IGM absorption lines
Absorption lines seen in the spectrum of a distant quasar. Adapted from Danforth & Shull (2008).
Ionized medium up to z=5
Considering that is a delta function
Upper limit from observation in quasars spectra up to : .
By inverting the above formula, we find the number density per neutral hydrogen:
Compare with typical cosmological densities:
Conclusion: significant amount of hydrogen in IGM is ionized.
Lyman alpha forest
High-resolution spectrum of the bright quasar Q1422+231. Credit: Ellison (2000).
Lyman alpha forest (cont.)
Optical spectra of quasars at about z=6 showing the Gunn-Peterson effect. Credit: Fan et al. (2004).
Optical depth at high-z
Observed evolution of the optical depth. Credit: Fan et al. (2006).
Evolution of the IGM
The volume averaged neutral fraction of the IGM versus redshift. Credit: Fan et al. (2006).
From the “Dark Ages” to the present
Artistic view of the cosmic evolution, with evidence on the Epoch of Reionization. Credit: NASA.
Classification of absorption systems
Lyman alpha forest
- numerous, weak lines from low-density hydrogen clouds
- identification: proto-galactic clouds
- identification: extended galactic halos
Damped Lyman alpha (DLA) systems
- Rare, strong hydrogen absorption, high column densities:
- identification: intervening galaxies
- An intervening galaxies often produce both metal and damped Lyman alpha absorptions
A DLA system
Spectrum of the QSO 1331+170 with an absorption around 3370 Angstrom. Credit: Pettini et al. (2004).
Types of QSO Absorption Systems
Spectrum of the quasar PKS 0545+039.
Distribution of column densities
Number density distribution of Lyman-alpha absorping systems. Credit: Hu et al. (1995).
Evolution of absorping systems
Cosmic evolution of the number density of absorping systems. Credit: Janknecht et al. (2006).
I materiali di supporto della lezione
Mortlock et al. (2011), Nature, "A luminous quasar at a redshift of z = 7.085", http://arxiv.org/pdf/1106.6088v1
Fan et al. (2006), " Observational constraints on Cosmic Reionization", Annual Review of Astronomy & Astrophysics, vol. 44, p.415
Progetto "Campus Virtuale" dell'Università degli Studi di Napoli Federico II, realizzato con il cofinanziamento dell'Unione europea. Asse V - Società dell'informazione - Obiettivo Operativo 5.1 e-Government ed e-Inclusion