Ingredients for the first star Reionization baryons the dark Ages`

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1 Between z 1100 and z 0 Ingedients fo the fist sta bayons the dak Ages` Paul van de Wef Steewacht Leiden,$& 0D\ electons The univese at z = 1089 ow do we get the univese to fom stas? Still a key question in cosmology: "fist light" Flat ΛCD univese: ¾ ¾ ¾ TCB =.75 ± 0.00 K ΩΛ=0.7 ΩCD=0. Ωb=0.04 The bayonic comonent consists of, e, Li and Be (isotoes). At ecombination, these nuclei catue electons and the gas filling the univese becomes atomic. ow do we fom stas out of this gas?

2 Fom gas to stas The bayonic comonent consists of, e, Li and Be (isotoes). At ecombination, these nuclei catue electons and the gas filling the univese becomes atomic. ow do we fom stas out of this gas? 7 Fist stuctues in the dak age In the cuent best CD model, the fist stuctues to fom ae the smallest (bottom-u). oweve, these ae dak matte halos; what we need to fom stas is collase of bayons. Poblem: gas essue can counteact o even sto gavitational collase of bayons. 8 Gavitational collase of gas clouds Fo gas clouds in viial equilibium, gavitation and essue balance eachothe: Ekin Eot = 0 oweve, if the gavitational enegy becomes fo some eason too negative, the cloud will collase: Ekin Eot < 0 Ekin = NkT = kt m fo sta fomation the mass has to exceed the Jeans mass J : J : T 0000 n with T in K and n in cm G 4 Eot = 5, = π R ρ R 15kT 1 15kT R > = 8π Gm ρ 4m π Gn 5k 15k T > G π m G n 9 The cosmological Jeans mass Gavitational collase with cooling Fagmentation J : T 0000 n with T in K and n in cm n (1z) T (1z) befoe decouling J = constant T (1z) afte decouling (adiabatic exansion) J (1z) / Poblem: gavity is dominated by dak matte. Theefoe this will only lead to hydostatic equilibium of the gas within the dak matte otential well, not gavitational collase. oweve, unlike the dak matte, the gas can cool > J begins to collase n inceases, but T constant: enegy adiated away J deceases smalle fagments unstable: fagmentation fagmentation density fagments inceases adiation taed inside fagments T inceases J inceases fagmentation stos otosta

3 ( (QUJ\ Radiative cooling of atomic hydogen gas %DOPU /\PDQ *URXQG6WDW DVFKQ Radiative cooling: collision excites atom, deexcitation by hoton emission; if hoton escaes fom gas, net effect is cooling of gas. So only woks if gas is wam enough to excite n= level: T>8000 K Atomic hydogen (helium etc) cannot adiatively cool below 8000 K (z~500)! 1 Cooling by olecula hydogen has enegy levels down to ~500 K, and could thus Give cooling to much lowe temeatues. Poblem: how do we fom in the ealy univese? ¾ diect adiative association is stictly fobidden by quantum mechanics ¾ at low z, foms on dust gains which act as catalyst: not ossible at high z ¾ thee-body ocesses ae only elevant at vey high densities (n > 10 9 cm - ) Solution: ecombination does not become quite comlete esidual fee electons oen a chemical athway to the fomation of 14 Timescale fo ecombination ne ne 1 t = = = R α n n α n e n : electon density e n : oton density R : numbe of ecombinations e sec and cm α = 10 T s t = T n Since n (1 z), we get t (1 z) at constant T at z = 9: t =10 8 yeas; at z = 0: t =10 11 yeas t always longe than age of the univese eionization neve comlete thee ae always esidual fee electons 15 Gas-hase chemisty Cooling by What do the fist stuctues look like? Two athways: e hν e hν Cooling halts when the column density becomes so lage that the hotons cannot escae the cloud. This haens at N( )>10 6 cm. Then the Jeans mass ises and fagmentation stos. At high z, the Jeans mass is much highe than at low z, because T emains high (inefficient cooling, high T CB ). ence the fist stas (so-called Poulation III stas) ae exected to be extemely massive. eaches abundance ~ 10-5 Othe molecules (D, Li) can also ovide adiative cooling but models show that cooling dominates. Bomm et al c They will aidly ionize a vey lage volume: the eionization of the univese

4 The fist sta 0 c c Photo-ionization equilibium of hydogen Full hydodynamics, chemisty and adiative tansfe simulation of the fomation of the fist sta (Abel et al 000) density Ionization ate R Qn Recombination ate R nen i Q is oduction ate of ionizing hotons Since ionization ate deends on n but ecombination ate on n, the ionization-ecombination equilibium will be stongly density-deendent. ence inhomogeneities (cluming) lay a majo ole (just like in nomal II egions). Dense clums ae had to ionize and may emain neutal. initial e-ovela stage individual souces escae hotons find thei way though high-density egions (high ecombination ate!) IG is two-hase medium D highly ionized egions D neutal egions ionization intensity vey inhomogeneous temeatue of hydogen atial ovela stage of hydogen ovela stage edshift evolution of log fom mean ionization density highe exosition by ionizing hotons! D ionization intensity inceases aidly ionization adiation does NOT each self-shielded, high-density clouds log of I faction Gnedin 000 D exansion into high-density gas D end of ovela hase D seveal unobscued souces 1 c D ionization intensity moe homogeneous gas density gas temeatue 4 4

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6 by what? James Webb Sace Telescoe ¾ assive zeo metallicity stas (Poulation III stas): oduce chaacteistic sectal lines ¾ Ealy (mini-)quasas: bight oint souce, hade sectum, hotons enetate deee; X-ays may catalyze fomation of sta fomation induced in low-mass halos ae the souces of eionization obsevable? JWST (6.5m infaed-otimized successo of ST, launch 010) will obseve the eoch of fist light 1 simulation of 1% of a dee JWST image when? Afte eionization Since we cannot (yet) obseve the souces of eionization diectly, we must ely on indiect methods to detemine the eoch of eionization. One method is the olaization stuctue of the cosmic micowave backgound, whee eionization should give a edshift-deendent lagescale olaization signal. This has vey ecently been detected by WAP. Result: z eion =17±5 Out of each with cuent instuments, but accessible with JWST. Afte eionization sta fomation will neve be the same: ¾ the fist massive stas oduce dust which catalyzes fomation aid fomation of molecula gas, cooling and sta fomation ¾ the fist massive stas ollute the InteGalactic edium (IG) with heavy elements which geatly incease the cooling ate stongly inceased sta fomation ate. As a esult, sta fomation is fom this eoch on much moe simila to sta fomation in the esent-day univese. The metals ejected by Po III stas should be taceable in the high-z IG quasa absotion lines can obe this