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Star Forming Galaxies at z >5: Properties and Implications for Reionization. Elizabeth Stanway (UW-Madison) Andrew Bunker (Exeter). - PowerPoint PPT Presentation
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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 HUBBLE SPACE
TELESCOPETELESCOPE
Need:Need:
ResolutionResolution
SensitivitySensitivity
Low BackgroundLow Background
HST/ACS Surveys:
GOODS (2003)
• 300 arcmin2 in b, v, i’, z’
• z’ (10) ~ 27 AB
• ~100 i’-drops to this limit
HUDF
• 11 arcmin2 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 Keck10-m Keck
8-m Gemini8-m Gemini
ESO VLTsESO VLTs
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=5.99Z=5.99
GOODS-S GOODS-S
SourceSource
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
Flim~1.5x10-19 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?
Blue Red
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
ZH
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
3-4m: Eyles,
Bunker, Stanway
et al.
m3.6m (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
(C30
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 Imagerse.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:And in the longer term:
JAMES WEBB SPACE TELESCOPEJAMES WEBB SPACE TELESCOPE
successor to Hubble (2013+)successor to Hubble (2013+)