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.

We revisit the evolution of the mass-metallicity relation of low- and high-redshift galaxies by using a sample of local analogs of high-redshift galaxies. These analogs share the same location of the UV-selected star-forming galaxies at z similar to 2 on the [O III]lambda 5007/H beta versus [N II]lambda 6584/H alpha nebular emission-line diagnostic (or BPT) diagram. Their physical properties closely resemble those in z similar to 2 UV-selected star-forming galaxies being characterized, in particular, by high ionization parameters (log q approximate to 7.9) and high electron densities (n(e) approximate to 100 cm(-3)). With the full set of well-detected rest-frame optical diagnostic lines, we measure the gasphase oxygen abundance in the SDSS galaxies and these local analogs using the empirical relations and the photoionization models. We find that the metallicity difference between the SDSS galaxies and our local analogs in the 8.5 < log(M-* M-Theta) < 9.0 stellar mass bin varies from -0.09 to 0.39 dex, depending on strong-line metallicity measurement methods. Due to this discrepancy, the evolution of mass-metallicity should be used to compare with the cosmological simulations with caution. We use the [S II]/H alpha and [O I]/H alpha BPT diagram to reduce the potential AGN and shock contamination in our local analogs. We find that the AGN/shock influences are negligible on the metallicity estimation.

Distance uncertainties plague our understanding of the physical scales relevant to the physics of star formation in extragalactic studies. The planetary nebulae luminosity function (PNLF) is one of very few techniques that can provide distance estimates to within similar to 10%; however, it requires a planetary nebula (PN) sample that is uncontaminated by other ionizing sources. We employ optical integral field unit spectroscopy using the Multi-Unit Spectroscopic Explorer on the Very Large Telescope to measure [O III] line fluxes for sources unresolved on 50 pc scales within the central star-forming galaxy disk of NGC 628. We use diagnostic line ratios to identify 62 PNe, 30 supernova remnants, and 87 H II regions within our fields. Using the 36 brightest PNe, we determine a new PNLF distance modulus of 29.91(-0.13)(+0.08) mag (9.59(-0.57)(+0.35) Mpc), which is in good agreement with literature values, but significantly larger than the previously reported PNLF distance. We are able to explain the discrepancy and recover the previous result when we reintroduce SNR contaminants to our sample. This demonstrates the power of full spectral information over narrowband imaging in isolating PNe. Given our limited spatial coverage within the Galaxy, we show that this technique can be used to refine distance estimates, even when IFU observations cover only a fraction of a galaxy disk.

We present an exhaustive census of Lyman alpha (Ly alpha) emission in the general galaxy population at 3 < z < 4.6. We use the Michigan/Magellan Fiber System (M2FS) spectrograph to study a stellar mass (M-*) selected sample of 625 galaxies homogeneously distributed in the range 7.6 < logM(*)/M-circle dot < 10.6. Our sample is selected from the 3D-HST/CANDELS survey, which provides the complementary data to estimate Ly alpha equivalent widths (W-Ly alpha) and escape fractions (f(esc)) for our galaxies. We find both quantities to anti-correlate with M-*, star formation rate (SFR), UV luminosity, and UV slope (beta). We then model the WLya distribution as a function of M-UV and beta using a Bayesian approach. Based on our model and matching the properties of typical Lyman break galaxy (LBG) selections, we conclude that theW(Ly alpha) distribution in such samples is heavily dependent on the limiting M-UV of the survey. Regarding narrowband surveys, we find their W-Ly alpha selections to bias samples toward low M-*, while their line-flux limitations preferentially leave out low-SFR galaxies. We can also use our model to predict the fraction of Ly alpha-emitting LBGs at 4 <= z <= 7. We show that reported drops in the Lya fraction at z >= 6, usually attributed to the rapidly increasing neutral gas fraction of the universe, can also be explained by survey M-UV incompleteness. This result does not dismiss reionization occurring at z similar to 7, but highlights that current data is not inconsistent with this process taking place at z > 7.

