Context : Submillimetre galaxies ( SMGs ) represent an important source population in the origin and cosmic evolution of the most massive galaxies .
Hence , it is imperative to place firm constraints on the fundamental physical properties of large samples of SMGs .

Aims : We determine the physical properties of a sample of SMGs in the COSMOS field that were pre-selected at the observed-frame wavelength of \lambda _ { obs } = 1.1 mm , and followed up at \lambda _ { obs } = 1.3 mm with the Atacama Large Millimetre/submillimetre Array ( ALMA ) .

Methods : We used the MAGPHYS model package to fit the panchromatic ( ultraviolet to radio ) spectral energy distributions ( SEDs ) of 124 of the target SMGs , which lie at a median redshift of z = 2.30 ( 19.4 % are spectroscopically confirmed ) .
The SED analysis was complemented by estimating the gas masses of the SMGs by using the \lambda _ { obs } = 1.3 mm dust emission as a tracer of the molecular gas component .

Results : The sample median and 16th–84th percentile ranges of the stellar masses , obscured star formation rates , dust temperatures , and dust and gas masses were derived to be \log ( M _ { \star } / { M } _ { \sun } ) = 11.09 ^ { +0.41 } _ { -0.53 } , { SFR } = 402 ^ { +661 } _ { -233 } { M } _ { \sun } ~ { } { yr } ^ { -1 } , T _ { dust } = 39.7 ^ { +9.7 } _ { -7.4 } K , \log ( M _ { dust } / { M } _ { \sun } ) = 9.01 ^ { +0.20 } _ { -0.31 } , and \log ( M _ { gas } / { M } _ { \sun } ) = 11.34 ^ { +0.20 } _ { -0.23 } , respectively .
The M _ { dust } / M _ { \star } ratio was found to decrease as a function of redshift , while the M _ { gas } / M _ { dust } ratio shows the opposite , positive correlation with redshift .
The derived median gas-to-dust ratio of 120 ^ { +73 } _ { -30 } agrees well with the canonical expectation .
The gas fraction ( M _ { gas } / ( M _ { gas } + M _ { \star } ) ) was found to range from 0.10 to 0.98 with a median of 0.62 ^ { +0.27 } _ { -0.23 } .
We found that 57.3 \% of our SMGs populate the main sequence ( MS ) of star-forming galaxies , while 41.9 \% of the sources lie above the MS by a factor of greater than three ( one source lies below the MS ) .
These super-MS objects , or starbursts , are preferentially found at z \gtrsim 3 , which likely reflects the sensitivity limit of our source selection .
We estimated that the median gas consumption timescale for our SMGs is \sim 535 Myr , and the super-MS sources appear to consume their gas reservoir faster than their MS counterparts .
We found no obvious stellar mass–size correlations for our SMGs , where the sizes were measured in the observed-frame 3 GHz radio emission and rest-frame UV .
However , the largest 3 GHz radio sizes are found among the MS sources .
Those SMGs that appear irregular in the rest-frame UV are predominantly starbursts , while the MS SMGs are mostly disk-like .

Conclusions : The physical parameter distributions of our SMGs and those of the equally bright , 870 \mu m selected SMGs in the ECDFS field ( the so-called ALESS SMGs ) are unlikely to be drawn from common parent distributions .
This might reflect the difference in the pre-selection wavelength .
Albeit being partly a selection bias , the abrupt jump in specific SFR and the offset from the MS of our SMGs at z \gtrsim 3 might also reflect a more efficient accretion from the cosmic gas streams , higher incidence of gas-rich major mergers , or higher star formation efficiency at z \gtrsim 3 .
We found a rather flat average trend between the SFR and dust mass , but a positive { SFR } - M _ { gas } correlation .
However , to address the questions of which star formation law ( s ) our SMGs follow , and how they compare with the Kennicutt-Schmidt law , the dust-emitting sizes of our sources need to be measured .
Nonetheless , the larger radio-emitting sizes of the MS SMGs compared to starbursts is a likely indication of their more widespread , less intense star formation activity .
The irregular rest-frame UV morphologies of the starburst SMGs are likely to echo their merger nature .
The current stellar mass content of the studied SMGs is very high , so they must quench to form the so-called red-and-dead massive ellipticals .
Our results suggest that the transition from high- z SMGs to local ellipticals via compact , quiescent galaxies ( cQGs ) at z \sim 2 might not be universal , and the latter population might also descend from the so-called blue nuggets .
However , z \gtrsim 4 SMGs could be the progenitors of higher redshift , z \gtrsim 3 cQGs , while our results are also consistent with the possibility that ultra-massive early-type galaxies found at 1.2 \lesssim z \lesssim 2 experienced an SMG phase at z \leq 3 .