COMPACT STARBURSTS IN –6 SUBMILLIMETER GALAXIES REVEALED BY ALMA.

We report the source size distribution, as measured by ALMA millimetric continuum imaging, of a sample of 13 AzTEC-selected submillimeter galaxies (SMGs) at –6. Their infrared luminosities and star formation rates (SFRs) are 2– and ∼200–600 yr⁻¹, respectively. The sizes of these SMGs range from 0.″10 to 0.″38, with a median of 0.″20 (FWHM), corresponding to a median circularized effective radius () of kpc, comparable to the typical size of the stellar component measured in compact quiescent galaxies at (cQGs)— kpc. The median surface SFR density of our SMGs is yr⁻¹ kpc⁻², comparable to that seen in local merger-driven (U)LIRGs rather than in extended disk galaxies at low and high redshifts. The discovery of compact starbursts in SMGs strongly supports a massive galaxy formation scenario wherein –6 SMGs evolve into the compact stellar components of cQGs. These cQGs are then thought to evolve into the most massive ellipticals in the local universe, mostly via dry mergers. Our results thus suggest that SMGs are the likely progenitors of massive local ellipticals, via cQGs, meaning that we can now trace the evolutionary path of the most massive galaxies over a period encompassing ∼90% of the age of the universe. [ABSTRACT FROM AUTHOR]