Metallicities and Physical Conditions in Star-forming Galaxies at z~1.0-1.5

Understand

We present a study of the mass-metallicity (M-Z) relation and H II region physical conditions in a sample of 20 star-forming galaxies at 1.0<z<1.5 drawn from the DEEP2 Galaxy Redshift Survey.

• Our analysis indicates that the zero point of the M-Z relationship evolves with redshift, in the sense that galaxies at fixed stellar mass become more metal-rich at lower redshift.
• Measurements of [O III]/H-beta and [N II]/H-alpha emission-line ratios show that, on average, objects in the DEEP2 1.0<z<1.5 sample are significantly offset from the excitation sequence observed in nearby H II regions and SDSS emission-line galaxies.
• In order to fully understand the causes of this offset, which is also observed in z~2 star-forming galaxies, we examine in detail the small fraction of SDSS galaxies that have similar diagnostic ratios to those of the DEEP2 sample.