ALMA 200 pc Resolution Imaging of Smooth Cold Dusty Disks in Typical z similar to 3 Star-forming Galaxies

Rujopakarn, W., Daddi, E., Rieke, G. H., Puglisi, A., Schramm, M., Pérez González, P. G., Magdis, G. E., Alberts, S., Bournaud, F., Elbaz, D., Franco, M., Kawinwanichakij, L., Kohno, K., Narayanan, D., Silverman, J. D., Wang, T., Williams, C. C. 2019. ALMA 200 pc Resolution Imaging of Smooth Cold Dusty Disks in Typical z similar to 3 Star-forming Galaxies. Astrophysical Journal 882, 2 DOI: 10.3847/1538-4357/ab3791

We present high-fidelity, 30 mas (200 pc) resolution ALMA rest-frame 240 mu m observations of cold dust emission in three typical main-sequence star-forming galaxies (SFGs) at z similar to 3 in the Hubble Ultra-Deep Field (HUDF). The cold dust is distributed within the smooth disklike central regions of star formation 1-3 kpc in diameter, despite their complex and disturbed rest-frame UV and optical morphologies. No dust substructures or clumps are seen down to similar or equal to 1-3 M-circle dot yr(-1) (1 sigma) per 200 pc beam. No dust emission is observed at the locations of UV-emitting clumps, which lie similar or equal to 2-10 kpc from the bulk of star formation. Clumpy substructures can contribute no more than 1%-7% of the total star formation in these galaxies (3 sigma upper limits). The lack of star-forming substructures in our HUDF galaxies is to be contrasted with the multiple substructures characteristic of submillimeter-selected galaxies (SMGs) at the same cosmic epoch, particularly the far-IR-bright SMGs with similarly high-fidelity ALMA observations of Hodge et al. Individual star-forming substructures in these SMGs contain similar to 10%-30% of their total star formation. A substructure in these SMGs is often comparably bright in the far-infrared to (or in some cases brighter than) our typical SFGs, suggesting that these SMGs originate from a class of disruptive events involving multiple objects at the scale of our HUDF galaxies. The scale of the disruptive event found in our main-sequence SFGs, characterized by the lack of star-forming substructures at our resolution and sensitivity, could be less violent, e.g., gas-rich disk instability or minor mergers.

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