On the galaxy stellar mass function, the mass-metallicity relation, and the implied baryonic mass function

A comparison between published field galaxy stellar mass functions (GSMFs) shows that the cosmic stellar mass density is in the range 4–8 per cent of the baryon density (assuming Ωb = 0.045). There remain significant sources of uncertainty for the dust correction and underlying stellar mass-to-light ratio even assuming a reasonable universal stellar initial mass function. We determine the z < 0.05 GSMF using the New York University – Value-Added Galaxy Catalog sample of 49968 galaxies derived from the Sloan Digital Sky Survey and various estimates of stellar mass. The GSMF shows clear evidence for a low-mass upturn and is fitted with a double Schechter function that has α2 ≃ −1.6. At masses below ∼ 108.5M⊙, the GSMF may be significantly incomplete because of missing low surface-brightness galaxies. One interpretation of the stellar mass-metallicity relation is that it is primarily caused by a lower fraction of available baryons converted to stars in low-mass galaxies. Using this principal, we determine a simple relationship between baryonic mass and stellar mass and present an ‘implied baryonic mass function’. This function has a faint-end slope, α2 ≃ −1.9. Thus, we find evidence that the slope of the low-mass end of the galaxy mass function could plausibly be as steep as the halo mass function. We illustrate the relationship between halo baryonic mass function → galaxy baryonic mass function → GSMF. This demonstrates the requirement for peak galaxy formation efficiency at baryonic masses ∼ 1011M⊙ corresponding to a minimum in feedback effects. The baryonic-infall efficiency may have levelled off at lower masses.