Strong RR Lyrae excess in the Hercules-Aquila Cloud

Abstract

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° < l < 55° and -45° < b < -25°, 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.

12 pages, 9 figures, 3 tables. Accepted for publication in MNRAS

References in corpus (5)

• The Hercules-Aquila Cloud
• The QUEST RR Lyrae Survey II: The Halo Overdensities in the First Catalog
• Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey
• La Silla QUEST RR Lyrae Star Survey: Region I
• Evidence for an Overluminosity of the Variable Star RR Lyr, and a Revised Distance to the LMC

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