z > 6 Surveys Represent the Current Frontier z > 6 Surveys Represent the Current Frontier

Motivation:

- census of earliest galaxies (z=6, =0.95 Gyr) - contribution of SF to cosmic reionization - constraints on early mass assembly - planning effective use of future facilities (ELTs,

JWST)

Developing complementary optical/IR techniques:

- Lyman break dropouts

- Ly emitters

- strong gravitational lensing by galaxy clusters

Some Key Issues Some Key Issues

• How effective are the various high z selection methods? - L*(z=6) i~26 where spectroscopy is hard

- spectroscopic samples biased to include strong L- great reliance on photometric redshifts

• Is there a decline in the UV luminosity density 3<z<6? - results are in some disagreement - differing trends in continuum drops & L emitters

• Significant stellar masses for post-burst z~6 galaxies - how reliable are the stellar masses?- inconsistent with declining SF observed 6<z<10? - does this imply an early intense period of activity? - in conflict with hierarchical models?

Continuum sources probed via dropout techniqueContinuum sources probed via dropout technique

z-dropout

Traditional dropout technique poorly-suited for z>6 galaxies:

- significant contamination (cool stars, z~2 passive galaxies)

- spectroscopic verification impractical below ~few L*

i-drop volumes: UDF (2.6 104), GOODS-N/S (5.105), Subaru (106) Mpc3

flux limits: UDF z<28.5, GOODS z<25.6, Subaru z<25.4

Stanway et al (2003)

Reducing Contamination from z~2 Passive GalaxiesReducing Contamination from z~2 Passive Galaxies

z~2 passive galaxies

Addition of a precise optical-infrared color (z - J) can, in addition to the (i - z) dropout cut, assist in rejecting z~2 passive galaxy contaminants.

(Stanway et al 2004)

(z – J)

(i – z)5.7 < z < 6.5

This contamination is ~10% at z~25.6 but is negligible at UDF limit (z~28.5)

Contamination by cool Galactic dwarfs - more worrisomeContamination by cool Galactic dwarfs - more worrisome

HST half-light radius Rh more effective than broad-band colors

Contamination at bright end (z<25.6) is significant (30-40%)

L dwarfs

E/S0

UDF z<25.6 (Stanway et al 2004)

ACS dropouts: Luminosity Dependent Evolution?ACS dropouts: Luminosity Dependent Evolution?

Bouwens et al (2006, ~500 sources at z=6!!!) propose L-dependent evolution - decline in abundance over 3<z<6 mostly for luminous sources – finally hierarchical growth??

If correct, this affects z-dependent integrated SF density measures corrected to some fiducial luminosity

z=3

Decline in Decline in UVUV over 3<z<6 has been controversial over 3<z<6 has been controversial

Bouwens et al 2005 Ap J 624, L5

Poisson errors fail to account for dispersion in claimed number of z~6 i-drops, because of varying ways of accounting for contamination plus cosmic variance (10% in GOODS; 40% in UDF)

Bunker et al 2004

Giavalisco et al 2004

Results from SubaruResults from Subaru

• HST offers superior photometry & resolution (important for stellar contamination) but SuPrimeCam has much bigger field (each pointing = 2 GOODS-N+S)

• Additional photometric bands developed to sort stellar contamination

• Shioya et al (2005): used intermediate band filters @ 709nm, 826nm to estimate stellar contamination in z~5 and z~6 samples respectively

• Shimasaku et al (2005) split z-band into two intermediate filters zB, zR - to measure UV continuum slope

These studies confirm decline indicated via HST studies

z~6 dropouts from Subaruz~6 dropouts from Subaru

• SDF dataset > 2 GOODS N+S; cosmic variance ~ 25%

• Confirm 5 abundance drop from z~3 to 6 (c.f. Bunker et al, HST)

• Luminosity dependent trends - more evolution in massive galaxies?

Remember: this is observed number not dust-corrected SFR

The Spitzer Space Telescope RevolutionThe Spitzer Space Telescope Revolution

A modest 60cm cooled telescope can see the most distant known objects and provide crucial data on their assembled stellar masses!

IRAC camera has 4 channels at 3.6, 4.5, 5.8 and 8 m corresponding to 0.5-1m at z~7!

• Egami et al (2005) - characterization of a lensed z~6.8 galaxy

• Eyles et al (2005) - old stars at z~6

• Yan et al (2005) - masses at z~5 and z~6

• Mobasher et al (2005) - a galaxy > 1011 M at z~6?

Spitzer detections of i-drops at z=6Spitzer detections of i-drops at z=6 #1 z=5.83 #3 z=5.78

• 4 i-drops in GOODS-S confirmed spectroscopically at Keck

• Ly emission consistent with SFR > 6 M yr-1

• IRAC detections from GOODS Super-Deep Legacy Program

Eyles et al (2005) MNRAS 364, 443

Spectral Energy Distributions of i-drops #1 z=5.83 #3 z=5.78

Spitzer + Ly emission constrains present & past star formation

Ages > 100 Myr, probable 250-650 Myr (but Universe is only 1 Gyr old!!! (7.5<zF<13.5)

Stellar masses: 2-4 1010 M (>20% L*)

VLT K

VLT K

Look at lines!!!!!

