Kinematic modelling of disk galaxies

Abstract

This is the second of a series of papers in which the kinematics of disk galaxies is studied by analysing spectroscopic data. Making use of the methods presented in Paper I, this work focuses on the large-scale distribution of disk and Dark Matter halo material by analysing the structure of warped galaxies. H i observations of three disk galaxies showing regular large-scale ("grand-design") warps are presented and their structure is analysed. The kinematics and geometry of the galaxies are modelled by fitting a tilted-ring model directly to the data cube, thereby avoiding problems due to orbit crowding or beam smearing.The galaxies follow the previously known "rules for the behaviour of warps". Furthermore, at large radii the H i disk settles into a relatively coplanar disk that is inclined with respect to the inner one. With increasing radius, the measured rotation velocity shows a rise. In one of the cases, NGC 5204, the rotation curve shows a jump at the transition radius. While the best fits in the other two cases also suggest that such a jump is present, the change in rotation velocity is compatible with a gradual rise. In two cases, the surface density of the warped H i layer shows a clear drop at the transition radius and decreases only very slowly further out, while this feature is not as clear for UGC 3580. A literature search shows that these properties are shared by a number of other galaxies. In all cases, an additional, slowly rotating gas layer is found to be present. The change in the rotation velocity and the remarkable geometry of the disks together indicate that the radius at which the warp starts marks the transition between two dynamical regimes, an inner one governed by the stellar disk and an outer one determined by the Dark Matter halo.

Outer and inner mass distributions of the irregular galaxies UGC 4284 and UGC 11861: constraining the baryonic content through stellar population synthesis studies

“…Kandalian & Kalloghlian (1998), Chapelon et al (1999) and Cabrera-Lavers & Garzón (2004) found evidence of a central isophotal distortion that they explain postulating the existence of a bar with diameter of 38 . Other authors did not confirm the presence of a bar in UGC 4284, nevertheless they encountered non-circular and off-plane gas motion in the inner region of UGC 4284 that they discuss as originated by a warped gaseous disk (Coccato et al 2004;Józsa 2007). Bearing in mind the purpose of the present study it is important to determine which kind of baryonic components do actually exist for UGC 4284, and given the incongruity of the above reported results we required to perform 2D isophotal analysis of the surface brightness of this galaxy, using GAL-FIT (Peng et al 2002(Peng et al , 2010) and considering at least three principal components: disk, bulge and bar.…”

Warps and Accretion

“…Indeed, Van der Kruit (2007) points out that often rotation curves show a sharp decline at the onset of the warp, while he explains this feature with a drop in the mass-surface density of the stellar disk. However, Józsa (2007) observes a distinct increase of the rotation velocity in the warped region in a sample of three disk galaxies, which certainly cannot be explained by a drop in the stellar surface-mass density. In M33, a similar increase at the onset of the warp is observed (Corbelli & Schneider 1997).…”

“…Indeed, it has been remarked that anomalous gas is observed in warped disks. Józsa (2007) finds anomalous gas to be present in three galaxies selected to show a prototype symmetric warp. Certainly, these findings do not allow to draw a direct connection of warping properties of galaxies and the existence of anomalous gas.…”

“…Detailed studies of the structure of warps hint at the fact that warps are quite longlived Briggs 1990, Józsa 2007. However, theoretical attempts to describe warps in a self-contained manner, in closed-box models consisting of a disk and an optional (misaligned) Dark Matter halo, without the need of external agents, have failed to explain the observations so far or fail in follow-up studies adding additional complexities (LyndenBell 1965, Hunter & Toomre 1969, Dekel & Shlosman 1983, Sparke & Casertano 1988, Kuijken 1991, Revaz & Pfenninger 2004, Nelson & Tremaine 1995, Dubinski & Kuijken 1995.…”

Structure and kinematics of the nearby dwarf galaxy UGCA 105

“…Some evidence for lagging, extraplanar gas in low-mass galaxies (NGC 2541, NGC 5204, UGC 3580) has been found by Józsa (2007). Kamphuis et al (2011) stated in a more detailed study of the H  structure of the dIrr UGC 1281 that a definite conclusion is not possible for UGC 1281 and that a faceon warp of the disk could reproduce the data as well as slowly rotating extraplanar gas, a lagging disk.…”