The EDGE-CALIFA Survey: Molecular and Ionized Gas Kinematics in Nearby Galaxies
Abstract
We present a systematic comparative study of molecular and ionized gas kinematics in galaxies, the first time such a comparison has been done for a large sample. These results are based on observations obtained by the EDGE survey, which measured spatially resolved 12CO(J=1-0) in 126 nearby galaxies at a typical spatial resolution of ~1.5 kpc. Every galaxy in EDGE has corresponding resolved ionized gas measurements from CALIFA, with a typical spatial resolution of ~1 kpc. Using a sub-sample of 17 galaxies where precise molecular gas rotation curves could be extracted, we derive CO and Hα rotation curves using the same geometric parameters out to ≥ 1 Re and compare their kinematics. We find that ~80% of our sample have smaller ionized rotation velocities than the molecular gas rotation velocities in the outer part of the rotation curve. In no case is the molecular gas rotation velocity measurably lower than that of the ionized gas. We suggest that this is due to extraplanar diffuse ionized gas in a thick, pressure supported disk which rotates more slowly with increasing height off the plane. Using the high spectral resolution observations available from CALIFA for the same galaxies, we measure Hγ velocity dispersions. We find that the galaxies in our subsample have sufficiently large ionized gas velocity dispersions to support a thick ionized gas disk. We perform kinematic simulations of thick disks and show that a thick disk with a vertical velocity gradient can reproduce the observed differences between the CO and Hα rotation velocities. There are no trends in the difference between the CO and Hα rotation velocities with global parameters, such as inclination, star formation rate, or morphology. We note, however, that nearly all of our galaxies exceed the star formation rate per unit area needed to have an extended diffuse ionized phase.
- Publication:
-
American Astronomical Society Meeting Abstracts #231
- Pub Date:
- January 2018
- Bibcode:
- 2018AAS...23113001L