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Tadaki, Ken-ichi; Genzel, Reinhard; Kodama, Tadayuki; Wuyts, Stijn; Wisnioski, Emily; Förster Schreiber, Natascha M; Burkert, Andreas; Lang, Philipp; Tacconi, Linda J.; Lutz, Dieter; Belli, Sirio; Davies, Richard I.; Hatsukade, Bunyo; Hayashi, Masao; Herrera-Camus, Rodrigo; Ikarashi, Soh; Inoue, Shigeki; Kohno, Kotaro; Koyama, Yusei; Mendel, J. Trevor; Nakanishi, Kouichiro; Shimakawa, Rhythm; Suzuki, Tomoko L.; Tamura, Yoichi; Tanaka, Ichi; Übler, Hannah; Wilman, Dave J. (2017): Bulge-forming galaxies with an extended rotating disk at z similar to 2. In: Astrophysical Journal, Vol. 834, No. 2, 135
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We present 0."2-resolution Atacama Large Millimeter/submillimeter Array observations at 870 mu m for 25 H alpha-seleced star-forming galaxies around the main sequence at z = 2.2-2.5. We detect significant 870 mu m 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-circle dot) > 11. We find nine galaxies to be associated with extremely compact dust emission with R-1/2,R-870 mu m < 1.5 kpc, which is more than a factor of 2 smaller than their rest-optical sizes, < R-1/2,R-1.6 mu m > = 3.2 kpc, and is comparable with optical sizes of massive quiescent galaxies at similar redshifts. As they have an exponential disk with Sersic index of < n(1.6 mu m)> = 1.2 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 <Sigma SFR1 kpc >= 40 M-circle dot yr (1) kpc (2), the intense circumnuclear starbursts can rapidly build up a central bulge with Sigma M-*,M-1 kpc > 10(10) M-circle dot kpc(-2) in several hundred megayears, i.e., by z similar to 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.