The signature of dark energy on the local Hubble flow

Abstract

Using N-body simulations of flat, dark energy dominated cosmologies, we show that galaxies around simulated binary systems resembling the Local Group (LG) have low peculiar 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 LCDM model, a LWDM model with a 2 keV warm dark matter candidate and a quintessence model (QCDM) with an equation of state parameter w=-0.6. The Hubble flow is significant 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 LWDM and QCDM models are marginally colder than in the LCDM one. The results of our simulations have been compared to existing data and 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 sigma = 88 +- 20 km/sec 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 few Mpc, corroborating the evidence gathered from observations of distant objects and the early Universe.