Kavli Affiliate: Yingjie Peng
| Summary:
Understanding the physical mechanisms that drive star formation is crucial for advancing our knowledge of galaxy evolution. We explore the interrelationships between key galaxy properties associated with star formation, with a particular focus on the impact of dark matter halos. Given the sensitivity of atomic hydrogen (HI) to external processes, we concentrate exclusively on central spiral galaxies. We find that the molecular-to-atomic gas mass ratio ($M_rm H_2/M_rm HI$) strongly depends on stellar mass and specific star formation rate (sSFR). In the star formation efficiency (SFE)-sSFR plane, most galaxies fall below the H$_2$ fundamental formation relation (FFR), with SFE$_rm HI$ being consistently lower than SFE$_rm H_2$. Using the improved halo masses derived by Zhao et al. (2025), for star-forming galaxies, both SFE$_rm HI$ and $M_rm H_2/M_rm HI$ increase rapidly and monotonically with halo mass, indicating a higher efficiency in converting HI to H$_2$ in more massive halos. This trend ultimately leads to the unsustainable state where SFE$_rm HI$ exceeds SFE$_rm H_2$ at halo mass around $10^12 hbox$M_odot$$. For halos with masses exceeding $10^12 hbox$M_odot$$, galaxies predominantly experience quenching. We propose a plausible evolutionary scenario in which the growth of halo mass regulates the conversion of HI to H$_2$, star formation, and the eventual quenching of galaxies. The disk size, primarily regulated by the mass, spin and concentration of the dark matter halo, also significantly influences HI to H$_2$ conversion and star formation. These findings underscore the critical role of dark matter halos as a global regulator of galaxy-wide star formation, a key factor that has been largely underappreciated in previous studies.
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