Molecular gas in the barred spiral M100 - II. 12 CO(1-0) interferometer observations and numerical simulations

TL;DR

This study combines high-resolution CO observations and numerical simulations to analyze the molecular gas distribution and dynamics in the nucleus of the barred spiral galaxy M100, revealing complex gas flow patterns and bar decoupling.

Contribution

It provides the first detailed mapping of molecular gas in M100's nucleus and develops models showing the nuclear bar's dynamic decoupling from the outer bar.

Findings

Molecular gas forms a two-armed spiral structure near the nucleus.

The gas exhibits a steep rotation curve and streaming motions indicative of a trailing spiral wave.

The best model shows a decoupled, faster nuclear bar rotating at 160 km/s/kpc.

Abstract

Using the IRAM interferometer we have mapped at high resolution (2"x1") the 12CO(1-0) emission in the nucleus of the doubled barred SABbc spiral M100. Molecular gas is distributed in a two spiral arm structure starting from the end points of the nuclear bar (r=600 pc) and a central source. The kinematics of the gas indicates the existence of a steep rotation curve (180 km/s at 100 pc) and strong streaming motions characteristic of a trailing spiral wave inside corotation. Gas flow simulations analyse the gas response to a gravitational potential derived from the K-band plate, including the two nested bars. We develop two families of models: first, a single pattern speed solution shared by the outer bar+spiral and by the nuclear bar, and secondly, a two independent bars solution, where the nuclear bar is dynamically decoupled and rotates faster than the primary bar. We found the best fit solution consisting of a fast pattern (160 km/s/kpc) for the nuclear bar (with corotation at 1.2 kpc) decoupled from the slow pattern of the outer bar+spiral (23 km/s/kpc, with corotation at 8-9 kpc).