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2021 ASROC Annual Meeting
National Chiayi University
May 21~23

Abstract

What causes the velocity discrepancy between CO and Hα rotation curves in nearby galaxies?

[ Oral ]

Yung-Chau Su (NTU/ASIAA); Lihwai Lin (ASIAA); Hsi-An Pan (MPIA);Bau-Ching Hsieh (ASIAA); Sebastian Sanchez (IAU); Carlos López Cobá (UNAM); Mallory Thorp (UVic); Sara Ellison (UVic)

We compare the CO(J=1-0) and Hα kinematics in 34 nearby galaxies, selected from the ALMaQUESTand EDGE-CALIFA surveys. We use 3-D Barolo, a 3D tilted ring model, to derive the CO and Hα rotation curves. Our result shows that ~65% (22/34) of our galaxies present slower Hα rotations compared to the CO rotations. The remaining galaxies (12/34) show consistent CO-Hα rotations within uncertainties. The median value of velocity differences between the CO and Hα is ~11.0km/s. For a circular velocity of 200 km/s (the median value in our sample), such a velocity difference underestimates the total dynamical mass by ~10%. Furthermore, the velocity difference between the CO and Hα rotations is found to correlate with the velocity dispersion difference between CO and Hα, suggesting that the pressure gradient plays a role in this phenomenon. After correcting for the asymmetric drift effect to our sample, the median value of the velocity differences decreases to 4.6km/s, which intern reduces the underestimation of dynamical mass to ~4.5%. Finally, by using the EW(Hα) as an indicator of the relative abundance of extra-planar diffuse ionized gas (eDIG), we analyze the samples which are thought to potentially have a negligible abundance of eDIG. In these samples, the underestimation of dynamical mass was reduced to ~1.5% based on the Hα rotation curves after asymmetric drift correction. This result suggests that the presence of eDIG also contributes to the velocity differences between CO and Hα rotations.