A Systematic Study of the Stellar Populations and ISM in Galaxies out to
  the Virgo Cluster
  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, and several cosmic void
regions. In each galaxy, through a pan-chromatic (160--1100nm) 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, lambda ~ 800nm, for mu_I >~ 24 mag/arcsec^2 and m_{I,TRGB} <~
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^2),
high-resolution (<~0.020"--0.065" [300--1000nm]), ultraviolet--near-infrared
imaging facility on a 4m-class space-based observatory.
