ATCA survey of ammonia in the galactic center: The temperatures of dense gas clumps between Sgr A* and Sgr B2

Abstract

We present a large-scale, interferometric survey of ammonia (1, 1) and (2, 2) toward the Galactic center observed with the Australia Telescope Compact Array. The survey covers Δℓ1° (150 pc at an assumed distance of 8.5 kpc) and Δb0.°2 (30 pc) which spans the region between the supermassive black hole Sgr A* and the massive star forming region Sgr B2. The resolution is 20″ (0.8 pc) and emission at scales ≳ 2′ (≳ 3.2 pc) is filtered out due to missing interferometric short spacings. Consequently, the data represent the denser, compact clouds and disregards the large-scale, diffuse gas. Many of the clumps align with the 100 pc dust ring and mostly anti-correlate with 1.2 cm continuum emission. We present a kinetic temperature map of the dense gas. The temperature distribution peaks at 38 K with a width at half maximum between 18 K and 61 K (measurements sensitive within T kin10-80 K). Larger clumps are on average warmer than smaller clumps which suggests internal heating sources. Our observations indicate that the circumnuclear disk 1.5 pc around Sgr A* is supplied with gas from the 20 km s-1 molecular cloud. This gas is substantially cooler than gas 3-15 pc away from Sgr A*. We find a strong temperature gradient across Sgr B2. Ammonia column densities correlate well with SCUBA 850 μm fluxes, but the relation is shifted from the origin, which may indicate a requirement for a minimum amount of dust to form and shield ammonia. Around the Arches and Quintuplet clusters we find shell morphologies with UV-influenced gas in their centers, followed by ammonia and radio continuum layers. © 2014. The American Astronomical Society. All rights reserved..