What question did this study set out to answer?

The study aims to analyze molecular gas and star formation rates in central rings of nearby galaxies and relate these to the morphological features of the host galaxies.

February 10, 2026

Molecular gas and star formation in central rings across nearby galaxies

Key Points

The study aims to analyze molecular gas and star formation rates in central rings of nearby galaxies and relate these to the morphological features of the host galaxies.
Utilized high-resolution CO(2-1) observations from the PHANGS-ALMA survey
Identified 20 central rings and measured their properties
Analyzed star formation rates using MUSE observations
Compared ring properties with host galaxy characteristics
Central rings have typical radii of about 400 pc and molecular gas masses of approximately log(M/M⊙) ∼ 8.1
Star formation rates of central rings are around 0.21 M⊙/yr
Central rings contribute 5.6% of the molecular gas mass and 5% of the star formation rate to their host galaxies
Longer bars correlate with more massive molecular central rings, with no direct link to classical bar strength parameters

Abstract

Nearby galaxies exhibit a variety of structures, including so-called central or (circum-) nuclear rings that are similar to the Milky Way (MW) Central Molecular Zone (CMZ). These rings are common in barred galaxies and can be gas-rich and highly star-forming. We aim to study the molecular gas content and star formation rate of central rings within nearby galaxies and link them to global galaxy properties, especially the bar morphology. We utilized 1, 100, pc) resolution CO (2-1) observations from the PHANGS-ALMA survey, visually identifying 20 central rings and determine their properties. For 14 of these rings, MUSE observations tracing star formation rate (SFR) surface density were available. We derived the rings' geometry, integrated molecular gas masses, SFRs, depletion times, and compared them to host galaxy and bar properties from the literature. (łesssim Molecular gas is an effective tracer for central rings. Previous studies have used ionized gas and dust tracers to identify central rings in galaxies of similar morphological types as the PHANGS galaxies (numerical Hubble type T∼-3 to T∼9). In comparison, molecular gas yields similar fractions of galaxies hosting central rings and similar radii distributions. The gaseous central rings have typical radii of ∼ 400_ -150 ^ +250, pc, molecular gas masses of łog (M_ /M_⊙) ∼8. 1_ mol -0. 23 ^ +0. 17, and SFRs of ∼ 0. 21_ -0. 16 ^ +0. 15, M_⊙/. As a result, they contribute 5. 6_ yr -2. 1 ^ +4. 5, % and -5 ^ +10, % to their host galaxies' molecular gas mass and SFR, respectively. While the MW CMZ sits at the lower end of the radius, molecular gas mass, and SFR distribution, it matches well in terms of ring molecular gas mass and SFR fraction, and depletion time. Longer bars contain more massive molecular central rings, but there is no correlation between the classical bar strength parameters (Q_ ɛ_ A₂^ and the ring's molecular gas content. Although absolute central ring properties (ring radius, molecular gas mass, SFR) likely depend on host galaxy properties, the similarities between the MW CMZ and PHANGS central rings in relative parameters (molecular gas and SFR fraction, depletion time) suggest that the processes of gas inflow and star formation are similar for central rings across nearby galaxies.

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