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Dynamical constraints on the galaxy-halo connection

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While the correlations of galaxy variables are known from surveys, and the correlations of halo variables from N-body simulations, the relation between galaxy and halo properties—the galaxy-halo connection—is far from clear. I will describe an ongoing programme aimed at constraining this connection using dynamical scaling relations of galaxies, in particular the Tully-Fisher (TFR), Faber-Jackson (FJR) and mass discrepancy-acceleration (MDAR) relations, and the Fundamental Plane (FP). I develop an Approximate Bayesian Computation framework to evaluate abundance matching-based models of the galaxy-halo connection by comparing the predicted and observed values of a number of summary statistics of these relations. I find that while abundance matching naturally accounts for several important statistics (including the slope and normalisation of the TFR , the tilt of the FP, and the “acceleration scale” of the MDAR ), others imply specific constraints on galaxy formation physics: haloes expand in response to disc formation, galaxy and halo specific angular momenta are similar, spirals occupy less massive haloes than ellipticals at fixed stellar mass, and surface brightness is correlated with halo mass or concentration. Several aspects of the relations, however, are difficult to accommodate within the abundance matching paradigm; these include the correlation of velocity and size residuals in spirals, and the small scatter of the FP and MDAR . These problems likely indicate correlations of galaxy and halo variables beyond the scope of current empirical models.

This talk is part of the Galaxies Discussion Group series.

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