Elizabeth Stanway (UW-Madison) Andrew Bunker (Exeter) Star Forming Galaxies at z>5: Properties and Implications for Reionization With: Richard Ellis (Caltech) Richard McMahon (IoA), Kevin Bundy, Tommaso Treu, Laurence Eyles, Mark Lacy, Amy Barger, Len Cowie Karl Glazebrook, Bob Abraham & the GLARE team

Outline Galaxies at z=6: I drop Selection Colour selection of galaxies Results from GOODS and the UDF Spectroscopic Follow Up GOODS sources - Results from Keck/DEIMOS GLARE - The Gemini Ly-  at Reionisation Era project Into the Infrared Wide-field Near IR surveys Results from Spitzer Implications for Reionisation The ionising background from i’-drop galaxies Finding reionising sources

Pushing to higher redshift- Finding Lyman break galaxies at z~6 : using i-drops. But problem: low z contaminants can have same i’-z’ colours

By selecting on rest-frame UV, get inventory of ionizing photons from star formation. i’-drops 5.6<z<7 But distant sources are: Faint (=> luminosity bias) Very compact

i.e. i.e. HUBBLE SPACE TELESCOPE Need:ResolutionSensitivity Low Background

HST/ACS Surveys: GOODS (2003) 300 arcmin 2 in b, v, i’, z’ z’ (10  ) ~ 27 AB ~100 i’-drops to this limit HUDF 11 arcmin 2 in b, v, i’, z’ z’ (10  ) ~ 28.5 AB ~50 i’-drops to this limit

The Luminosity Function of i’-drop Galaxies Use luminosity function to predict numbercounts Folds in selection function and effective volume due to luminosity bias Case 1 - No evolution in LF shape  *=  *(z=3) / 6 Case 2 - L*, ,  * all varying => Best fit LF is steeper, with brighter L*

The UV Luminosity Density History If only the bright end is considered, UV luminosity density falls sharply at z > 4 If integrating over LF, a steeper function gives only small decline in luminosity density with redshift. => Need to better constrain z=6 LF to understand UV photon budget

10-m Keck 8-m Gemini ESO VLTs

Spectroscopy I - Keck/DEIMOS Have targeted > 30 sources in GOODS-N, GOODS-S and HUDF Exposure times ~5-10 hours per mask, ~ ,000Å Redshifts found at 5.6<z<6.4, analysis ongoing Large contaminant fraction in early work - later improved Z=5.99 GOODS-S Source Bunker, Stanway, Ellis et al (in prep)

Spectroscopy II - GLARE in the UDF Gemini/GMOS spectroscopy of i’-drop sources in the HUDF > 35 hours on a single slitmask. ~45 targets. Campaigns in 2003 and 2004 F lim ~1.5x ergs s -1 cm -2 Detects continuum sources, and high EW Ly-  emission sources

The (very tentative) EW Distribution of GLARE Ly-alpha Emitters Detections Limits Note long high EW tail - Two distinct populations?

BlueRed UDF NICMOS - Deep but Small - J and H band - Isolate contaminants - Observed Near- IR => Rest frame Ultraviolet - Many i’-drops are very blue - Very young? - Unusual IMF?

Wide Field Near IR Surveys

Z H J A Survey around the HDFN The Number Density of Low Mass Stars Example candidates: Fields to follow: SSA13, SSA22, A370, LHNW, LH- N amongst others

Spitzer Detections of z=6 Galaxies - z=5.83 galaxy Detected in GOODS IRAC 3-4  m: Eyles, Bunker, Stanway et al.

m 3.6  m (AB) ~24 (~1microJy) For JWST/NIRSPEC: R=1000 S/N>10 in 100ksec Ca H&K, G-band, MgIb (vel disp)

Implications for Reionization From Madau, Haardt & Rees (1999) -amount of star formation required to ionize Universe (C 30 is a clumping factor). Assumes standard IMF, IGM properties etc.

Implications for Reionization To z’ AB =28.5 our UDF data has star formation at z=6 which is 3x less than that required AGN number density is too low. => Is this a puzzle? Solutions: We go down to 1M_sun/yr - but  may be steep (lots of low luminosity sources - forming globulars?) IGM may be warmer, more clumped, escape fraction may be high Cosmic variance can be very large - deep data from UDF IMF could be unusual - top heavy? IGM largely reionised already by this redshift

Narrow Band Imagers e.g. DAZLE - Dark Ages 'z' Lyman-alpha Explorer (IoA - Richard McMahon, Ian Parry; AAO - Joss Bland- Hawthorne Also: UKIDSS, FLAMINGOS, SALT-IR TMT, OWL etc. Next Steps: Further Into the IR

And in the longer term: JAMES WEBB SPACE TELESCOPE successor to Hubble (2013+)