Correlations of ALMA CO(2–1) with JWST Mid-infrared Fluxes Down to Scales of ≲100 pc in nearby Star-forming Galaxies from PHANGS

Abstract We investigate the correlations of CO (2-1) emission ( I CO ) with polycyclic aromatic hydrocarbons (PAH) ( I F770W,PAH and I F1130W ) and dust ( I F2100W ) emission down to scales of ≲100 pc, by applying raddest , a novel regression technique recently developed by T. Jing & C. Li that effectively handles uncertainties and outliers in data sets, to 19 nearby star-forming galaxies in the PHANGS sample. We find that for the majority of the data points in all galaxies, the scaling of I CO with I F770W,PAH , I F1130W , and I F2100W can be well described by log–log linear relations, though with substantial dependence on ionization conditions (i.e., H ii -like, composite-like, and AGN-like). Under given ionization conditions, significant galaxy-to-galaxy variations are identified, and are primarily attributed to variations of intercept b , which exhibits clear bimodality. This bimodality is related to the normalized overall host galaxy star formation rate, such as specific star formation and star formation efficiency. The differences in slope k and intrinsic scatter σ across different MIR bands ( I F770W,PAH , I F1130W , and I F2100W ) are minor compared to their galaxy-to-galaxy variations. All parameters ( k , b , and σ ) depend on the spatial scale of measurement, suggesting that the coupling among CO, PAH, and dust is regulated by different mechanisms at varying scales. We identify deviations from the log–log linear relation in the brightest regions, primarily characterized by a flattening of the slope. No significant (3 σ ) correlations are found between global properties and the best-fit parameters. We discuss the comparison to previous studies and plausible physics behind the statistical results obtained in this work.