| Summary: | Local, massive galaxies are seen to host very old stellar populations. This indi cates that a significant fraction of the stellar mass was formed during early epochs. The discovery of intense starburst galaxies at high redshifts have suggested that such galaxies are part of an evolutionary sequence towards today’s massive galax ies. This master’s thesis provides an introductory theoretical background in the history and very basics of the study of galaxies, techniques and methods in ob servational radio astronomy, and evolution of distant, massive galaxies. After this summary, two redshift z=2.5-2.8 sources, discovered by the South Pole Telescope (SPT), are analysed through the visibility-based lens modeling tool visilens. Spectra and galaxy-galaxy gravitational lensing models are obtained from ∼ 0.1 00 resolution data from the Atacama Large Millimeter/submillimeter Array of the CO(3-2) line from SPT0125-47 and SPT2134-50. Results indicate magnifications of µ = 15.4 ± 0.9 for SPT0125-47 and µ = 20.2 ± 2.9 for SPT2134-50. The cor responding FWHMs are (380 ± 47) km s−1 and (550 ± 87) km s−1 , which leads to intrinsic line luminosities L 0 CO(3−2) = (5.1 ± 0.84)1010 K km s−1 pc2 and L 0 CO(3−2) = (1.5 ± 0.31)1010 K km s−1 pc2 , respectively. From previous derived relations, the gas masses are determined to Mgas = (3.4±1.1)1010 M and Mgas = (1.6±0.49)1010 M respectively. The molecular gas mass estimates are similar to dynamical estimates assuming rotation, which suggests that the inner region of these galaxies are gas dominated. A skewed emission line and magnification for SPT0125-47 suggests that this source is either a rotating disc or a system of galaxy mergers.
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