The Grism Lens-Amplified Survey from Space (GLASS). II. Gas-phase
  metallicity and radial gradients in an interacting system at z~2
  We present spatially resolved gas-phase metallicity for a system of three
galaxies at z=1.85 detected in the Grism Lens-Amplified Survey from Space
(GLASS). The combination of HST's diffraction limit and strong gravitational
lensing by the cluster MACS J0717+3745 results in a spatial resolution of
~200-300 pc, enabling good spatial sampling despite the intrinsically small
galaxy sizes. The galaxies in this system are separated by 50-200 kpc in
projection and are likely in an early stage of interaction, evidenced by
relatively high specific star formation rates. Their gas-phase metallicities
are consistent with larger samples at similar redshift, star formation rate,
and stellar mass. We obtain a precise measurement of the metallicity gradient
for one galaxy and find a shallow slope compared to isolated galaxies at high
redshift, consistent with a flattening of the gradient due to gravitational
interaction. An alternative explanation for the shallow metallicity gradient
and elevated star formation rate is rapid recycling of metal-enriched gas, but
we find no evidence for enhanced gas-phase metallicities which should result
from this effect. Notably, the measured stellar masses log(M/Msun) = 7.2-9.1
probe to an order of magnitude below previous mass-metallicity studies at this
redshift. The lowest mass galaxy has properties similar to those expected for
Fornax at this redshift, indicating that GLASS is able to directly study the
progenitors of local group dwarf galaxies on spatially resolved scales. Larger
samples from the full GLASS survey will be ideal for studying the effects of
feedback, and the time evolution of metallicity gradients. These initial
results demonstrate the utility of HST spectroscopy combined with gravitational
lensing for characterizing resolved physical properties of galaxies at high
redshift.
