The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of a baseline build of 150 identical spectrographs (arrayed as 75 unit pairs) fed by 33,600 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.

We study the feeding and feedback of the nucleus of M51 by considering gravitational torques, responsible for gas inflow, in relation to the local distribution of dense gas.

We present new results on the spectrally resolved Ly alpha emission of three Ly alpha-emitting field galaxies at z similar to 2.4 with high Lya equivalent width (> 100 angstrom) and Lya luminosity (similar to 10(43) erg s(-1)). At 120 km s(-1) (FWHM) spectral resolution, the prominent double-peaked Lya profile straddles the systemic velocity, where the velocity zero point is determined from spectroscopy of the galaxies' rest-frame optical nebular emission lines. The average velocity offset from systemic of the stronger redshifted emission component for our sample is 176 km s(-1) while the average total separation between the redshifted and main blueshifted emission components is 380 km s(-1). These measurements are a factor of similar to 2 smaller than for UV-continuum-selected galaxies that show Lya in emission with lower Lya equivalent widths. We compare our Lya spectra to the predicted line profiles of a spherical "expanding shell" Ly alpha radiative transfer grid that models large-scale galaxy outflows. Specifically, blueward of the systemic velocity where two galaxies show a weak, highly blueshifted (by similar to 1000 km s(-1)) tertiary emission peak, the model line profiles are a relatively poor representation of the observed spectra. Since the neutral gas column density has a dominant influence over the shape of the Lya line profile, we caution against equating the observed Lya velocity offset with a physical outflow velocity, especially at lower spectral resolution where the unresolved Lya velocity offset is a convoluted function of several degenerate parameters. Referring to rest-frame ultraviolet and optical Hubble Space Telescope imaging, we find that galaxy-galaxy interactions may play an important role in inducing a starburst that results in copious Lya emission as well as perturbing the gas distribution and velocity field, both of which have strong influence over the Lya emission line profile.

The Mitchell Spectrograph (a.k.a. VIRUS-P) on the 2.7m Harlan J. Smith telescope at McDonald Observatory is currently the largest field of view (FOV) integral field unit (IFU) spectrograph in the world (1.7'. x 1.7'.). It was designed as a prototype for the highly replicable VIRUS spectrograph which consists of a mosaic of IFUs spread over a 16'. diameter FOV feeding 150 spectrographs similar to the Mitchell. VIRUS will be deployed on the 9.2 meter Hobby-Eberly Telescope (HET) and will be used to conduct the HET Dark Energy Experiment (HETDEX). Since seeing first light in 2007 the Mitchell Spectrograph has been widely used, among other things, to study nearby galaxies in the local universe where their internal structure and the spatial distribution of different physical parameters can be studied in great detail. These observations have provided important insight into many aspects of the physics behind the formation and evolution of galaxies and have boosted the scientific impact of the 2.7 meter telescope enormously. Here I review the contributions of the Mitchell Spectrograph to the study of nearby galaxies, from the investigation the spatial distribution of dark matter and the properties of supermassive black holes, to the studies of the process of star formation and the chemical composition of stars and gas in the ISM, which provide important information regarding the formation and evolution of these systems. I highlight the fact that wide field integral field spectrographs on small and medium size telescopes can be powerful cost effective tools to study the astrophysics of galaxies. Finally I briefly discuss the potential of HETDEX for conducting studies on nearby galaxies. The survey parameters make it complimentary and competitive to ongoing and future surveys like SAMI and MANGA.

Survey observations of the three-dimensional locations of galaxies are a powerful approach to measure the distribution of matter in the universe, which can be used to learn about the nature of dark energy, physics of inflation, neutrino masses, etc. A competitive survey, however, requires a large volume (e. g., V-survey similar to 10 Gpc(3)) to be covered, and thus tends to be expensive. A "sparse sampling" method offers a more affordable solution to this problem: within a survey footprint covering a given survey volume, V-survey, we observe only a fraction of the volume. The distribution of observed regions should be chosen such that their separation is smaller than the length scale corresponding to the wavenumber of interest. Then one can recover the power spectrum of galaxies with precision expected for a survey covering a volume of V-survey (rather than the volume of the sum of observed regions) with the number density of galaxies given by the total number of observed galaxies divided by V (survey) (rather than the number density of galaxies within an observed region). We find that regularly-spaced sampling yields an unbiased power spectrum with no window function effect, and deviations from regularly-spaced sampling, which are unavoidable in realistic surveys, introduce calculable window function effects and increase the uncertainties of the recovered power spectrum. On the other hand, we show that the two-point correlation function (pair counting) is not affected by sparse sampling. While we discuss the sparse sampling method within the context of the forthcoming Hobby-Eberly Telescope Dark Energy Experiment, the method is general and can be applied to other galaxy surveys.

We use broadband photometry extending from the rest-frame UV to the near-IR to fit the individual spectral energy distributions of 63 bright (L(Ly alpha) > 10(43) erg s(-1)) Ly alpha emitting galaxies (LAEs) in the redshift range 1.9 < z < 3.6. We find that these LAEs are quite heterogeneous, with stellar masses that span over three orders of magnitude, from 7.5 < log M/M-circle dot < 10.5. Moreover, although most LAEs have small amounts of extinction, some high-mass objects have stellar reddenings as large as E(B - V) similar to 0.4. Interestingly, in dusty objects the optical depths for Ly alpha and the UV continuum are always similar, indicating that Ly alpha photons are not undergoing many scatters before escaping their galaxy. In contrast, the ratio of optical depths in low-reddening systems can vary widely, illustrating the diverse nature of the systems. Finally, we show that in the star-formation-rate-log-mass diagram, our LAEs fall above the "main-sequence" defined by z similar to 3 continuum selected star-forming galaxies. In this respect, they are similar to submillimeter-selected galaxies, although most LAEs have much lower mass.

