Starbursts from z~3 to 7-10Starbursts from z~3 to 7-10Daniel Schaerer (Geneva Observatory, OMP Toulouse)

• Stellar populations:

ages, star formation histories,

masses, (IMF, metallicities, …)• Reddening:

amount

(attenuation law, …)• StarFormationRate and SFR density

in z ~ 3 to 7-10 galaxies

(LBG and Lyman-α emitters)

Outline• Observables & methods – brief comments• Lyman Break Galaxies (LBG) at z~3

– Stellar populations, SF histories, reddening ...• LBG at z ~4 – 6

– Comparing their properties with z~3 – …including UDF

• Lyman-α emitters (LAE)• Distant galaxies seen through the Gravitational Telescope

– Properties of two lensed z ~6-7 galaxies– Searches for z ~ 7 – 10 galaxies and first results

Not discussed: ERO, sub-mm galaxies, red galaxies at z>3, …

Main observables:• Detailed spectroscopy -- rarely available at z>~3

age, SF history, IMF (from line fits) cf. talk Leitherer attenuation (from UV slope or Balmer decrement) cf. poster Noll+ abundances (eg. from R23, or from UV lines) cf. talks Rix, Mehlert,

de Mello

kinematics, masses cf. talk Erb

• Narrowband flux, « poor » spectroscopy z, emission line flux, EW

• Broad-band flux SED, zphot

– Detailed SED fits…– Beta-slope attenuation

• Average SED(z), luminosity functions, …

Observables & methods

this review

Observables & methods – SED degeneracies

1) age – reddening degeneracy (UV restframe):UV slope depends on age, SF history, reddening (+law)

Can be « broken » in some special cases! E.g.:- Presence of emission line (EL) ongoing SF (young burst or continuous SF)- Flat/rising slope + EL Strong extinction- Very steep (blue) slope young + no/little extinctionOr by adding: * restframe optical data (near-IR, SPITZER)* UV lines (cf. Leitherer talk)

2) A priori UV slope NOT metallicity indicator! For « normal » metallicities (Z>~1/50 Zsun) little dependent on Z. Very metal-poor populations: FLATTER slope due to nebular continuum !

Only possible if statistical correlations hold (e.g. Heckman et al. 1998)

LBG at z~3

Sawicki & Yee (1998, ApJ, 115, 1329):

* 17 spectroscopically confirmed LBG in HDF

with photometry in seven bands (UBVIJHK)

UV-optical (restframe) coverage to break

the UV age-degeneracy

* Assume: Calzetti attenuation law, Salpeter IMF, Bruzual & Charlot (BC) synthesis models,

variable metallicity,

* SED chi2 fitting free parameters:

age, reddening , SF history (burst/SFR=const)

Also: SFR, stellar mass estimates (from best-fit model, not standard conversion factors)

Large samples with spectroscopic redshift (~1000, e.g. Shapley et al. 2003)

Imaging: mostly optical (UV restframe), some also with near-IR

LBG at z~3Sawicki & Yee (1998, ApJ, 115, 1329):

* Extinction: non-zero, median E(B-V)~0.28

[A_V~1, factor ~16 at 1600 Ang]

* Age (of dominant population): young

(<~0.2 Gyr)

From sample spanning z~2 to 3.5, i.e. ~1 Gyr

episodic SF, not extended and continuous

* SFR: median ~59 Msun/yr (h100-2)

* Stellar mass: from burst or SFR=const models

median ~109 Msun

LBG at z~3Papovich et al. (2001, ApJ, 559, 620):

* 33 LBG in HDF-N with UBVIJHK

* Assume: Calzetti attenuation law, Bruzual & Charlot (BC) synthesis models, variable metallicity, Madau Ly-forest attenuation

* SED chi2 fitting free parameters:

age, reddening , SF history (exp. declining), IMF

Similar results as Sawicki & Yee (1998)

See also study of Shapley et al. (2001)

But: none of these studies includes information from

presence of Lyman-α

Main results:* mass estimates* typical ages: ~30 Myr to 1 Gyr now confirmed by SPITZER/IRAC mid-IR obs. (Barmby et al. 2004) * no young AND dust free object* From Δt of sample and relative absence of quiescent objects recurrent SF

Papovich et al. (2001)

Age – e-folding timeprob.distribution

Age – stellar mass probability distribution

Age – dust attenuation probability distribution

LBG at z > 3: from 3 to 4

• No detailed SED analysis of galaxies with z >>3

(cf. Schaerer & Pello 2004: 3 lensed galaxies with z>~6)

• UV luminosity density @ z=4 ~ identical to z=3:

