Clumpy and Extended Starbursts in the Brightest Unlensed Submillimeter Galaxies

TL;DR

This study uses high-resolution ALMA imaging to reveal complex, clumpy, and extended starburst structures in three of the brightest unlensed submillimeter galaxies at z=3-4, indicating intense, localized star formation possibly driven by galaxy mergers.

Contribution

First detailed high-resolution ALMA observations of the central structures in bright unlensed submillimeter galaxies, revealing complex clumpy and extended starburst regions.

Findings

Central regions contain multiple ~200 pc clumps with high star formation rate densities.

68-90% of emission is extended over >1 kpc, indicating widespread star formation.

Luminosity surface densities are similar to local ULIRGs, suggesting intense starburst activity.

Abstract

The central structure in three of the brightest unlensed z=3-4 submillimeter galaxies are investigated through 0.015" - 0.05" (120 -- 360~pc) 860 micron continuum images obtained using the Atacama Large Millimeter/submillimeter Array (ALMA). The distribution in the central kpc in AzTEC1 and AzTEC8 are extremely complex, and they are composed of multiple ~200 pc clumps. AzTEC4 consists of two sources that are separated by ~1.5 kpc, indicating a mid-stage merger. The peak star formation rate densities in the central clumps are ~300 - 3000 Msun/yr/kpc^2, suggesting regions with extreme star formation near the Eddington Limit. By comparing the flux obtained by ALMA and Submillimeter Array (SMA), we find that 68-90% of the emission is extended (> 1 kpc) in AzTEC 4 and 8. For AzTEC1, we identify at least 11 additional compact (~200 pc) clumps in the extended 3 - 4 kpc region. Overall, the data presented here suggest that the luminosity surface densities observed at < 150 pc scales are roughly similar to that observed in local ULIRGs, as in the eastern nucleus of Arp 220. Between 10 to 30% of the 860 micron continuum is concentrated in clumpy structures in the central kpc while the remaining flux is distributed over > 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.