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Starbursts from z~3 to 7-10 Daniel 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

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starbursts from z 3 to 7 10 daniel schaerer geneva observatory omp toulouse
Starbursts 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
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, …

observables methods
Observables & methods

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, …

this review

observables methods sed degeneracies
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

extinction

Or 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
LBG at z~3

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

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

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)

lbg at z 36
LBG at z~3

Sawicki & 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 37
LBG at z~3

Papovich 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

slide8

Age – e-folding time

prob.distribution

Age – dust attenuation

probability distribution

Age – stellar mass probability distribution

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)

lbg at z 3 from 3 to 4

0 1 2 3 4 5

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) -- GOODS
    • Ouchi 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)
lbg at z 3 from 3 to 5

0 1 2 3 4 5

LBG at z > 3: from 3 to 5
  • Ouchi 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.)

z~5 spectroscopic follow-ups:

*  Iwata et al. poster

*  Douglas,Bremer+ (talk, poster)

after

before

LF

integration

lbg at z 5 cont
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 6
i-dropouts: LBG at z~6

HST -- 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?)

z_phot

extinction

z_phot

Stanway et al.

i dropouts lbg at z 613
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
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 emitters lae
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)

slide16

Z=0

Z=10-7

Z=10-5

Schaerer (2003)

Z=1/50 - 2 Zsun

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)

 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 ?

 NO ! Wang et al. (2004)

slide17

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

* 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!

slide18

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

Abell 370 HCM 6A, z=6.56

Hu et al. 2002, ApJ, 568, L75

  • NB excess
  • asymetric emission line (Lya)
  • no secondary image
  • magnification 4.5 (1.6 mag)
slide19

SPITZER/IRAC sensitivity

Prediction:

IRAC/SPITZER (non detection) could

confirm strong extinction

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 estimate

Observed/predicted Lyα flux ~ 9-66%

(Hu+Haiman 2002: ~1/5)

 No indication on age, metallicity

Schaerer & Pelló (2004)

slide20

Object detected with IRAC/SPITZER !

(Egami et al. 2004)

 Above results compatible with SPITZER

observations

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 !

Schaerer & Pelló (2004)

slide21

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

* 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 core

Prime targets: z ~ 7 to 10 galaxies

Abell 1689 - ACS / HST

slide22

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)

slide23

J-H

H-K

Z~9 critical line

Optical dropouts

slide24

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

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

first spectroscopic confirmation of a possible z 10 lensed source abell 1835 ir1916
First spectroscopic confirmation of a possible z=10 lensed source (Abell 1835-IR1916)
  • Redshift indicators:
  • 1) photometric-z ~ 9-11
  • 2) emission line with z=10.0 if Ly-α
  • 3) 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…
slide26

z=2.52

Metal-poor HII galaxy (SBS 0335-052)

AV=3.6 !!

easy to verify…

News from Abell 1835-IR1916

* 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 excluded!

slide27

A1835-1055:z=7.89 if Ly ; unlikely [OII]3727 z=1.9;

or z= 1.16 if [OIII]5007 (no [OIII]4959)

or z= 1.2238 if H_beta (no [OIII]5007)

In Summary:

3 spectroscopic "confirmation" runs/ 2 clusters

6 priority 1 targets:

1 confirmed high-z

2 to be confirmed

2 no-detected

1 low-z Efficiency ~3050%

2 secondary targets:

1 confirmed high-z

1 low-z

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

A1835:2 observing runs:

4 priority targets 1 confirmed/ 1 no-detected/ 1 low-z/ 1 tb confirmed

2 secondary targets 1 confirmed high-z / 1 low-z

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

A1835-1143: faint line to be confirmed  Data reduction ongoing

A1835-1736: no detection within the J band

A1835-1916: z=10.0 Lyemitter

Also: AC114: 1 observing run/ 2 nights/ 2 1rst priority candidates

summary
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