The Galactic Center Molecular Zone From l = -10 to 10 degrees at 1.1 mm in the Dust Continuum

The 1.1 mm dust continuum in the inner 20 square degrees of our Galaxy is analyzed using the Bolocam Galactic Plane Survey (BGPS). The central two degrees constitutes the brightest portion of the Galactic plane at 1.1 mm. Over 95% of the emission is associated with dense gas traced by CS, HCN, and HCO⁺ in the central 200 pc of the Galaxy. Near l = 0 degrees, the scale-height of the Galactic center population is an order-of-magnitude smaller and the mean surface brightness is an order of magnitude greater than the inner Molecular Ring along this line-of-sight. The scale-height increases and the average surface brightness decreases away from Sgr A, especially towards l = 1.5 degrees. In addition to compact cores, 1.1 mm emission traces an extensive network of fainter filaments, cavities, and molecular cloud rims. Comparison with MSX and Spitzer infrared images shows that nearly 30% of the BGPS cores at positive longitudes are associated with infrared dark clouds (IRDCs) at 3.5 to 6 μm. These cores must be in front of the Galactic bulge stars, consistent with being located in a major dust lane at the leading edge of the stellar bar whose positive longitude side is closer to the Sun. About 20% of the BGPS features are associated with 8 μm PAHs emission from the surfaces of clouds irradiated by the ambient radiation field. Some filaments in the inner molecular zone trace warm cloud edges while others are associated with the walls of cavities containing HII regions and supernova remnants. We speculate that the majority of cavities not associated with known objects trace the fossil remnants of extinct HII regions and SNR.