Galaxy formation with cosmic strings and massive neutrinos

Abstract

A detailed calculation of the growth of linear density perturbations induced by a loop of cosmic string in a universe presently dominated by light massive neutrinos is presented. The constant pulling of the cosmic string overcomes free-streaming damping so that cosmological structure develops in a bottom-up fashion different from hot dark matter scenarios without cosmic strings. An accurate semianalytic method for evolving the spherical perturbation around a loop through the collapse stage is developed. Applying this method, it is shown that halos with flat rotation curves form with circular rotation speed of about 50 km/s or greater. The Tremaine and Gunn phase-space constraint limits the compactness of the neutrino halos so that this scenario cannot explain dwarf spheroidals with compact dark halos. The galaxy luminosity function is estimated from the loop size distribution by applying the Faber-Jackson relation to the calculated rotation speeds, and good agreement is found with a Schechter function of slope alpha = 1.4. 59 references.