THE SPIN ALIGNMENTS IN GALAXY PAIRS AS A TEST OF BOUNCING COUPLED DARK ENERGY

We investigate the effect of coupled dark energy (cDE) on the spin alignments in isolated pairs of galactic halos using the publicly available data from the hydrodynamic cDE simulations (H-CoDECs) that were run for various cDE models such as EXP001, EXP002, EXP003 (with exponential potential and constant coupling), EXP008e3 (with exponential potential and exponential coupling), and SUGRA003 (with supergravity potential and negative constant coupling), as well as for a standard ΛCDM cosmology (with the WMAP7 parameters). Measuring the cosines of the angles between the spin axes in isolated pairs of galactic halos for each model and determining its probability density distribution, we show that for the SUGRA003 model with bouncing cDE the null hypothesis of no spin alignment in pairs of galactic halos is rejected at a 99.999% confidence level. In contrast, the ΛCDM cosmology yields no significant signal of spin alignment, and the other four cDE models also exhibit only weak signals of spin alignments. The strength of the spin alignment signal is found to be almost independent of the total halo mass and separation distance in galaxy pairs. Showing also that no signal is detected from the Sloan Digital Sky Survey DR 7, we conclude that the spin alignments in galaxy pairs are in principle a unique test of bouncing cDE models.