Motivated by the idea that a subset of HVCs trace dark matter substructure in the Local Group, we search for signs of star formation in the Smith Cloud, a nearby ~2x10^6 Msun HVC currently falling into the Milky Way. Using GALEX NUV and WISE/2MASS NI
R photometry, we apply a series of color and apparent magnitude cuts to isolate candidate O and B stars that are plausibly associated with the Smith Cloud. We find an excess of stars along the line of sight to the cloud, but not at a statistically significant level relative to a control region. The number of stars found in projection on the cloud after removing an estimate of the contamination by the Milky Way implies an average star formation rate surface density of 10^(-4.8 +/- 0.3) Msun yr^(-1) kpc^(-2), assuming the cloud has been forming stars at a constant rate since its first passage through the Milky Way ~70 Myr ago. This value is consistent with the star formation rate expected based on the average gas density of the cloud. We also discuss how the newly discovered star forming galaxy Leo P has very similar properties to the Smith Cloud, but its young stellar population would not have been detected at a statistically significant level using our method. Thus, we cannot yet rule out the idea that the Smith Cloud is really a dwarf galaxy.
We relate transitions in galaxy structure and gas content to refueling, here defined to include both the external gas accretion and the internal gas processing needed to renew reservoirs for star formation. We analyze two z=0 data sets: a high-qualit
y ~200-galaxy sample (the Nearby Field Galaxy Survey, data release herein) and a volume-limited ~3000-galaxy sample with reprocessed archival data. Both reach down to baryonic masses ~10^9Msun and span void-to-cluster environments. Two mass-dependent transitions are evident: (i) below the gas-richness threshold scale (V~125km/s), gas-dominated quasi-bulgeless Sd--Im galaxies become numerically dominant, while (ii) above the bimodality scale (V~200km/s), gas-starved E/S0s become the norm. Notwithstanding these transitions, galaxy mass (or V as its proxy) is a poor predictor of gas-to-stellar mass ratio M_gas/M_*. Instead, M_gas/M_* correlates well with the ratio of a galaxys stellar mass formed in the last Gyr to its preexisting stellar mass, such that the two ratios have numerically similar values. This striking correspondence between past-averaged star formation and current gas richness implies routine refueling of star-forming galaxies on Gyr timescales. We argue that this refueling underlies the tight M_gas/M_* vs. color correlations often used to measure photometric gas fractions. Furthermore, the threshold and bimodality scale transitions reflect mass-dependent demographic shifts between three refueling regimes --- accretion dominated, processing dominated, and quenched. In this picture, gas-dominated dwarfs are explained not by inefficient star formation but by overwhelming gas accretion, which fuels stellar mass doubling in <~1Gyr. Moreover, moderately gas-rich bulged disks such as the Milky Way are transitional, becoming abundant only in the narrow range between the threshold and bimodality scales.
