Strong Bars, Strong Inflow: The Effect of Bar Strength on Gas Inflow

TL;DR

The paper addresses how bar strength regulates gas inflow and turbulence in disk galaxies. It employs Hα spectroscopy of 18 nearby galaxies from Galaxy Zoo DESI and uses pPXF to fit emission lines and extract EW[Hα] profiles alongside ionized-gas velocity dispersion, enabling a direct comparison across strongly barred, weakly barred, and unbarred systems. The results show that strong bars produce a characteristic three-peaked EW[Hα] morphology and higher velocity dispersions (median $173.0~\mathrm{km\,s^{-1}}$) relative to weaker or absent bars, with robust statistical separation between SB and the other classes. This supports a scenario where strong bars drive efficient central gas inflow and enhanced turbulence, while weak bars have a more limited dynamical impact; the authors plan to extend the analysis to larger samples (e.g., MaNGA) to generalize the findings.

Abstract

Stellar bars are elongated structures in disk galaxies that can torque and funnel gas inward, influencing galaxy evolution. While strong bars are known to induce rapid inflow, the impact of weaker bars remains less certain. We collected spectroscopic data using the Isaac Newton Telescope to analyze 18 nearby galaxies (strongly barred, weakly barred, and unbarred) drawn from Galaxy Zoo DESI. We obtained spatial profiles of equivalent width (EW) and ionized gas velocity dispersion by fitting Gaussian profiles to the Hα emission line. Strongly barred galaxies exhibit a distinctive three-peaked EW[Hα] structure, consistent with inward funneling of gas. Weakly barred systems lack this pattern, which suggests limited inflow. Velocity dispersion distributions further distinguish the bar types, with strongly barred galaxies showing significantly higher values than weakly barred and unbarred systems. These results suggest that strong bars drive gas inflow, while weak bars exert a limited dynamical influence.

Figures (1)

• Figure 1: Top left: Example pPXF fit to the H$\alpha$ emission line for a strongly barred galaxy (SB3). The upper panel shows the flux-calibrated observed spectrum (maroon), the stellar continuum derived from MILES templates (pink), and the total model (yellow), while the lower panel shows the residuals between the data and the model. Top right: Kernel density estimates of the velocity dispersion distributions for no bar (maroon), weak bar (pink), and strong bar (yellow) galaxies. Densities are normalized by the number of data points in each subsample, and vertical dashed lines indicate the median velocity dispersion for each class. Bottom: Equivalent-width profiles of H$\alpha$ for strongly barred (left) and weakly barred (right) galaxies. Gray points with error bars show the individual EW[H$\alpha$] measurements along the bar as a function of normalized distance from the galaxy center. The colored curves indicate a three-point running median of the measurements. The vertical dashed line marks the bar center ($R=0$).