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Shocks and torques produced by non-axisymmetric structures such as spiral arms and bars may transport gas to galaxy central regions. We test this hypothesis by studying the dependence of the concentration of CO luminosity ( C CO ) and molecular gas ( C mol ) and the star formation rate ( C SFR ) in the central ∼2 kpc on the strength of non-axisymmetric disk structure using a sample of 57 disk galaxies selected from the EDGE-CALIFA survey. The C mol is calculated using a CO-to-H 2 conversion factor that decreases with higher metallicity and higher stellar surface density. We find that C mol is systematically 0.22 dex lower than C CO . We confirm that high C mol and strong non-axisymmetric disk structure are more common in barred galaxies than in unbarred galaxies. However, we find that spiral arms also increase C mol . We show that there is a good correlation between C mol and the strength of non-axisymmetric structure (which can be due to a bar, spiral arms, or both). This suggests that the stronger the bars and spirals, the more efficient the galaxy is at transporting cold gas to its center. Despite the small subsample size, the C mol of the four Seyferts are not significantly reduced compared to inactive galaxies of similar disk structure, implying that the active galactic nucleus feedback in Seyferts may not notably affect the molecular gas distribution in the central ∼2 kpc. We find that C SFR tightly correlates with C mol in both unbarred and barred galaxies. Likewise, elevated C SFR is found in galaxies with strong disk structure. Our results suggest that the disk structure, either spirals or bars, can transport gas to the central regions, with higher inflow rates corresponding to stronger structure, and consequently boost central star formation. Both spirals and bars play, therefore, an essential role in the secular evolution of disk galaxies.
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This content will become publicly available on June 4, 2026
Dynamically Driven Evolution of Molecular Gas in the Barred Spiral Galaxy M83 Traced by CO J = 2–1/1–0 Line Ratio Variations
Abstract We show the variations of the COJ= 2–1/1–0 line ratio (R21/10) across the barred spiral galaxy M83, using the 46 pc resolution data from the Atacama Large Millimeter/submillimeter Array. TheR21/10map clearly evidences the systematic large-scale variations as a function of galactic structures. Azimuthally, it starts from lowR21/10≲ 0.7 in the interarm regions and becomes high ≳0.7 in the bar and spiral arms, suggesting that the density and/or kinetic temperature of molecular gas increase by about a factor of 2–3. This evolution is seen even in the parts of spiral arms without star formation, andR21/10is often elevated even higher to ∼0.8–1.0 when Hiiregions exist in the vicinity. Radially,R21/10starts very high ≳1.0 at the galactic center, remains low ≲0.7 in the bar region, increases to ≳0.7 around the bar end, and again decreases to ≲0.7 in the rest of disk where the spiral arms dominate. The evolutionary sequence is synchronized with galactic rotation, and therefore, it is determined largely by the galactic structures and dynamics and is governed by the galactic rotation timescales. TheR21/10map also shows that the influence of stellar feedback is localized and limited. Massive, large, and non-star-forming molecular structures have lowR21/10, which also suggests that the bulk molecular gas in the disk is not regulated by stellar feedback, but more likely by galactic structures and dynamics. These results are consistent with suggestions by the earlier studies of the Milky Way and other barred spiral galaxies, and thus, are likely general among barred spiral galaxies in the local Universe.
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- PAR ID:
- 10649864
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 986
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 29
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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