Star Formation at the End of the Dark Ages

Transcription

1 Star Formation at the End of the Dark Ages...or when (rest-frame) UV becomes (observed) IR Piero Madau University of California Santa Cruz

2 Distant Star Formation: what who came first? neanderthal

3 Outline cosmogonic preliminaries formation of the earliest bound structures, stars, and massive black holes feedback on the IGM: the first miniquasars where are Population III remnants today?

4 post-recombination Universe H +! H He ++! He + cosmic zdec=1088±1, tdec=(372±14) kyr after the big bang, Universe becomes optically thin to Thomson scattering! at this epoch the electron fraction x drops below 13% and CMB cools below 3000 K! we understand the microphysics of the post-recombination Universe well: recombination freezes out with H and He recombination with RECFAST n e n H " x #10 $5 1/ % 2 M /h% b

5 cosmic dark ages zrei! residual free electrons keeps T IGM =T CMB until thermalization redshift: z t =750 (! b h) 2/5!150! Universe becomes semi-opaque again after reionization. WMAP measurement of electron scattering optical depth " e =0.17±0.04 implies z rei =17±5 Cosmic Dark Ages " e = z rei cdz $ (1+ z)h(z) # T n e (z) % x (1+ z) 3 / 2 &1 0 [ ]

6 CDM substructure z=0 <("M/M) 2 > 1/2 cold warm hot! no minimum scale for the gravitational aggregation of collisionless cold dark matter (CDM) " 2 M = #($M / M) 2 % = 1 ' ( dkk 2 P(k)T 2 (k)w 2 (kr) 2& 2 0

7 host lens galaxy QSO substructures Metcalf & PM 01

8 ! baryons do not feel DM clumps with mass below M J =(4#/3)$(5# kt IGM /3G$m p µ) 3/2 = 2.5%10 5 M " & M -1/2 h -1 (atigm /µ) 3/2 filtering Jeans

9 H2 molecules in post-recombination universe log (fractional abundance) redshift (1+z)! residual free electrons serve as catalysts for the formation of H2 through the negative ion H - : H + e " # H " + $. H " + H # H 2 + e "! H 2 is the main source of cooling in the first generation of gravitationally bound gas clouds H2 cooling inefficient below T~200 K and n~10 4 cm -3 Jeans mass M J = " 6 # b$ 3 J %10 3 '1/ M & n 2 3 / 2 4 T 200

10 first stars in 3# peaks (M

11 Primordial Star Formation final mass initial stellar mass Heger & Woosley 02

12 Pregalactic Enrichment z=10, rvir=0.75 kpc, vesc(0)=75 km/s, resolution=20 pc Mori, Ferrara, & PM 02

13 Keck/ESI spectra of SDSS quasars R=45km/s (1.3Å FWHM) SDSS (zem=5.42) Integration W 0 (3') (må) S/N SDSS (zem=5.80) 3h SDSS (z em =6.30) 9h h Pettini et al 03

14 C IV (( , C IV absorption z

15 mass density of C IV &CIV=(H0mCIV/c$crit) )Nf(N)dN f(n)=dn/dndx absorption distance X(z)=(2/3&M){[&M(1+z) 3 +& * ] 1/2-1} ) Nf(N)dN="N i (C IV)/+X; f(n),n -1.8 if (C IV/C)#f(z) - pregalactic enrichment

16 An early assembly epoch for the SDSS bright QSOs SDSS QSOs radiate with L=L E,M BH! M BH =2-3%10 9 M " time to grow from m " to M BH is +t = 4.5%10 7 ln(m BH /m " ) yr ~ 17 e-foldings = 7%10 8 yr (.=0.1, m"=150 M") comparable to age of the z 6

17 X-ray preheating Kuhlen & PM 1 Mpc ENZO: AMR grid-based hybrid code (hydro+nbody, Bryan & Norman) Dynamic range=32,768 >9800 grids, >2.2e7 grid cells Level 0: mesh cells -- M p = M " Level 1: mesh cells -- M p = M " + 6 levels of AMR for gas -- Mb=0.012 M"

18 *CDM, z in =99, z fin =15 z=25 high-' peak Mh=7%10 5 M" ENZO modified to include effect of a radiation point-source z=21 turn on 150 M" MBH accreting at Eddington rate and shining for a Salpeter timescale LX, 1// (200 ev<h/<10 kev) Code evolves the nonequilibrium rate eqs for 9 species: H, H +, H -,e, He, He +, He ++, H 2, H + 2

19 no miniquasar z=15 with miniquasar Temperature

20 Diemand, PM, Moore 05 z=14 z=0

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22 Summary In spite of remarkable recent progress, many fundamental questions in the formation and evolution of cosmic structure remain only partially answered:! how and when was the Universe reheated? We know that some galaxies and QSOs where already shining when the Universe was <10 9 yr old.! but when did the first luminous structure form and how bright were they? We believe there is a strong coupling between the thermodynamic state of the IGM and the process of galaxy formation.! but what `feedback mechanisms are at work in this interaction? The effect of the heat input from the first generation of sources on later ones remains an open question! what is the precise location and degree of metal enrichment of most of the baryons in the Universe?! what is the link between SMBHs and galaxy formaiion? And did the first MBHs form in subgalactic units far up in the merger hierarchy, well before the bulk of the stars observed today?

23 Probing early structure formation: future is bright and expensive! ALMA Constellation X LOFAR, SKA, PAST LISA James Webb ST

24 The end