AGN feedback is invoked as one of the most relevant mechanisms that shape the evolution of galaxies. Our goal is to understand the interplay between AGN feedback and the interstellar medium in M 51, a nearby spiral galaxy with a modest AGN and a kpc-scale radio jet expanding through the disc of the galaxy. For this purpose, we combine molecular gas observations in the CO(1-0) and HCN(1-0) lines from the Plateau de Bure interferometer with archival radio, X-ray, and optical data. We show that there is a significant scarcity of CO emission in the ionisation cone, while molecular gas emission tends to accumulate towards the edges of the cone. The distribution and kinematics of CO and HCN line emission reveal AGN feedback effects out to r similar to 500 pc, covering the whole extent of the radio jet, with complex kinematics in the molecular gas which displays strong local variations. We propose that this is the result of the almost coplanar jet pushing on molecular gas in different directions as it expands; the effects are more pronounced in HCN than in CO emission, probably as the result of radiative shocks. Following previous interpretation of the redshifted molecular line in the central 5 '' as caused by a molecular outflow, we estimate the outflow rates to be (M) over dot(H2) similar to 0.9 M-circle dot/yr and (M) over dot(dense) similar to 0.6 M-circle dot/yr, which are comparable to the molecular inflow rates (similar to 1 M-circle dot/yr); gas inflow and AGN feedback could be mutually regulated processes. The agreement with findings in other nearby radio galaxies suggests that this is not an isolated case, and is probably the paradigm of AGN feedback through radio jets, at least for galaxies hosting low-luminosity active nuclei.

We present the integrated stellar mass-metallicity relation (MZR) for more than 1700 galaxies included in the integral field area SDSS-IV MaNGA survey. The spatially resolved data allow us to determine the metallicity at the same physical scale (effective radius, R-eff) using a heterogeneous set of 10 abundance calibrators. In addition to scale factors, the shape of the MZR is similar for all calibrators, consistent with those reported previously using single-fiber and integral field spectroscopy. We compare the residuals of this relation against the star formation rate (SFR) and specific SFR (sSFR). We do not find a strong secondary relation of the MZR with either SFR or sSFR for any of the calibrators, in contrast with previous single-fiber spectroscopic studies. Our results agree with a scenario in which metal enrichment happens at local scales, with global outflows playing a secondary role in shaping the chemistry of galaxies and cold-gas inflows regulating the stellar formation.

The spatial distribution of dust in galaxies affects the global attenuation, and hence inferred properties, of galaxies. We trace the spatial distribution of dust in five approximately kiloparsec fields of M31 by comparing optical attenuation with the total dust mass distribution. We measure the attenuation from the Balmer decrement using Integral Field Spectroscopy and the dust mass from Herschel far-IR observations. Our results show that M31's dust attenuation closely follows a foreground screen model, contrary to what was previously found in other nearby galaxies. By smoothing the M31 data, we find that spatial resolution is not the cause for this difference. Based on the emission-line ratios and two simple models, we conclude that previous models of dust/gas geometry need to include a weakly or non-attenuated diffuse ionized gas (DIG) component. Due to the variation of dust and DIG scale heights with galactic radius, we conclude that different locations in galaxies will have different vertical distributions of gas and dust and therefore different measured attenuation. The difference between our result in M31 with that found in other nearby galaxies can be explained by our fields in M31 lying at larger galactic radii than the previous studies that focused on the centers of galaxies.

We compare the structure of molecular gas at 40 pc resolution to the ability of gas to form stars across the disk of the spiral galaxy M51. We break the PAWS survey into 370 pc and 1.1 kpc resolution elements, and within each we estimate the molecular gas depletion time (tau(mol)(Dep)), the star-formation efficiency per free-fall time (epsilon(ff)), and the mass-weighted cloud-scale (40 pc) properties of the molecular gas: surface density, Sigma, line width, sigma, and b equivalent to Sigma/sigma(2) proportional to alpha(-1)(vir), a parameter that traces the boundedness of the gas. We show that the cloud-scale surface density appears to be a reasonable proxy for mean volume density. Applying this, we find a typical star-formation efficiency per free-fall time, epsilon(ff)() similar to 0.3%-0.36%, lower than adopted in many models and found for local clouds. Furthermore, the efficiency per free-fall time anti-correlates with both Sigma and sigma, in some tension with turbulent star-formation models. The best predictor of the rate of star formation per unit gas mass in our analysis is b equivalent to Sigma/sigma(2), tracing the strength of self-gravity, with tau(mol)(Dep) proportional to b(-0.9). The sense of the correlation is that gas with stronger self-gravity (higher b) forms stars at a higher rate (low tau(mol)(Dep)). The different regions of the galaxy mostly overlap in tau(mol)(Dep) as a function of b, so that low b explains the surprisingly high tau(mol)(Dep) found toward the inner spiral arms found by Meidt et al. (2013).