The Distribution and Baryonic Content of the Ly? Forest at z<0.5

1
The Distribution and Baryonic Content of the H I
Absorbers at zlt0.5
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 1821643 0.297 24 19)
• HE0226-4110 0.495 10 30
• PG1116215 0.177 24 19
• PG1259593 0.478 15 34
• PG1116215 Sembach et al. (2004)
• PG1259593 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 lt3? are rejected.

HE0226-4110 Spectra
6
Broad Ly? Absorption
PG1259593 (Richter et al. 2004)
bgt40km.s-1 if purely thermal Tgt105 K
7
The distribution and Evolution of b
Hu et al. 1995, Kim et al. 2002
Fraction of systems with bgt50 km.s-1 three times
larger at z lt 0.5 than at z gt 1.5, five times
larger if bgt70 km.s-1.
Median b 31 km.s-1 at z lt 0.5 b 26 km.s-1 at
z gt 1.5
8
Distribution and Evolution of N(H I)

• Ly? Line Density
• log N(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 Function
f(NHI)

• Z slope ?
• gt 1.5 ?1.5
• (Tytler 87, Petitjean et al. 93, Hu et al. 95, )
• lt0.1 1.65?0.07
• (Penton et al. 2004)
• lt0.3 2.04?0.23
• (Davé Tripp 1998)
• lt0.5 1.70?0.10

Present sample zlt0.5
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Baryon Density Narrow Ly? Absorption Lines (b40
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
  (bthermal0.7b, Davé Tripp 2001, and bmedian28
  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
(40ltb150 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!
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IGM Baryon Density Summary

• b log N(H I) ?(Ly?)/?b
• (km.s-1 ) (cm-2) (?b0.044)
• Ph.Ion.IGM 40 13.20,16.20 gt 0.14
• Ph.Ion.IGM 40 12.42,16.20 0.28
• (Ph.Ion.IGM 150 12.42,16.20 0.42)
• WHIM gt 40 13.20,16.20 gt 0.21

13
Summary

• E140M/STIS and FUSE observations reveal narrow
  and broad H I absorptions in low-z IGM, tracers
  of the warm photoionized IGM (T104 K) and WHIM
  (T105-106 K).
• The Doppler parameter b increases with decreasing
  redshift.
• A larger fraction of systems have bgt40 km.s-1 at
  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, but the 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)!!!