Kavli Affiliate: Yingjie Peng
| First 5 Authors: Jing Dou, Yingjie Peng, Qiusheng Gu, Luis C. Ho, Alvio Renzini
| 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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