Systematic difference between ionized and molecular gas velocity dispersion in $z\sim1-2$ disks and local analogues

M. Girard; D. B. Fisher; A. D. Bolatto; R. Abraham; R. Bassett; K. Glazebrook; R. Herrera-Camus; E. Jiménez; L. Lenkić; D. Obreschkow

doi:10.3847/1538-4357/abd5b9

paper

Systematic difference between ionized and molecular gas velocity dispersion in $z \sim 1 - 2$ disks and local analogues

arXiv:2101.04122 · doi:10.3847/1538-4357/abd5b9

Abstract

We compare the molecular and ionized gas velocity dispersion of 9 nearby turbulent disks, analogues to high-redshift galaxies, from the DYNAMO sample using new ALMA and GMOS/Gemini observations. We combine our sample with 12 galaxies at $z \sim$ 0.5-2.5 from the literature. We find that the resolved velocity dispersion is systematically lower by a factor $2.45 \pm 0.38$ for the molecular gas compared to the ionized gas, after correcting for thermal broadening. This offset is constant within the galaxy disks and indicates the co-existence of a thin molecular and thick ionized gas disks. This result has a direct impact on the Toomre $Q$ and pressure derived in galaxies. We obtain pressures $\sim 0.22$ dex lower on average when using the molecular gas velocity dispersion, $σ_{0, m o l}$ . We find that $σ_{0, m o l}$ increases with gas fraction and star formation rate. We also obtain an increase with redshift and show that the EAGLE and FIRE simulations overall overestimate $σ_{0, m o l}$ at high redshift. Our results suggest that efforts to compare the kinematics of gas using ionized gas as a proxy for the total gas may overestimate the velocity dispersion by a significant amount in galaxies at the peak of cosmic star formation. When using the molecular gas as a tracer, our sample is not consistent with predictions from constant efficiency star formation models, even when including transport as a source of turbulence. Feedback models with variable star formation efficiency, $ε_{f f}$ , and/or feedback efficiency, $p_{*} / m_{*}$ , better predict our observations.

arXiv commentAccepted for publication in ApJ. 19 pages, 6 figures

Systematic difference between ionized and molecular gas velocity dispersion in $z \sim 1 - 2$ disks and local analogues

Abstract

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Systematic difference between ionized and molecular gas velocity dispersion in z∼1−2 disks and local analogues

Abstract

References in corpus (92)

Cited by in corpus (36)

Systematic difference between ionized and molecular gas velocity dispersion in $z \sim 1 - 2$ disks and local analogues