High Resolution Spectroscopy of the IGM: How High? Jill Bechtold, University of Arizona

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High Resolution Spectroscopy of the IGM How
High?Jill Bechtold, University of Arizona

• Central Question How were large galaxies like
  our Milky Way assembled out of small star forming
  fragments and the intergalactic gas during the
  last 10 billion years?
• Technique UV spectra of background quasars and
  starburst galaxies to study the IGM and its
  evolving relationship to luminous and dark matter
  in the Universe

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Outline

• Science which really requires gt10m aperture
• IGM tomography using multiple sight-lines
• 
  Simulation of H I from Cen
  Simcoe (1997)
• Spectral resolution how high?

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A 3D map of Galaxies and Gas

• How does gas collapse to form galaxies?
• How do large-scale structures affect the
  formation of stars and galaxies?
• How do galaxies and AGN enrich the gas?
• What environmental processes effect the variety
  of morphological type, stellar populations, age
  and metallicity we see in present-day galaxies?

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Key MeasurementMeasure Lyman series, metals and
H2 absorption using multiple background AGN and
correlate with galaxy redshift survey

• Need to sample a volume large enough to sample
  cosmic variance
• --gt similar volume to 2dF or SDSS survey, so
  several hundred Mpc on a side
• --gt 5x5 square degrees
• --gt 100,000 galaxy redshifts
• --gt mean separation of background AGN needs to be
  0.1 arcmin2 or few hundred per square degree

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Surface density of probes

• From Wolf et al. 2004

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Why do you need high spectral resolution?

• Resolve line widths, in order to fit profiles
  and derive temperatures and column densities
• Resolve velocity structure of profile into
  components ie physically distinct clouds of gas
  moving in the gravitational potential of the host
  galaxy
• Detect weak transitions of rare elements, to be
  on the linear part of the curve-of-growth, and to
  probe diagnostics of nucleosynthesis and depletion

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Why do you need high spectral resolution?

• FOS
• 280 km/s
• STIS
• 12 km/s
• Jannuzi 2004

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Lines-of-site Observed to date by STIS
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Simulated Lyman alpha forest spectra
R16 Quasar z(em)1.7 30 HST orbits E(B-V)0.05
STIS E230M
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R19
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R23
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What spectral resolution?Thermal Widths of
Absorption Lines

• 100 K 6,000 K
  100,000 K
• (diffuse ISM) (WHIM) (Coronal,
  IGM)
• A b R b
  R b R
• Hydrogen 1 1.29 140,000 9.99 18,000
  40.8 4400
• Helium 4 0.64 280,000 5.00 36,000
  20.4 8900
• Carbon 12 0.37 485,000 2.88 62,000
  11.8 15,000
• Nitrogen 14 0.35 523,000 2.67 67,000
  10.9 27,000
• Oxygen 16 0.32 560,000 2.50 72,000
  10.2 18,000
• Iron 56 0.17 1,052,000 1.34 134,000
  5.5 33,000
• A atomic weight
• b Doppler width in km/sec (2kT/m)1/2
• R (FWHM)

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Spectral resolution

• Follow Schroeder (2000) for a classical echelle
  spectrograph

Where R spectral resolution d1
the size of the spectrograph beam D
diameter of primary mirror d blaze
angle of the echelle grating f
width of slit if diffraction limited then
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Spectral resolution
Assume 10 inch beam, blaze 67 degrees then the
spectral resolution, R, is
The slit projects to the detector with width w in
microns given by
Where r anamorphic demagnification ( 1)
f focal ratio of the spectrograph
camera So for 5 micron pixels, 2 pixel sampling,
slit width 3x the diffraction limit, f 5,
camera is 4 feet long --gt ok
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Summary

• Pairs of quasars --gt IGM structure require 4m
  class telescope
• IGM tomography --gt m23 quasars, 20m or greater
  telescope aperture multiplexed
• R 106 spectrographs feasible, and would be
  necessary to probe T100 K diffuse ISM
• R20,000 100,000 have adequate resolution for
  coronal gas, WHIM, and IGM