1. High Resolution Spectroscopy of the IGM: How High
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

2. Outline Science which really requires >10m aperture:
IGM tomography using multiple sight-lines
Simulation of H I from Cen & Simcoe (1997)
Spectral resolution: how high?

3. 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?

4. Key Measurement: Measure 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
--> similar volume to 2dF or SDSS survey, so several hundred Mpc on a side
--> 5x5 square degrees
--> 100,000 galaxy redshifts
--> mean separation of background AGN needs to be 0.1 arcmin^2 or few hundred per square degree

5. Surface density of probes
From Wolf et al. 2004

6. 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

7. Why do you need high spectral resolution?
FOS:
280 km/s
STIS:
12 km/s
Jannuzi

8. Lines-of-site Observed to date by STIS

9. Simulated Lyman alpha forest spectra
Quasar z(em)=1.7
30 HST orbits
E(B-V)=0.05
STIS E230M

10. R=19

11. R=23

12. What spectral resolution? Thermal Widths of Absorption Lines
100 K ,000 K ,000 K
(diffuse ISM) (WHIM) (Coronal, IGM)
A b R b R b R
Hydrogen , ,
Helium , ,
Carbon , , ,000
Nitrogen , , ,000
Oxygen , , ,000
Iron ,052, , ,000
A = atomic weight
b = Doppler width in km/sec = (2kT/m)1/2
R (FWHM) =

13. Follow Schroeder (2000) for a classical echelle spectrograph:
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

14. 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 --> ok

15. Summary
Pairs of quasars --> IGM structure require 4m class telescope
IGM tomography --> m=23 quasars, 20m or greater telescope aperture; multiplexed
R= 106 spectrographs feasible, and would be necessary to probe T=100 K diffuse ISM
R=20,000 – 100,000 have adequate resolution for coronal gas, WHIM, and IGM