The Local Group: the ultimate deep field

Near-field cosmology - using detailed observations of the Local Group and its environs to study wide-ranging questions in galaxy formation and dark matter physics - has become a mature and rich field over the past decade. There are lingering concerns, however, that the relatively small size of the present-day Local Group (similar to 2 Mpc diameter) imposes insurmountable sample-variance uncertainties, limiting its broader utility. We consider the region spanned by the Local Group's progenitors at earlier times and show that it reaches 3 arcmin approximate to 7 comoving Mpc in linear size (a volume of approximate to 350 Mpc(3)) at z = 7. This size at early cosmic epochs is large enough to be representative in terms of the matter density and counts of dark matter haloes with M-vir(z = 7) less than or similar to 2 x 10(9) M-circle dot. The Local Group's stellar fossil record traces the cosmic evolution of galaxies with 10(3) less than or similar to M-star (z = 0)/M-circle dot less than or similar to 10(9) (reaching M-1500 > -9 at z similar to 7) over a region that is comparable to or larger than the Hubble Ultra-Deep Field (HUDF) for the entire history of the Universe. In the JWST era, resolved stellar populations will probe regions larger than the HUDF and any deep JWST fields, further enhancing the value of near-field cosmology.