The EDGE-CALIFA Survey: Molecular and Ionized Gas Kinematics in Nearby Galaxies

We present a comparative study of molecular and ionized gas kinematics in nearby galaxies. These results are based on observations from the EDGE survey, which measured spatially resolved CO(J = 1-0) in 126 nearby galaxies. Every galaxy in EDGE has corresponding resolved ionized gas measurements from CALIFA. Using a sub-sample of 17 rotation-dominated, star-forming 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 R . We find that ∼75% of our sample galaxies have smaller ionized gas rotation velocities than the molecular gas 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 the lower ionized gas rotation velocity can be attributed to a significant contribution from extraplanar diffuse ionized gas in a thick, turbulence-supported disk. Using observations of the Hγ transition, also available from CALIFA, we measure ionized gas velocity dispersions and find that these galaxies have sufficiently large velocity dispersions to support a thick ionized gas disk. Kinematic simulations show that a thick disk with a vertical rotation velocity gradient can reproduce the observed differences between the CO and Hα rotation velocities. Observed line ratios tracing diffuse ionized gas are elevated compared to typical values in the midplane of the Milky Way. In galaxies affected by this phenomenon, dynamical masses measured using ionized gas rotation curves will be systematically underestimated. © 2018. The American Astronomical Society. All rights reserved..R.C.L. would like to thank Filippo Fraternali and Federico Lelli for useful discussions and advice. The authors would also like to thank the anonymous referee for constructive comments. R.C.L. and A.D.B. acknowledge support from the National Science Foundation (NSF) grants AST-1412419 and AST-1615960. A.D.B. also acknowledges visiting support by the Alexander von Humboldt Foundation. P.T. and S.N.V. acknowledge support from NSF AST-1615960. S.F.S. acknowledges the PAPIIT-DGAPA-IA101217 project and CONACYT-IA-180125. R.G.B. acknowledges support from grant AYA2016-77846-P. L.B. and D.U. are supported by the NSF under grants AST-1140063 and AST-1616924. D.C. acknowledges support by the Deutsche Forschungsgemeinschaft (German Research Foundation, or DFG) through project number SFB956C. T.W. acknowledges support from the NSF through grants AST-1139950 and AST-1616199. This study makes use of data from the EDGE (http://www.astro.umd.edu/EDGE/) and CALIFA (http://califa.caha.es/) surveys and numerical values from the HyperLeda database (http://leda.univ-lyon1.fr). Support for CARMA construction was derived from the Gordon and Betty Moore Foundation, the Kenneth T. and Eileen L. Norris Foundation, the James S. McDonnell Foundation, the Associates of the California Institute of Technology, the University of Chicago, the states of California, Illinois, and Maryland, and the NSF. CARMA development and operations were supported by the NSF under a cooperative agreement and by the CARMA partner universities. This research is based on observations collected at the Centro Astronomico Hispano-Aleman (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut fur Astronomie (MPA) and the Instituto de Astrofisica de Andalucia (CSIC). The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc

The EDGE-CALIFA Survey: Molecular and Ionized Gas Kinematics in Nearby Galaxies

We present a comparative study of molecular and ionized gas kinematics in nearby galaxies. These results are based on observations from the EDGE survey, which measured spatially resolved 12CO(J = 1-0) in 126 nearby galaxies. Every galaxy in EDGE has corresponding resolved ionized gas measurements from CALIFA. Using a sub-sample of 17 rotation- dominated, star-forming 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 R e . We find that ̃75% of our sample galaxies have smaller ionized gas rotation velocities than the molecular gas 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 the lower ionized gas rotation velocity can be attributed to a significant contribution from extraplanar diffuse ionized gas in a thick, turbulence-supported disk. Using observations of the Hγ transition, also available from CALIFA, we measure ionized gas velocity dispersions and find that these galaxies have sufficiently large velocity dispersions to support a thick ionized gas disk. Kinematic simulations show that a thick disk with a vertical rotation velocity gradient can reproduce the observed differences between the CO and Hα rotation velocities. Observed line ratios tracing diffuse ionized gas are elevated compared to typical values in the midplane of the Milky Way. In galaxies affected by this phenomenon, dynamical masses measured using ionized gas rotation curves will be systematically underestimated