Large Scale Streaming in the Wake of a Loop of Cosmic String

Extract

Large-scale streaming can be caused by a single “strange attractor” located at a distance D ∼ 45h⁻¹ Mpc from our galaxy (Faber, these proceedings). These observations can be interpreted in terms of a wake of a large loop of cosmic string laid down at z ≤ 1000. The velocity field induced by a stationary loop modeled as a thin spherical shell has a radial dependence v ∼ r⁻¹, consistent with the observed. Zeldovich spectrum of density perturbations would result in v ∼ r⁻³. The stationary loop model can account for the observed amplitude of the peculiar velocity (v ≃ 500km/s at D ≃ 45h⁻¹ Mpc) only if the dimensionless string tension Gμ/c² is large, ≳ 7 × 10⁻⁶. When peculiar velocities of the loops are taken into account, the estimate of μ can be lowered: The loop is now able to spread its influence. The flow induced by the loop with the physical radius R_s = 36h⁻¹ kpc moving initially with v_s = 0.1c and laid down at z=500 is shown in the top portion of the diagram below. The distances are in h⁻¹ Mpc's. The initial comoving loop size and location are indicated by a circle and the present-day location by a dot. Bottom part of the figure shows the line-of-sight peculiar velocities with respect to the microwave background seen by the observer located at the point marked with the square. The loop induces v = 480km/s at ∼ 35h⁻¹ Mpc from the nonlinear part of the diagram - presumed location of the “strange attractor” - providing that its mass is M_s = 9 × μR_s, with Gμ/c² = 5 × 10⁻⁶. A loop with R_s ≃ 300h⁻¹ kpc deposited later, at z = 125, would result in v = 520km/s on a scale of 45h⁻¹ Mpc.