1. The Large Area Lyman-  Survey (LALA) Junxian Wang University of Science and Technology of China Beijing, July. 2008

2. LALA Collaborators  ASU: Sangeeta Malhotra, James Rhoads, Steven Finkelstein, Norman Grogin  China: JunXian Wang, Chun Xu,  Baltimore: Norbert Pirzkal, Katarina Kovac  Tucson: Buell Jannuzi, Arjun Dey, Michael Brown  Berkeley Diaspora: Hy Spinrad, Dan Stern, Steve Dawson

3. outline  introduction to LAEs (Lyman-  emitting galaxies) and the Large Area Lyman-Alpha survey (LALA)  Physical properties of LAEs  Constraints on cosmic re-ionization

4. What are LAEs?  Lyman-Alpha Emitting galaxies

5. Why study LAEs?  Lyα gives an easy way to spot high-z 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

6. The Gunn-Peterson Test and LAEs

7. Comparing the Ly-  and Gunn- Peterson Tests Gunn- Peterson Lyman α Threshold neutral fraction in uniform IGM 10 -4 0.1 In nonuniform IGM 10 -2 > 0.1 Source propertiesVery rare, bright.Common, faint. Redshift coverage Continuous.Discrete from ground; continuous above atmosphere.

8. How to detect LAEs?

9. 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).

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

11. Selection criteria  5  detection in narrow band  0.75mag color excess  4  color excess  <2  detection in veto band

12.  Success rate up to >70%  Contaminants include variable sources, asteroids, satellite trails, noise spikes in NB, foreground emission line galaxies ([OIII], [OII], etc).

13. LALA z=6.5 Source  Gemini GMOS spectrum shows an Asymmetric line and no continuum.  Nod and shuffle helps eliminate the possibility of other lines if [OIII] (5007) (Rhoads et al. 2004, ApJ; Gemini spectrum reduced by Chun Xu.)

14. Blank sky spectral search for LAEs  Integrated field unit  Multi-slit masks + narrow band filter  Long slits (behind strong lensing)

15. Blank sky search for Lyman alpha lines

16. LBG vs LAE ?

17. Origin of the Lyman break Steidel & Hamilton 1992

19. LBG in E-CDFS, R=22.8, z=3.38 strong Ly  emission (EW=60Å, SFR UV ≥350 M  /yr) numerous chemical absorption features (6 hr IMACS exposure) Ly  SiII OI/SiII CII FeII SiIV SiII CIV MUSYC Gawiser et al 2005

20. Windows for Narrowband Surveys Z=6.9

21. LALA filters  FWHM ~ 80Å (trade-off between sensitivity and volume)  Z ~ 4.5, 6559Å, 6611Å, 6650Å, 6692Å, 6730Å  Z ~ 5.7, 8150Å, 8230Å  Z ~ 6.5, 9180Å

22. LALA Survey Overview zVolume (Field)SensitivityCandidates, Spectroscopic Success rate 4.5 (5 filters) 1.4x10 6 Mpc (Bootes, Cetus,CDF-S) 1.7x10 -17 ergs/s/cm 2 400; > 70% 5.7 (2 filters) 4 x10 5 Mpc (Bootes, CDF-S) 1x10 -17 ergs/s/cm 2 ~50; ~70% 6.5 (1 filter) 1.5x10 5 Mpc (Bootes, CDF-S) 2x10 -17 ergs/s/cm 2 3; 1 of 3 confirmed.

23. LBG (broad band dropout)LAE (narrow band excess) Large volumeSmall volume continuous redshiftcertain redshifts, but deeper Hard to identifyEasy to identify sensitive to UV continuum sensitive to Ly  line Luminous galaxiesFainter galaxies trace the large scale structure

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

25. 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.

