Origin of the Cartwheel Galaxy: Disk Instability?

Abstract

The linear theory and N -body simulations are used to present a new, alternative model of the galaxy A0035-324 (the "Cartwheel"), which is the most striking example of the relatively small class of ring galaxies. The model is based on the gravitational Jeans-type instability of both axisymmetric (radial) and nonaxisymmetric (spiral) small-amplitude gravity perturbations (e.g., those produced by spontaneous disturbances) of a dynamically cold subsystem (identified as the gaseous component) of an isolated disk galaxy. The simplified model of a galaxy is used in which stars (and a dark matter, if it exists at all) do not participate in the disk collective oscillations and just form a background charge. In the theory presented here, a case for both purely radial solutions and purely spiral solutions to the equations of motion of an infinitesimally thin gaseous disk is made, which is associated with both a radial density wave and a dominant spiral density wave which propagate outwards creating a rough ring and a number of spiral arms. Through three-dimensional numerical simulation of a collisionless set of many particles, I associate these gravitationally unstable axisymmetric waves and nonaxisymmetric waves with growing clumps of matter which take on the appearance of a ring and spokes of mass blobs.

Gravitationally unstable gaseous disks of flat galaxies

“…Sufficient temperature (the sound speed c s (2Ω/κ)c T ≈ 2c T , or Toomre's stability parameter Q = 2−2.5, respectively) and core-dominated exponential-like mass density distribution prevent the Jeans instability from occurring. The secular evolution of disk galaxies, therefore, proceeds in the direction of increasing central mass concentration in the baryonic material, of extending outer portions, and of dynamical heating of the galactic material (see also Griv et al 2002 andGriv &Gedalin 2004 for a discussion). The diffusion in configuration space is due entirely to the almost aperiodic (in a rotating frame) growth of the nonresonant Jeans-unstable disturbances in a self-gravitating system subject to a time-dependent potential.…”

Stability of galactic discs: finite arm-inclination and finite-thickness effects★

“…1 therein), Snytnikov et al (2004, fig. 4 therein), Griv (2005), Alexander et al (2008), Cuzzi, Hogan & Shariff (2008), Cossins, Lodato & Clarke (2009), and Cai et al (2010).…”

Angular Momentum Transport in Astrophysical Disks

“…0 * J eters of the disk determine the pattern speed of growing nonaxisymmetric perturbations (in a rotating frame): and it should almost instantaneously (see below for a time estimate) take the form of a cartwheel (Griv 2005). Clearly, in the latter case of both ring and spiral excitation, the distribution of the surface density along the spiral arms is not uniform, but describes a sequence of maxima that might be identified with forming giant gaseous complexes in galaxies or with giant to the minimum on the dispersion curve given by eq.…”

“…This dynamical instability is driven by a strong nonresonant interaction of the gravity fluctuations with the bulk of the particle population, and the dynamics of Jeans perturbations can be characterized as a nonresonant interaction: in equation (7), and q ‫ע‬ lk ( 0 l p * . One concludes that Toomre's Q-parameter, , of 0, 1 Q p c /c s T !1 suggests that the disk is likely to be subject to both radial and spiral instabilities and might therefore be clumpy (Griv 2005). Contrarily, if the uncooled disk is thin and warm, but (or , respectively),…”