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Hydro simulations and SAMs: two sides of the same coin arXiv:1109.4635 Eyal Neistein TMoX group, MPE Garching Collaborators: Sadegh Khochfar, Claudio Dalla-Vecchia, Joop Schaye Eyal Neistein Dekel 60 Hydrodynamic simulations (HYDs) Typical questions: • How each process affects the galaxy mass? (feedback, SF, Cooling) • Why changing the parameters of a given process (e.g. SF) do not affect the galaxies? What is `self-regulation’? • What is the physics missing in order to reproduce the observational results (e.g. the LF)? • Can we extrapolate the results of one zoom simulation into a large volume easily? • Can we easily quantify the differences between different codes/parameters? We need a tool to post-process a HYD ! Eyal Neistein Dekel 60 Semi-analytic models (SAMs) Can we use a SAM in order to interpret HYDs? What is a SAM? • Each galaxy is described by only 3 numbers • Use the same underlying DM merger trees as in the HYD fs – star formation fc – cooling; fd – feedback fa - accretion Is this description accurate? Unique? Do we need only hot & cold gas? Is it the right tool ?? Eyal Neistein Dekel 60 Project outline 1. We take a HYD that was run over a cosmological box (OWLS, Schaye+10) 2. We extract the rates of: accretion, cooling, feedback, and SF directly from the HYD 3. We save these rates as function of halo mass and redshift only HYD f f (M , z) 4. We run our SAM using the above recipes over the merger trees that are extracted from the HYD Recipes: fs, fc, fd, fa SAM Dark matter merger trees Eyal Neistein Dekel 60 The history of one galaxy We follow all the particles, and check which got heated/cooled/SF/accreted fs – star formation fc – cooling; fd – feedback fa - accretion Eyal Neistein Dekel 60 How similar are the galaxies? Galaxies are compared on an object-by-object basis: The HYD & SAM are similar at a level of ~0.1 dex Eyal Neistein Dekel 60 Star-formation rates The SFR includes more scatter than integrated properties (like stellar mass) Eyal Neistein Dekel 60 Efficiency values The HYD physics is different from typical SAMs Eyal Neistein Dekel 60 One-phase model Assume that each galaxy is composed from ‘gas’ and ‘stars’ only: Works well!! Bouche +(2010), Krumholz & Dekel (2011); Khochfar & Silk (2011); Dave+ (2011) Eyal Neistein Dekel 60 SAM based on only one galaxy? We chose 3 random galaxies from the box ( ) The SAM recipes are extracted from one galaxy only The SAM runs over the entire volume Works well!! Eyal Neistein Dekel 60 Summary • HYD and SAM agree quite well, once efficiencies are matched on average • The SAM can be very simple, even one phase model is enough • All the recipes are summarized as a function of the host halo mass and redshift • The evolution of one galaxy includes enough information to extract the baryonic behavior • We have a common language for both SAMs & HYDs Happy birthday Avishai ! Eyal Neistein Dekel 60