On the Kennicutt-Schmidt scaling law of submillimetre galaxies
Journal
Date Issued
2017
Author(s)
Abstract
The star formation rate per unit area correlates well with the gas surface
density for different types of galaxies. However, this Kennicutt-Schmidt law
has not yet been examined for a large, homogeneously selected sample of SMGs,
which could provide useful SF implementation information for models of massive
galaxy formation and evolution. We aim at determining the K-S law parameters
for the first time for a well-selected, statistical sample of SMGs. We used
ALMA to conduct a 0.2" resolution, 870 $\mu$m imaging survey of 40 SMGs in
COSMOS, which were initially selected at 1.1 mm. We analysed a sample of 32/40
target SMGs, for which our new ALMA 870 $\mu$m data provide information about
the spatial extent of dust emission, and all of which have dust-obscured SFR
and dust-based gas mass estimates available from our previous study. We divided
our sample into equally large subsamples of main-sequence objects and
starbursts, and found their K-S relations to be of the form $\Sigma_{\rm SFR}
\propto \Sigma_{\rm gas}^{0.81\pm0.01}$ and $\Sigma_{\rm SFR} \propto
\Sigma_{\rm gas}^{0.84\pm0.39}$, respectively. The slightly sub-linear K-S
slopes we derived suggest that the SF efficiency is nearly constant across the
$\Sigma_{\rm gas}$ range probed. Under the assumption of a Galactic CO-to-H$_2$
conversion factor for the whole sample, the MS SMGs obey a constant global SFE
of about 21% per 100 Myr, while that of starburst SMGs is about 27%. The
corresponding gas depletion times are $\sim480$ Myr and 370 Myr. On average,
our SMGs have $\Sigma_{\rm gas}\gtrsim10^{3.9}$ M$_{\odot}$ pc$^{-2}$, which
suggests that they are Eddington-limited. This is consistent with the
theoretical expectation of a linear K-S relation for such systems. However,
size measurements of the CO-emitting regions of SMGs, and the $\alpha_{\rm CO}$
values of SMGs are needed to further constrain their $\Sigma_{\rm gas}$ values.
Volume
602
Start page
L9
Issn Identifier
0004-6361
Rights
open.access
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