CLUMPY AND EXTENDED STARBURSTS IN THE BRIGHTEST UNLENSED SUBMILLIMETER GALAXIES

摘要

The central structure in three of the brightest unlensed z = 3-4 submillimeter galaxies is investigated through 0".015-0".05 (120-360 pc) 860 mu m continuum images obtained using the Atacama Large Millimeter/submillimeter Array ( ALMA). The distribution in the central kiloparsec in AzTEC1 and AzTEC8 is extremely complex, and they are composed of multiple similar to 200 pc clumps. AzTEC4 consists of two sources that are separated by similar to 1.5 kpc, indicating a mid-stage merger. The peak star formation rate densities in the central clumps are similar to 300-3000Me yr(-1) kpc(-2), suggesting regions with extreme star formation near the Eddington limit. By comparing the flux obtained by ALMA and Submillimeter Array, we find that 68%-90% of the emission is extended (greater than or similar to 1 kpc) in AzTEC4 and 8. For AzTEC1, we identify at least 11 additional compact (similar to 200 pc) clumps in the extended 3-4 kpc region. Overall, the data presented here suggest that the luminosity surface densities observed at less than or similar to 150 pc scales are roughly similar to that observed in local ULIRGs, as in the eastern nucleus of Arp 220. Between 10% and 30% of the 860 mu m continuum is concentrated in clumpy structures in the central kiloparsec, while the remaining flux is distributed over greater than or similar to 1 kpc regions, some of which could also be clumpy. These sources can be explained by a rapid inflow of gas such as a merger of gas-rich galaxies, surrounded by extended and clumpy starbursts. However, the cold mode accretion model is not ruled out.