26. Physical Properties of Ly-α Galaxies  numerous LAEs with EWs > 200 Å  stellar populations are expected to produce peak EWs 100Å~200Å (Charlot & Fall 1993), EW ~ 80 Å for a normal stellar population.  Very hot stars?  Accretion power (i.e, Active Galactic Nuclei)?  Continuum preferentially suppressed by dust? (Neufeld 1991; Hansen & Oh 2005)

27. A Bright High Equivalent Width Galaxy

28. What is causing the emission?  Malhotra and Rhoads (2002) found numerous LAEs with EWs > 200 Å  stellar populations are expected to produce peak equivalent widths 100Å< EWmax<200Å (Charlot & Fall 1993), EW ~ 80 Å for a normal stellar population.  Large EW could be produced via star formation if the stellar photospheres were hotter than normal  Could be true in:  Low metallicity galaxies  Galaxies with an extreme IMF  Both scenarios possible in primitive galaxies, which contain young stars and little dust

29. Large equivalent widths  EW could be enhanced from the geometry of the ISM  Dusty clouds embedded in a tenuous inter-cloud medium  The high EWs can also be reproduced by active galactic nuclei, most likely type 2 AGNs,  The broad-lined (type I) AGNs are ruled out because we see no evidence of broad emission lines from either narrow-band imaging or spectroscopy.

30.  None of 101 imaged Ly  emitters were detected in X- ray individually

31.  neither in stacked images  Left: all Ly  emitters (effective exposure time 11.2 Ms)  Right: Ly  emitter with Ly  EW > 240Å

32. Lyman-α to X-ray ratios  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. Wang et al 2004, ApJ Letters 608, L21

33. 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)

34. 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.

35. The role of dust: enhance the line EW Ly  photons UV photons 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

36. Dusty Scenario  If the dust is primarily in cold neutral clouds:  Lyα photons scatter of the clouds and spent most of their time in the inter-cloud medium  ICM hot, mainly ionized  Continuum photons penetrate deep into the clouds and suffer greater extinction (Neufeld 1991; Hansen & Oh 2006)  ISM of our Galaxy is known to be clumpy down to small scales  If the continuum is more absorbed than the Lyα photons, than the transmitted EW is larger than the source EW

37. Two populations of LAEs? Finkelstein et al. 2008

38. Ages and Masses  We found the best-fit ages and masses for different categories of Lyman alpha galaxies: Ly  line strengthAge (Myr) Stellar Mass (10 8 solar masses; 100,000,000*mass of Sun) Low20023.75 High41.08

39. How does this compare?  Other galaxies at similar redshift have masses ~ 10 9-10 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 ~ 10 11 solar masses; ~ 10 billion years old.

40. Why is this interesting?  Compared to the Milky Way, the LAE’s are much smaller.  Consistent with hierarchical clustering theory of galaxy growth.  Compared with other high-redshift galaxies:  Our ages and masses are consistent with other studies of similar objects  One study derived smaller masses than ours, but their galaxies were fainter, so our results are consistent.

41. A Brief History of the Universe  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: ? Big Bang Last Scattering Dark Ages Galaxies, Clusters, etc. Reionization G. Djorgovski First Galaxies

42. 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.

43. Dawson et al. 2007

44. Charting Reionization Current evidence: Combine the Lyman α and Gunn-Peterson tests so far to study the evolution of the mass averaged neutral fraction, x: There is no contradiction between the GP effect at z=6.2 and the Ly α at z=6.5.

45. Madau Plot

46. Extension to redshifts z > 7

47.  Windows in the atmospheric OH spectrum continue into the J and H bands, though narrower.  Newest NIR cameras have A  sufficient for plausible LBG and Ly-  searches.  Especially with the help of strong lensing  Several efforts under way …  Horton et al 2004 (DAzLE project): VLT + DAzLE) z ~ 7.7  Smith et al (see Barton et al 2004): Gemini + NIRI, z ~ 8.2  Stark et al. 2007: Keck +NIRSPEC 6 candidates between z=8.7 and z=10.2  Willis et al ( “ ZEN ” project): VLT +ISAAC, z ~ 8.8  Cuby et al: VLT +ISAAC, z ~ 8.8  Nilsson et al: ELVIS @ VISTA

48. Z-Band Dropout behind cluster H JZ NB 1.06 Credit: Wei Zheng

49. Spectroscopic Followup  Approximately 12 bright z-band dropout candidates at AB < 25  VLT/ISAAC, low-resolution (6-8 objects), short exposure (1-2 hr)  Gemini-S/GNIRS medium resolution (4 objects)  None was confirmed yet

53. Wait for JWST?

54. Thank you!