Kinematic Downsizing at z~2

Raymond C. Simons; Susan A. Kassin; Jonathan R. Trump; Benjamin J. Weiner; Timothy M. Heckman; Guillermo Barro; David C. Koo; Yicheng Guo; Camilla Pacifici; Anton Koekemoer; Andrew W. Stephens

doi:10.3847/0004-637X/830/1/14

paper

Kinematic Downsizing at z~2

arXiv:1606.00009 · doi:10.3847/0004-637X/830/1/14

Abstract

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 $V_{r o t}$ and integrated gas velocity dispersion $σ_{g}$ ) 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 ( $lo g M_{*} / M_{⊙} ≳ 10.2$ ) 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 $V_{r o t} / σ_{g}$ 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 ( $lo g M_{*} / M_{⊙} ≲ 10.2$ ) 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 $V_{r o t}$ . 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.

21 pages, 9 figures, 2 tables, submitted to ApJ

Kinematic Downsizing at z~2

Abstract

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