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¨C1100 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 ¦ÌI¡«>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.¡ä¡ä02¨C0.¡ä¡ä065 [300¨C1000 nm]), ultraviolet¨Cnear-infrared imaging facility on a 4m-class space-based observatory.
Jansen, R; Scowen, P; Beasley, M; Gallagher, J; Connel, R; and Calzetti, D, "A Systematic Study of the Stellar Populations and ISM in Galaxies out to the Virgo Cluster" (2009). Astronomy Department Faculty Publication Series. 974.