MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is a 6-yr Sloan Digital Sky Survey (SDSS-IV) survey that will obtain spatially resolved spectroscopy from 3600 to 10 300 angstrom for a representative sample of ove10 000 nearby galaxies. In this paper, we present the analysis of nebular emission-line properties using observations of 14 galaxies obtained with P-MaNGA, a prototype of the MaNGA instrument. By using spatially resolved diagnostic diagrams, we find extended star formation in galaxies that are centrally dominated by Seyfert/LINER-like emission, which illustrates that galaxy characterizations based on single fibre spectra are necessarily incomplete. We observe extended low ionization nuclear emission-line regions (LINER)-like emission (up to 1R(e)) in the central regions of three galaxies. We make use of the Ha equivalent width [EW(H alpha)] to argue that the observed emission is consistent with ionization from hot evolved stars. We derive stellar population indices and demonstrate a clear correlation between D-n(4000) and EW(H delta(A)) and the position in the ionization diagnostic diagram: resolved galactic regions which are ionized by a Seyfert/LINER-like radiation field are also devoid of recent star formation and host older and/or more metal-rich stellar populations. We also detect extraplanar LINER-like emission in two highly inclined galaxies, and identify it with diffuse ionized gas. We investigate spatially resolved metallicities and find a positive correlation between metallicity and star formation rate surface density. We further study the relation between N/O versus O/H on resolved scales. We find that, at given N/O, regions within individual galaxies are spread towards lower metallicities, deviating from the sequence defined by galactic central regions as traced by Sloan 3-arcsec fibre spectra. We suggest that the observed dispersion can be a tracer for gas flows in galaxies: infalls of pristine gas and/or the effect of a galactic fountain.

Galaxy proto-clusters at z greater than or similar to 2 provide a direct probe of the rapid mass assembly and galaxy growth of present-day massive clusters. Because of the need for precise galaxy redshifts for density mapping and the prevalence of star formation before quenching, nearly all the proto-clusters known to date were confirmed by spectroscopy of galaxies with strong emission lines. Therefore, large emission-line galaxy surveys provide an efficient way to identify proto-clusters directly. Here we report the discovery of a large-scale structure at z - 2.44 in the Hobby Eberly Telescope Dark Energy Experiment (HETDEX) Pilot Survey. On a scale of a few tens of Mpc comoving, this structure shows a complex overdensity of Ly alpha emitters (LAE), which coincides with broadband selected galaxies in the COSMOS/UltraVISTA photometric and zCOSMOS spectroscopic catalogs, as well as overdensities of intergalactic gas revealed in the Ly alpha absorption maps of Lee et al. We construct mock LAE catalogs to predict the cosmic evolution of this structure. We find that such an overdensity should have already broken away from the Hubble flow, and part of the structure will collapse to form a galaxy cluster with 10(14.5 +/- 0.4) M-circle dot by z = 0. The structure contains a higher median stellar mass of broadband selected galaxies, a boost of extended Lya nebulae, and a marginal excess of active galactic nuclei relative to the field, supporting a scenario of accelerated galaxy evolution in cluster progenitors. Based on the correlation between galaxy overdensity and the z = 0 descendant halo mass calibrated in the simulation, we predict that several hundred 1.9 < z < 3.5 proto-clusters with z = 0 mass of >10(14.5) M-circle dot will be discovered in the 8.5 Gpc(3) of space surveyed by the HETDEX.

Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), one of three core programs in the Sloan Digital Sky Survey-IV, is an integral-field spectroscopic survey of roughly 10,000 nearby galaxies. It employs dithered observations using 17 hexagonal bundles of 2'' fibers to obtain resolved spectroscopy over a wide wavelength range of 3600-10300 angstrom. To map the internal variations within each galaxy, we need to perform accurate spectral surface photometry, which is to calibrate the specific intensity at every spatial location sampled by each individual aperture element of the integral field unit. The calibration must correct only for the flux loss due to atmospheric throughput and the instrument response, but not for losses due to the finite geometry of the fiber aperture. This requires the use of standard star measurements to strictly separate these two flux loss factors (throughput versus geometry), a difficult challenge with standard single-fiber spectroscopy techniques due to various practical limitations. Therefore, we developed a technique for spectral surface photometry using multiple small fiber-bundles targeting standard stars simultaneously with galaxy observations. We discuss the principles of our approach and how they compare to previous efforts, and we demonstrate the precision and accuracy achieved. MaNGA's relative calibration between the wavelengths of H alpha and H beta has an rms of 1.7%, while that between [N II] lambda 6583 and [O II] lambda 3727 has an rms of 4.7%. Using extinction-corrected star formation rates and gas-phase metallicities as an illustration, this level of precision guarantees that flux calibration errors will be sub-dominant when estimating these quantities. The absolute calibration is better than 5% for more than 89% of MaNGA's wavelength range.

We develop a simple analytical model that tracks galactic metallicities governed by star formation and feedback to gain insight from the observed galaxy stellar mass-metallicity relations over a large range of stellar masses and redshifts. The model reveals the following implications of star formation and feedback processes in galaxy formation. First, the observed metallicity relations provide a stringent upper limit for the averaged outflow mass-loading factors of local galaxies, which are similar to 20 for M-* similar to 10(9)M(circle dot) galaxies and monotonically decrease to similar to 1 for M-* similar to 10(11)M. galaxies. Second, the inferred upper limit for the outflow mass-loading factor sensitively depends on whether the outflow is metal-enriched with respect to the interstellar medium metallicity. If half of the metals ejected from supernovae leave the galaxy in metal-enriched winds, the outflow mass-loading factor for galaxies at any mass can barely be higher than similar to 10, which puts strong constraints on galaxy formation models. Third, the relatively lower stellar-phase to gas-phase metallicity ratio for lower-mass galaxies indicates that low-mass galaxies are still rapidly enriching their metallicities in recent times, while high-mass galaxies are more settled, which seems to show a downsizing effect in the metallicity evolution of galaxies. The analysis presented in the paper demonstrates the importance of accurate measurements of galaxy metallicities and the cold gas fraction of galaxies at different redshifts for constraining star formation and feedback processes, and demonstrates the power of these relations for constraining the physics of galaxy formation.

In this work, we show how the stellar mass (M-*) of galaxies affects the 3 < z < 4.6 Ly alpha equivalent width (EW) distribution. To this end, we design a sample of 629 galaxies in the M-* range 7.6 < logM(*)/M-circle dot < 10.6 from the 3D-HST/CANDELS survey. We perform spectroscopic observations of this sample using the Michigan/Magellan Fiber System, allowing us to measure Ly alpha fluxes and use 3D-HST/CANDELS ancillary data. In order to study the Ly alpha EW distribution dependence on M-*, we split the whole sample in three stellar mass bins. We find that, in all bins, the distribution is best represented by an exponential profile of the form dN(M-*)/dEW = W-0(M-*)(-1)A(M-*)e(-EW/W0(M*)). Through a Bayesian analysis, we confirm that lower M-* galaxies have higher Lya EWs. We also find that the fraction A of galaxies featuring emission and the e-folding scale W-0 of the distribution anti-correlate with M-*, recovering expressions of the forms A(M-*) = -0.26(.13)logM(*)/M-circle dot + 3.01(1.2) and W-0(M-*) = -15.6(3.5)logM(*)/M-circle dot + 166(34). These results are crucial for proper interpretation of Ly alpha emission trends reported in the literature that may be affected by strong M-* selection biases.

NGC 1042 is a late-type bulgeless disk galaxy that hosts low-luminosity active galactic nuclei (AGNs) coincident with a massive nuclear star cluster. In this paper, we present the integral field spectroscopy studies of this galaxy, based on the data obtained with the Mitchell spectrograph on the 2.7 m Harlan J. Smith telescope. In the central 100-300 pc region of NGC 1042, we find a circumnuclear ring structure of gas with enhanced ionization, which we suggest is mainly induced by shocks. Combining this with the harmonic decomposition analysis of the velocity field of the ionized gas, we propose that the shocked gas is the result of gas inflow driven by the inner spiral arms. The inflow velocity is similar to 32 +/- 10 km s(-1), and the estimated mass-inflow rate is similar to 1.1 +/- 0.3 x 10(-3) M-circle dot yr(-1). The mass-inflow rate is about one hundred times the black hole's mass-accretion rate (similar to 1.4 x 10(-5) M-circle dot yr(-1)) and slightly larger than the star-formation rate in the nuclear star cluster (7.94 x 10(-4) M-circle dot yr(-1)), implying that the inflow material is enough to feed both the AGN activity and star formation in the nuclear star cluster. Our study highlights that secular evolution can be important in late-type unbarred galaxies like NGC 1042.

