe. These galaxies often show a color gradient from the blue to red in both major and minor axis which is probably dominated by a stellar population gradient. Finally, we discuss the impact of flat galaxies on galaxy evolution because these objects may display one of the most abundant products of the formation of galactic disks (Matthews et al. 1999b). Since flat galaxies are often found to be more or less isolated systems and merger scenarios do not explain the origin of pure disks it seems that these quiescent evolving objects are of great interest on the disk-forming stages of galaxy evolution.



DOI 10.1002/asna.200385022

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