A HighResolution Survey of LowRedshift O VI Absorbers

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A High-Resolution Survey of Low-Redshift O VI
Absorbers

• ApJ Supps, July 2008
• (astro-ph 0706.1214)
• Todd M. Tripp, Kenneth R. Sembach, David V.
  Bowen, Blair D. Savage, Edward B. Jenkins,
  Nicolas Lehner, Philipp Richter, Bastien Aracil

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A High-Resolution Survey of Low-Redshift O VI
Absorbers
Not a friendly face?

• ApJ Supps, July 2008
• (astro-ph 0706.1214)
• Todd M. Tripp, Kenneth R. Sembach, David V.
  Bowen, Blair D. Savage, Edward B. Jenkins,
  Nicolas Lehner, Philipp Richter, Bastien Aracil

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Exciting new results from The Journal of Sleep
Research

• Olaf Lahl from the University of Düsseldorf
  reports
• Falling asleep for only six minutes is enough to
  significantly enhance memory
• Slumber is especially important for doing clever
  stuff such as extracting the gist of what has
  been learned.

see Scientific American, May 2008
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The Missing BaryonsShock-Heated Intergalactic
Gas?

• When gas accretes onto a galaxy, heating and
  cooling must occur. But how does this work in
  detail?
• Cen Ostriker (1999)
• Dave et al. (1999)
• Hydrodynamic simulations of cosmological
  structure growth
• 30 - 50 predicted to be in low-density,
  shock-heated gas at 105 - 106 K

Difficult to observe!
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UV Probes of Warm-Hot Gas

• Equilibrium and nonequilibrium ion fractions from
  Gnat Sternberg (2007)

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High spectral resolution is crucial
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Galactic Winds and Feedback
WIYN HST image of M82 (Gallagher et al.)
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HSTFUSE Studies of Low-z O VI Absorbers
See also Penton et al. 2000a,b 2002 2004 Chen
Prochaska 2000 Chen et al. 2005 Prochaska et
al. 2004, 2006 Shull et al. 1998, 2003 Stocke
et al. 2004,2006 Danforth Shull 2005
Danforth et al. 2006,2008 Tumlinson et al. 2005
Cooksey et al. 2007 Thom Chen 2008a,b
Detailed studies of particular absorption
systems Tripp et al. 2000,2001,2002,2005,2006
Tripp Savage 2000 Savage et al. 2005 Jenkins
et al. 2005 Aracil et al. 2006 Complete sight
line surveys Sembach et al. 2001 Savage et al.
2002 Jenkins et al. 2003 Richter et al. 2004
Sembach et al. 2004 Lehner et al. 2006, 2007
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Two Flavors of O VI Systems
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O VI - H I Velocity Offsets
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Number of O VI Absorbers per Unit Redshift

• Sample of 16 low-z QSOs
• STIS echelle (E140M) and FUSE spectra
• 51 intervening O VI absorbers comprised of 77
  individual components(excluding systems within
  5000 km/s of the QSO redshift)
• 14 associated O VI systems (34 components)
• Absorber redshifts range from 0.002 to 0.495

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Squeezing all the juice out
Tumlinson et al. 2005
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Squeezing all the juice out
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Wheres Waldo?A comment on line-identification
strategy

• Challenge for you find the absorption-line
  doublet

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Wheres Waldo?A comment on line-identification
strategy

• Challenge for you find the absorption-line
  doublet

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Line widths an important clue
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Multiphase O VI Absorbers
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Components that are well-aligned
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Collisional ionization equilibrium fails (H I
lines too narrow).

• What about non-equilibrium models?

Curves non-eq. radiatively cooling plasma models
of Gnat Sternberg (2007)
Caveat Gnat Sternberg neglect photoionization
by the UV bkg.
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Pure photoionization?
(Schaye 2001)
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O VI in Interfaces?
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Low-z O VI Absorbers Toward PG0953415 (Tripp et
al. 2006)

• z 0.06807 Nearest galaxy gt195 kpc away or L lt
  0.04 L
• (nearest known galaxy 736 kpc)
• z 0.14232
• Nearest galaxy ? 155 kpc

Surprising result the z 0.06807 absorber has a
high metallicity Z 0.5 Z(solar). How did
such high-metallicity gas end up so far from
luminous galaxies? But, is this a fluke?? Where
are the O VI systems typically found in a larger
sample?
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A few things to recite before the 6-minute nap

• 30 of the intervening O VI absorbers have simple
  profiles that are well-aligned with H I
• These simple absorbers are either photoionized
  or they arise in interface layers on the surface
  of colder clouds (like HVCs?)
• The rest of the intervening systems are complex
  and can accommodate warm-hot gas (only a few
  systems show strong evidence of hot gas though)
• Absorbers can be found far from luminous galaxies
  (better statistics needed!)

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Turbulent Mixing Layers?

• Magnetohydrodynamic simulation from Esquivel,
  Benjamin, Lazarian, Cho, Leitner (2006)

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The Hot Halo of the Milky Way
Left All-sky HVC map (Galactic
coords.) High-velocity clouds detected in 21cm
emission (contours) and O VI absorption (filled
circles). Colors indicate velocity as shown by
the scale bar. Sembach et al. 2003 Wakker et al.
2003 Savage et al. 2003
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Some closing comments

• Low-z O VI absorbers are ubiquitous, and the
  number per unit redshift agrees approximately
  with predictions from cosmological simulations
• However, the simplest interpretation of the data
  indicate that many are cold and probably
  photoionized is this still consistent with the
  simulations?
• It remains possible (in some contexts, e.g.,
  HVCs, even likely) that the O VI arises in
  interfaces between cool gas and a hotter phase.
• Such interfaces are not adequately modeled by
  large-scale simulations, but detailed interface
  models do not fully explain the observations
  either
• A good problem for plasma physicists!

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Absorption is 6 dex more sensitive!
Ly? vs. 21 cm
4? line log N(H I) 12.8
3? line log N(H I) 18.6
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Quasars bright enough for high-resolution
spectroscopy with GHRS or STIS are rare.
Consequently
Why COS?

• Statistics of existing samples are poor
• Most observations have modest S/N
• QSOs are known behind interesting galaxies or
  structures but have usually been too faint to
  observe

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High spectral resolution is crucial
Aracil, Tripp, Bowen, Prochaska, Frye (2006)
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