Central Spiral Structure of Molecular Gas in Maffei 2

Abstract

The distribution and kinematics of molecular gas in the central region of the barred spiral galaxy Maffei2 were investigated using a data set of ¹²CO(1-0),¹²CO(2-1), CS(2-1) lines, and 103GHz 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 x2 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∼100pc. The mass concentration within R = 35pc is estimated to be 2×10⁸M_odot. The high mass concentration is consistent with theoretical predictions concerning the creation of such a nuclear spiral structure. Acomparison 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 x1 and x2 orbits and the star-forming region appears after 2×10⁵yr, which is comparable to the free-fall time of dense gas traced by the CS line (∼10⁵cm^-3).