Papovich et al. (2004) -- GOODSOuchi et al. (2004) -- SUBARU

Deep Fields global average SFR ~const if same reddening

• Reddening ~constant between z~3 and 4 (from UV colors: i-z’; Ouchi et al. 2004) But: Papovich et al. (2004): possible « blueing » (decrease of mean age, reddening, decrease of M/L)

Ouchi et al. (2004)

0 1 2 3 4 5

LBG at z > 3: from 3 to 5Ouchi et al. (2004) -- SUBARU Deep Fields (BVRiz’): ~2600 LBG at z~4-5

Possible decrease of UV luminosity density from z~3 to 5 – also Iwata et al. (2003) – HDF-N/SUBARU (Viz’) Lehnert & Bremer (2003) – Riz + spectroscopy

z~5: basically no information on reddening since i band affected by Lyman-α forest but: colors consistent with little reddening (L&B03+)• Important uncertainty at z>~5: integration

of LF ! No difference in observed LF from z ~3 to 5

(Ouchi et al.) 0 1 2 3 4 5

afterbeforeLF integration

z~5 spectroscopic follow-ups:* Iwata et al. poster* Douglas,Bremer+ (talk, poster)

LBG at z ~ 5 (cont.)Samples & follow-ups:

1) Iwata et al. (2003) – HDF-N/SUBARU (Viz’) Deep spectroscopy of 17 objects with FOCAS/SUBARU: Ando et al. (2004)

8 confirmed at z~4.5 – 5.2 7 with no or weak Ly-α emission, but relatively strong IS abs.lines In contrast with z~3 LBG ! Due to selection of brightest objects (>L*) ?

2) Lehnert & Bremer (2003) – Riz + spectroscopy cf. poster+talk Bremer+ Bremer et al. (2004) – Viz (Chandra Deep Field S)

6 of 13 galaxies confirmed by Ly-α emission (flux ~(0.2-2.5)*e-17) + break « high » EW(Ly-α) indicative of young age and/or ongoing SF X-ray non-detections: SB or < weak AGN

UV luminosity density from these and brighter objects insufficient to maintain ionisation Sources of reionisation fainter than MAB(1700Ang) > - 21

3) Ouchi et al. (2004) -- SUBARU Deep Fields (BVRiz’)no spectroscopic follow-up yet ?!

i-dropouts: LBG at z~6HST -- UDF: (ACS i’z’+ NICMOS JH)

* Bunker et al. (2004): 54 candidates i’-dropouts over 11 arcmin2 part of UDF (ACS only).

Determine LF, SFR density, …

* Stanway et al. (2004): ~27 candidates with i’z’JH

(z-J) color ~flat spectral slope – SB!

possibly bluer than LBGs at lower z

(lower reddening?, young populations?)

Stanway et al.z_phot z_photextinction

i-dropouts: LBG at z~6

HDF-N (i’z’/ACS + JH/NICMOS) and RDCS field (i’z’/ACS + JKs/ISAAC):

Bouwens et al. (2003 , 2004)

* 11+1 objects with optical + near-IR,

total 21+2 candidates with z>~6

* (z-J) color ~flat spectral slope – SB

* H or K: large uncertainties

no information on stellar populations

* detailed derivations of UV luminosity

density (SFR density) using different

methods and accounting for surface

brightness dimming => SFRD ~14x Stanway

small decrease (39±21 %) of SFRD

from z ~3 to 6

Going beyond z ~ 6-6.5 …

Requires:

* HST: UDF -- ACS+NICMOS (JH): some z dropouts with blue J-H ?!

cf. talk Thompson, poster Bouwens et al.

* HST: ACS grism spectroscopy (Ly-α break up to z ~7; cf. Rhoads et al.04)

* deep JH AND K photometry (J: 7-10 dropout)

present: combined with gravitational lensing !! Future: 30m tel.,JWST

* other selection technique: emission line search

(Lyman-α emitters (LAE))

with narrowband filters, tunable filters, « blind » searches (long-slit spectroscopy, IFU)… in optical or near-IR

So far: successfully applied to from z~2-4 to 6.58

Lyman-α emitters (LAE)

• Numerous LAE searches: see e.g. reviews by Spinrad (2003), Taniguchi et al. (2003)

• Currently used to trace SFR(z) out to

z~6.6 (also clustering properties…)

But: Lyman-α gives only lower limit on

SFR, since affected by several

« destruction » processes (dust,

ISM geometry + kinematics)

• Most LAE are detected in very few (1!)

or no broad-band filter

Little known about their properties,

stellar populations, nature, relation with LBG …Taniguchi et al. (2004)

High median EW(Ly-a) ! AGN ? Very-metal poor objects or Pop III ? Extreme/”massive” IMFs ?

