In this work, we study a system of two galaxies at z ~ 2, when the Universe was undergoing its peak of star formation activity. One of them is star-forming IR-bright galaxy for which we detect the CO emission line with ALMA. The other is a smaller satellite galaxy with low IR-radio luminosities. We study the physical properties of this system and check their variation with respect to different CO excitation ratios, CO conversion factors and dust attenuation laws. We use CIGALE - a spectral energy distribution modeling code - that relies on the energetic balance between the UV and the IR, to derive some of the key physical properties of the two galaxies, namely their star formation rates, stellar masses, and dust luminosities. We investigate the variation of physical properties using two different wavelength domains, the ultraviolet (UV) and the infrared (IR).  We find that the star formation rate and the stellar mass of the ALMA-detected galaxy, places it on the main sequence of star-forming galaxies. The molecular gas mass derived with the CO luminosity is far below the gas fraction of typical star-forming galaxies at z=2. The low molecular gas content results in a depletion time of 0.26 Gyrs, and its position on the CO to IR luminosities suggests the main-sequence (MS) activity only when using a galactic conversion factor and a low excitation ratio. The CO emission line does not constrain well the dynamics of the ULIRG and does not recover the molecular gas effectively. We discuss these properties and suggest that Astarte might be experiencing a decrease of star formation activity and is quenching through the main sequence following a starburst (SB) epoch.