The Relationship between Stellar Mass, Gas Metallicity, and Star
  Formation Rate for Halpha-selected Galaxies at z~0.8 from the NewHalpha
  Survey
  Using a sample of 299 Ha-selected galaxies at z~0.8, we study the
relationship between galaxy stellar mass, gas-phase metallicity, and star
formation rate (SFR), and compare to previous results. We use deep optical
spectra obtained with the IMACS spectrograph at the Magellan telescope to
measure strong oxygen lines. We combine these spectra and metallicities with
(1) rest-frame UV-to-optical imaging, which allows us to determine stellar
masses and dust attenuation corrections, and (2) Ha narrowband imaging, which
provides a robust measure of the instantaneous SFR. Our sample spans stellar
masses of 10^9 to 6*10^11 solar masses, SFRs of 0.4 to 270 solar masses per
year, and metal abundances of 12+log(O/H)~8.3-9.1 (~0.4-2.6 solar metallicity).
The correlations that we find between the Ha-based SFR and stellar mass (i.e.,
the star-forming "main sequence"), and between the stellar mass and
metallicity, are both consistent with previous z~1 studies of star-forming
galaxies. We then study the relationship between the three properties using
various plane-fitting techniques (Lara-Lopez et al.) and a curve-fitting
projection (Mannucci et al.). In all cases, we exclude strong dependence of the
M-Z relation on SFR, but are unable to distinguish between moderate and no
dependence. Our results are consistent with previous mass-metallicity-SFR
studies. We check whether dataset limitations may obscure a strong dependence
on the SFR by using mock samples drawn from the SDSS. These experiments reveal
that the adopted signal-to-noise cuts may have a significant effect on the
measured dependence. Further work is needed to investigate these results, and
to test whether a "fundamental metallicity relation" or a "fundamental plane"
describes star-forming galaxies across cosmic time.
