Searching for the first galaxies

1. 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

2. Z=0.158

3. How to find high redshift galaxies? • Look very hard • Get lucky • Look next to something else • Watch the fireworks • Look smart (LBG, Lyman-α galaxies, submm) • get some help • etc Credit: Mark Dickinson

4. Galaxy Clusters as a“Cosmic Telescopes”

6. Lyman α from Young Galaxies 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

7. The Narrowband Search Method • take images in both broad and narrow filters. • Emission line sources appear faint or absent in broad filter • The blue “veto filter” eliminates foreground emission line objects (demand < 2σ).

8. The Narrowband Search Method • take images in both broad and narrow filters. • Emission line sources appear faint or absent in broad filter

9. Iye et al. 2006

10. LBG vs LAE ?

11. Origin of the Lyman break Steidel & Hamilton 1992

13. 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) OI/SiII SiII SiII FeII CIV SiIV CII MUSYC Gawiser et al 2005 Ly 

14. Windows for Narrowband Surveys Z=6.9

16. A Large Scale Structure at z~6 Spatial distribution of z=5.75 galaxies in the CDF-S region. (Wang et al. 2005, ApJL)

17. Lyman- Surveys 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.

18. Physical Properties of Ly-α Galaxies 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)

19. Lyman-α to X-ray ratios 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.

20. Composite Ly-α Galaxy Spectrum 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%

21. The role of dust: reduce the line EW Ly photons Continuum photons Ly photons take longer path to escape, thus are more likely to be absorbed by smoothly distributed dust.

22. The role of dust: enhance the line EW 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. Ly photons UV photons Hansen & Oh 2006

23. A Brief History of the Universe Big Bang • Last scattering: z=1089, t=379,000 yr • Today: z=0, t=13.7 Gyr • Reionization: z=6-20, t=0.2-1 Gyr • First galaxies: ? Last Scattering Dark Ages First Galaxies Reionization Galaxies, Clusters, etc. G. Djorgovski

24. Reionization: a phase transition. • The detection of Gunn-Peterson trough(s) in z > 6 quasars show neutral IGM at z~6. (Becker et al. 2001, Fan et al. 2002.) • This implies a qualitative change: enough photons existed after z=6 to ionize the IGM, but not before.

25. Comparing the Ly- and Gunn-Peterson Tests

26. Charting Reionization 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:

27. Madau Plot

28. Ages and Masses • We found the best-fit ages and masses for different categories of Lyman alpha galaxies:

29. How does this compare? • Other galaxies at similar redshift have masses ~ 109-10 solar masses. • These are consistent with our lowest line strength objects, which are also the brightest, and thus easier to detect in a normal survey. • The higher line strength objects are much fainter, which is why we only found them when we looked for the emission line. • Fainter usually means smaller, and we see this in their lower mass. • Milky Way ~ 1011 solar masses; ~ 10 billion years old.

30. Extension to redshifts z > 7

31. Z-Band Dropout behind cluster H NB 1.06 Z J Credit: Wei Zheng

32. Blank sky search for Lyman alpha lines

35. Wait for JWST?

36. Thank you!