  Spectroscopic observations from the Large Binocular Telescope and the Very
Large Telescope reveal kinematically narrow lines (~50 km/s) for a sample of 14
Extreme Emission Line Galaxies (EELGs) at redshifts 1.4 < z < 2.3. These
measurements imply that the total dynamical masses of these systems are low (<
3x10^9 M_sun). Their large [O III] 5007 equivalent widths (500-1100 Angstroms)
and faint blue continuum emission imply young ages of 10-100 Myr and stellar
masses of 10^8-10^9 M_sun, confirming the presence of a violent starburst. The
dynamical masses represent the first such determinations for low-mass galaxies
at z > 1. The stellar mass formed in this vigorous starburst phase represents a
large fraction of the total (dynamical) mass, without a significantly massive
underlying population of older stars. The occurrence of such intense events in
shallow potentials strongly suggests that supernova-driven winds must be of
critical importance in the subsequent evolution of these systems.
