We examine the redshift evolution of standard strong emission-linediagnostics for Hbeta-selected star-forming galaxies using the local SDSSsample and a new z = 0.2 - 2.3 sample obtained from HST WFC3 grism and KeckDEIMOS and MOSFIRE data. We use the SDSS galaxies to show that there is asystematic dependence of the strong emission-line properties on Balmer-lineluminosity, which we interpret as showing that both the N/O abundance and theionization parameter increase with increasing line luminosity. Allowing for theluminosity dependence tightens the diagnostic diagrams and the metallicitycalibrations. The combined SDSS and high-redshift samples show that there is noredshift evolution in the line properties once the luminosity correction isapplied, i.e., all galaxies with a given L(Hbeta) have similar strongemission-line distributions at all the observed redshifts. We argue that thebest metal diagnostic for the high-redshift galaxies may be aluminosity-adjusted version of the [NII]6584/Halpha metallicity relation.

The first stars, known as Population III (PopIII), produced the first heavyelements, thereby enriching their surrounding pristine gas. Previous detectionsof metals in intergalactic gas clouds, however, find a heavy element enrichmentlarger than $1/1000$ times that of the solar environment, higher than expectedfor PopIII remnants. In this letter we report the discovery of a Lyman limitsystem (LLS) at $z=3.53$ with the lowest metallicity seen in gas withdiscernable metals, $10^{-3.41\pm0.26}$ times the solar value, at a levelexpected for PopIII remnants. We make the first relative abundance measurementin such low metallicity gas: the carbon-to-silicon ratio is $10^{-0.26\pm0.17}$times the solar value. This is consistent with models of gas enrichment by aPopIII star formation event early in the Universe, but also consistent withlater, Population II enrichment. The metals in all three components comprisingthe LLS, which has a velocity width of 400 km s$^{-1}$, are offset in velocityby $\sim+6$ km s$^{-1}$ from the bulk of the hydrogen, suggesting the LLS wasenriched by a single event. Relative abundance measurements in thisnear-pristine regime open a new avenue for testing models of early gasenrichment and metal mixing.

We report an expanded sample of visual morphological classifications from theGalaxy and Mass Assembly (GAMA) survey phase two, which now includes 7,556objects (previously 3,727 in phase one). We define a local (z <0.06) sample andclassify galaxies into E, S0-Sa, SB0-SBa, Sab-Scd, SBab-SBcd, Sd-Irr, and"little blue spheroid" types. Using these updated classifications, we derivestellar mass function fits to individual galaxy populations divided both bymorphological class and more general spheroid- or disk-dominated categorieswith a lower mass limit of log(Mstar/Msun) = 8 (one dex below earliermorphological mass function determinations). We find that all individualmorphological classes and the combined spheroid-/bulge-dominated classes arewell described by single Schechter stellar mass function forms. We find thatthe total stellar mass densities for individual galaxy populations and for theentire galaxy population are bounded within our stellar mass limits and derivean estimated total stellar mass density of rho_star = 2.5 x 10^8 Msun Mpc^-3h_0.7, which corresponds to an approximately 4% fraction of baryons found instars. The mass contributions to this total stellar mass density by galaxiesthat are dominated by spheroidal components (E and S0-Sa classes) and by diskcomponents (Sab-Scd and Sd-Irr classes) are approximately 70% and 30%,respectively.

Elements heavier than zinc are synthesized through the (r)apid and (s)lowneutron-capture processes. The main site of production of the r-processelements (such as europium) has been debated for nearly 60 years. Initialstudies of chemical abundance trends in old Milky Way halo stars suggestedcontinual r-process production, in sites like core-collapse supernovae. Butevidence from the local Universe favors r-process production mainly during rareevents, such as neutron star mergers. The appearance of a europium abundanceplateau in some dwarf spheroidal galaxies has been suggested as evidence forrare r-process enrichment in the early Universe, but only under the assumptionof no gas accretion into the dwarf galaxies. Cosmologically motivated gasaccretion favors continual r-process enrichment in these systems. Furthermore,the universal r-process pattern has not been cleanly identified in dwarfspheroidals. The smaller, chemically simpler, and more ancient ultra-faintdwarf galaxies assembled shortly after the first stars formed, and are idealsystems with which to study nucleosynthesis events such as the r-process.Reticulum II is one such galaxy. The abundances of non-neutron-capture elementsin this galaxy (and others like it) are similar to those of other old stars.Here, we report that seven of nine stars in Reticulum II observed withhigh-resolution spectroscopy show strong enhancements in heavy neutron-captureelements, with abundances that follow the universal r-process pattern abovebarium. The enhancement in this "r-process galaxy" is 2-3 orders of magnitudehigher than that detected in any other ultra-faint dwarf galaxy. This impliesthat a single rare event produced the r-process material in Reticulum II. Ther-process yield and event rate are incompatible with ordinary core-collapsesupernovae, but consistent with other possible sites, such as neutron starmergers.