We present a compelling case for a systematic and comprehensive study of the resolved and unresolved stellar populations, ISM, and immediate environments of galaxies throughout the local volume, defined here as D < 20Mpc. This volume is our cosmic backyard and the smallest volume that encompasses environments as different as the Virgo, Ursa Major, Fornax and (perhaps) Eridanus clusters of galaxies, a large number and variety of galaxy groups (e.g., Sculptor, M81, M83, CVn I and II clouds, M51, M101, M74, NGC 5866, M104, and M77 groups), and several cosmic void regions. In each galaxy, through a pan-chromatic (∼160–1100 nm) set of broad-band and diagnostic narrow-band filters, ISM structures and individual luminous stars to ∼ > 1mag below the TRGB should be resolved on scales of <5 pc (at D∼ <20Mpc, ∼800 nm, for μI∼>24mag arcsec−2 and mTRBG I ∼ <27.5mag). Resolved and unresolved stellar populations would be analyzed through color-magnitude and color-color diagram fitting and population synthesis modeling of multi-band colors and would yield physical properties such as spatially resolved star formation histories. The ISM within and around each galaxy would be analyzed using key narrow-band filters that distinguish photospheric from shock heating and provide information on the metallicity of the gas. Such a study would finally allow unraveling the global and spatially resolved star formation histories of galaxies, their assembly, satellite systems, and the dependences thereof on local and global environment within a truly representative cosmic volume. The proposed study is not feasible with current instrumentation but argues for a wide-field (∼ >250 arcmin2), high-resolution (∼ <0.′′02–0.′′065 [300–1000 nm]), ultraviolet–near-infrared imaging facility on a 4m-class space-based observatory.
Jansen, Rolf A.; Scowen, Paul; Beasley, Matthew; Gallagher, John; O'Connell, Robert; Calzetti, Daniela; Oey, Sally; Windhorst, Rogier; and Woodruff, Robert, "A Systematic Study of the Stellar Populations and ISM in Galaxies out to the Virgo Cluster: near field cosmology within a representative slice of the local universe" (2009). Astronomy Department Faculty Publication Series. 20.