The signature of dark energy on the local Hubble flow

Using N-body simulations of flat, dark energy-dominated cosmologies, we show that galaxies around simulated binary systems resembling the Local Group (LG) have lowpeculiar velocities, in good agreement with observational data. We have compared results for LG-like systems selected from large, high-resolution simulations of three cosmologies: a Lambda CDM model, a Lambda WDM model with a 2-keV warm dark matter candidate, and a quintessence (QCDM) model with an equation-of-state parameter w = -0.6. The Hubble flow is significantly colder around LGs selected in a flat, Lambda-dominated cosmology than around LGs in open or critical models, showing that a dark energy component manifests itself on the scales of nearby galaxies, cooling galaxy peculiar motions. Flows in the Lambda WDM and QCDM models are marginally colder than in the Lambda CDM one. The results of our simulations have been compared to existing data and to a new data set of 28 nearby galaxies with robust distance measures (Cepheids and surface brightness fluctuations). The measured line-of-sight velocity dispersion is given by sigma(H) = (88 +/- 20 km s(-1)) x (R/7 Mpc). The best agreement with observations is found for LGs selected in the Lambda CDM cosmology in environments with -0.1 < delta rho/rho < 0.6 on scales of 7 Mpc, in agreement with existing observational estimates on the local matter density. These results provide new, independent evidence for the presence of dark energy on scales of a few megaparsecs, corroborating the evidence gathered from observations of distant objects and the early Universe.