Connection between Nonaxisymmetric Structures and Neutral Gas Distribution in Disk Galaxies

Abstract Nonaxisymmetric structures, such as bars and spiral arms, are known to concentrate molecular gas and star formation in galaxy centers, actively building up the pseudobulges. However, the direct link between the neutral (i.e., molecular and atomic) gas distribution and the exerted torque forces over a broader radial range of galactic disks still remains to be explored. In the present work, we investigate this link by carefully evaluating the torque force field using the 3.6 μ m images for 17 The H i Nearby Galaxy Survey galaxies, and measuring neutral gas distribution on resolved atomic and molecular line maps. We find that galaxies with stronger torque forces show a more concentrated neutral gas distribution over the disk scale, defined as half the isophotal radius at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>25.5</mml:mn> <mml:mspace width="0.25em"/> <mml:mi>mag</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>arcsec</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> . The correlation holds regardless of whether the neutral gas fraction or the effective stellar mass surface density is controlled for. In addition, kiloparsec-scale neutral gas overdensities tend to be located close to the local maxima of torque forces. Most of these correlations involving the torque forces are comparatively stronger than those using the traditional Fourier amplitudes to quantify the nonaxisymmetric structures. These results are consistent with the scenario that nonaxisymmetric structures exert torque forces and trigger dissipative processes to transport gas inward, not only to build the pseudobulges but also to fuel the inner disk growth. In this regard, nonaxisymmetric structures inducing stronger torque forces appear to be more efficient in these processes.