Ken Ichi Tadaki, Reinhard Genzel, Tadayuki Kodama, Stijn Wuyts, Emily Wisnioski, Natascha M Förster Schreiber, Andreas Burkert, Philipp Lang, Linda J. Tacconi, Dieter Lutz, Sirio Belli, Richard I. Davies, Bunyo Hatsukade, Masao Hayashi, Rodrigo Herrera-Camus, Soh Ikarashi, Shigeki Inoue, Kotaro Kohno, Yusei Koyama, J. Trevor MendelKouichiro Nakanishi, Rhythm Shimakawa, Tomoko L. Suzuki, Yoichi Tamura, Ichi Tanaka, Hannah Ubler, Dave J. Wilman

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We present 0.″2-resolution Atacama Large Millimeter/submillimeter Array observations at 870 μm for 25 Hα-seleced star-forming galaxies around the main sequence at z = 2.2-2.5. We detect significant 870 μm continuum emission in 16 (64%) of these galaxies. The high-resolution maps reveal that the dust emission is mostly radiated from a single region close to the galaxy center. Exploiting the visibility data taken over a wide uv distance range, we measure the half-light radii of the rest-frame far-infrared emission for the best sample of 12 massive galaxies with log(M /M o) > 11. We find nine galaxies to be associated with extremely compact dust emission with R 1/2,870 μm <1.5 kpc, which is more than a factor of 2 smaller than their rest-optical sizes, , and is comparable with optical sizes of massive quiescent galaxies at similar redshifts. As they have an exponential disk with Sérsic index of in the rest-optical, they are likely to be in the transition phase from extended disks to compact spheroids. Given their high star formation rate surface densities within the central 1 kpc of M o yr-1 kpc-2, the intense circumnuclear starbursts can rapidly build up a central bulge with ΣM ∗,1 kpc > 1010 M o kpc-2 in several hundred megayears, i.e., by z ∼ 2. Moreover, ionized gas kinematics reveal that they are rotation supported with an angular momentum as large as that of typical star-forming galaxies at z = 1-3. Our results suggest that bulges are commonly formed in extended rotating disks by internal processes, not involving major mergers.

Original languageEnglish
Article number135
Pages (from-to)1-10
Number of pages10
JournalAstrophysical Journal
Issue number2
Early online date9 Jan 2017
Publication statusPublished - 10 Jan 2017


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