Probing the epoch of formation of slowly rotating galaxies

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About one fifth of all stellar mass in the present-day Universe is locked in large galaxies that have two very special properties: they do not form stars and their stars do not show an ordered motion within the body of the galaxy. These systems are considered the end products of galaxy evolution, and are very different from galaxies at all other epochs. The proposed project is about understanding how galaxies attain this end state: how they stop forming stars and become quiescent, how they change their shapes from disks to spheroids, and how their stars lose the angular momentum inherited from the star-forming gas?The project targets a specific range in the redshift space (z<1), covering the last 8 billion years of galaxy evolution. Numerical simulations predict this to be the epoch when a substantial fraction of all galaxies changes from “fast rotators” (having high angular momentum) to “slow rotators” (having low angular momentum), a transformation of which we have no clear picture so far. The current evidence suggests that stars in galaxies in the distant universe (high redshift) largely form within rotating disks of gas, and therefore inherit the high angular momentum and relatively ordered rotation. A few known examples of massive galaxies at high redshifts, that had already stopped forming stars, indicate that stars in such systems have ordered motions and high angular momenta. This implies that star formation quenching processes characteristic for the distant universe do not significantly change the internal dynamical structure of galaxies. The differences between galaxies at high and low redshifts indicate there is a strong evolution of the internal structure of galaxies during the intervening several billion years. Yet, we have very little evidence of how this transformation happens, what are the main processes that facilitate it, and how it is related to the cessation of star formation. The project is going to map stellar kinematics (ordered and random motions) across galaxies, measure the stellar angular momentum and determine the intrinsic shape of galaxies, as a function of time (redshift). Furthermore, the project will determine the episodes of star formation and match it with the evidence for changes in internal dynamical structure of galaxies. The sample of galaxies for which this will be done is unprecedentedly large, comprising several hundreds of objects observed with the integral-field unit (IFU) MUSE on the VLT. This ensures the project will achieve its goals stated above, as well as facilitate a comparison with properties of local systems obtained through benchmark IFU studies of past years (e.g. ATLAS3D, Califa, Sami, MaNGA). Finally, the project will provide the first observational constraints for models and numerical simulations on the redshift evolution of the stellar angular momentum.