Quantifying the decline in CO(2-1) intensity around PHANGS-HST star clusters: Constraints on molecular gas dispersal, stellar feedback, and cluster formation efficiency

Year: 2026

Type: preprint

Abstract: We combine the largest survey of star clusters in nearby galaxies to-date, PHANGS-HST, with maps of molecular gas maps from PHANGS-ALMA to constrain the efficiency of cluster formation and the typical timescales over which clusters become dis-associated from their natal molecular gas. We analyse 29,233 clusters in 36 galaxies using CO maps at 150 pc resolution. For each star cluster with stellar mass $\geq 10^{3.5}$ M$_\odot$, we measure the radial profiles of CO(2-1) integrated intensity and obtain local background-subtracted CO intensity, $I_{\rm CO}^{\rm bkgsub}$, at cluster centre. We group the clusters by age and mass to quantify the dependence of $I_{\rm CO}^{\rm bkgsub}$ and corresponding molecular gas mass, $M_{\rm mol}$, on these cluster properties. To account for the cluster mass ($M_{\rm SC}$) dependence, we also calculate the normalised mass ratio of $(M_{\rm mol}/M_{\rm SC})$. We find that CO intensity varies systematically with cluster age and mass. Clusters that are spatially associated with H$α$ emission exhibit the highest $I_{\rm CO}^{\rm bkgsub}$ of 7.4 K km s$^{-1}$, corresponding to a $M_{\rm mol}/M_{\rm SC}$ ratio of 82 and implying a cluster formation efficiency ($ε_{\rm obs}$) of $\sim 1.2\%$. Young clusters without associated H$α$ emission show lower and age-dependent $I_{\rm CO}^{\rm bkgsub}$ and $M_{\rm mol}/M_{\rm SC}$, decreasing from 1.3 K km s$^{-1}$ and 15 for clusters with age 1-3 Myr, to a level $\approx$ 0 for clusters older than 9--10 Myr. Clusters older than 10 Myr show no statistical excess of CO intensity. We use the clusters with H$α$ association as initial conditions to model the impact of cluster drift and demonstrate that this is unlikely to drive the observed cluster-gas spatial disassociation on short timescales of 4-6 Myr. Instead, early stellar feedback seems likely to be the main driver.

Source: arXiv (Cornell University)

DOI: 10.48550/arxiv.2609.31838

Language: English

Topic: Astrophysics and Star Formation Studies

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

SDG: Climate action

Open Access status: green

Funders: National Science Foundation, National Aeronautics and Space Administration, Space Telescope Science Institute, National Radio Astronomy Observatory, Deutsche Forschungsgemeinschaft, Agence Nationale de la Recherche, National Science Council, Centre National d’Etudes Spatiales, Korea Astronomy and Space Science Institute, Centre National de la Recherche Scientifique, National Astronomical Observatory of Japan, Agencia Nacional de Investigación y Desarrollo, Natural Sciences and Engineering Research Council of Canada, Science and Technology Facilities Council, National Institutes of Natural Sciences, Agencia Estatal de Investigación, Institut National de Physique Nucléaire et de Physique des Particules

OpenAlex ID: W7214743900