Michael Shull (University of Colorado)

Transcription

1 Early Galaxies, Stars, Metals, and the Epoch of Reionization Michael Shull (University of Colorado) Far-IR Workshop (Pasadena, CA) May 29, 2008

2 Submillimeter Galaxies: only the brightest? How long? [dust forming? de-shrouding]

3 Some Big Picture Questions (1) When and how did the first galaxies form? Was the IMF different? (Mmax, Mmin, slope) Where did the first metals & dust come from? Which galaxies reionized the IGM? Star-formation, ionization efficiency? Primordial coolants? (H2, metals, dust) (2) How did later stars/galaxies assemble? Mergers, cold accretion, rise of metallicity Black Hole Co-Evolution and deshrouding Duration of rapid-accretion, dusty phase?

4 CMB Optical Depth (5-year data: Hinshaw etal 2008) τe = ± zrei 10.8 ± 1.4 This optical depth can be produced by a fully ionized IGM (at z zr 7) τe = 0.05 Plus additional optical depth Δτe 0.03 at z > 7

5 Shull & Venkatesan 2008 CMB Opt Depth: τe (0.05)[(1+zr)/8] 3/2 ioniz by stars/agn (z 7) Barkana 2003

6 Evolution of Low-Metal Stars Tumlinson, Shull, & Venkatesan (2003, ApJ, 584, 608) Why important? Pop III Increased Teff for Pop III stars Pop II at low metallicity Z C = 10-8, 10-7, Msun dominate the IGM ionization but for how long? 10 7 to 10 8 yrs

7 When is the transition (Zero-metal to Pop II stars?) Tumlinson, Venkatesan, & Shull (2004) ApJ, 612, 602 Zero-Metal Peak ~100 Msun Produce Msun of heavy elements (O, Si, Fe) Msun Pair Instability Supernovae

8 Cosmology: Halo Mass Distribution and Baryon fraction fb(z) = baryon fraction in halos f*(z) = fraction of stars formed efficiency of ionization (Ioniz Frac) = fb(z) [f*(z) Nγ fesc(z)] / (clumping) Star formation and stellar astrophysics Interstellar physics and radiative transfer

9 Ionization Efficiency = [f* Nγ fesc ] (type of halos and stars needed at zr > 7) Low Efficiency (zero-metal stars) (Z >10-3 Zsun) High-Effic. Tvir 10 3 K Shull & Venkatesan 2008 Extra CMB optical depth (at z > zr) Pop III mini-halos, stars transition to Pop II

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11 High-Redshift Star Formation (z = 12.5) -- Cosmic Web H2 cooling

12 What might the First Stars look like? Slow cooling and gravitational collapse of proto-galactic clouds (Abel 2007)

13 Ricotti, Gnedin, & Shull 2008 (ApJ, arxiv: ) < Z < 0.05 Zsun Molecular Hydrogen in Z < 5x10-4 Zsun the Dark Ages With positive feedback xh T 5000 K No feedback

14 Early Star Formation (Mini-halos) DM Halos: f* = x10 7 Msun

15 Star-Formation Rates SFR 0.05 Msun/yr M* 5x10 6 Msun MDM 10 8 Msun

16 Predictions for JWST (K-band) [dwarf primordial galaxies at z > 8] NIRCAM detection limit (10 5 sec) 100 njy sources 10 per field

17 Structure Formation & Metal Transport Oppenheimer, Davé, & Finlator (Princeton Univ.)

18 Growth rate of IGM metallicity (for SFR density over 1 Gyr) Z 1% solar in Gyr Assumed metal yield y m = (per M sun ) SFR density scaled to peak value (z = 2-6) SFR 0.1 M sun yr -1 Mpc -3

19 The first stars, galaxies, and quasars enrich the surrounding gas High-mass stars make O, Si, Fe (and some C) They are prodigious LyC emitters (reionization) What happens next? When does gas cooling exceed adiabatic heating? At what Zcrit does F-S cooling exceed H2 cooling? Transition from (zero-metal) to Pop II stars? Dependence on stellar mass range (O, Si, Fe)? Time-dependent cooling, coupling to CMB?

20 Duration of Metal-Free Phase? (Self-polluting 10 6 Msun halos at z =10-20) t 10 7 to 10 8 yr Rvir = (160 pc) M6 1/3 [20/(1+z)] Tvir = (1060 K) M6 2/3 [(1+z)/20] nvir, H = (0.27 cm -3 ) [(1+z)/20] 3 The rest of metals blow out into the IGM

21 Molecular Cooling (H2 rotational lines) Strongest transitions are from ortho-h 2 (J = 3-1) and from para (J = 2-0) rotational states, excited in neutral clouds primarily by H o - H2 collisions Strongest transitions have critical densities ncr 10 3 to 10 4 cm μm J=3 J = 2 0 (28.22 microns) T exc = 510 K J = 3 1 (17.03 microns) T exc = 1015 K Santoro & Shull (2006, 2008) 28 μm J=2 J=1 J=0

22 Abundant Heavy Elements (with ground-state fine structure lines*) No fine structure in S II, Mg II, Ca II, Ar I C II (2p) 2 P1/2,3/2 O I (2p 4 ) 3 P2,1,0 Si II (3p) 2 P1/2,3/2 Fe II (4s 3d 6 ) 6 D9/2,7/ microns & microns 34.8 microns microns *Assume ionization state set by FUV photons (E < 13.6 ev) Thus, dominant ions are C II, Si II, Fe II

23 Locus of Minimum Zcrit values High-mass stars: nucleosynthetic products (O, Si, Fe) % Solar q Low-density Zcrit track LTE High-density values for Zcrit

24 3.2 3 Time-dependent Cooling zi = 30 Santoro & Shull 2008 temperature 2.8 [Fe/H] = log(t/k) 2.4 Inflection Pt K TCMB 80 K log(n/cm^(-3)) Cooling to n = 10 4 cm -3 requires Zcrit 10-2 Zsun at n = 100 cm -3

25 Jeans Mass [Fe/H] = -4.0 [Fe/H] = Msun 10 Msun LTE fsantoro 17-Oct :57 [1]

26 Fine-Structure Line Luminosities (LTE) (10 8 Msun cooling at 200 K and 0.01 Zsun) [FeII] 26 μm [OI] 63 μm [SiII] 34.8 μm Strongest lines: Fe II 26 μm, O I 63 μm and Si II 35 μm [O I] 63 μm redshifted into the FIR/sub-mm (e.g., 350 μm window) Li = erg/s Fluxes (z=4) to W m -2

27 H2 emission will be much stronger in merging systems More gas ( Msun) and hotter (shocks)

28 Astrophysical Summary Primordial Dwarf galaxies (106-7 Msun) njy sources (K-band) Reionization (z 8-10) by early massive stars and BHs (X-rays) High-z: individual values of Z(C, O, Si, Fe) - enhanced O,Si,Fe) Primordial cooling H 2 and FS lines: FIR at to W m -2 (easier to detect H2 in shocked/merging systems) These observations will require major (large) telescopes