In this paper we use strong line calibrations of N/O and O/H in MaNGA spaxeldata to explore the systematics introduced by variations in N/O on variousstrong-line metallicity diagnostics. We find radial variations in N/O at fixedO/H which correlate with total galaxy stellar-mass; and which can induce $\sim40 \%$ systematic uncertainties in oxygen abundance gradients whennitrogen-dependent abundance calibrations are used. Empirically, we find thatthese differences are associated with variation in the local star formationefficiency, as predicted by recent chemical evolution models for galaxies, butwe cannot rule out other processes such as radial migration and the accretionof passive dwarf galaxies also playing a role.

We present ALMA Band 6 (nu=233GHz, lambda=1.3mm) continuum observationstowards 68 'normal' star-forming galaxies within two Coma-like progenitorstructures at z=2.10 and 2.47, from which ISM masses are derived, providing thelargest census of molecular gas mass in overdense environments at theseredshifts. Our sample comprises galaxies with a stellar mass range of1x10^9M_sun - 4x10^11M_sun with a mean M_*~6x10^10M_sun. Combining thesemeasurements with multiwavelength observations and SED modeling, wecharacterize the gas mass fraction and the star formation efficiency, and inferthe impact of the environment on galaxies' evolution. Most of our detectedgalaxies (~70%) have star formation efficiencies and gas fractions similar tothose found for coeval field galaxies and in agreement with the field scalingrelations. However, we do find that the proto-clusters contain an increasedfraction of massive, gas-poor galaxies, with low gas fractions (f_gas<6-10%)and red rest-frame ultraviolet/optical colors typical of post-starburst andpassive galaxies. The relatively high abundance of passive galaxies suggests anaccelerated evolution of massive galaxies in proto-cluster environments. Thelarge fraction of quenched galaxies in these overdense structures also impliesthat environmental quenching takes place during the early phases of clusterassembly, even before virialization. From our data, we derive a quenchingefficiency of E_q~0.45 and an upper limit on the quenching timescale ofT_q<1Gyr.

We investigate a large sample of massive galaxies at $z\sim1$ with combined$HST$ broad-band and grism observations to constrain the star-formationhistories of these systems as they transition from a star-forming state toquiescence. Among our sample of massive $(M_*>10^{10}~{\rm M_\odot})$ galaxiesat $0.7<z<1.2$, dust-corrected H$\alpha$ and UV star-formation indicators agreewith a small dispersion ($\sim0.2$~dex) for galaxies on the main sequence, butdiverge and exhibit substantial scatter ($\sim0.7$~dex) once they dropsignificantly below the star-forming main sequence. Significant H$\alpha$emission is present in galaxies with low dust-corrected UV SFR values as wellas galaxies classified as quiescent using the $UVJ$ diagram. We compare theobserved H$\alpha$ flux distribution to the expected distribution assumingbursty or smooth star-formation histories, and find that massive galaxies at$z\sim1$ are most consistent with a quick, bursty quenching process. Thissuggests that mechanisms such as feedback, stochastic gas flows, and minormergers continue to induce low-level bursty star formation in massive galaxiesat moderate redshift, even as they quench.