We have exploited the Hubble Space Telescope ( HST ) CANDELS J and H -band WFC3/IR imaging to study the properties of ( sub ) millimetre galaxies within the GOODS-South field .
After using the deep radio ( VLA 1.4 GHz ) and Spitzer ( IRAC 8 \mu m ) imaging to identify galaxy counterparts for the ( sub ) millimetre sources , we have then utilised the new CANDELS WFC3/IR imaging in two ways .
First , the addition of new deep near-infrared photometry from both HST and ( at K -band ) the VLT to the existing GOODS-South database has enabled us to derive improved photometric redshifts and stellar masses , confirming that the ( sub ) millimetre sources are massive ( \langle { M } _ { \star } \rangle = 2.2 \times 10 ^ { 11 } \pm 0.2 { M _ { \odot } } ) galaxies at z \simeq 1 - 3 .
Second , we have exploited the depth and resolution of the WFC3/IR imaging to determine the sizes and morphologies of the galaxies at rest-frame optical wavelengths \lambda _ { rest } > 4000 Å .
Specifically , we have fitted two-dimensional axi-symmetric galaxy models to the WFC3/IR images , varying luminosity , axial ratio , half-light radius r _ { 1 / 2 } , and Sérsic index n .
Crucially , the wavelength and depth of the WFC3/IR imaging enables modelling of the mass-dominant galaxy , rather than the blue high surface-brightness features which often dominate optical ( rest-frame ultraviolet ) images of ( sub ) millimetre galaxies , and can confuse visual morphological classification .
As a result of this analysis we find that > 95 % of the rest-frame optical light in almost all of the ( sub ) millimetre galaxies is well-described by either a single exponential disk ( n \simeq 1 ) , or a multiple-component system in which the dominant constituent is disk-like .
We demonstrate that this conclusion is completely consistent with the results of recent high-quality ground-based K -band imaging sampling even longer rest-frame wavelengths , and explain why .
These massive disk galaxies are reasonably extended ( \langle r _ { 1 / 2 } \rangle = 4.5 \pm 0.5 kpc ; median r _ { 1 / 2 } = 4.0 kpc ) , consistent with the sizes of other massive star-forming disks at z \simeq 2 .
In many cases we find evidence of blue clumps within the sources , with the mass-dominant disk component becoming more significant at longer wavelengths .
Finally , only a minority of the sources show evidence for a major galaxy-galaxy interaction .
Taken together , these results support the view that most ( sub ) millimetre galaxies at z \simeq 2 are simply the most extreme examples of normal star-forming galaxies at that era .
Interestingly , the only two bulge-dominated galaxies are also the two lowest-redshift sources in the sample ( z \simeq 1 ) , a result which may reflect the structural evolution of high-mass galaxies in general .