A non-corotating gas component in an extreme starburst at z = 4.3

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Tadaki, Ken-ichi; Iono, Daisuke; Yun, Min S.; Aretxaga, Itziar; Hatsukade, Bunyo;  Lee, Minju M.; Michiyama, Tomonari; Nakanishi, Kouichiro; Saito, Toshiki; Ueda, Junko; Umehata, Hideki

Accepted for publication in Astrophysical Journal (arXiv: 2001.04638v1)


We report the detection of a non-corotating gas component in a bright unlensed submillimeter galaxy at z=4.3, COSMOS-AzTEC-1, hosting a compact starburst. ALMA 0.17 and 0.09 arcsec resolution observations of [CII] emission clearly demonstrate that the gas kinematics is characterized by an ordered rotation. After subtracting the best-fit model of a rotating disk, we kinematically identify two residual components in the channel maps. Both observing simulations and analysis of dirty images confirm that these two subcomponents are not artificially created by noise fluctuations and beam deconvolution. One of the two has a velocity offset of 200 km/s and a physical separation of 2 kpc from the primary disk and is located along the kinematic minor axis of disk rotation. We conclude that this gas component is falling into the galaxy from a direction perpendicular to the disk rotation. The accretion of such small non-corotating gas components could stimulate violent disk instability, driving radial gas inflows into the center of galaxies and leading to formation of in-situ clumps such as identified in dust continuum and CO. We require more theoretical studies on high gas fraction mergers with mass ratio of 1:>10 to verify this process.

[C ii] channel maps, the best-fit models and the residuals.
[C II] channel maps, best-fit (disk) models and the residuals are shown in the velocity range from −225 km s−1 to +225 km s−1. The image size is 1′′×1′′. Contours are plotted every 2sigma from 3sigma. Stars and crosses mark the positions of [C II] subcomponents and dust clumps, respectively.

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