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The Hercules Thick Disk Cloud (Larsen et al. 2008) was initially discoveredas an excess in the number of faint blue stars between quadrants 1 and 4 of theGalaxy. The origin of the Cloud could be an interaction with the disk bar, atriaxial thick disk or a merger remnant or stream. To better map the spatialextent of the Cloud along the line of sight, we have obtained multi-color UBVRphotometry for 1.2 million stars in 63 fields approximately 1 square degreeeach. Our analysis of the fields beyond the apparent boundaries of the excesshave already ruled out a triaxial thick disk as a likely explanation (Larsen,Humphreys and Cabanela 2010) In this paper we present our results for the starcounts over all of our fields, determine the spatial extent of the over densityacross and along the line of sight, and estimate the size and mass of theCloud. Using photometric parallaxes, the stars responsible for the excess arebetween 1 and 6 kiloparsecs from the Sun, 0.5 -- 4 kpc above the Galacticplane, and extends approximately 3-4 kiloparsecs across our line of sight. Itis thus a major substructure in the Galaxy. The distribution of the excessalong our sight lines corresponds with the density contours of the bar in theDisk, and its most distant stars are directly over the bar. We also see throughthe Cloud to its far side. Over the entire 500 square degrees of sky containingthe Cloud, we estimate more than 5.6 million stars and 1.9 million solar massesof material. If the over density is associated with the bar, it would exceed1.4 billion stars and more than than 50 million solar masses. Finally, we arguethat the Hercules-Aquila Cloud (Belokurov et al. 2007) is actually the HerculesThick Disk Cloud.

Mapping the Asymmetric Thick Disk: II Distance, Size and Mass of the Hercules Thick Disk Cloud