Living with Neighbors. VI. Unraveling the Dual Impact of Bars on Star Formation in Paired Galaxies Using DESI

TL;DR

This study tackles how stellar bars regulate star formation during galaxy interactions by exploiting a large DESI-LS DR8 sample with Galaxy Zoo DESI bar classifications and quantified bar strength and length. It reveals a dual mode: bars catalyze central starbursts when the interacting companion is gas-rich and star-forming, and promote SF quenching when the companion is gas-poor and passive, with bar length amplifying the response. The analysis uses careful pair selection and matched control samples to isolate bar-driven effects from environmental biases, showing that bar presence alone does not trigger interactions. The findings provide a coherent framework linking kpc-scale bar dynamics to external gas supply, offering reconciled explanations for past conflicting results and guiding future spatially resolved studies.

Abstract

We present a comprehensive investigation into the influence of stellar bars on star formation (SF) in galaxy pairs, using a large sample of low-redshift galaxies ($0.02$\,$<$\,z\,$<$\,$0.08$) from the DESI Legacy Imaging Surveys DR8. Our analysis examines whether bars enhance or suppress SF during pair interactions, and how these outcomes depend on the star-forming properties of companion galaxies. We find that bars either catalyze or inhibit SF in their host galaxies, depending on the companion's SF activity. In particular, barred galaxies paired with actively star-forming companions experience more pronounced central starbursts (with sSFR up to $\sim$\,2.5 dex higher) than unbarred counterparts, whereas those with passive companions often have suppressed SF (sometimes below isolated galaxy levels). The notion of the dual role of bars can reconcile conventional conflicting reports of bar-driven enhancement versus quenching of SF activity. Bars, well known to regulate kpc-scale dynamics, may also link to the impact of external environments: when a star-forming companion provides sufficient gas, bars drive central starbursts, whereas in gas-poor interactions, bars hasten gas depletion and contribute to SF suppression. This work highlights the necessity of accounting for both internal structure and companion properties to fully understand SF regulation in interacting galaxies.

Figures (9)

• Figure 1: The example DESI-LS multiband images of galaxy pairs in which the target galaxy host a stellar bar. For each system, we indicate the normalized bar length ($L_{\rm Bar}/D_{25}$) and the projected separation between the target and its companion ($r_{\rm Nei}$). The target barred galaxy is marked with a white arrow in each panel.
• Figure 2: Top: The normalized distributions of redshift (left), stellar mass (middle), and local density (right) for paired galaxies (purple) and the initial, unmatched sample of isolated, unbarred galaxies (dashed gray). Bottom: Same as the top panels, but comparing the matched sample of paired galaxies (purple) to the final control sample of isolated, unbarred galaxies (solid gray). The $p$-values from K-S test confirm the statistical consistency between the matched samples, validating the effectiveness of our control selection. Black error bars on the histograms represent Poisson uncertainties for the control sample.
• Figure 3: The normalized distributions of the sSFR of the nearest companion galaxy for paired systems, categorized by bar classification of the target galaxy: unbarred (left; dashed black), weakly barred (middle; solid purple), and strongly barred (right; solid purple). For reference, the distribution for all paired systems, irrespective of bar classification, is shown as solid gray histogram in each panel. The vertical gray dashed line indicates the sSFR threshold, $\textrm{Log}(\rm sSFR_{\rm Nei}) = -11 \space \rm yr^{-1}$, used to separate star-forming and quiescent companions in our analysis.
• Figure 4: The normalized distributions of the sSFR of target galaxies in pairs, categorized by bar classification: unbarred (left; dashed black), weakly barred (middle; solid purple), and strongly barred (right; solid purple). For comparison, the corresponding distribution for the control sample of isolated, unbarred galaxies is shown as solid gray histogram in each panel. Paired galaxies are further subdivided by the SF activity of their companions: systems with star-forming companions are shown in dashed blue, while those with quiescent companions are shown in dashed red.
• Figure 5: Top: The distributions of projected separation vs. the sSFR of target galaxies in pairs, categorized by bar classification: unbarred (left; black dots), weakly barred (middle; purple dots), and strongly barred (right; purple dots). Dashed black and solid purple lines indicate the median trends for each subsample. For comparison, isolated, unbarred control sample are shown as gray points with dashed gray median lines. Shaded bands represent the statistical uncertainty derived from jackknife resampling. Bottom: The same as the top panels, but the pair sample is further subdivided based on the SF activity of the companion galaxy: systems with star-forming companions are shown in blue, and those with quiescent companion in red. Median trends for each subsample are shown as blue and red lines, respectively.