It is commonly believed that galaxies use , throughout the Hubble time , a very small fraction of the baryons associated to their dark matter halos to form stars .
This so-called low ” star formation efficiency ” f _ { \star } \equiv M _ { \star } / f _ { b } M _ { halo } , where f _ { b } \equiv \Omega _ { b } / \Omega _ { c } is the cosmological baryon fraction , is expected to reach its peak at nearly L ^ { \ast } ( at efficiency \approx 20 \% ) and decline steeply at lower and higher masses .
We have tested this using a sample of nearby star-forming galaxies , from dwarfs ( M _ { \star } \simeq 10 ^ { 7 } M _ { \odot } ) to high-mass spirals ( M _ { \star } \simeq 10 ^ { 11 } M _ { \odot } ) with H i rotation curves and 3.6 \mu m photometry .
We fit the observed rotation curves with a Bayesian approach by varying three parameters , stellar mass-to-light ratio \Upsilon _ { \star } , halo concentration c and mass M _ { halo } .
We found two surprising results : 1 ) the star formation efficiency is a monotonically increasing function of M _ { \star } with no sign of a decline at high masses , and 2 ) the most massive spirals ( M _ { \star } \simeq 1 - 3 \times 10 ^ { 11 } M _ { \odot } ) have f _ { \star } \approx 0.3 - 1 , i.e .
they have turned nearly all the baryons associated to their haloes into stars .
These results imply that the most efficient galaxies at forming stars are massive spirals ( not L ^ { \ast } galaxies ) , they reach nearly 100 % efficiency and thus , once both their cold and hot gas is considered into the baryon budget , they have virtually no missing baryons .
Moreover , there is no evidence of mass quenching of the star formation occurring in galaxies up to halo masses of M _ { halo } \approx { a few } \times 10 ^ { 12 } M _ { \odot } .