Gas-to-dust mass ratios in local galaxies over a 2 dex metallicity range
Abstract
Aims. The goal of this paper is to analyse the behaviour of the
gas-to-dust mass ratio (G/D) of local Universe galaxies over a wide metallicity range. We
especially focus on the low-metallicity part of the G/D vs metallicity relation and
investigate several explanations for the observed relation and scatter.Methods. We assembled a total of 126 galaxies, covering a 2 dex
metallicity range and with 30% of the sample with 12 + log(O/H)≤ 8.0. We homogeneously determined the dust
masses with a semi-empirical dust model including submm constraints. The atomic and
molecular gas masses have been compiled from the literature. We used two XCO scenarios to
estimate the molecular gas mass: the Galactic conversion factor, XCO,MW, and a
XCO that depends on the metallicity
XCO,Z
(∝Z-2). We
modelled the observed trend of the G/D with metallicity using two simple power laws (slope
of –1 and free) and a broken power law. Correlations with morphological type, stellar
masses, star formation rates, and specific star formation rates are also discussed. We
then compared the observed evolution of the G/D with predictions from several chemical
evolution models and explored different physical explanations for the observed scatter in
the G/D values.Results. We find that out of the five tested galactic parameters,
metallicity is the main physical property of the galaxy driving the observed G/D. The G/D
versus metallicity relation cannot be represented by a single power law with a slope of –1
over the whole metallicity range. The observed trend is steeper for metallicities lower
than ~8.0. A large scatter is
observed in the G/D values for a given metallicity: in metallicity bins of ~0.1 dex, the dispersion around the mean
value is ~0.37 dex. On
average, the broken power law reproduces the observed G/D best compared to the two power
laws (slope of –1 or free) and provides estimates of the G/D that are accurate to a factor
of 1.6. The good agreement of observed values of the G/D and its scatter with respect to
metallicity with the predicted values of the three tested chemical evolution models allows
us to infer that the scatter in the relation is intrinsic to galactic properties,
reflecting the different star formation histories, dust destruction efficiencies, dust
grain size distributions, and chemical compositions across the sample. Conclusions. Our results show that the chemical evolution of
low-metallicity galaxies, traced by their G/D, strongly depends on their local internal
conditions and individual histories. The large scatter in the observed G/D at a given
metallicity reflects the impact of various processes occurring during the evolution of a
galaxy. Despite the numerous degeneracies affecting them, disentangling these various
processes is now the next step.
Origin : Publication funded by an institution
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