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The Distribution and Baryonic Content of the H I Absorbers at z<0.5

The Distribution and Baryonic Content of the H I Absorbers at z<0.5. Nicolas Lehner, UW-Madison. Collaborators. Blair Savage, Bart Wakker (UW-Madison) Ken Sembach (STScI) Todd Tripp (UMass) Philipp Richter (Bonn Univ.). Introduction.

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The Distribution and Baryonic Content of the H I Absorbers at z<0.5

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  1. The Distribution and Baryonic Content of the H I Absorbers at z<0.5 Nicolas Lehner, UW-Madison

  2. Collaborators • Blair Savage, Bart Wakker (UW-Madison) • Ken Sembach (STScI) • Todd Tripp (UMass) • Philipp Richter (Bonn Univ.)

  3. Introduction • The Ly forest at low-z and high-z provides a powerful tool to probe the distribution and evolution of baryonic matter in the universe. • High-z Ly forest is typically observed with 6-8 km.s-1 resolution spectra. • The spectral resolutions of UV observations for the low-z IGM were typically 19-300 km.s-1. • Now, several STIS E140M (6.8 km.s-1) observations of low-z QSOs.

  4. FUSE and STIS E140M Observations • Wavelength coverage: 910 to 1730Å • STIS/E140M Resolution: 6.8 km.s-1 • FUSE Resolution: 20 km.s-1 zQSO S/N S/N (STIS) (FUSE) (H 1821+643 0.297 24 19) HE0226-4110 0.495 10 30 PG1116+215 0.177 24 19 PG1259+593 0.478 15 34 PG1116+215: Sembach et al. (2004) PG1259+593: Richter et al. (2004) HE0226-4110 FUSE and STIS Spectra (Lehner et al. 2005)

  5. Analysis • Line IDs. • Profile fitting. • Apparent optical depth. • b and N are measured simultaneously. • Detections <3 are rejected. HE0226-4110 Spectra

  6. Broad Ly Absorption PG1259+593 (Richter et al. 2004) b>40km.s-1; if purely thermal: T>105 K

  7. The distribution and Evolution of b Hu et al. 1995, Kim et al. 2002 Fraction of systems with b>50 km.s-1 three times larger at z < 0.5 than at z > 1.5, five times larger if b>70 km.s-1. Median b = 31 km.s-1 at z < 0.5 b = 26 km.s-1 at z > 1.5

  8. Distribution and Evolution of N(H I) Ly Line Density: logN(H I) dN/dz b ≤ 150 km.s-1 [13.20,16.20] 114  25 [13.64,16.20] 44  10 b ≤ 40 km.s-1 [13.20,16.20] 77  25 [13.64,16.20] 32  10 See Weymann et al. (1998), Impey et al. (1999), Penton et al. (2004). Sample completeness: log N(H I)13.2

  9. The Differential Density Distribution Functionf(NHI) Z slope  > 1.5 1.5 (Tytler 87, Petitjean et al. 93, Hu et al. 95,… ) <0.1 1.650.07 (Penton et al. 2004) <0.3 2.040.23 (Davé &Tripp 1998) <0.5 1.700.10 Present sample z<0.5

  10. Baryon Density: Narrow Ly Absorption Lines (b≤40 km.s-1): The mean gas density to the critical density is in the photoionized IGM (Schaye 2001): (NLy)≈2.2x10-9 /(h 12)(T4)0.59 f(NHI) (NHI)1/3 dNHI 12 = 0.05, H I photionization rate in 10-12 s-1(Davé & Tripp 2001). T4 = 2.3, gas temperature in units of 104 K (bthermal=0.7b, Davé & Tripp 2001, and bmedian=28 km.s-1). h = 0.7, Hubble constant (Spergel et al. 2003). f(NHI) the differential density distribution function.

  11. Baryon Density: Broad Ly Absorption Lines (40<b≤150 km.s-1): Cosmological mass density of the BLy absorbers in terms of today density can be written (Richter et al. 2004; Sembach et al. 2004): (BLy)1.667x10-23 fHI NHI/X fHI is the conversion factor between H I and H, function of temperature (Sutherland & Dopita 1993). Collisional ionization equilibrium (CIE) and pure thermal broadening are assumed. BUT NO metallicity correction needed!

  12. IGM Baryon Density Summary b log N(H I) (Ly)/b (km.s-1) (cm-2) (b=0.044) Ph.Ion.IGM ≤ 40 [13.20,16.20] > 0.14 Ph.Ion.IGM ≤ 40 [12.42,16.20] ≈ 0.28 (Ph.Ion.IGM≤ 150 [12.42,16.20] ~ 0.42) WHIM > 40 [13.20,16.20] > 0.21

  13. Summary • E140M/STIS and FUSE observations revealnarrowandbroadHI absorptions in low-z IGM, tracers of the warm photoionized IGM (T≤104 K) and WHIM (T~105-106 K). • The Doppler parameter b increases with decreasing redshift. • A larger fraction of systems have b>40 km.s-1at low-z than at high-z. • The observed baryonic content of the low-z IGM is enormous: photoionized 30-40%, WHIM at least 20-40%, butthe shallowest, broadest H I absorptions are still to be discovered!

  14. Concluding remarks • The low redshift IGM fundamental to follow the evolution of the IGM with z. • We need to increase the current sample. • Systematic search for metals. • Systematic deep galaxy redshift survey. • We need Cosmic Origin Spectrograph (COS)!!!

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