Searching for the Progenitor Galaxy of Omega Centauri Using RR Lyrae Spectra

Abstract

Radial velocities of 32 RR Lyrae stars from the Catalina Real-time Transient Survey in the neighborhood of Omega Centauri were measured from low-resolution spectra taken by the Goodman Spectrograph on SOAR, Cerro Pachón, Chile. An over-density of stars with the same velocity as the cluster would imply that these stars were once part of ω Cen but have since been tidally stripped, supporting the hypothesis that ω Cen is the remain of a nucleated dwarf galaxy. This study is the most complete of any one similar, covering an area of 100 sq. degrees around the cluster and using RR Lyrae stars known to have similar distance to the cluster. Statistical tests comparing the distribution of RR Lyrae velocities to the expected distribution of velocities of halo stars show no over-density of stars at the velocity of ω Cen or any other velocity, discarding the presence of any substructure in this part of the sky....