The Large Area Lyman- Survey (LALA)

Junxian WangUniversity 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

10-4 0.1

In nonuniform IGM

10-2 > 0.1

Source properties Very 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, SFRUV ≥350

M/yr) numerous chemical absorption features (6 hr

IMACS exposure)

Ly

SiII

OI/SiII

CIIFeII

SiIV

SiII

CIV

MUSYCGawiser 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

z Volume (Field) Sensitivity Candidates,

Spectroscopic Success rate

4.5 (5 filters)

1.4x106 Mpc

(Bootes, Cetus,CDF-S)

1.7x10-17 ergs/s/cm2 400; > 70%

5.7 (2 filters)

4 x105 Mpc

(Bootes, CDF-S)

1x10-17 ergs/s/cm2 ~50; ~70%

6.5 (1 filter)

1.5x105 Mpc (Bootes, CDF-S)

2x10-17 ergs/s/cm2 3; 1 of 3 confirmed.

LBG (broad band dropout)

LAE (narrow band excess)

Large volume Small volume

continuous redshift certain redshifts, but deeper

Hard to identify Easy to identify

sensitive to UV continuum

sensitive to Ly line

Luminous galaxies Fainter 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- SurveysA 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.

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

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 photonsLy 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

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 strength Age (Myr)Stellar Mass (108 solar

masses; 100,000,000*mass of Sun)

Low 200 23.75

High 4 1.08

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 ScatteringDark Ages

Galaxies, Clusters, etc.

Reionization

G. Djorgovski

First Galaxies

Dawson et al. 2007

Charting ReionizationCurrent 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.

Thank you!