Nature puzzling !BUT: Many metal free objects at z < 6 expected ?? High EW real? Uncertainties in EW from NB ?

Schaerer (2003)

Z=1/50 - 2 Zsun

Z=0

Z=10-7

Z=10-5

Lyman-α emitters (LAE) at z~ 4.5 – 5.7

LALA survey (4m Kitt Peak):BVRIz’+ 2 narrowband at z=4.5, 5.7* 157 z=4.5 LAE candidates

(Malhotra & Rhoads 2002) * 18 z=5.7 LAE candidates

(Rhoads & Malhotra & 2001)

NO ! Wang et al. (2004)

* Keck Follow-up spectroscopy of z=5.7 candidates: 3 of 4 confirmed (Rhoads et al. 2002) * no other UV lines detected (but deep enough?) (Wang et al., Dawson et al. 2004)* overall SED ? Nature of LALA sources puzzling !

Similar programs: Hu et al. (2004): SUBARU deep imaging, similar selection criteria 26 z=5.7 candidates, 19 confirmed (DEIMOS/Keck) less than 25% have EW(Ly-a) > 240 Ang! Difference due to deeper imaging !? Ajiki et al. (2002, 2004): several LAE, none with EW(Ly-a) > 200 Ang!

Lyman-α emitters (LAE) at z~ 4.5 – 5.7

Hu et al. 2002, ApJ, 568, L75Hu et al. 2002, ApJ, 568, L75

Abell 370 HCM 6A, z=6.56

• NB excessNB excess•asymetric emission line (Lya)asymetric emission line (Lya)• no secondary imageno secondary image• magnification 4.5 (1.6 mag)magnification 4.5 (1.6 mag)

z >~6-7 galaxies seen through the “Gravitational Telescope”

Prediction:IRAC/SPITZER (non detection) could

confirm strong extinction

SPITZER/IRAC sensitivity

Abell 370 HCM 6A, z=6.56

Main results from spectral fitting:

* Good fits with burst models: age ~ 100-200 Myr, ~no extinction -- BUT no Lyα emission expected then !!

* Good fits with SFR=const + non negligible extinction (AV~1.)

SFR ~ 80-300 Msun/yr (cf. Hu et al.: 9 Msun/yr)

Also mass, luminosity estimateObserved/predicted Lyα flux ~ 9-66%

(Hu+Haiman 2002: ~1/5) No indication on age, metallicity

Schaerer & Pelló (2004)

Abell 2218 KESR, z undetermined (~6-7)

Observations: VIZJHK (HST: WFPC2, ACS, NICMOS), spectroscopic UL on continuum flux (9000-9300 Ang), no emission line – Kneib et al. (2004)

Main results from spectral fitting:* Photometric redshift well behaved z~5.8—6.8* Age: 5-90 Myr (up to 200 Myr)* Best fits: generally little / no extinction* Absence of Lyα NOT SURPRISING ! Intrinsic: too old population Emission present but destroyed (…)

* Quite strong degeneracies in age, SF histories, extinction law !

Object detected with IRAC/SPITZER !(Egami et al. 2004)

Above results compatible with SPITZER observations

Schaerer & Pelló (2004)

Searching for z ~7-10 galaxies with the “Gravitational Telescope”

Abell 1689 - ACS / HST

* Target clusters: “lensing” galaxy clusters with well-defined mass models existing deep optical imaging (ground/HST)

typically 1—3 mag amplification* Ultra-deep NIR (JHK) exposures in cluster corePrime targets: z ~ 7 to 10 galaxies

J-H

H-K

Search for lensed distant/primeval/PopIII galaxies at z > 7

Step 1) Ultra-deep JHK (ISAAC/VLT) + existing optical imaging (HST,…): Traditional drop-out technique + blue rest-frame UV spectrum photometric redshift estimate + selection of starbursts

Step 2) Follow-up near-IR « high-res » spectroscopy (ISAAC): emission line (Ly-a, HeII?) search redshift + other properties !?

