  The epoch when low-mass star forming galaxies (LMSFGs) form the bulk of their
stellar mass is uncertain. While some models predict an early formation, others
favor a delayed scenario until later ages of the universe. We present
constraints on the star formation histories (SFHs) of a sample of LMSFGs
obtained through the analysis of their spectral energy distributions using a
novel approach that (1) consistently combines photometric (broadband) and
spectroscopic (equivalent widths of emission lines) data, and (2) uses
physically motivated SFHs with non-uniform variations of the star formation
rate (SFR) as a function of time. The sample includes 31 spectroscopically
confirmed LMSFGs (7.3 < log M*/Msun < 8.0) at 0.3 < z_spec < 0.9 in the
Extended-Chandra Deep Field-South field (E-CDF-S). Among them, 24 were selected
with photometric stellar mass log M*/Msun < 8.0, 0.3 < z_phot < 1.0, and NB816
< 26 AB mag; the remaining 7 were selected as blue compact dwarfs (BCDs) within
the same photometric redshift and magnitude ranges. We also study a secondary
sample of 43 more massive spectroscopically confirmed galaxies (8.0 < log
M*/Msun < 9.1), selected with the same criteria. The SFRs and stellar masses
derived for both samples place our targets on the standard main sequence of
star forming galaxies. The median SFH of LMSFGs at intermediate redshifts
appears to form 90% of the median stellar mass inferred for the sample in the
0.5-1.8 Gyr immediately preceding the observation. These results suggest a
recent stellar mass assembly for LMSFGs, consistent with the cosmological
downsizing trends. We find similar median SFH timescales for the more massive
secondary sample.
