Wednesday, January 2, 2013

Jerusalem WS lecture notes: 06. The First Galaxies and Reionisation

By A. Loeb, with a short, but brilliant skit on adventure and creativity in science, slides uploaded here.
  • spectrum of the sky:
  • dip: Ly\alpha photons keep the gas coupled to its kinetic temperature
  • most of the comoving volume of the Universe is at high redshifts:
  • SDSS LRGs: 0.001 of the observable volume of the Universe (Loeb &Wyithe 2008)
  • What is the best time to be a cosmologist? At early time, Hubble scale grows, but due to expansion the comoving distance starts to shrink: objects enter and exit the horizon. The optimal cosmic epoch for precision cosmology was at z = 10 (
  • LF at various redshifts -- DM haloes mass slope
  • H, He cooling curve: no excitation at lower energies (T < 10^4), H_2 becomes important at lower T
  • Pop. 3.1 stars -- the very first stars, ~10^8 Myr after BB, SF conditions were differented, higher T: ~200K
  • Pop 3.2 stars: UV photons ionize surrounding gas --> much more efficient cooling by forming H_2, HD, HD radiative cooling --> gravitational instabilities
  • galaxies much more clustered on scales ~100 comoving Mpc than at present -- not many regions exceed the collapse threshold: bias, numerical bottleneck (need large dynamic range)
  • at higher redshifts (~8) you need to produce more photons per baryons to keep the IGM reionized
  • Pop3 observables:
    • stellar remnants:
    • Pair instability supernovae: best-understood SNe, Cooke et al. 2012. Lasts for years: long duration, luminosity comparable to SN II. 160-240 M_sol progenitors: if you start with a few hundredths M_sol progenitor, winds don't reduce the mass enough to avoid the PI SN. Collisionally-formed stars.
    • Long GRBs: seen to the edge of the obs. Universe, jets are drilling a hole in the star, followed by SN. Cosmological stretch of time: longer observation time
  • Ly\alpha forest: probing ISM by QSO spectra
  • Spin transition: Harward connection: horn antenna, snowballs, spin temperature, 21 cm tomography, cosmological evolution of the 21cm signal, X-ray heating (stellar mass BHs? X-ray binaries? AGNs?), LOS anisotropy: Kaiser effects, Pritchard & Loeb 2011, 'CMB is old', EDGES experiment: reionisation was not abrupt, EOR signal
  • extension to other lines: emission (CO, C, C II) by groups of galaxies: unresolved galaxy survey

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