Modeling entire disk galaxies is a difficult task for the most advanced computer system, resulting in the small scale physics of the interstellar medium being simplified, often to a single phase (or fixed two or three phase) gas. Simulations of local patches, however, reveal a complex ISM; a turbulent mix where many forces compete during star formation. This suggests global models are likely to be a poor approximation to reality and that we may be missing important clues in the evolution of galactic systems. That said, observations show simple relations between global star formation and gas density, indicating the opposite is true and the detail of the ISM is not important. So can we ignore the fine structure on large scales and if so why? If we can't, are there evolution ramifications that we miss through these simplified pictures? In this talk, I present some of the first global models that develop a multiphase ISM, comparing isothermal systems with galaxies that contain feedback and background heating to try and uncover the most important parameters in star formation in disc galaxies.

An unresolved question in galaxy evolution is whether the star formation histories of low mass systems are preferentially dominated by global starbursts or modes that are more quiescent and continuous. In this talk, I will quantify the prevalence of global starbursts in dwarf galaxies at the present epoch, and infer their characteristic durations, frequencies and amplitudes in the past. I will give an verview of the 11 Mpc Hα UV Galaxy Survey (11HUGS), the primary dataset used for this analysis, which provides Hα and GALEX UV imaging for an approximately volume-limited, statistical sample of star-forming galaxies within 11 Mpc of the Milky Way. Our approach is to directly tally the number of bursting dwarfs in a complete local sample, and to compute the fraction of star formation that is concentrated in these systems. The resulting starburst number and mass fractions (6% and 22% respectively) are then combined with integrated B-V colors, Hα EWs, and stellar evolutionary synthesis models in order to place constraints on the average starburst duty cycle.

Stellar mass and metallicity are important metrics of the galaxy evolution process. Understanding how these quantities evolve with time and in relation to one another is key to understanding the physical processes that govern the efficiency and timing of star formation in galaxies. We summarize current observational constraints on the mass-metallicity relation from z=0 to z=2. We discuss the limitations of “closed box” models for understanding the mass-metallicity relation and discuss progress that has been made using cosmological simulations.

Recent data have revealed a very clear distinction between the abundance patterns of the thick and thin disks, particularly for alpha elements, suggesting a different origin for each of these components. I will present the effect of assuming different formation timescales for the thick and thin disk on the variation of the abundance ratios of several elements with metallicity. I show that a model that assumes that the thin disk was formed on a longer timescale than the thick disk can account for the observed abundance ratio shifts between the tick and thin disk stars. Moreover, these observations offer a powerful constraint on stellar yields in general (massive stars, low and intermediate mass stars and SNIa) and their dependency on metallicity.

Star formation, interstellar medium (ISM) evolution, and galaxy evolution are closely coupled. I will review recent progress in studies of star formation law and ISM evolution in nearby galaxies. Measurements of star formation rate have been significantly improved with recent instruments. The lack of high-resolution observations of the ISM is the bottleneck of the studies of star formation law. In addition to the review, I will introduce recent results from the CO survey of the entire M51 disk with the CARMA interferometer and Nobeyama 45-m telescope. With its high resolution and high image fidelity, the CARMA and Nobeyama map is unveiling ISM evolution in large-scale galactic dynamics. I will show the interplay of galactic dynamics, ISM evolution, and star formation in M51.

We present HST VI data, ground-based UBVRI and H? imaging, and HI data obtained with the VLA of the closest known massive low surface brightness galaxy, UGC2302. This galaxy is similar to M33 in size and gas mass, but it is five times less luminous. Massive LSBs represent an extreme star formation environment, both locally within their disks, and on a larger scale, often residing in under-dense regions of the universe. Thus systems like this provide an interesting window into the evolution of disk galaxies. With these data we can (1) determine the star formation history of this system, and (2) do a comprehensive comparison between the abundance and distribution of stars, star formation, and neutral gas in unprecedented detail for such a disk LSB. This will allow us to better understand how star formation proceeds in “quiescent” galaxies where there’s plenty of fuel (HI) but not much fire (stars).

We review results from the Spitzer MIPS instrument regarding the spatial distribution of cold dust emission in a variety of nearby galaxies, focusing on their outer disks. Large masses of cold dust can be retained in objects of varying physical size and morphological type, including galaxies quite low in mass. The cold dust emission represented by the MIPS 70 and 160 micron images extends well beyond the optical and near-infrared disks of M31 and M33, as is also the case for nearby starbursting dwarfs. The amount of detectable cold dust emission is dependent on the amount of diffuse, non-ionizing ultraviolet photons produced by the young stellar population. Therefore, many more galaxies with lower rates of star formation may have large amounts of very cold dust that escape detection. The existence of such cold dust halos allows us to probe issues regarding the assembly, storage, and retention of dust in disk galaxies and to better understand how the dust interacts with its environment. For instance, tracing gas-to-dust ratios far into disks allows us to distinguish between methods of dust production and transportation, and comparing with other wavelengths enables us to locate the sources of dust heating.

The opacity of a spiral disk due to dust absorption influences every measurement we make of it in the UV and optical. Two separate techniques directly measure the total absorption by dust in the disk: calibrated distant galaxy counts and overlapping galaxy pairs. The main results from both so far are a semi-transparent disk with more opaque arms and a relation between surface brightness and disk opacity. In the Spitzer era, SED models of spiral disks add a new perspective on the role of dust in spiral disks. Combined with the overall opacity from galaxy counts, we can derive a typical optical depth and size of the dusty ISM clouds: 0.4 and 60 pc, respectively. Current work on galaxy counts is in the ACS fields of M51, M101 and M81. Occulting galaxies offer the possibility of probing the history of disk opacity from higher redshift occulting pairs. Evolution in disk opacity could influence distance measurements (SN1a, Tully-Fisher relation). Here we present first results from spectroscopically selected occulting pairs in the SDSS. The redshift range for this sample is limited but does offer a first insight into disk opacity evolution as well as a reference for higher redshift measurements.

In our new VLA HI survey of carefully selected Virgo spirals (VIVA: the VLA Imaging of Virgo in Atomic gas), we find galaxies at various stripping stages. We present the HI properties of the VIVA sample and discuss the cause of HI stripping in a range of density regions, i.e. how the HI gas content of galaxies get affected as they fall into the cluster.