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The Intergalactic Medium: Where the Baryons Are

The Intergalactic Medium: Where the Baryons Are. Romeel Davé, Univ. of Arizona. A Review by Epoch. Reionization z=20  6 High-z IGM z=6  2 Low-z IGM z=2 0. WMAP: Reionization z~20. t = 0.17  0.04 (for best-fit L CDM model).  z reioniz =11-30 (95%). Kogut et al 2003.

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The Intergalactic Medium: Where the Baryons Are

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  1. The Intergalactic Medium:Where the Baryons Are Romeel Davé, Univ. of Arizona

  2. A Review by Epoch • Reionization z=206 • High-z IGM z=62 • Low-z IGM z=20

  3. WMAP: Reionization z~20 • t = 0.17  0.04 (for best-fit LCDM model). • zreioniz=11-30 (95%) Kogut et al 2003 Spergel et al 2003

  4. SDSS: Reionization z~6 • Gunn-Peterson trough (no Lya flux) at z>6. Fan et al 2003

  5. The First Star • >100M • SN or Collapsar? (140-240M) • 2nd Star: Suppress or stimulate? (Pop II.5) • Z~10-4Pop II

  6. Tvir<104 K, M<108M Sources or sinks of ionizing photons? (i.e. Can H2 Form?) If sources, can reionize at z~15. If sinks, can delay or lengthen reionization. Detect with 21cm emission/absorption? The Minihalo Epoch Shapiro et al 2003

  7. Galactic Subunits Stars+Lya cooling rad’n • Tvir>104K  HI line cooling • Top-heavy IMF • Detectable with JWST or 30m scope • Lya? HeII (1640)? Lya top-heavy IMF HeII Z=0 IMF HeII top-heavy IMF

  8. WMAP+SDSS=Trouble? • Rad X-fer models: Reionization happens quickly. • Matches SDSS, but not WMAP t. fneutral r/<r> T Gnedin 2000

  9. Double Reionization: A Likely Story? • First stars massive, top-heavy IMF, efficient ionizers • Early X-rays  H2, minihalo sources • Universe recombines, Pop II star can’t keep up. • Final reionization at z~6 from Pop II. Cen 2003

  10. Gunn-Peterson trough + HI halos Highly ionized gas tracing LSS From D. Weinberg The Optical Lya Forest From W. Sargent • 60’s: Early spectra described by uniform trough + individual clouds (pressure or gravity-confined HI). • 90’s: Keck/HIRES spectra described by a tiny neutral component tracing Cosmic Web. • A great success of CDM hydro simulations.

  11. The Lya Forest “For Free” • Simulations designed to reproduce LSS +ionizing background expected from quasars  Lya forest • Can constrain cosmology! Weinberg et al 2002

  12. Line Counting Statistics • Column density distribution is a power law: d2N/dNHIdX  NHI-1.5, over 10 orders of magnitude in NHI Hernquist et al 1996

  13. us The Fluctuating Gunn-Peterson Approximation tHI=A(z)r1.6GHI-1 Ly∝DM1.6 -1 z=3 CDM 11h-1Mpc * quasar H I Column Density, projected 200 kpc slice Dark: 1013 cm-2 Light: 1016 cm-2

  14. The Power of the FGPA • Baryon density: <tHI> + GHI Wb Rauch et al (1997): Wb > 0.017 h-2 • IGM Metallicity: tHI (r,T) + GHI + Metal lines  Z(r) • IGM Temperature: TIGM(r)  HeII reionization • Mass Power Spectrum: tHI + gas traces DM  Pmatter(k)

  15. The Enriched Lya Forest: Who ordered this? • Metals live far from galaxies! • Seen in almost all NHI>1014.5 absorbers (d~few @ z=3) • [C/H] ~ -2.5 • Early blowout or in situ enrichment? Songaila 2002

  16. Metallicity(d,t) Two ways: • Measure Z in ions tracing different densities. • Measure Z in a single ion at different NHI. Hellsten et al 1998 Davé et al 1998

