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Semi-Analytic Modeling of Galaxy Formation

Semi-Analytic Modeling of Galaxy Formation. PhD student: Elena Ricciardelli Supervisor: prof. Alberto Franceschini. Halo merger tree. Given an halo with mass M1 at z1 we find an halo at z2>z1 through EPS Theory Halo progenitors searched until all The masses fall below the mass

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Semi-Analytic Modeling of Galaxy Formation

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  1. Semi-Analytic Modeling of Galaxy Formation PhD student:Elena Ricciardelli Supervisor:prof. Alberto Franceschini

  2. Halo merger tree Given an halo with mass M1 at z1 we find an halo at z2>z1 through EPS Theory Halo progenitors searched until all The masses fall below the mass resolution (40 km/s) The algorithm is taken from Sheth & Lemson (1999), not dependent on time-step

  3. Barions • At the bottom, assign a barion mass : • initially assumed at virial temperature: • At the bottom 1 halo  1 galaxy • During halo merger, galaxies inside them keep their identity • Galaxy mergers only after a timescale given by DYNAMICAL FRICTION

  4. Cooling: COLD MODE  for low mass, high z objects HOT MODE  for high mass, low z objects Star formation: QUIESCENT MODE  cold gas converted in stars disks BURST MODE  a starburst triggered after a galaxy merger, up to100% of gas is converted in stars in a period of 100 Myr  bulge

  5. SN feedback: a certain fraction of stars is in massive, fast evolving stars that become SNII energy injection in ISM by SN AGN feedback: RADIO MODE: continual and quiescent accretion on to a central SMBH, order of magnitude below Eddinghton limit QSO MODE:during galaxy mergers the gas mass accreted is proportional to the total cold gas mass with an efficiency dependent on the ratio of the masses of the merging galaxies

  6. Local Mass Functions Stellar Mass function: Good match with observations but we have an eccess of low-mass objects Dominated by bulge at high masses and by disks at low masses BH Mass function: Again overprediction of low-mass objects (slightly dependent on seed mass ) • Cole et. al., 2001 • SAM

  7. Evolution of Stellar Mass Function Slightly evolution at low-mass, but quite high evolution in the bright-end Most massive objects seem to assemble their stars at low redshift

  8. Star Formation Histories I • SFH for central • galaxies of haloes of • different mass • The peak of SF is at • about z=2 for all the • haloes • Galaxies in rich • environment (high • mass halos) form first, • high formation redshift FORMATION REDSHIFT: redshift at which 50% of the present stars are formed

  9. Star Formation Histories II • MADAU PLOT: • The peak of SF at z=2 • in agreement with data • from Hopkins et al. 2004 • SFR at high z is too low, • we need a mechanism • which enhance SF at • high z • Galaxies in most massive • haloes form their stars • first, peak of SFR at z=2-3

  10. Conclusions • Goog match of stellar and bh mass functions in the local Universe with the observed ones, even if we overpredict the faint end of the MFs • Galaxies in rich environments seem to form stars more quikly in the past, so they have high formation redshifts • The evolution of Stellar Mass Functions and of the SFR show that SF at high redshift is too low

  11. Global Mass function Grid of halo masses at z=0: up to Mass resolution given by Timestep carefully chosen In order to match CMFs and MFs of the PS formalism

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