It has been established for decades that rotation curves deviate from the Newtonian gravity expectation given baryons alone below a characteristic acceleration scale g† ∼ 10−8 cm s−2, a scale promoted to a new fundamental constant in MOND-type theories. In recent years, theoretical and observational studies have shown that the star formation efficiency (SFE) of dense gas scales with surface density, SFE ∼ Σ/Σcrit with Σcrit ∼ (pÛ/m∗)/(π2 G) ∼ 1000 M pc−2 (where pÛ/m∗ is the momentum flux output by stellar feedback per unit stellar mass formed). We show that the star formation efficiency, more correctly, scales with the gravitational acceleration, i.e. that SFE ∼ gtot/gcrit ≡ (G Menc/R2)/([pÛ/m∗]/π), where Menc(< r) is the total gravitating mass and gcrit = (pÛ/m∗)/π = π G Σcrit ≈ 10−8 cm s−2 ≈ g†. It follows that the characteristic galactic acceleration g† corresponds to the acceleration scale above which SF is 'efficient' (and outflows 'inefficient'), and so baryons inevitably dominate the mass. This also explains the “deep MOND” scaling gobs ∼ (gbaryon g†)1/2 (where gbaryon is the acceleration due to baryons alone) apparent at low accelerations. We further show that g† can be expressed in terms of fundamental constants (gravitational constant, proton mass, and Thomson cross-section): g† ∼ 0.1 G mp/σT.
|Original language||English (US)|
|State||Published - Oct 14 2019|
- Cosmology: dark matter
- Galaxies: evolution
- Galaxies: formation
ASJC Scopus subject areas