Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21360701f&link_type=abstract
American Astronomical Society, AAS Meeting #213, #607.01
Other
Scientific paper
I study star formation rates (SFR) and stellar masses in bulges of nearby disk galaxies. For this we construct a new SFR indicator that linearly combines data from Spitzer Space Telescope (SST) and The Galaxy Evolution Explorer (GALEX). All bulges are found to be forming stars irrespective of bulge type (pseudobulge or classical bulge). At present day SFR the mean pseudobulge could have grown the present day stellar mass in 9 Gyr. Classical bulges have the lowest specific SFR implying a growth times that are longer than a Hubble time, and thus the present day SFR does not likely play a major role in the evolution of classical bulges. In almost all galaxies in this sample the specific SFR (SFR per unit stellar mass) of the bulge is higher than that of the outer disk. This suggests that almost all galaxies are increasing their B/T through internal star formation. More massive (and mor dense) pseudobulges have higher SFR density, this correlation is consistent with the hypothesis that an extend SFR is significantly altering the stellar mass of pseudobulges.
These results are consisitent with a scenario in which bulge growth via internal star formation is a natural, and near ubiquitous phenomenon in disk galaxies. Those galaxies with large classical bulges are not affected by the in situ bulge growth, likely because the majority of their stellar mass comes from some other phenomenon. Yet, those galaxies with out a classical bulge, over long periods of extended star formation are able to growth a pseudobulge. Though cold accretion is not ruled out, for pseudobulge galaxies an addition of stellar mass from mergers or accretion is not required to explain the bulge mass. In this sense, many galaxies with pseudobulges may very well be bulgeless (or ``quasi-bulgeless'') galaxies.
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