We map the large-scale sub-structure in the Galactic stellar halo using accurate 3D positions of ~14,000 RR Lyrae reported by the Catalina Sky Survey. In the heliocentric distance range of 10-25 kpc, in the region of the sky approximately bounded by 30{\deg} < l < 55{\deg} and -45{\deg} < b < -25{\deg}, there appears to be a strong excess of RRab stars. This overdensity, peaking at 18 kpc, is most likely associated with the so-called Hercules-Aquila Cloud, previously detected using Main Sequence tracers at similar distances in the Sloan Digital Sky Survey data. Our analysis of the period-amplitude distribution of RR Lyrae in this region indicates that the HAC is dominated by the Oosterhoff I type population. By comparing the measured RR Lyrae number density to models of a smooth stellar halo, we estimate the significance of the observed excess and provide an updated estimate of the total luminosity of the Cloud's progenitor.
@article{arxiv.1401.4354,
title = {Strong RR Lyrae excess in the Hercules-Aquila Cloud},
author = {Iulia T. Simion and Vasily Belokurov and Mike Irwin and Sergey E. Koposov},
journal= {arXiv preprint arXiv:1401.4354},
year = {2014}
}
Comments
12 pages, 9 figures, 3 tables. Accepted for publication in MNRAS