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Accretion through cosmic time

Accretion through cosmic time. Joss Bland-Hawthorn (University of Sydney). Growth of fluctuations. Linear theory Basic elements have been understood for 30 years (Peebles, Sunyaev & Zeldovich) Numerical codes agree to better than 0.1% (Seljak+ 2003). CMBFAST (Seljak & Zaldarriaga 1996).

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Accretion through cosmic time

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  1. Accretion through cosmic time Joss Bland-Hawthorn (University of Sydney)

  2. Growth of fluctuations • Linear theory • Basic elements have been understood for 30 years (Peebles, Sunyaev & Zeldovich) • Numerical codes agree to better than 0.1% (Seljak+ 2003) CMBFAST (Seljak & Zaldarriaga 1996) relativistic fluid eqn solved explicitly (Mo et al. book) Bland-Hawthorn

  3. So is there evidence for accretion when atoms formed after decoupling from photons?After the CMB at To ~ 380,000 yr (z ~ 1089), the next epoch where we see evidence for action is z ~ 10 galaxies (To ~ 480 Myr).The period z ~ 1089 to z ~ 10 is known as the dark ages.But that's not stopped astrophysicists from predicting what signatures might be observable one day, say, with the SKA (e.g. Stu Wyithe at Melbourne).You can now follow many of the key papers since 1999. Nice calculator: http://www.astro.ucla.edu/~wright/ACC.html Bland-Hawthorn

  4. Main science driver of Square Kilometer Array (SKA) ~ 2020+ Accretion studies will be greatly advanced after the SKA comes on line. We will need the intervening decade+ to properly treat gas physics in cosmological simulations. This is a topic of the future! Bland-Hawthorn

  5. A lot of high-z astrophysics is done using the PS approximation. You learn a great deal by cramming in more physical processes than is possible in a full universal N-body simulation (where force calcs take a lot of time). But you are doing this in a statistical sense by making a long list of blobs you want to work with – an excel spread sheet is all you need! Bland-Hawthorn

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  8. Dark Ages: z~1089 to z~200, i.e. 380,000 to 6 million years? What options do we have to see anything post recombination? 2001 Wereally only have the HI 21cm hyperfine spin-flip transition. Bland-Hawthorn

  9. Dark Ages: a serious black out from z~1089 onwards ? In a neutral hydrogen universe, we really have only the spin (excitation) temperature Ts to work with and it needs to be different from TCMB CMB photons keep TS close to TCMB until z~200 through ICS so the universe is effectively dark to us. To detect HI, we need to decouple, but how? n1 hyperfine state due to spin flip  = 21.16 cm no ground state • Two ways: (A) Spin exchange between H atoms (Purcell & Field 1956) efficiency depends on local TK and density (B) Ly pumping: H then decays to hyperfine level (Field-Wouthuysen Effect) efficiency depends on local UV field (T = Ly temperature) Ly produced by UV radiation basically decouples HI from the CMB, but you need a source of UV emission, e.g. stars, QSOs, shocks? Bland-Hawthorn

  10. So what about accretion after decoupling? Power spectrum of n, T fluctuations vs. co-moving wavenumber The expanding universe was filled with cooling CMB and cooling HI… CDM density Baryon density Baryon temperature (TK) Photon temperature (TCMB) Why the Dark Ages? TK is bound on largest scales to TCMB by ICS until z~200 but decouples after that. Then TS ~ TK < TCMB so HI seen absorption against CMB until z~30. After that, collisions are rare, HI invisible again, except that H2 cooling inside mini-haloes starts. First stars, Lyα pumping, HI emission. gas heading for mini halos Bland-Hawthorn

  11. This paper showed how primordial gas (H, He) could cool without metals (no stars had been born yet to create them). We return to this topic in the lectures on first stars and galaxies. Bland-Hawthorn

  12. z ~ 150: TK falls below TCMB for the first time i.e. mean density is sufficient to collisionally couple TS to TK such that HI universe is mostly in absorption… Furlanetto & Loeb (2004): strongest HI emission from gas compressing into large-scale IGM shocks Shapiro et al (2006): strongest HI emission from gas compressing into mini halos (104 < M < 108); they find large-scale shocks of lesser importance T = TS-TCMB 0.5 Mpc co-moving box z<20: Ly pumping from first sources takes over… Bland-Hawthorn

  13. TS-TCMB Not defined Can’t use black In absorption Warming up but still in absorption Diffuse HI reionized Bland-Hawthorn

  14. First stars Bland-Hawthorn

  15. When did the first star form? ???? 1σ Maybe as early as z~65? But certainly by z~20-30 4σ 5σ Bland-Hawthorn

  16. 2008 atomic H, He H2 The basic physics is quite simple: dm/dt ~ Jean’s mass / infall time Bland-Hawthorn

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  18. The initial core that forms in the First Stars has the same mass as the hydrostatic (stable) core that forms in stars today. The difference lies in how much gas is accreted onto the outer layers in the next few million years as gas freefalls onto the core. Star forming regions today have Tgas ~ 10K But in the early Universe, Tgas ~ 200-400 K i.e. 100x accretion rate we infer today to form stars Thus First Stars may have grown to ~103 M !!! Bland-Hawthorn

  19. Radiative feedback around the first stars. V Bromm et al.Nature459, 49-54 (2009) doi:10.1038/nature07990

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  22. Pair instability supernova (PISN) leaves no black hole behind For a forming star with a mass 130-250 M, the core gets so hot that gamma rays collide and form matter/antimatter pairs which drain the energy. The star collapses converting a huge fraction of the mass to 56Ni. Such sources may have been seen in the local universe?! Bland-Hawthorn

  23. Where did the first black holes come from? Follow the “Salpeter argument” I give in my Saas Fee lecture notes (2013). I gave you a link to these in the work assignment. The fact that we see powerful quasars at z~7 (see figure above) argues for some “black hole” seed at much earlier times. These must be the very rare objects that could grow at the fastest possible rate to get to mBH ~ 109 M. Bland-Hawthorn

  24. FAR FIELD To=12.90 Gyr

  25. Do these first black holes affect the chemical elements we see today? Almost certainly YES. When the first supernovae explode, we suspect that an uncertain fraction of all the metals cooked fall back towards the black hole formed at the centre. Which elements are affected in the fallback is highly controversial. Bland-Hawthorn

  26. Can we detect specific signatures of the first stellar generations today? We don’t know yet since our first star models produce chemical signatures that we can’t easily relate to the most metal poor stars (in our Galaxy) or to the most metal poor clouds at the highest redshifts. Are we looking in the wrong place? Globular cluster: These are a puzzle. [Fe/H] = -1.5 but many are >12 Gyr old! Metal poor star, [Fe/H] < -5 Faint dwarf Bland-Hawthorn

  27. Most metal-poor star CS 22892-052 There is a subtle clue here that the star is indeed extremely old. Can you spot it? [Fe/H] < -5

  28. New development: very metal poor DLAs

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