Independent z~6 UDF Spitzer analysisIndependent z~6 UDF Spitzer analysis

3 sources at z=5.9, Yan et al Ap J 634, 109 (2005)

Confirms high stellar masses and prominent Balmer breaks

Spitzer detection of a resolved J-drop in UDF

Criterion: (J – H)AB > 1.3 plus no detection in combined ACS

While prominent detection in all 4 IRAC bands

JD2: strong K/3.6m break potential high mass z~7 sourceMobasher et al (2005) Ap J 635, 832

STARBURST99: z=6.6; EB-V =0.0; Z=0.02, zF>9

BC03: z=6.5; EB-V =0.0; Z=0.004, zF>9

Stellar Mass: 2-7 1011 M dependent on AGN contamination

High mass, two breaks, but not confirmed spectroscopically – risk of foreground

Mobasher et al (2005)

Uncertainty in Redshift and Stellar Mass

~ 25% chance of being z~2.5

Abundance of Massive Galaxies at z~6: A Crisis?

Abundance of massive galaxies at z~6 with CDM in terms of their implied halo masses, assuming

• Scalo IMF

• SF efficiency 20%

Find a 1013 M halo in the tiny UDF is a problem!

Yan et al

Eyles et al

Barkana & Loeb (2005)

z = 5.8

z = 15

Mobasher et al

Summary Summary

• Great progress using v,i,z,J-band drop outs to probe abundance of SF galaxies from 3<z<10: Bouwens et al discuss the properties of 506 I-band dropouts to z~29.5!

• In practice, these samples are contaminated by foreground stars, z~2 galaxies etc to an extent which remains controversial. We are unlikely to resolve this definitively with spectroscopy until era of ELTs.

• Comoving SF rate declines from z~3 to z~6 (and probably beyond)

• Contribution of lower luminosity systems less clear

• Spitzer’s IRAC can detect large numbers of z~5-6 galaxies and it seems many have high masses (one spectacularly so!) and signatures of mature stellar populations - implies earlier activity

• Reconciling mature galaxies at z~6 with little evidence for SF systems with 7<z<10 may turn out to be a very interesting result

Strong lensing & the hi-z UniverseStrong lensing & the hi-z Universe

Zwicky (1937) predicted its utility

From curiosity associated with verification of General Relativity to practical tool for cosmologists

Lensed pair Lensed pair dropoutdropout behind Abell2218: SED behind Abell2218: SED Implies Established Stellar Population @ z~7Implies Established Stellar Population @ z~7

Key parameters:

SFR = 2.6 M yr-1

Mstar ~ 5-10 108 M

z ~ 6.8 0.1

age 40 – 450 Myr (7 < zF < 12)

Age > e-folding SF time more luminous during active phase?

(Egami et al 2005)

Several groups are now surveying more lensing clusters - Given small search area, such sources may be very common

z > 6 Lyman z > 6 Lyman Surveys Surveys

Complementary techniques:

- narrow band imaging techniques (f< 10-17 cgs, L< 5. 1042 cgs, SFR~3 M yr-1, V~2. 105 Mpc3) at z=6

- lensed spectra (f< 3.10-19, L< 1041, SFR~0.1 M yr-1, V <50 Mpc3)

Origin: ionizing flux absorbed by H gas Ly photons

Lyman alpha emission: n=21, E=10.2eV, 1216Å

Efficient: as much as 6-7% of young galaxy light may emerge in L depending on IMF, metallicity etc.

1 M yr-1 = 1.5 1042 ergs sec-1 (Kennicutt 1998)(no dust, normal IMF)

Panoramic Imaging Camera on SubaruPanoramic Imaging Camera on Subaru

Megacam

Suprime-Cam

Can survey distant Universe for Lyman alpha emitters by constructing narrow-band filters and comparing with signal in suitably-chosen broad-band filters

Large Scale Structure @ z=5.7 via 515 LyLarge Scale Structure @ z=5.7 via 515 Ly emitters emitters

Ouchi et al 2005 Ap J 620 L1

Narrow bands in `quiet’ windows in night sky spectrumNarrow bands in `quiet’ windows in night sky spectrum

z(L) = 4.7 5.7 6.6 6.9

Requires panoramic imaging as z range is small

Airglow spectrum

Selection & spectroscopic verification of interlopersSelection & spectroscopic verification of interlopers

Hu et al (2003) z=5.7 survey

Compare signal in nb filter with broad-band signal using Subaru

Spectroscopic follow-up of candidates with Keck

5007Å

3727Å

1216Å

Example: LyExample: Ly Emitters at z=6.5 Emitters at z=6.5

Very distant Subaru Ly emitters:

(a) z=6.541, W = = 130, SFR=9

(b) z=6.578, W = 330, SFR=5

Kodaira et al (2003) PASJ 55, 17

spectra

z=5.7 Ly Luminosity Function

Shimasaku et al astro-ph/0602614

Comprehensive Subaru nb survey of 725 arcmin2

89 candidates

28/39 spec. confirmed

<EW> ~230 Å - normal stellar popn.

Malhotra & Rhoads 2004

LyLy Emitters at z~6.6 (Taniguchi et al 2005) Emitters at z~6.6 (Taniguchi et al 2005)

Two color criteria:

(z - NB921) > 1.0 and(i - z) > 1.3

Yields 58 candidates

Spectra confirm 9-14 out of 20 (45-70%)

Two key results:

-L emitters less significant than dropouts as contributors to SFR at z~6.6

-Yet an increasing fraction with increasing redshift (less evolution from z~3-6 than dropouts)