2005/09/08 by G. H. Heald, G. Heald, Richard J. Rand +6
Physics and Astronomy · #Astrophysics #Astrophysics and Star Formation Studies #Asymmetry #Azimuth #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy rotation curve #Geometry #Halo #Mechanics #Optics #Physics #Rotation (mathematics) #Spiral galaxy #Stellar, planetary, and galactic studies #Velocity gradient #astro-ph
paper · pdf · doi:10.1086/497902
published as Astrophys.J.636:181-199,2005 · 18 pages, 18 figures. Uses emulateapj.cls. Accepted for publication in ApJ
arxiv created 2005/09/08 · openalex publication_date 2005/12/21 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
We present imaging Fabry-Perot observations of Hα emission in the nearly edge-on spiral galaxy NGC 5775. We have derived a rotation curve and a radial density profile along the major axis by examining position-velocity (PV) diagrams from the Fabry-Perot data cube, as well as a CO 2-1 data cube from the literature. PV diagrams constructed parallel to the major axis are used to examine changes in azimuthal velocity as a function of height above the midplane. The results of this analysis reveal the presence of a vertical gradient in azimuthal velocity. The magnitude of this gradient is approximately 1 km s -1 arcsec -1 , or about 8 km s -1 kpc -1 , although a higher value of the gradient may be appropriate in localized regions of the halo. The evidence for an azimuthal velocity gradient is much stronger for the approaching half of the galaxy, although earlier slit spectra are consistent with a gradient on both sides. There is evidence for an outward radial redistribution of gas in the halo. The form of the rotation curve may also change with height, but this is not certain. We compare these results with those of an entirely ballistic model of a disk-halo flow. The model predicts a vertical gradient in azimuthal velocity that is shallower than the observed gradient, indicating that an additional mechanism is required to further slow the rotation speeds in the halo.