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

1. 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)

2. 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, …

3. 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

4. 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)

5. 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)

6. 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

7. 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

8. 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)

9. 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)

10. 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

11. 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 ?!

12. 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.

13. 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

14. 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

15. 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)

16. 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)

17. 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!

18. 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)

19. 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)

20. 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)

21. 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

22. 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)

23. J-H H-K Z~9 critical line Optical dropouts

24. First spectroscopic confirmation of a possible z=10 lensed source (Abell 1835-IR1916) Pelló, Schaerer, Richard, Le Borgne, Kneib, 2004, A&A 415, L19

25. 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…

26. 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!

27. 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

28. 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