On the Last 10 Billion Years of Stellar Mass Growth in Star-Forming
  Galaxies
  The star formation rate - stellar mass relation (SFR-M*) and its evolution
(i.e., the SFR main sequence) describes the growth rate of galaxies of a given
stellar mass and at a given redshift. Assuming that present-day star-forming
galaxies were always star-forming in the past, these growth rate observations
can be integrated to calculate average star formation histories (SFHs). Using
this Main Sequence Integration (MSI) approach, we trace present-day massive
star-forming galaxies back to when they were 10-20% of their current stellar
mass. The integration is robust throughout those epochs: the SFR data
underpinning our calculations is consistent with the evolution of stellar mass
density in this regime. Analytic approximations to these SFHs are provided.
Integration-based results reaffirm previous suggestions that current
star-forming galaxies formed virtually all of their stellar mass at z<2. It
follows that massive galaxies observed at z>2 are not the typical progenitors
of star-forming galaxies today.
  We also check MSI-based SFHs against those inferred from analysis of the
fossil record -- from spectral energy distributions (SEDs) of star-forming
galaxies in the Sloan Digital Sky Survey, and color magnitude diagrams (CMDs)
of resolved stars in dwarf irregular galaxies. Once stellar population age
uncertainties are accounted for, the main sequence is in excellent agreement
with SED-based SFHs (from VESPA). Extrapolating SFR main sequence observations
to dwarf galaxies, we find differences between MSI results and SFHs from CMD
analysis of ACS Nearby Galaxy Survey Treasury and Local Group galaxies.
Resolved dwarfs appear to grow much slower than main sequence trends imply, and
also slower than slightly higher mass SED-analyzed galaxies. This difference
may signal problems with SFH determinations, but it may also signal a shift in
star formation trends at the lowest stellar masses.
