Reduction of bar fraction in paired galaxies in the SDSS

TL;DR

This study investigates how galaxy interactions influence bar structures by comparing the bar fraction in a large SDSS galaxy-pair sample to carefully matched isolated controls. Bar strength is quantified via $e_{\mathrm{Bar}}$ from ellipse fits, and analyses are performed across projected separation, mass ratio, bulge prominence ($B/T$), and relative orientation ($A_i$). The main result is a robust suppression of the bar fraction for very close pairs ($d_{\mathrm{p}}<25$ $h^{-1}$ kpc), driven primarily by mergers and, within mergers, by weak bars; strong bars are largely resilient. The suppression is strongest in massive hosts undergoing major mergers, with bulge concentration offering partial protection, while the pair orientation has little effect. These findings support a picture in which tidal perturbations during major mergers disrupt pre-existing bars and shape their evolution, contributing to our understanding of how interactions regulate disk galaxy structure.

Abstract

We investigate the bar fraction in galaxy pairs from the SDSS to assess how galaxy interactions affect bar structures. Compared to isolated galaxies, close pairs exhibit a significantly reduced bar fraction at projected separations within 25 kpc. This reduction is driven almost entirely by systems showing clear merger or disturbance signatures, indicating that tidal interactions suppress bars. The decline is dominated by a decrease in weak bars, while the fraction of strong bars remains largely unchanged. Bar suppression is primarily associated with major mergers and is strongest in massive host galaxies. A weaker but statistically significant suppression is detected in minor mergers only for massive galaxies with small bulges. In contrast, no significant dependence of bar suppression on the relative orientation between pair members is found. These findings provide observational evidence that tidal perturbations in major mergers play a key role in regulating bar evolution.

Figures (4)

• Figure 1: Distribution of control parameters for the paired sample and control samples. The red solid lines represent the paired galaxies, while the black dashed lines denote the mean of the $100$ control samples, and the gray shaded regions indicate the $\pm 1\sigma$ scatter across the $100$ iterations. The four panels show the distributions of stellar mass ($\log M_\star$), redshift ($z$), surface density ($\log \Sigma_5$), and bulge-to-total ratio ($B/T$), respectively.
• Figure 2: The upper sub-panel shows the overall bar fraction ($f_\mathrm{Bar}$) as a function of projected separation ($d_{\text{p}}$): black solid circles denote the galaxy pair sample, while gray dashed circles (with error bars) represent the mean of $100$ control samples (error bars indicate the standard error across the $100$ repeats. The lower sub-panel displays the difference in bar fraction ($\Delta f_\mathrm{Bar}$) between galaxy pairs and control samples (red solid circles, with error bars reflecting the combined uncertainty of the pair and control samples). The number of paired galaxies contributing to each data point is indicated above the horizontal axis in the lower sub-panel.
• Figure 3: Combined plots of $\Delta f_\mathrm{Bar}$ as a function of galaxy properties for galaxy pairs with projected separations $d_{\text{p}} < 25\ h^{-1}\ \text{kpc}$. Top: $\Delta f_\mathrm{Bar}$ versus stellar mass $\log M_\star$; Middle: $\Delta f_\mathrm{Bar}$ versus bulge-to-total ratio $B\slash T$; Bottom: $\Delta f_\mathrm{Bar}$ versus relative position angle $A_i$. Colors indicate different mass-ratio intervals, with sample sizes $N$ shown in the legend: blue ($-1.5 < \log (M_\star / M_{\mathrm{neigh}}) < -0.5$), orange ($-0.5 < \log (M_\star / M_{\mathrm{neigh}}) < 0.5$), and green ($0.5 < \log (M_\star / M_{\mathrm{neigh}}) < 1.5$). Error bars represent the uncertainties in $\Delta f_\mathrm{Bar}$.
• Figure 4: Left panel: $f_\mathrm{Bar}$ of close-pair subsamples classified by the presence or absence of merger/disturbance signatures within $d_{\text{p}} < 25\ h^{-1}\ \text{kpc}$. Blue and orange bars represent paired galaxies and their matched controls, respectively. Error bars indicate the uncertainties in $f_\mathrm{Bar}$. The corresponding sample sizes are annotated for each subsample. Right panel: Distribution of bar strength ($e_\mathrm{Bar}$) for paired galaxies (red solid histogram) and control galaxies. Here, the black dashed histogram denotes the mean of 100 independent control samples, while the gray shaded region represents the $\pm 1\sigma$ scatter across these 100 iterations. The $y$-axis shows raw galaxy counts