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

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 < 20 Mpc. 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, M 81, M 83, CVn I and II clouds, M 51, M 101, M 74, NGC 5866, M 104, and M 77 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 ∼ >1 mag below the TRGB should be resolved on scales of <5 pc (at D ∼ <20 Mpc, λ∼800 nm, for μI∼>24 mag arcsec −2 and m I ∼ <27.5 mag). 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 arcmin), high-resolution ( ∼ <0.02–0.065 [300–1000 nm]), ultraviolet–near-infrared imaging facility on a 4 m-class space-based observatory.