Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21112302b&link_type=abstract
American Astronomical Society, AAS Meeting #211, #123.02; Bulletin of the American Astronomical Society, Vol. 39, p.953
Mathematics
Logic
Scientific paper
I present results from a project that combines imaging, spectroscopy, and HST-based morphologies for a sample of star-forming galaxies to examine which physical properties govern mass-dependent evolution of field galaxies. We calculated specific star formation rates (SSFR = SFR / M*) to determine how star formation efficiency changes as a function of stellar mass, redshift, and morphology. We find a clear separation between disk-dominated (sersic n > 2.5) and bulge-dominated galaxies, such that disky galaxies have higher SSFRs and lower stellar masses at all redshifts. The highest mass galaxies have the lowest SSFRs at each redshift while low-mass galaxies form stars with the highest efficiency. For stellar masses greater than 10^11 Msun, SSFRs steeply drop as star formation shuts off, showing that even the star-forming population of high-mass galaxies have less efficient star formation than galaxies of lower mass. Low- and intermediate-mass galaxies form a ``ridge'' in SSFR that lies along lines of constant SFR. There exists an upper envelope in SSFR at all redshifts that also lies roughly parallel to lines of constant SFR. The reddest star-forming, disk-dominated galaxies decrease in number from z > 1 to z = 0.6 while the bluest quiescent, disk-dominated galaxies increase in number at z < 0.6. The change in star formation activity occurs more quickly than the change in morphological state. We find that a simple constant, exponential, or power law SFH do not reproduce our observed results and suggest that the overall decrease in the upper envelop of SSFR describes a progressively later onset of star formation for lower mass galaxies and a decrease in the intensity of bursty star-forming episodes with time.
Bauer Amanda E.
Drory Niv
Hill Gary J.
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