Bar Formation in Disc Galaxies: Internal Kinematics and Environmental Influence in MaNGA Galaxies

TL;DR

The study addresses how bars in disc galaxies relate to internal kinematics and environment using MaNGA data. It shows that barred galaxies have more centrally concentrated stellar mass within $1R_e$ and $2R_e$, and exhibit lower inner angular momentum $\lambda_{R_e}$; at fixed $M_\star$, barred systems have higher $M_*/M_{\rm dyn}$ and lower $\lambda_R$. Bar fractions are bimodal with respect to the tidal strength $Q_{\mathrm{nn}}$, peaking in isolated systems and in strong interactions, implying that internal secular processes dominate bar formation while environment can trigger or boost bars in predisposed discs. These findings support theoretical bar formation and secular evolution frameworks and provide observational benchmarks for the role of environment in shaping barred galaxies.

Abstract

We explore how the physical properties of disc galaxies relate to the presence of bars using data from the SDSS-IV MaNGA survey. By combining internal kinematical properties and environmental diagnostics, we find that barred galaxies are more frequently associated with centrally concentrated stellar mass distributions (within 1 and 2 effective radii) and exhibit lower values of the stellar angular momentum $λ_{Re}$. At fixed total stellar mass, barred galaxies exhibit: (i) higher stellar mass, and (ii) lower angular momentum, both in their inner regions than their unbarred counterparts. We find a bimodal dependence of the bar fraction on tidal interactions produced by the nearest neighbour. Specifically, the bar fraction peaks in the most isolated galaxies, where bars form unequivocally through internal secular processes, decreases at intermediate interaction strengths, and rises again in the strong interaction regime, likely reflecting the role of dense environments in sustaining or triggering bars. Our results suggest that internal gravitational instabilities are the primary driver of bar formation. External tidal perturbations play a secondary role, capable of triggering or enhancing bar formation in galaxies that are already internally predisposed. Our findings provide robust observational validation of theoretical bar formation and evolution models in galaxies.

Figures (5)

• Figure 1: Volume-weighted fraction of barred galaxies, $f_{\mathrm{bar}}$, as a function of: (a) total stellar mass, $\log M_{\star}$; (b) stellar-to-dynamical mass ratio, $M_{\star}/M_{\mathrm{dyn}}$ (measured within $R_e$ and $2R_e$); and (c) stellar angular momentum, $\lambda_R$ (also within $R_e$ and $2R_e$). The fraction is computed by binning the sample along the x–axis and taking the ratio of barred to total galaxies in each bin. Solid lines indicate the mean values in each panel, while the shaded regions correspond to the $1\sigma$ confidence intervals derived via bootstrap resampling. Blue (red) histogram displays the number of unbarred (barred) galaxies in each corresponding bin. On average, the bar fraction increases with stellar mass, and barred galaxies are more likely to be found in systems with high stellar mass dominance and low stellar angular momentum in their central regions.
• Figure 2: Volume-weighted stellar-to-dynamical mass ratio (measured within $R_e$ and $2R_e$) as a function of total stellar mass, $\log M_{\star}$, for barred (red lines and shaded regions) and unbarred (blue lines and shaded regions) galaxies. On average, barred galaxies exhibit a higher stellar mass dominance in their central regions at fixed total stellar mass than their unbarred counterparts.
• Figure 3: Volume-weighted stellar angular momentum, $\lambda_{R}$, (measured within $R_e$ and $2R_e$) as a function of the total stellar mass, $\log M_{\star}$, for barred (red lines and shaded regions) and unbarred (blue lines and shaded regions) galaxies. On average, above $\log M_{\star} \sim 9.7 M_{\odot}$, where the bar fraction significantly increases, barred galaxies exhibit lower stellar angular momentum than unbarred galaxies.
• Figure 4: Volume-weighted bar fraction, $f_{\mathrm{bar}}$, as a function of the tidal strength exerted by the first nearest neighbour, $Q_{\mathrm{nn}}$. Red (blue) histogram displays the number of barred (unbarred) galaxies in each $Q_{\rm nn}$ bin. The bar fraction shows a bimodal two-peak distribution, the first one at lowest $Q_{\mathrm{nn}}$ values, corresponding to galaxies minimally affected by external tidal perturbations (isolated galaxies), and the second one at high $Q_{\mathrm{nn}}$ values corresponding to tidal affected galaxies. The red point represents galaxies for which $Q_{\rm nn}$ could not be estimated due to the absence of a nearby neighbour. These cases are flagged as “NULL” in Argudo_Fernandez2015, and we assign them a value of $Q_{\rm nn} = - 7$ for visualization purposes.
• Figure 5: Bar fraction isocontours in key two-dimensional parameter spaces. All panels use volume-weighted statistics to account for survey incompleteness. Contours enclose $15-50\%$ of the sample, with colour gradients indicating the bar fraction. Panel (a): Stellar-to-dynamical mass ratio ($M_\star / M_\mathrm{dyn}$) versus specific angular momentum proxy ($\lambda_{R_e}$). Bar fraction increases toward systems that are simultaneously more stellar dominated and less rotationally supported, consistent with bar-driven secular evolution. Panel (b): Stellar-to-dynamical mass ratio versus tidal strength parameter ($Q_{nn}$). Bar fraction peaks in galaxies with both high stellar dominance and moderate-to-high tidal strength, suggesting that interactions enhance bar formation in already bar-prone systems. Panel (c): $\lambda_{R_e}$ versus $Q_{nn}$. Bar fraction declines at high $\lambda_{R_e}$, while at low $\lambda_{R_e}$ two populations emerge: one showing strong tidal interactions, and another more isolated. This suggests the existence of two bar formation pathways, one driven by intrinsic disc instabilities and another induced by the environment. These multi-dimensional trends highlight that no single parameter governs bar formation; instead, bars emerge from a combination of internal dynamical conditions and external tidal influences.