Warm greetings to KIAA-PKU from CFA@USTC. Searching for the first galaxies. Junxian Wang University of Science and Technology of China Beijing, June. 2008. Z=0.158. How to find high redshift galaxies?. Look very hard Get lucky
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Credit: Mark Dickinson
Young galaxies forming their first stars produce copious ionizing radiation, hence strong Lyman- emission.(Partridge and Peebles 1967)
In principle, up to 6-7% of a young galaxy’s luminosity may emerge in the Lyman α line (for a Salpeter IMF).
High z LAEs not detected until 30 years later
There are now over a dozen research groups,
Over thousands candidate Lyman- galaxies,
Over hundreds spectroscopically confirmed
Up to a redshift of 6.96
Steidel & Hamilton 1992
LBG in E-CDFS, R=22.8, z=3.38strong Ly emission (EW=60Å, SFRUV ≥350 M/yr) numerous chemical absorption features (6 hr IMACS exposure)
Gawiser et al 2005
Spatial distribution of z=5.75 galaxies in the CDF-S region. (Wang et al. 2005, ApJL)
A partial listing of Lyman- surveys since the first discovered field Ly- galaxies:
z < 4: Hu et al 1998, Kudritzki et al 2000, Stiavelli & Scarlatta 2003, Fynbo et al, Palunas et al,
4 < z < 5: LALA; Venemans et al 2002; Ouchi et al 2002;
5 < z < 6: LALA, Hu et al 2003; Ajiki et al 2003, 2003; Wang et al 2005; Ouchi et al 2005; Santos et al 2004; Martin & Sawicki 2004;
6 < z < 7: Hu et al 2002, Kodaira et al 2003, Taniguchi et al 2004, LALA (Rhoads et al 2004), Cuby et al 2003, Tran et al 2004, Santos et al 2004, Stern et al 2005.
7 < z < 9: Several surveys in progress, no confirmed detections yet.
Large line to continuum ratios are common. (Malhotra & Rhoads 2002, ApJ Lett 565, L71):
Very hot stars?
Accretion power (i.e, Active Galactic Nuclei)?
Continuum preferentially suppressed by dust? (Neufeld 1991; Hansen & Oh 2005)
Wang et al 2004, ApJ Letters 608, L21
Individual Lyman-α emitters are consistent with some but not all Type-II QSOs, and most are consistent with Seyfert IIs.
The composite Ly-α to X-ray ratio strongly rules out a large fraction of AGN in the Ly-α sample.
Optical spectra show no sign of C IV or HeII lines.
These would be expected for AGN.
(Dawson et al 2004, ApJ 617, 707)
AGN fraction < 10%
Ly photons take longer path to escape, thus are more likely to be absorbed by smoothly distributed dust.
Ly photons can be scattered off at the surface of cold dust clumps, thus could avoid being absorbed by dust grains, while the continuum could be severely attenuated.
Hansen & Oh 2006
Galaxies, Clusters, etc.
There is no contradiction between the GP effect at z=6.2 and the Ly α at z=6.5.
Current evidence: Combine the Lyman α and Gunn-Peterson tests so far to study the evolution of the mass averaged neutral fraction, x:
Credit: Wei Zheng