© 2016. The American Astronomical Society. All rights reserved.The ALFALFA Ha survey utilizes a large sample of H i-selected galaxies from the ALFALFA survey to study star formation (SF) in the local universe. ALFALFA Ha contains 1555 galaxies with distances between ~20 and ~100 Mpc. We have obtained continuum-subtracted narrowband Ha images and broadband R images for each galaxy, creating one of the largest homogeneous sets of Ha images ever assembled. Our procedures were designed to minimize the uncertainties related to the calculation of the local SF rate density (SFRD). The galaxy sample we constructed is as close to volume-limited as possible, is a robust statistical sample, and spans a wide range of galaxy environments. In this paper, we discuss the properties of our Fall sample of 565 galaxies, our procedure for deriving individual galaxy SF rates, and our method for calculating the local SFRD. We present a preliminary value of log(SFRD[M? yr-1 Mpc-3]) = -1.747 ± 0.018 (random) ± 0.05 (systematic) based on the 565 galaxies in our Fall sub-sample. Compared to the weighted average of SFRD values around z ˜ 2, our local value indicates a drop in the global SFRD of a factor of 10.2 over that lookback time.
Van Sistine, A., Salzer, J. J., Sugden, A., Giovanelli, R., Haynes, M. P., Janowiecki, S., ... Wilcots, E. M. (2016). THE ALFALFA Ha SURVEY. I. PROJECT DESCRIPTION and the LOCAL STAR FORMATION RATE DENSITY from the FALL SAMPLE. Astrophysical Journal, 824(1). https://doi.org/10.3847/0004-637X/824/1/25