The Lyman Alpha Forest

By Shira Mitchell

Big Bang

Star Formation

Neutral universe

Ionized universe

When did stars form?

Wavelength

What is a Spectrum?

The distribution of energy emitted by a radiant source

Wavelength

Intensity

Atoms

n=1

n=2n=3n=4

Hydrogen Atom Energy Levels

Photon

1216 A

Electron excited

Atoms

n=1

n=2n=3n=4

Hydrogen Atom Energy Levels

Electron excited

Absorption

Wavelength Wavelength Wavelength

Intensity

Redshift

z = Observed wavelength - Rest wavelengthRest wavelength

The Cosmological Redshift is a redshift caused by the expansion of space.

Hubble’s Lawv = H*r.

v = recessional velocityr = distance from EarthH = Hubble's constant, 50-100 km/sec/Mpc (a megaparsec is 3,000,000 light-years)Hubble constant sets the rate at which the Universe is expanding.

Redshift• z = 6 farther back to the universe’s beginnings than z = 3

•Astronomers speak of the history of the universe in terms of red-shifts

Quasars

Short for quasi-stellar radio sources. They are bright active galaxy nuclei with huge

red-shifts and therefore, far distances

Quasar Spectrums

Wavelength

Intensity

Neutral hydrogen absorbed this light

Quasar Spectrums

Why is there a forest?

If the universe has so much hydrogen, why is there no trough?

The hydrogen must be ionized because ionized hydrogen can not absorb light.

Why is the hydrogen ionized?

The radiation from stars

Therefore, to find the trough, one must look at very very distant quasars to look for the trough back towards the universe’s beginnings.

Looking for the Trough

13 Apr 2000

Using the powerful Keck telescope on Mauna Kea in Hawaii, Robert Becker and his colleagues detected the imprint of neutral atoms on light from quasar J1030 0524, one of the most distant objects yet found. They found that, over a region of the spectrum corresponding to millions of years of cosmic history, no light from the quasar gets through -- it is all absorbed in intergalactic space.

Looking for the Trough

Quasar Spectrums

z=5.80

z=6.28

z = 6 means it left the sources less than a billion years after the Big Bang

Gun-Peterson Trough

Why is this important?

To understand the complex universe we live in today, it is

necessary to understand its evolution from an early state of

simplicity.

Current Progress

• Some astrophysicists are not satisfied with the trough in the z=6.28 quasar.

• A deeper understanding of the physics of reionization may be required

• Some astrophysicists and cosmologists have turned to computer simulations

Work Cited

• http://nedwww.ipac.caltech.edu/level5/Sept01/Rauch/Rauch4.html

• http://www.seds.org/~rme/cosmol.html

• http://astron.berkeley.edu/~mwhite/darkmatter/bbn.html

• http://astron.berkeley.edu/~john/lya.html

• http://nedwww.ipac.caltech.edu/level5/March01/Barcana/Bar1.html

• http://www.ticam.utexas.edu/CCV/projects/DiDi/cosmo/cosmo.html

• SPECTRA OF THE MOST DISTANT QUASARS ELUCIDATE THE REIONIZATION OF THE COSMOS, By Schwarztschild, Bertram, Physics Today, 00319228, Oct2001, Vol. 54, Issue 10 (Database: MasterFILE select)

• Cosmic Coincidences: Darkmatter, Mankind and anthropic cosmology, by John Bribbin and Martin Rees

• http://www.scienceagogo.com/news/20010710012750data_trune_sys.shtml