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+)