Mathematics – Logic
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21543205f&link_type=abstract
American Astronomical Society, AAS Meeting #215, #432.05; Bulletin of the American Astronomical Society, Vol. 42, p.367
Mathematics
Logic
Scientific paper
We present results from two surveys of nearby disk galaxies using the Spitzer Space Telescope. First, we calculate bulge-disk decompositions for every disk galaxy (within 20 Mpc) with IRAC data in the Spitzer archive. Second, for a subset of those galaxies we use MIPS and GALEX data to study the star formation rates (hereafter SFR). Our aim is to study bulges. Observations indicate that bulges in nearby disk galaxies are bimodal in nature. This dichotomy may indicate that those bulges, and the galaxies in which they reside, have very different evolutionary histories. `Classcial bulge’ are similar in properties to elliptical galaxies (morphologically featureless, non-star forming, and have high Sersic index). Conversely, `pseudobulges’ are similar to disk galaxies (central few hundred parsecs show spiral morphology, actively forming stars, and have low Sersic index). Pseudobulges are likely formed through quiescent processes, such as secular evolution, minor mergers/accretion, or a mixture of the two.
We find the following results: 1. Pseudobulges are constructed very differently than E-type galaxies. Unlike ellipticals and classical bulges, pseudobulges exhibit a positive correlation between luminosity and surface brightness, and little-to-no correlation between size and luminosity. 2. The present day SFR in pseudobulges is likely tied to pseudobulge formation. Correlations between SFR density and bulge mass are consistent with internal growth of pseudobulges. Also, SFR of pseudobulges is connected to the mass of the outer-disk. These are not true for classical bulges. 3. Low-SFR pseudobulges are shown to likely be mixed classical and pseudobulge galaxies. 4. Finally, we find that the most common type of bulge in the local Universe is actively star forming pseudobulges. These results suggest that current theories of galaxy evolution greatly over predict the number of major mergers in the Universe.
Drory Niv
Fisher David B.
Kormendy John
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