Halogas: HI observations and modeling of the nearby edge-on spiral galaxy NGC4565

Abstract

We present 21cm observations and models of the neutral hydrogen in NGC4565, a nearby, edge-on spiral galaxy, as part of the Westerbork Hydrogen Accretion in LOcal GAlaxieS survey. These models provide insight concerning both the morphology and kinematics of H I above, as well as within, the disk. NGC4565 exhibits a distinctly warped and asymmetric disk with a flaring layer. Our modeling provides no evidence for a massive, extended H I halo. We see evidence for a bar and associated radial motions. Additionally, there are indications of radial motions within the disk, possibly associated with a ring of higher density. We see a substantial decrease in rotational velocity with height above the plane of the disk (a lag) of -40+5-20 km s -1 kpc-1 and -30+5-30 km s -1 kpc-1 in the approaching and receding halves, respectively. This lag is only seen within the inner 475 (14.9kpc) on the approaching half and 425 (13.4kpc) on the receding half, making this a radially shallowing lag, which is now seen in the H I layers of several galaxies. When comparing results for NGC4565 and those for other galaxies, there are tentative indications of high star formation rate per unit area being associated with the presence of a halo. Finally, H I is found in two companion galaxies, one of which is clearly interacting with NGC4565. © 2012. The American Astronomical Society. All rights reserved.