  17. CIV+OVI = Metal gradient • Q1422+2309 HIRES (zforest~3.53.1) • OVI (d~1) seen in CIV systems (d~5). • OVI NOT seen in weaker HI systems. •  dlogZ/dlogd > 0.5 • Hard (9 Ry) photons aplenty  HeII reionization not complete until z~3.1 Davé et al. 1998

  18. Pixel Optical Depth Method Schaye et al. 2003 [C/H] = -3.47 +0.08(z-3) +0.65(log d-0.5)

  19. The Helium Lya Forest • Like HI, tHeII becomes unmeasurably opaque near reionization (doh!). • Large scatter at low-z: Patchiness? Croft et al 1997 Smette et al. 2002

  20. TIGM and He Reionization Theuns et al 2002 • When Helium reionizes to HeII, heat is released  TIGM goes up  tHI goes down • Detected in 1100 SDSS quasars! • zr,He=3.4, Dz=0.4

  21. Mass Power Spectrum • Fluctuations in tHIflucts in rDMpower spectrum! • For LCDM: Wm=0.38±0.09 +2.2(G-0.15) • Not sensitive to TIGM or (plausibly) varying Jn • Largest uncertainty: Continuum fit, i.e. <teff> Croft et al 2002

  22. Galactic Winds & the IGM • Galaxies affect IGM in 2 ways: Photoionization & Evacuation • Good agreement at large scales, but puzzling lack of flux at <500 kpc • Implies LARGE evacuation radii. • Can have significant effect on PLya(k) Kollmeier et al. 2003

  23. from B. Jannuzi The UV Lya Forest (z<1.5)

  24. z=3 Hubble expansion drives rapid evolution until z~2. z=1 Diminishing J counteracts Hubble expansion from z~20. z=0 Structure formation has little effect on forest evolution. Davé et al 1999

  25. Evolution of the Forest • “Break” in dN/dz around z~1.5. • Break in sims from dropping Jn, not structure formation or new population. • Sims break at too high z?  Star forming galaxies contribute lots to Jn Kim et al 2002 Davé et al 1999

  26. The FGPA at low-z • d-NHI relation tight at high-z • Scatter  at low-z from shock heating • Evolution in amplitude Evolution in NHI(d) • More bad news for low-z Lya studies! . Davé 2001

  27. STIS: Moving on up… PG 0953+415 and HS 1821+643 vs. artificial spectra (Davé & Tripp 2001) Large thermal component TIGM TIGM 5000  Amplitude agreement HI HI(z=0.17) = 10-13.30.7 s-1

  28. Wr(Å) fraction Lya Absorbers & Galaxies • Wr(r): Extended gaseous halos? • No… just matter clustering. Chen et al. 1998 Davé et al 1999

  29. Legend translation: Warm-Hot: 105<T<107K Condensed: Galaxies Diffuse: Ly Forest Hot: Clusters (T>107K) Baryons today are ~equally divided between bound structures, shocked IGM (WHIM), and diffuse IGM. Where are the Baryons? Davé et al 2001

  30. In a WHIM • Warm-hot gas: T=105-107 K • Low-density  Low SXRB contribution. • Very hard to detect in HI absorption or X-ray emission. Cen & Ostriker 1999

  31. OVI: Missing Baryon Tracer? • OVI traces warm-hot collisional gas and diffuse photoionized gas Fang & Bryan 2001 Chen et al 2003

  32. Conclusions • IGM contains most baryons at all epochs, and is an emerging tool for studying LSS and galaxy formation. • Reionization epoch is the “first frontier”; lots of ideas, few answers, exciting future. • Simulations accurately reproduce observations of post-reionization IGM, and can be understood via the FGPA. • Using simulations to provide “value-added” interpretations of data has yielded (e.g.): • Mass power spectrum at z~3 • Metallicity-density relation in diffuse IGM • Baryon density / ionizing background evolution • With COS, future looks promising for extending similar precision to low-z IGM studies. After that?...

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