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

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

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

What are LAEs?  Lyman-Alpha Emitting galaxies

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

The Gunn-Peterson Test and LAEs

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

How to detect LAEs?

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).

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

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

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

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.)

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

Blank sky search for Lyman alpha lines

LBG vs LAE ?

Origin of the Lyman break Steidel & Hamilton 1992

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

Windows for Narrowband Surveys Z=6.9

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

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

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

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

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 < z < 9: Several surveys in progress, no confirmed detections yet.

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)

A Bright High Equivalent Width Galaxy

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

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.

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

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

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

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)

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.

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

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

Two populations of LAEs? Finkelstein et al. 2008

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) Low High41.08

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

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.

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

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 )  This implies a qualitative change: enough photons existed after z=6 to ionize the IGM, but not before.

Dawson et al. 2007

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.

Madau Plot

Extension to redshifts z > 7

 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: VISTA

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

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

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