The Relationship between Stellar Mass, Gas Metallicity, and Star Formation Rate for Halpha-selected Galaxies at z~0.8 from the NewHalpha Survey

TL;DR

This study investigates how stellar mass, gas metallicity, and star formation rate interrelate in galaxies at z~0.8, finding no strong dependence of metallicity on SFR, consistent with previous research, but dataset limitations may influence this result.

Contribution

It provides new measurements of galaxy properties at z~0.8 and examines the mass-metallicity-SFR relation using various fitting techniques, highlighting potential dataset biases.

Findings

No strong dependence of metallicity on SFR was observed.

Results are consistent with previous studies at similar redshifts.

Dataset limitations may affect the detection of SFR dependence.

Abstract

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.