Where are the stars?

The 2dFGRS is used in conjunction with the 2MASSXSC to study the near-IR light and stellar mass content of the local Universe. Mock galaxy catalogues, constructed from cosmological N-body simulations and semi-analytical galaxy formation models, are used to gauge the accuracy with which quantities can be recovered. The mean luminosity densities of the Universe are found to be rho_J=(3.57+/-0.11)10^8 h Lsol/Mpc^3 and rho_KS=(7.04+/-0.23)10^8 h Lsol/Mpc^3 (statistical uncertainty). Using the 2PIGG catalogue, the group dynamical mass-to-light ratio in the K_S band is found to increase by a factor of ~3 when going from groups with total bJ-band luminosities of 310^10 h^-2 Lsol to rich clusters, which have typical values of Upsilon_K~80 h Upsilon_sol. Taking into account the bias introduced by uncertainties in estimating galaxy stellar masses from luminosities, a value of Omega_ h=(0.99+/-0.03)10^-3 is measured, assuming that a Kennicutt stellar IMF is applicable to all galaxies. The 2PIGGs are then used to study the distribution of the stellar content of the local Universe. The three main conclusions are: (1) a slowly rising stellar M/L_KS is found with the clusters having the largest value of ~0.6 Upsilon_sol, (2) in contrast, the fraction of mass in stars decreases with increasing group size, reaching ~510^-3 h for the rich clusters, and (3) in answer to the question posed in the title, most stellar mass is contained in Local Group-sized objects (M~210^12 h^-1 Msol) with only ~2% in clusters with M>510^14 h^-1 Msol.