We present a study of the excitation conditions and metallicity of ionized gas (Z(gas)) in eight nearby barred and unbarred spiral galaxies from the VIRUS-P Exploration of Nearby Galaxies (VENGA) survey, which provides high spatial sampling and resolution (median similar to 387 pc), large coverage from the bulge to outer disc, broad wavelength range (3600-6800 angstrom), and medium spectral resolution (similar to 120 km s(-1) at 5000 angstrom). Our results are: (1) We present high resolution gas excitation maps to differentiate between regions with excitation typical of Seyfert, LINER, or recent star formation. We find LINER-type excitation at large distances (3-10 kpc) from the centre, and associate this excitation with diffuse ionized gas (DIG). (2) After excluding spaxels dominated by Seyfert, LINER, or DIG, we produce maps with the best spatial resolution and sampling to date of the ionization parameter q, star formation rate, and Z(gas) using common strong line diagnostics. We find that isolated barred and unbarred spirals exhibit similarly shallow Z(gas) profiles from the inner kpc out to large radii (7-10 kpc or 0.5-1.0 R-25). This implies that if profiles had steeper gradients at earlier epochs, then the presentday bar is not the primary driver flattening gradients over time. This result contradicts earlier claims, but agrees with recent IFU studies. (3) The Z(gas) gradients in our z similar to 0 massive spirals are markedly shallower, by similar to 0.2 dex kpc(-1), than published gradients for lensed lower mass galaxies at z similar to 1.5-2.0. Cosmologically motivated hydrodynamical simulations best match this inferred evolution, but the match is sensitive to adopted stellar feedback prescriptions.

The cloud-scale density, velocity dispersion, and gravitational boundedness of the interstellar medium (ISM) vary within and among galaxies. In turbulent models, these properties play key roles in the ability of gas to form stars. New high-fidelity, high-resolution surveys offer the prospect to measure these quantities across galaxies. We present a simple approach to make such measurements and to test hypotheses that link small-scale gas structure to star formation and galactic environment. Our calculations capture the key physics of the Larson scaling relations, and we show good correspondence between our approach and a traditional "cloud properties" treatment. However, we argue that our method is preferable in many cases because of its simple, reproducible characterization of all emission. Using, low-J (CO)-C-12 data from recent surveys, we characterize the molecular ISM at 60 pc resolution in the Antennae, the Large Magellanic Cloud (LMC), M31, M33, M51, and M74. We report the distributions of surface density, velocity dispersion, and gravitational boundedness at 60 pc scales and show galaxy-to-galaxy and intragalaxy variations in each. The distribution of flux as a function of surface density appears roughly lognormal with a 1 sigma width of similar to 0.3 dex, though the center of this distribution varies from galaxy to galaxy. The 60 pc resolution line width and molecular gas surface density correlate well, which is a fundamental behavior expected for virialized or free-falling gas. Varying the measurement scale for the LMC and M31, we show that the molecular ISM has higher surface densities, lower line widths, and more self-gravity at smaller scales.

The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of 156 identical spectrographs (arrayed as 78 pairs) fed by 35,000 fibers, each 1.5 arcsec diameter, at the focus of the upgraded 10 m Hobby-Eberly Telescope (HET). VIRUS has a fixed bandpass of 350-550 nm and resolving power R similar to 700. VIRUS is the first example of industrial-scale replication applied to optical astronomy and is capable of surveying large areas of sky, spectrally. The VIRUS concept offers significant savings of engineering effort, cost, and schedule when compared to traditional instruments.