We investigate the evolution of galaxy gas-phase metallicity (O/H) over the range z = 0 − 3.3 using samples of ∼ 300 galaxies at z ∼ 2.3 and ∼ 150 galaxies at z ∼ 3.3 from the MOSDEF survey. This analysis crucially utilizes different metallicity calibrations at z ∼ 0 and z > 1 to account for evolving ISM conditions. We find significant correlations between O/H and stellar mass (M * ) at z ∼ 2.3 and z ∼ 3.3. The low-mass power law slope of the mass-metallicity relation is remarkably invariant over z = 0 − 3.3, such that O/H∝M 0.30 * at all redshifts in this range. At fixed M * , O/H decreases with increasing redshift as dlog(O/H)/dz = −0.11 ± 0.02. We find no evidence that the fundamental metallicity relation between M * , O/H, and star-formation rate (SFR) evolves out to z ∼ 3.3. We employ analytic chemical evolution models to place constraints on the mass and metal loading factors of galactic outflows. The efficiency of metal removal increases toward lower M * at fixed redshift, and toward higher redshift at fixed M * . These models suggest that the slope of the mass-metallicity relation is primarily set by the scaling of the outflow metal loading factor with M * , not by the change in gas fraction as a function of M * . The evolution toward lower O/H at fixed M * with increasing redshift is driven by both higher gas fraction (leading to stronger dilution of ISM metals) and higher metal removal efficiency. These results suggest that the processes governing the smooth baryonic growth of galaxies via gas flows and star formation hold in the same form over at least the past 12 Gyr.

We present detections of [O iii]λ4363 and direct-method metallicities for star-forming galaxies at z = 1.7 − 3.6. We combine new measurements from the MOSFIRE Deep Evolution Field (MOSDEF) survey with literature sources to construct a sample of 18 galaxies with direct-method metallicities at z > 1, spanning 7.5 < 12+log(O/H) < 8.2 and log(M * /M ) = 7 − 10. We find that strong-line calibrations based on local analogs of high-redshift galaxies reliably reproduce the metallicity of the z > 1 sample on average. We construct the first mass-metallicity relation at z > 1 based purely on direct-method O/H, finding a slope that is consistent with strong-line results. Directmethod O/H evolves by 0.1 dex at fixed M * and SFR from z ∼ 0 − 2.2. We employ photoionization models to constrain the ionization parameter and ionizing spectrum in the high-redshift sample. Stellar models with super-solar O/Fe and binary evolution of massive stars are required to reproduce the observed strong-line ratios. We find that the z > 1 sample falls on the z ∼ 0 relation between ionization parameter and O/H, suggesting no evolution of this relation from z ∼ 0 to z ∼ 2. These results suggest that the offset of the strong-line ratios of this sample from local excitation sequences is driven primarily by a harder ionizing spectrum at fixed nebular metallicity compared to what is typical at z ∼ 0, naturally explained by super-solar O/Fe values at high redshift caused by rapid formation timescales. Given the extreme nature of our z > 1 sample, the implications for representative z ∼ 2 galaxy samples at ∼ 10 10 M are unclear, but similarities to z > 6 galaxies suggest that these conclusions can be extended to galaxies in the epoch of reionization.

The Kepler Mission provides nearly continuous monitoring of ∼156,000 objects with unprecedented photometric precision. Coincident with the first data release, we presented a catalog of 1879 eclipsing binary systems identified within the 115 deg 2 Kepler field of view (FOV). Here, we provide an updated catalog augmented with the second Kepler data release which increases the baseline nearly fourfold to 125 days. Three hundred and eighty-six new systems have been added, ephemerides and principal parameters have been recomputed. We have removed 42 previously cataloged systems that are now clearly recognized as short-period pulsating variables and another 58 blended systems where we have determined that the Kepler target object is not itself the eclipsing binary. A number of interesting objects are identified. We present several exemplary cases: four eclipsing binaries that exhibit extra (tertiary) eclipse events; and eight systems that show clear eclipse timing variations indicative of the presence of additional bodies bound in the system. We have updated the period and galactic latitude distribution diagrams. With these changes, the total number of identified eclipsing binary systems in the Kepler FOV has increased to 2165, 1.4% of the Kepler target stars. An online version of this catalog is maintained at http://keplerEBs.villanova.edu.

We use extensive spectroscopy from the MOSFIRE Deep Evolution Field (MOSDEF) survey to investigate the relationships between rest-frame optical emission line equivalent widths (W ) and a number of galaxy and ISM characteristics for a sample of 1134 star-forming galaxies at redshifts 1.4 z 3.8. We examine how the equivalent widths of [O II]λλ3727, 3730, Hβ, [O III]λλ4960, 5008, [O III] + Hβ, Hα, and Hα + [N II]λλ6550, 6585, depend on stellar mass, UV slope, age, star-formation rate (SFR) and specific SFR (sSFR), ionization parameter and excitation conditions (O32 and [O III]/Hβ), gasphase metallicity, and ionizing photon production efficiency (ξ ion ). The trend of increasing W with decreasing stellar mass is strongest for [O III] (and [O III]+Hβ).More generally, the equivalent widths of all the lines increase with redshift at a fixed stellar mass or fixed gas-phase metallicity, suggesting that high equivalent width galaxies are common at high redshift. This redshift evolution in equivalent widths can be explained by the increase in SFR and decrease in metallicity with redshift at a fixed stellar mass. Consequently, the dependence of W on sSFR is largely invariant with redshift, particularly when examined for galaxies of a given metallicity. Our results show that high equivalent width galaxies, specifically those with high W ([O III]), have low stellar masses, blue UV slopes, young ages, high sSFRs, ISM line ratios indicative of high ionization parameters, high ξ ion , and low metallicities. As these characteristics are often attributed to galaxies with high ionizing escape fractions, galaxies with high W are likely candidates for the population that dominates cosmic reionization.

We combine Hα and Hβ spectroscopic measurements and UV photometry for a sample of 673 galaxies from the MOSDEF survey to constrain hydrogen-ionizing photon production efficiencies (ξ ion ) at z = 1.4 − 2.6. We find log(ξ ion /[s −1 /erg s −1 Hz −1 ]) = 25.06 (25.34), assuming the Calzetti (SMC) curve for the UV dust correction and a scatter of 0.28 dex in ξ ion distribution. After accounting for observational uncertainties and variations in dust attenuation, we conclude that the remaining scatter in ξ ion is likely dominated by galaxy-to-galaxy variations in stellar populations, including the slope and upper-mass cutoff of the initial mass function, stellar metallicity, star-formation burstiness, and stellar evolution (e.g., single/binary star evolution). Moreover, ξ ion is elevated in galaxies with high ionization states (high [Oiii]/[Oii]) and low oxygen abundances (low [Nii]/Hα and high [Oiii]/Hβ) in the ionized ISM. However, ξ ion does not correlate with the offset from the z ∼ 0 star-forming locus in the BPT diagram, suggesting no change in the hardness of ionizing radiation accompanying the offset from the z ∼ 0 sequence. We also find that galaxies with blue UV spectral slopes ( β = −2.1) have elevated ξ ion by a factor of ∼ 2 relative to the average ξ ion of the sample ( β = −1.4). If these blue galaxies are similar to those at z > 6, our results suggest that a lower Lyman continuum escape fraction is required for galaxies to maintain reionization, compared to the canonical ξ ion predictions from stellar population models. Furthermore, we demonstrate that even with robustly dust-corrected Hα, the UV dust attenuation can cause on average a ∼ 0.3 dex systematic uncertainty in ξ ion calculations.