Peak star formation efficiency and no missing baryons in massive spirals. (arXiv:1812.05099v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Posti_L/0/1/0/all/0/1">Lorenzo Posti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fraternali_F/0/1/0/all/0/1">Filippo Fraternali</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marasco_A/0/1/0/all/0/1">Antonino Marasco</a> (University of Groningen)
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” $f_starequiv
M_star/f_{rm b} M_{rm halo}$, where $f_{rm b}equivOmega_{rm
b}/Omega_{rm c}$ 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 ($M_starsimeq 10^7 M_odot$) to high-mass
spirals ($M_starsimeq 10^{11} M_odot$) with HI 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 $M_{rm halo}$. 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 ($M_starsimeq 1-3 times 10^{11} M_odot$) have $f_starapprox
0.3-1$, 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 their gas is also considered, 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 $M_{rm halo}approx {rm
a, few}times 10^{12} M_odot$.
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” $f_starequiv
M_star/f_{rm b} M_{rm halo}$, where $f_{rm b}equivOmega_{rm
b}/Omega_{rm c}$ 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 ($M_starsimeq 10^7 M_odot$) to high-mass
spirals ($M_starsimeq 10^{11} M_odot$) with HI 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 $M_{rm halo}$. 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 ($M_starsimeq 1-3 times 10^{11} M_odot$) have $f_starapprox
0.3-1$, 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 their gas is also considered, 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 $M_{rm halo}approx {rm
a, few}times 10^{12} M_odot$.
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