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تسجيل مستخدم جديدKinematic Downsizing at z~2
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We present results from a survey of the internal kinematics of 49 star-forming galaxies at z$,sim,$2 in the CANDELS fields with the Keck/MOSFIRE spectrograph (SIGMA, Survey in the near-Infrared of Galaxies with Multiple position Angles). Kinematics (rotation velocity $V_{rot}$ and integrated gas velocity dispersion $sigma_g$) are measured from nebular emission lines which trace the hot ionized gas surrounding star-forming regions. We find that by z$,sim,$2, massive star-forming galaxies ($log,M_*/M_{odot}gtrsim10.2$) have assembled primitive disks: their kinematics are dominated by rotation, they are consistent with a marginally stable disk model, and they form a Tully-Fisher relation. These massive galaxies have values of $V_{rot}/sigma_g$ which are factors of 2-5 lower than local well-ordered galaxies at similar masses. Such results are consistent with findings by other studies. We find that low mass galaxies ($log,M_*/M_{odot}lesssim10.2$) at this epoch are still in the early stages of disk assembly: their kinematics are often supported by gas velocity dispersion and they fall from the Tully-Fisher relation to significantly low values of $V_{rot}$. This kinematic downsizing implies that the process(es) responsible for disrupting disks at z$,sim,$2 have a stronger effect and/or are more active in low mass systems. In conclusion, we find that the period of rapid stellar mass growth at z$,sim,$2 is coincident with the nascent assembly of low mass disks and the assembly and settling of high mass disks.
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