SUGAR-1 Spectrometry in Ultraviolet of GAlaxies at Redshift-1

This paper describes the outcome of the work performed during the 28th Alpbach Summer School, focused on the theme The Birth, Life and Death of Stars. We propose a mission consisting of a large aperture (3.5m main mirror diameter) UV space telescope, with capabilities for imaging and low, medium and high resolution spectroscopy. Even though such a telescope can have multiple scientific applications, we suggest a survey-type mission (SUGAR-1), dedicated mainly to the spectroscopic study of starburst galaxies at redshift
z ~ 1, which corresponds to an epoch of enhanced star formation density in the history of the Universe and, in particular, to the time when our Solar System was born. Stars are the fundamental building blocks of galaxies. A major aspect of understanding galaxy formation and evolution is to understand their star formation history. Starburst galaxies are galaxies experiencing intense star forming activity and exhibiting strong UV emission from a young, hot stellar population. The study of starbursts helps us to understand the star formation process, and its influence on the environment and processes in the interstellar gas. The study of the star formation rate (SFR) at various redshifts is possible from the intensities of the H, H, OII and OIII lines, and the luminosity of the UV continuum. These can be used to generate Madau plots, which are diagnostic.
Madau plots indicate that a peak of star formation in the history of the Universe occurred at z ~ 1, which corresponds to -5 Gyr, i.e. the moment of the birth of our own Solar System. Observations of this era will enable us to investigate the initial conditions in galaxies like ours when the formation was triggered. By observing a large number of galaxies at 0.4 < z < 1.1, we can learn about the properties of the star formation processes and the conditions of the interstellar medium (ISM) and its chemical properties at this moment of enhanced star formation. Spectroscopy and imaging in the UV will have a great impact on galaxy evolution modeling, since they will provide insight on whether the time corresponding to z = 1 was a time of massive galaxy formation, or if the massive star formation of that time took place in already established galaxies, which were formed at a much earlier stage in the evolution of the Universe. Moreover, studies of the Universe at z ~ 1 are of cosmological relevance, because according to the Cosmological Standard Model, it is precisely at z ~ 1 when the Universe underwent a phase transition from ΩMatter being larger than ΩDarkEnergy, to the opposite. Therefore, to investigate this interesting time in the evolution of the Universe, we suggest the construction of a dedicated UV telescope with a pre-defined science mission to perform Spectrometry in Ultraviolet GAlaxies at Redshift-1 (SUGAR-1). In what follows, a more detailed description of the mission science goals is given. We will show how the science goals are transformed into science requirements for the mission, which are turned into telescope and instrument requirements. Then a brief description will be given of the main technical aspects of the mission (spacecraft structure, electronics, power and orbit). The spacecraft mass and cost budgets of the mission are addressed, ending with a final summary.