Central Spiral Structure of Molecular Gas in Maffei 2

Abstract

Abstract The distribution and kinematics of molecular gas in the central region of the barred spiral galaxy Maffei 2 were investigated using a data set of $^{12}$ CO(1-0), $^{12}$ CO(2–1), CS(2–1) lines, and 103 GHz continuum. We found that the offset ridges along the kpc-scale bar continue to the central spiral structure embedded in a weak oval structure, which is regarded as an $x$ 2 orbit in the bar potential. The spiral structure continues toward the center, diverging from the oval structure. The size of these structures is less than $R$$\sim$ 100 pc. The mass concentration within $R =$ 35 pc is estimated to be $2 \times 10^{8} M_{\odot}$ . The high mass concentration is consistent with theoretical predictions concerning the creation of such a nuclear spiral structure. A comparison with tracers of dense gas and star-forming region suggests that the dense molecular gas traced by the CS(2–1) line is formed at the crossing points of the $x$ 1 and $x$ 2 orbits and the star-forming region appears after $2 \times 10^{5}$ yr, which is comparable to the free-fall time of dense gas traced by the CS line ( $\sim$$10^{5}$ cm $^{-3}$ ).