Pelló, Schaerer (2001-2003), Barton et al.(2004)

Z~9 critical line

Optical dropouts

H-K

J-H

First spectroscopic confirmation of a possible z=10 lensed source (Abell 1835-IR1916)

Pelló, Schaerer, Richard, Pelló, Schaerer, Richard, Le Borgne, Kneib, 2004, Le Borgne, Kneib, 2004, A&A 415, L19 A&A 415, L19

First spectroscopic confirmation of a possible z=10 lensed source (Abell 1835-IR1916)

Redshift indicators:1) photometric-z ~ 9-112) emission line with z=10.0 if Ly-α3) galaxy on top of critical line for z>~9

* Intrinsic flux: >~ 28.5 – 29. magAB in H and Ks * Magnification factor ~25-100 (3.5 to 5 magnitudes)* Ly-alpha line flux ~ (4.1±0.5)x10-18 erg/s/cm2

Derived properties: (z=10. 460 Myr after Big Bang)* SFR(UV) ~ 2-3 Msun yr-1, SFR(Ly-a) >~ 0.03-0.09

Difference due to: loss of Ly-a photons (ISM geometry,…) partial IGM transmission as source z >> 6!* UV slope no extinction & young population

* Mass estimate (Salpeter IMF 1-100 Msun): M* ~ (9-50).106 Msun (young bursts or const SFR) heavier than massive GC, typical for super star cluster

…properties as expected for young z~10 proto-galaxy…

News from Abell 1835-IR1916

z=2.52Metal-poor HII galaxy (SBS 0335-052)

AV=3.6 !!easy to verify…

* H-band spectroscopy: low z (~2.5) solution excluded* additional photometry (Z, SZ bands):non-detections - compatible with A&A results Schaerer et al. (2004)-- also other attempts to detect IR1916 in optical

* re-analysis of ISAAC spectroscopy (Weatherley et al., astro-ph): non-standard technique not suited to complex observational setup

* GEMINI/NIRI H-band imaging (Bremer et al. 2004): not detected in H spurious? transient source ? Probability = ?

upcoming HST ACS+NICMOS observations of Abell1835 & AC114 fields other z ~7-9 candidates

(Richard et al. + Pello et al. 2004)

NOW ex

cluded

!

A1835:A1835: 2 observing runs:2 observing runs: 4 priority targets4 priority targets 1 confirmed/ 1 no-detected/ 1 low-z/ 1 tb confirmed 1 confirmed/ 1 no-detected/ 1 low-z/ 1 tb confirmed 2 secondary targets2 secondary targets 1 confirmed high-z / 1 low-z 1 confirmed high-z / 1 low-z

A1835-2582 A1835-2582 (Richard et al. 2003): z=1.67, [OIII]5007, 4959, H_beta (Richard et al. 2003): z=1.67, [OIII]5007, 4959, H_beta detecteddetected

A1835-775:A1835-775: z=1.888 double line 10760A /10765.5A; likely [OII]3727 z=1.888 double line 10760A /10765.5A; likely [OII]3727

A1835-1055:A1835-1055: z=7.89z=7.89 if Ly if Ly ; unlikely [OII]3727 z=1.9; ; unlikely [OII]3727 z=1.9; or z= 1.16 if [OIII]5007 (no [OIII]4959)or z= 1.16 if [OIII]5007 (no [OIII]4959) or z= 1.2238 if H_beta (no [OIII]5007)or z= 1.2238 if H_beta (no [OIII]5007)

A1835-1143: faint line to be confirmed Data reduction ongoingA1835-1736: no detection within the J bandA1835-1916: z=10.0 Ly emitter Also: AC114:AC114: 1 observing run/ 2 nights/ 2 1rst priority candidates 1 observing run/ 2 nights/ 2 1rst priority candidates

In Summary:In Summary: 3 spectroscopic "confirmation" runs/ 2 clusters3 spectroscopic "confirmation" runs/ 2 clusters 6 priority 1 targets6 priority 1 targets:: 1 confirmed high-z1 confirmed high-z 2 to be confirmed2 to be confirmed 2 no-detected 2 no-detected 1 low-z Efficiency ~301 low-z Efficiency ~3050% 50% 2 secondary targets2 secondary targets:: 1 confirmed high-z 1 confirmed high-z 1 low-z1 low-z

Summary• LBGs at z~3:

– Relatively young populations (<~0.3 Gyr)

– Recurrent/episodic SF!

– Moderate extinction (E(B-V) ~0.3)

– Masses (~5-10x 109 Msun, SFR ~60 Msun/yr), also metallicities …

• Reddening in LBGs: similar between z ~3 and 4. No clear indication for z > 4.

Tendency towards bluer colors (less reddening, younger pops ?) at z~5 to 6.

• SFR density (from LBGs and LAE): ~ constant between z ~3 and 4.

Possible decrease at z>~5 -- Important uncertainty: low end of LF

• LALA sources (high EW(Ly-α)): Nature puzzling!

• Two lensed z~6-7 galaxies: 1 « high » extinction, 1 negligible.

SPITZER/IRAC observations: age up to 200-400 Myr.

• Search for z~7-10 galaxies with VLT + Gravitational Telescope:

Quite efficient! z=10 object !?, Other z~7-8.5 confirmed + candidates