spin(e)

Observational information on the morphology of galaxies and its dependence on environment is routinely becoming available for galaxies up to redshifts two and beyond. Galaxies appear quite different at high redshifts, and quite far from the current Hubble sequence. Thanks to a well-established paradigm of cosmological structure formation, many of the boundary conditions for galaxy formation are now well defined. Modern simulations based on this paradigm have established a tight connection between the geometry and dynamics of the large-scale structure of matter on the one hand, and the evolution of the physical properties of forming galaxies on the other. Key questions formulated decades ago are nevertheless not well answered. What are the main drivers determining the morphology of galaxies, which are responsible for establishing the Hubble sequence? When did this happen? What is the role of acquired angular momentum in shaping galaxies? Can we understand the complete "baryon cycle", where the evolution of the anisotropic IGM and galaxies are studied simultaneously? Cold flows are predicted and debated, but no smoking gun exists in the real world. This proposal aims at filling this gap: theorists and observers will work together to try and find proof of cold flows’ existence and understand the details of how they affect the structure of galaxies, in particular for the build-up of angular momentum. Over the past few years, our team has developed a suite of novel algorithms, based on recent progress in topology and computational geometry, to trace filaments right to the core of star forming galaxies. In parallel we have developed the corresponding theory in a series of papers. The “persistent skeleton” can now be implemented on noisy discrete large catalogues such as the SDSS, VIPERS, or future surveys like e-BOSS. Combining state of the art simulations, extraction tools and observational surveys should give us the unique opportunity to statistically constrain the anisotropic environment of simulated and observed galaxies (geometry, connectivity and dynamic of accretion) in order to explain the Hubble sequence. We have recently proposed a novel paradigm for the acquisition of disc angular momentum via filamentary flows. We found a closer connection between the 3D geometry and dynamics of the neighbouring cosmic web and the properties of embedded galaxies than originally suggested by the standard hierarchical formation paradigm. At these scales, the surrounding asymmetric gravitational patch ejects gas from the neighbouring voids towards their encompassing filaments, until the cold flows are swallowed by the galaxy, advecting their newly acquired angular momentum. The corresponding net distribution of angular momentum hereby seems to define the morphology of that galaxy. The evolution of the Hubble sequence is therefore driven by the geometry of the cosmic web. Conversely, the distribution of galaxy properties measured relative to their cosmic web should reflect this process. Our purpose is to explore fully the impact of these propositions on the origin of the Hubble sequence. We will rely on observations and numerical expertise to automate the extraction of skeletons and morphological parameters of galaxies from mock, public and proprietary catalogues. We will interpret galaxy evolution within the complex anisotropic 3D structure of the cosmic web, and verify that filamentary flows indeed feed the disc’s angular momentum in galaxies. We will also provide a critical assessment of the respective role of merger/interaction history, secular evolution driven by instabilities, stellar feedback, wind and nuclear activity, as a function of cosmic time. We will use state-of-the-art “full-physics” cosmological simulations, theoretical priors, and observed surveys to disentangle the relative effects of all these interconnected influences, which will be crucial for a detailed understanding of the origin of the Hubble sequence.