The mass-metallicity relation at z~1-2 and its dependence on star
  formation rate
  We present a new measurement of the gas-phase mass-metallicity relation
(MZR), and its dependence on star formation rates (SFRs) at 1.3 < z < 2.3. Our
sample comprises 1056 galaxies with a mean redshift of z = 1.9, identified from
the Hubble Space Telescope Wide Field Camera 3 (WFC3) grism spectroscopy in the
Cosmic Assembly Near-Infrared Deep Extragalactic Survey (CANDELS) and the WFC3
Infrared Spectroscopic Parallel Survey (WISP). This sample is four times larger
than previous metallicity surveys at z ~ 2, and reaches an order of magnitude
lower in stellar mass (10^8 M_sun). Using stacked spectra, we find that the MZR
evolves by 0.3 dex relative to z ~ 0.1. Additionally, we identify a subset of
49 galaxies with high signal-to-noise (SNR) spectra and redshifts between 1.3 <
z < 1.5, where H-alpha emission is observed along with [OIII] and [OII]. With
accurate measurements of SFR in these objects, we confirm the existence of a
mass-metallicity-SFR (M-Z-SFR) relation at high redshifts. These galaxies show
systematic differences from the local M-Z-SFR relation, which vary depending on
the adopted measurement of the local relation. However, it remains difficult to
ascertain whether these differences could be due to redshift evolution, as the
local M-Z-SFR relation is poorly constrained at the masses and SFRs of our
sample. Lastly, we reproduced our sample selection in the IllustrisTNG
hydrodynamical simulation, demonstrating that our line flux limit lowers the
normalization of the simulated MZR by 0.2 dex. We show that the M-Z-SFR
relation in IllustrisTNG has an SFR dependence that is too steep by a factor of
around three.
