Peak star formation efficiency and no missing baryons in massive spirals

Lorenzo Posti; Filippo Fraternali; Antonino Marasco

doi:10.1051/0004-6361/201935553

paper

Peak star formation efficiency and no missing baryons in massive spirals

arXiv:1812.05099 · doi:10.1051/0004-6361/201935553

Abstract

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" $f_{⋆} \equiv M_{⋆} / f_{b} M_{halo}$ , where $f_{b} \equiv Ω_{b} / Ω_{c}$ is the cosmological baryon fraction, is expected to reach its peak at nearly $L^{*}$ (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 ( $M_{⋆} ≃ 1 0^{7} M_{⊙}$ ) to high-mass spirals ( $M_{⋆} ≃ 1 0^{11} M_{⊙}$ ) with HI rotation curves and 3.6 $μ$ m photometry. We fit the observed rotation curves with a Bayesian approach by varying three parameters, stellar mass-to-light ratio, halo concentration and mass. We found two surprising results: 1) the star formation efficiency is a monotonically increasing function of $M_{⋆}$ with no sign of a decline at high masses, and 2) the most massive spirals ( $M_{⋆} ≃ 1 - 3 \times 1 0^{11} M_{⊙}$ ) have $f_{⋆} \approx 0.3 - 1$ , 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 $L^{*}$ 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 $M_{halo} \approx a few \times 1 0^{12} M_{⊙}$ .

arXiv commentaccepted for publication in A&A

Peak star formation efficiency and no missing baryons in massive spirals

Abstract

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