NGC 4013 is a distinctly warped galaxy with evidence of disk-halo activity. Through deep HI observations and modeling we confirm that the HI disk is thin (central exponential scale height of with an upper limit of 4 or 280 pc), but flaring. We detect
a vertical gradient in rotation velocity (lag), which shallows radially from a value of -35 +7/-28 km/s/kpc at 1.4 (5.8 kpc), to a value of zero near R_25 (11.2 kpc). Over much of this radial range, the lag is relatively steep. Both the steepness and the radial shallowing are consistent with recent determinations for a number of edge-ons, which have been difficult to explain. We briefly consider the lag measured in NGC 4013 in the context of this larger sample and theoretical models, further illuminating disk-halo flows.
To further understand the origins of and physical processes operating in extra-planar gas, we present observations and kinematic models of HI in the two nearby, edge-on spiral galaxies NGC 3044 and NGC 4302. We model NGC 3044 as a single, thick disk.
Substantial amounts of extra-planar HI are also detected. We detect a decrease in rotation speed with height (a lag) that shallows radially, reaching zero at approximately R25. The large-scale kinematic asymmetry of the approaching and receding halves suggests a recent disturbance. The kinematics and morphology of NGC 4302, a Virgo Cluster member, are greatly disturbed. We model NGC 4302 as a combination of a thin disk and a second, thicker disk, the latter having a hole near the center. We detect lagging extra-planar gas, with indications of shallowing in the receding half, although its characteristics are difficult to constrain. A bridge is detected between NGC 4302 and its companion, NGC 4298. We explore trends involving the extra-planar HI kinematics of these galaxies, as well as galaxies throughout the literature, as well as possible connections between lag properties with star formation and environment. Measured lags are found to be significantly steeper than those modeled by purely ballistic effects, indicating additional factors. Radial shallowing of extra-planar lags is typical and occurs between 0.5R25 and R25, suggesting internal processes are important in dictating extra-planar kinematics.
We present 21-cm observations and models of the neutral hydrogen in NGC 4565, a nearby, edge-on spiral galaxy, as part of the Westerbork Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) survey. These models provide insight concerning both the morpholog
y and kinematics of HI above, as well as within, the disk. NGC 4565 exhibits a distinctly warped and asymmetric disk with a flaring layer. Our modeling provides no evidence for a massive, extended HI 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/kpc and -30 +5/-30 km s/kpc in the approaching and receding halves, respectively. This lag is only seen within the inner ~4.75 (14.9 kpc) on the approaching half and ~4.25 (13.4 kpc) on the receding, making this a radially shallowing lag, which is now seen in the HI layers of several galaxies. When comparing results for NGC 4565 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, HI is found in two companion galaxies, one of which is clearly interacting with NGC 4565.
We present 21-cm observations and models of the HI kinematics and distribution of NGC 4244, a nearby edge-on Scd galaxy observed as part of the Westerbork Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) survey. Our models give insight into the HI kine
matics and distribution with an emphasis on the potential existence of extra-planar gas as well as a negative gradient in rotational velocity with height above the plane of the disk (a lag). Our models yield strong evidence against a significantly extended halo and instead favor a warp component along the line of sight as an explanation for some of the observed thickening of the disk. Based on these models, we detect a lag of -9 +3/-2 km s-1 kpc-1 in the approaching half and -9 +/-2 km s-1 kpc-1 in the receding half. This lag decreases in magnitude to -5+/-2 km s-1 kpc-1 and -4+/-2 km s-1 kpc-1 near a radius of 10 kpc in the approaching and receding halves respectively. Additionally, we detect several distinct morphological and kinematic features including a shell that is probably driven by star formation within the disk.
