The European Extremely Large Telescope Studying the first galaxies at z>7 Ross McLure Institute for Astronomy, Edinburgh University

2 Studying the first galaxies at z>7 Outline n Motivation for studying high-redshift galaxies n Current techniques for selecting galaxies at high redshift n What do we know about 4<z<6 regime? n The current observational boundary at z=7 n The need for ELT to push to z>8

3 Studying the first galaxies at z>7 Motivation 1: WMAP and quasar surveys at z>5 show that the “epoch of reionisation” probably occurs within the redshift interval 6<z<11 Important to understand how reionisation occured, and what sources were responsible Fan et al.

4 Studying the first galaxies at z>7 Motivation 2: WMAP and quasar surveys at z>5 show that the “epoch of reionisation” probably occurs within the redshift interval 6<z<11 Understanding galaxy evolution at high redshift Theoretical models can now predict luminosities, masses, sizes and morphologies of high-redshift galaxies. However, still few observational constraints at z>5 Bower et al. (2006) ?

5 Studying the first galaxies at z>7 Selecting galaxies at high redshift Two basic techniques: 1. Lyman-break selection (LBGs) 2. Narrow-band selection of Lyman alpha emitters (LAEs) B V R i z J H K 3.6μm 4.5μm McLure et al. [2008)

6 Studying the first galaxies at z>7 Selecting galaxies at high redshift Two basic techniques: 1. Lyman-break selection (LBGs) 2. Narrow-band selection of Lyman alpha emitters (LAEs) B V R i z J H K 3.6μm 4.5μm z=5.5 BC model McLure et al. [2008)

7 Studying the first galaxies at z>7 Selecting galaxies at high redshift Two basic techniques: 1. Lyman-break selection (LBGs) 2. Narrow-band selection of Lyman alpha emitters (LAEs) z=4.7z=5.7z=6.6 Narrow-band filters sample dark region between sky lines Clean selection method if combined with deep multi-wavelength imaging data However: Selects over very narrow redshift range => large area detectors needed Only a minority of z>4 galaxies appear to be strong Lyman-alpha emitters

8 Studying the first galaxies at z>7 What do we know about the 3<z<6 galaxy population? Much recent progress has come from combining: 1. Ultra-deep HST imaging - faint-end of high-z luminosity function 2. Deep, wide-area, ground-based imaging - bright end of LF + clustering properties 3. Deep IRAC imaging with Spitzer - stellar masses + “old” stellar populations

9 Studying the first galaxies at z>7 The depth and spatial resolution of the HST ACS imaging in the Ultra Deep Field and wider GOODS N+S fields has been crucial Has allowed high-redshift luminosity function be traced as faint as ~0.1 L* However: Very small areas (HUDF ~13 arcmin 2 ] Potential for large cosmic variance, particularly at bright-end of LF What do we know about the 3<z<6 galaxy population?

10 Studying the first galaxies at z>7 B-drops at z~4 V-drops at z~5 i-drops at z~6 Adapted from Bouwens et al. (2007) What do we know about the 3<z<6 galaxy population?

11 Studying the first galaxies at z>7 Small area of HST fields means there is virtually no information brighter than M* What do we know about the 3<z<6 galaxy population?

12 Studying the first galaxies at z>7 Studying the most luminous objects at z>5 with UKIDSS Ultra-Deep Survey (UDS) McLure et al. (2006, 2008) Deepest, wide-area (1 square degree), near-IR survey undertaken >200 times larger than UDF - picks up rare bright objects

13 Studying the first galaxies at z>7 Studying the most luminous objects at z>5 with UKIDSS Ultra-Deep Survey (UDS) McLure et al. (2006, 2008) Deep, wide area, imaging allows much improved determination of bright end of z=5 and z=6 luminosity function Combined with deep HST data, allows determination of LF evolution over full 10L*<L<0.1L* luminosity range Evolution of M* by ~0.7 magnitudes over the redshift interval 5<z<6

14 Studying the first galaxies at z>7 Studying the most luminous objects at z>5 with UKIDSS Ultra-Deep Survey (UDS) McLure et al. (2006, 2008) 1. Wide area allows accurate clustering analysis: r o =8 Mpc, halo masses ~ 5x10 11 M  2. Stacking analysis allows estimate of typcal stellar masses: M stars ~ M  3. Combination of LF and typical M/L allows estimate of stellar mass function/density Stellar mass in place by z~6 is ~4x10 6 M  Mpc -3 Suggests significant levels of starformation at z>7

15 Studying the first galaxies at z>7 Grey square is an estimate of starformation rate necessary for reionisation (Stiavelli et al. 2003) Appears that z~6 galaxy population maybe be insufficient Suggests significant contribution from earlier galaxy population at z>7 Bouwens et al. (2008) Is the starformation rate at z~6 enough to reionise the Universe?

16 Studying the first galaxies at z>7 Current redshift record holder is z=6.96 LAE (Iye et al. 2006) Narrow-band imaging sensitive to range 6.94<z<7.11 Ultra-deep ground based imaging from Subaru Deep Field

17 Studying the first galaxies at z>7 Current redshift record holder is z=6.96 LAE (Iye et al. 2006) Narrow-band imaging sensitive to range 6.94<z< hour spectrum with FOCAS Asymmetric Ly-alpha line detected at ~5 sigma Starformation rate estimated to be ~10 M  yr -1 NO CONTINUUM DETECTED!

18 Studying the first galaxies at z>7 z phot =7.6, M stars 2x10 9 M , SFR~ 8 M  yr -1 Abell 1689, z= candidates at z~7.4 from GOODS fields Candidates now regularly appearing at 7<z<8 Bradley et al. (2008) Bouwens et al. (2008)

19 The galaxy population at 7<z<9 Good evidence that we need to break z>7 barrier for full census of objects responsible for reonisation Many candidate z>7 candidates will come from: HST WFC3, Ultra-VISTA survey, Hyper-Suprime cam Ideally, would like to spatially resolve these objects and study their continuum spectra, not just Lyman-alpha

20 The galaxy population at 7<z<9 Likely sizes of z>7 galaxies Lots of observational evidence that high-redshift galaxies are extremely small... Difficult to resolve z~6 LBGs with HST ACS at 100 mas (R e <1 kpc) Source plain reconstruction of lensed sources at high-z suggest also they are sub-kpc in scale..... Two knots of starformation at z=7.6 ~ 300 pc in diameter ( 50 mas ) Bradley et al. (2008) Need ELT working at the diffraction limit in the near-IR to study structure/morphology of these objects

21 The galaxy population at 7<z<9 Would like continuum spectra to determine UV slope, stellar ages, metallicity Would also like R~5000 to reduce problem of sky-lines (or OH suppression) Stiavelli (2008) ~100 hours with 8m to reach J~25 ~100 hours with ELT to reach J~27 Need ELT-class telescope to reach z~6-7 objects we already know about Spectra of z>7 galaxies This is only ~L* at 7<z<8 Surface density of a ~few/sq. arcmin

22 Studying the first galaxies at z>7 Summary n Galaxy population studies at 4<z<6 have made rapid progress in recent years n Probably need substantial starformation from z>7 galaxies to reionise the Universe n First credible z>7 galaxy candidates now being published n ELT+AO should be able to spatially resolve z>7 objects n ELT already required to obtain continuum spectra of L* galaxies at z~6 we already know about.....

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