Quasar Absorption Lines

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1 Tracing the Cosmic Web with Diffuse Gas DARK MATTER GAS STARS NEUTRAL HYDROGEN Quasar Absorption Lines use quasars as bright beacons for probing intervening gaseous material can study both galaxies and diffuse gas that produces no luminosity at any wavelength 1

2 Astrophysics from (Quasar) Absorption Lines each line tells us the precise redshift, the amount of material intersected, and the temperature/velocity of the gas via the width of the absorption line can detect neutral H in amounts that are ~7 orders of magnitude smaller than required for 21-cm observations, at essentially any redshift (provided you can find a background source that is suitably bright, of course!) associated metal lines, if present, tell us the degree of chemical enrichment, ionization state, density, etc. Universal Timeline Best current estimate of the age of the universe The Bright Ages It appears that the era that dominates the assembly of stellar mass (and black hole accretion) was 9-12 Gyr ago Lyman α observable from the ground 2

3 zquasar=0.27 λobs=(1+zcloud)x1216 Angstroms The Lyman Alpha Forest of Neutral Hydrogen zquasar=3.20 λobs=(1+zcloud)x1216 Angstroms 3

4 Probing The Intergalactic Medium Using Quasar Absorption Lines * Quasar Keck/HIRES Quasar Spectrum HI C IV Observer Modern Lyman Alpha Forest Paradigm: Amount of HI present in a region of density ρ depends only on ρ and the radiation field intensity dark matter potential baryons HI isotropic UV radiation field 4

5 GOAL: the primordial dark matter power spectrum CMB physics z = 1100 dynamics Continuum fitting Lya physics z < 6 dynamics + termodynamics Temperature, metals, noise Tegmark & Zaldarriaga 2002 Why the Lyman alpha forest? Very small matter overdensities and absence of complicated baryon physics... The Re-Ionization of the Universe After recombination, the universe became largely neutral (mostly H) At some later time, sources of H-ionizing photons were able to ionize the gas in the IGM What were the sources, and when did it happen?? CBR observations had suggested as high as z~20 (now revised downward in redshift based on 3-year WMAP results), but QSO absorption lines suggest it could be happening before our eyes at z~6 5

6 Three stages Pre-overlap Overlap Post-overlap From Haiman & Loeb In the very highest redshift quasars, the forest is so thick that it begins to look like a completely absorbed medium. Some evidence that at z~6, the intergalactic medium is rapidly becoming entirely neutral. 6

7 IGM Lyman alpha Troughs in the Highest-redshift Quasars only ~20 such QSOs in the entire sky! (these are from the Sloan Digital Sky Survey) on-set of complete absorption by the IGM at z>5.8? is it the end of the reionization era? The Re-Ionization of the Universe Recent controversy: are there enough sources of ionizing photons (quasars and young galaxies) to do the job? Answers may need to await the James Webb Space Telescope, which will be the IR Hubble in ~8 years 7

8 Ionizing Photon Producers?? Galaxies Quasars Properties of Galaxies from Absorption Line Studies For many years, was the only access to information on high redshift galaxies Now that we have the ability to observe galaxies at similar redshifts, provides access to entirely different information detailed chemical abundances of many species different kind of selection criteria gas cross-section rather than luminosity exquisitely detailed physical conditions galaxy/igm interface - energetics of feedback processes and their effects on galaxy formation Together with direct observations of galaxies, can observe most of the baryons in the distant universe and compare to the dark matter distribution 8

9 Galaxies and the IGM Idea is to: Observe the relative distribution of young galaxies and the diffuse IGM Place constraints on the evironmental influences of galaxy formation and the feedback of star formation and AGN. Directly measure the largescale effects of feedback (if any) Using Galaxies as Absorption Line Probes galaxies at z>2 begin to overtake QSOs in surface density on the sky within observational limits (by a factor of ~50!) true IGM tomography 9

10 Gaseous envelopes around galaxies at high redshifts ~250 kpc (luminous sizes ~3 kpc) Densely Sampling the QSO z 10

11 57 kpc Pixel Optical Depth Results (O. Rakic, Leiden) 11