Little Blue Dots in the Hubble Space Telescope Frontier Fields:
  Precursors to Globular Clusters?
  Galaxies with stellar masses <10^7 Msun and specific star formation rates
sSFR>10^{-7} yr^{-1} were examined on images of the Hubble Space Telescope
Frontier Field Parallels for Abell 2744 and MACS J0416.1-02403. They appear as
unresolved "Little Blue Dots" (LBDs). They are less massive and have higher
sSFR than "blueberries" studied by yang et al. (2017) and higher sSFR than
"Blue Nuggets" studied by Tacchella et al.(2016). We divided the LBDs into 3
redshift bins and, for each, stacked the B435, V606, and I814 images convolved
to the same stellar point spread function (PSF). Their radii were determined
from PSF deconvolution to be ~80 to ~180 pc. The high sSFR suggest that their
entire stellar mass has formed in only 1% of the local age of the universe. The
sSFRs at similar epochs in local dwarf galaxies are lower by a factor of ~100.
Assuming that the star formation rate is epsilon_ff M_gas/t_ff for efficiency
epsilon_ff, gas mass M_gas, and free fall time, t_ff, the gas mass and
gas-to-star mass ratio are determined. This ratio exceeds 1 for reasonable
efficiencies, and is likely to be ~5 even with a high epsilon_ff of 0.1. We
consider whether these regions are forming today's globular clusters. With
their observed stellar masses, the maximum likely cluster mass is ~10^5 M_sun,
but if star formation continues at the current rate for ~10t_ff~50 Myr before
feedback and gas exhaustion stop it, then the maximum cluster mass could become
~10^6 M_sun.
