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First stars. When did the first star form?. ????. 1σ. Maybe as early as z~65? But certainly by z~20-30. 4σ. 5σ. 2008. atomic H, He. H 2. The basic physics is quite simple: dm/dt ~ Jean’s mass / infall time. - PowerPoint PPT Presentation

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  • Bland-HawthornFirst stars

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  • Bland-HawthornWhen did the first star form?Maybe as early as z~65?But certainly by z~20-30

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  • Bland-Hawthornatomic H, HeH2The basic physics is quite simple:dm/dt ~ Jeans mass / infall time 2008

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  • Bland-HawthornThe 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 Ki.e. 100x accretion rate we infer today to form stars

    Thus First Stars may have grown to ~103 M !!!

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  • V Bromm et al. Nature 459, 49-54 (2009) doi:10.1038/nature07990Radiative feedback around the first stars.

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  • Pair instability supernova (PISN) leaves no black hole behindBland-HawthornFor 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?!

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  • Bland-HawthornWhere did the first black holes come from?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.

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  • To=12.90 GyrFAR FIELD

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  • Bland-HawthornDo 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.

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  • Bland-HawthornCan we detect specific signatures of the first stellar generations today?We dont know yet since our first star models produce chemical signatures that we cant 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?Metal poor star, [Fe/H] < -5Faint dwarfGlobular cluster:

    These are a puzzle.[Fe/H] = -1.5 but manyare >12 Gyr old!

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

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  • New development: very metal poor DLAs

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  • Drop-out galaxiesThere is also the veto filter trick to look for Lya in a narrow filter, not in others, esp. for emission line sources. Famous work at Subaru.

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  • FAR FIELDTo=12.88 Gyr

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  • is this believable?

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  • Star formation & QSO activity with cosmic timeHopkins & Beacom (2006)

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  • Main science driver of the James Webb Space Telescope (JWST) ~ 2018+Bland-Hawthorn

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  • Bland-HawthornMain 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!

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  • Extremely Large Telescopes 2020 ff

  • Chem. Entwicklung d. MilchstrasseChem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Barkana & Loeb 07 figs; Naoz+ 06; Miralda-Escude 2003Not sure we believe that z~65 model still? Too early to form a star?The curves are 5sig, 4sig, 3sig fluctuations from RHS to LHSChem. Entwicklung d. MilchstrasseThe initial mass of the hydrostatic core that switches on is the same for the first stars,And for stars today. The difference is in the accretion that occurs onto that seed.Heavy elements today cool gas down to 10K, but H2 cooling only gets you to 200-300K.Mass growth rate = Jeans Mass / infall time ~ Cs^3/G ~ T^3/2 so the only things thatForm early on will have mass accretion rates vastly higher than modern stars, presumablyIn rare 10^6 Msun halos.Chem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Chem. Entwicklung d. MilchstrasseV^2 = GM/R, we can rearrange and differentiate to get Chem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Chem. Entwicklung d. MilchstrasseRecent paper by Chen, Heger, Woosley et al saying first stars ~ 55,000 Msun? (Heger)Chem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Chem. Entwicklung d. MilchstrasseIonized bubbles are shown in blue, and regions of high molecule abundance in green. The large residual free electron fraction inside the relic Hii regions, left behind after the central star has died, rapidly catalyses the reformation of molecules. The abundance of HD molecules allows the primordial gas to cool to the temperature of the CMB, possibly leading to the formation of population III.2 stars after these regions have re-collapsed so that gas densities are sufficiently high again for gravitational instability to occur77. The latter process takes of the order of the local Hubble time, thus imposing a 100Myr delay in star formation. The relatively high molecule abundance in relic Hii regions, along with their increasing volume-filling fraction, leads to a large optical depth to LymanWerner photons over physical distances of the order of several kiloparsecs (ref. 47). The development of a high optical depth to LymanWerner photons over such short length-scales, combined with a rapidly increasing volume filling fraction of relic Hii regions, suggests that the optical depth to LymanWerner photons over cosmological scales may be very high, acting to suppress the build-up of a background LymanWerner radiation field, and mitigating negative feedback on star formation75. Note the strongly clustered nature of early star formation. Visualization courtesy of the Texas Advanced Computing Center (based on data from ref. 47).*Chem. Entwicklung d. MilchstrasseReionization is when enough of these bubbles overlapChem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Chem. Entwicklung d. MilchstrasseChem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Barkana & Loeb 07 figs; Naoz+ 06; Miralda-Escude 2003Not sure we believe that z~65 model still? Too early to form a star?The curves are 5sig, 4sig, 3sig fluctuations from RHS to LHSChem. Entwicklung d. Milchstrassez=20 is only 600 Myr before z=7, if that's the epoch of the first starSalpeter times ~ 15 or so???*Chem. Entwicklung d. MilchstrasseFrom Bland-Hawthorn & Freeman (2013) Saas Fee lecture notesChem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Chem. Entwicklung d. MilchstrasseDm/dt = m, solution m=m_seed Exp[T/Ts], so-called e-folding timeChem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Chem. Entwicklung d. MilchstrasseChem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Barkana & Loeb 07 figs; Naoz+ 06; Miralda-Escude 2003Not sure we believe that z~65 model still? Too early to form a star?The curves are 5sig, 4sig, 3sig fluctuations from RHS to LHSChem. Entwicklung d. MilchstrasseChem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Barkana & Loeb 07 figs; Naoz+ 06; Miralda-Escude 2003Not sure we believe that z~65 model still? Too early to form a star?The curves are 5sig, 4sig, 3sig fluctuations from RHS to LHSChem. Entwicklung d. MilchstrasseSneden et al 1996 ff. (Anna Frebel, Norbert Christlieb, etc.)There is a whole interesting lecture on how they find these stars,Like prospecting for gold. Big Australian effort (John, Mike, Gary, etc. at ANU)Chem. Entwicklung d. MilchstrasseAAO summer student 2006-7Chem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Chem. Entwicklung d. MilchstrasseJennifer Johnston?Chem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Chem. Entwicklung d. MilchstrasseDont forget the last strong UV line weLy-alpha we can barely detect at z ~7Chem. Entwicklung d. MilchstrasseN. Christlieb/SS03*Chem. Entwicklung d. MilchstrasseThese are found with the filter drop-out technique*Chem. Entwicklung d. MilchstrasseThis is all SFH, the QSO activity looks similarChem. Entwicklung d. MilchstrasseN. Christlieb/SS03*