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Elizabeth Stanway (UW-Madison) Andrew Bunker (Exeter)

Star Forming Galaxies at z >5: Properties and Implications for Reionization. Elizabeth Stanway (UW-Madison) Andrew Bunker (Exeter).

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Elizabeth Stanway (UW-Madison) Andrew Bunker (Exeter)

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  1. Star Forming Galaxies at z>5: Properties and Implications for Reionization Elizabeth Stanway (UW-Madison)Andrew Bunker (Exeter) 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

  2. 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-a 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

  3. 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

  4. 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

  5. Need: Resolution Sensitivity Low Background i.e. HUBBLE SPACE TELESCOPE

  6. HST/ACS Surveys: • GOODS (2003) • 300 arcmin2 in b, v, i’, z’ • z’ (10s) ~ 27 AB • ~100 i’-drops to this limit • HUDF • 11 arcmin2 in b, v, i’, z’ • z’ (10s) ~ 28.5 AB • ~50 i’-drops to this limit

  7. 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 => f*=f*(z=3) / 6 Case 2 - L*, a, f* all varying => Best fit LF is steeper, with brighter L*

  8. 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

  9. ESO VLTs 10-m Keck 8-m Gemini

  10. Spectroscopy I - Keck/DEIMOS Have targeted > 30 sources in GOODS-N, GOODS-S and HUDF Exposure times ~5-10 hours per mask, ~7000-10,000Å 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)

  11. 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 Flim~1.5x10-19 ergs s-1 cm-2 Detects continuum sources, and high EW Ly-a emission sources

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

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

  14. Wide Field Near IR Surveys

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

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

  17. m3.6m (AB) ~24 (~1microJy) For JWST/NIRSPEC: R=1000 S/N>10 in 100ksec Ca H&K, G-band, MgIb (vel disp)

  18. Implications for Reionization From Madau, Haardt & Rees (1999) -amountof star formation required to ionize Universe(C30 is a clumping factor). Assumes standard IMF, IGM properties etc.

  19. 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 a 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

  20. Next Steps: Further Into the IR 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.

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

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