We present the results from a Very Large Telescope/SINFONI and Keck/NIRSPEC near-infrared spectroscopic survey of 16 Ly alpha emitters (LAEs) at z = 2.1-2.5 in the COSMOS and GOODS-N fields discovered from the Hobby Eberly Telescope Dark Energy Experiment Pilot Survey. We detect rest-frame optical nebular lines (H alpha and/or [O III] lambda 5007) for 10 of the LAEs and measure physical properties, including the star formation rate (SFR), gas-phase metallicity, gas mass fraction, and Ly alpha velocity offset. We find that LAEs may lie below the mass-metallicity relation for continuum-selected star-forming galaxies at the same redshift. The LAEs all show velocity shifts of Ly alpha relative to the systemic redshift ranging between +85 and +296 km s(-1) with a mean of +180 km s(-1). This value is smaller than measured for continuum-selected star-forming galaxies at similar redshifts. The Ly alpha velocity offsets show a moderate correlation with the measured SFR (2.5 sigma), but no significant correlations are seen with the SFR surface density, specific SFR, stellar mass, or dynamical mass (less than or similar to 1.5 sigma). Exploring the role of dust, kinematics of the interstellar medium (ISM), and geometry on the escape of Ly alpha photons, we find no signature of selective quenching of resonantly scattered Ly alpha photons. However, we also find no evidence that a clumpy ISM is enhancing the Ly alpha equivalent width. Our results suggest that the low metallicity in LAEs may be responsible for yielding an environment with a low neutral hydrogen column density and less dust, easing the escape of Ly alpha photons over that in continuum-selected star-forming galaxies.

We compare the H beta line strengths of 1.90 < z < 2.35 star-forming galaxies observed with the near-IR grism of the Hubble Space Telescope with ground-based measurements of Ly alpha from the HETDEX Pilot Survey and narrow-band imaging. By examining the line ratios of 73 galaxies, we show that most star-forming systems at this epoch have a Ly alpha escape fraction below similar to 6%. We confirm this result by using stellar reddening to estimate the effective logarithmic extinction of the H beta emission line (c(H beta) = 0.5) and measuring both the H beta and Ly alpha luminosity functions in a similar to 100,000 Mpc(3) volume of space. We show that in our redshift window, the volumetric Ly alpha escape fraction is at most 4.4(-1.2)(+2.1)%, with an additional systematic similar to 25% uncertainty associated with our estimate of extinction. Finally, we demonstrate that the bulk of the epoch's star-forming galaxies have Ly alpha emission line optical depths that are significantly greater than that for the underlying UV continuum. In our predominantly [O-III] lambda 5007- selected sample of galaxies, resonant scattering must be important for the escape of Ly alpha photons.

We present an overview of a new integral field spectroscopic survey called MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV) that began on 2014 July 1. MaNGA will investigate the internal kinematic structure and composition of gas and stars in an unprecedented sample of 10,000 nearby galaxies. We summarize essential characteristics of the instrument and survey design in the context of MaNGA's key science goals and present prototype observations to demonstrate MaNGA's scientific potential. MaNGA employs dithered observations with 17 fiber-bundle integral field units that vary in diameter from 12 '' (19 fibers) to 32 '' (127 fibers). Two dual-channel spectrographs provide simultaneous wavelength coverage over 3600-10300 angstrom at R similar to 2000. With a typical integration time of 3 hr, MaNGA reaches a target r-band signal-to-noise ratio of 4-8 (angstrom(-1) per 2 '' fiber) at 23 AB mag arcsec(-2), which is typical for the outskirts of MaNGA galaxies. Targets are selected with M* greater than or similar to 10(9) M-circle dot using SDSS-I redshifts and i-band luminosity to achieve uniform radial coverage in terms of the effective radius, an approximately flat distribution in stellar mass, and a sample spanning a wide range of environments. Analysis of our prototype observations demonstrates MaNGA's ability to probe gas ionization, shed light on recent star formation and quenching, enable dynamical modeling, decompose constituent components, and map the composition of stellar populations. MaNGA's spatially resolved spectra will enable an unprecedented study of the astrophysics of nearby galaxies in the coming 6 yr.

We present a new method for inferring the metallicity (Z) and ionization parameter (q) of H II regions and star-forming galaxies using strong nebular emission lines (SELs). We use Bayesian inference to derive the joint and marginalized posterior probability density functions for Z and q given a set of observed line fluxes and an input photoionization model. Our approach allows the use of arbitrary sets of SELs and the inclusion of flux upper limits. The method provides a self-consistent way of determining the physical conditions of ionized nebulae that is not tied to the arbitrary choice of a particular SEL diagnostic and uses all the available information. Unlike theoretically calibrated SEL diagnostics, the method is flexible and not tied to a particular photoionization model. We describe our algorithm, validate it against other methods, and present a tool that implements it called IZI. Using a sample of nearby extragalactic H II regions, we assess the performance of commonly used SEL abundance diagnostics. We also use a sample of 22 local H II regions having both direct and recombination line (RL) oxygen abundance measurements in the literature to study discrepancies in the abundance scale between different methods. We find that oxygen abundances derived through Bayesian inference using currently available photoionization models in the literature can be in good (similar to 30%) agreement with RL abundances, although some models perform significantly better than others. We also confirm that abundances measured using the direct method are typically similar to 0.2 dex lower than both RL and photoionization-model-based abundances.