Molecular Loops in the Galactic Center: Evidence for Magnetic Flotation

Abstract

The central few hundred parsecs of the Milky Way host a massive black hole and exhibit very violent gas motion and high temperatures in molecular gas. The origin of these properties has been a mystery for the past four decades. Wide-field imaging of the (12)CO (rotational quantum number J = 1 to 0) 2.6-millimeter spectrum has revealed huge loops of dense molecular gas with strong velocity dispersions in the galactic center. We present a magnetic flotation model to explain that the formation of the loops is due to magnetic buoyancy caused by the Parker instability. The model has the potential to offer a coherent explanation for the origin of the violent motion and extensive heating of the molecular gas in the galactic center.

Stochastic non-circular motion and outflows driven by magnetic activity in the Galactic bulge region

“…The model may not be fully appropriate as the interpretation from an observational point. First, the bar potential alone is not able to create high-b features up to 200 pc above the plane; these loops are better explained by the Parker instability (Fukui et al 2006). There is no other driving mechanism known to expel gas up to that height by only stellar gravity.…”

“…In fact, Fukui et al (2006) discovered two large molecular loops, loop 1 and loop 2, at a radius of 700-pc from the center, which are triggered by magnetic buoyancy (Parker instability;Parker 1966); while the main focus in Parker (1966) was aimed at the Galactic disk, he already suggested that the magnetic activity might become even more important in the central few 100 pc. Subsequently, Fujishita et al (2009);Torii et al (2010a,b); Riquelme et al (2010); Kudo et al (2011) presented analyses of more detailed observational properties of these molecular loops, and it was shown that the molecular loops are also well reproduced by magneto-hydrodynamical (MHD, hereafter) simulations (Shibata & Matsumoto 1991;Machida et al 2009;Takahashi et al 2009).…”

“…One can see turbulent poloidal field lines excited by MRI and Parker instability, whereas the toroidal component slightly dominates the poloidal (radial and vertical) component as will be discussed in §3.3. In the lower panel that zooms in the central region, we pick up -shaped field lines excited by Parker instability, which are actually observed in the Galactic center region (Fukui et al 2006). This turbulent state is sustained in a quasi-steady manner after the field strength is saturated.…”

On Linear Instability and Stability of the Rayleigh–Taylor Problem in Magnetohydrodynamics

“…Using the condition (1.11), we change the above weak form as follows 8) which implies thatũ is a weak solution to (4.1).…”

“…The corresponding compressible isentropic model of (1.1) reads as follows. 8) where µ 0 := µ + ν, ν denotes the bulk viscosity and 3ν + 2µ ≥ 0. The pressure p is usually determined through the equations of state.…”