Spectroscopic Studies of Spectroscopic Studies of z~5.7 and z~6.5 Galaxies: z~5.7 and z~6.5 Galaxies:

Implications for ReionizationImplications for Reionization

Esther HuEsther Hu

University of Hawaii, Institute for University of Hawaii, Institute for AstronomyAstronomy

IAU Colloq. 199, Shanghai 18 March 2005IAU Colloq. 199, Shanghai 18 March 2005

OverviewOverview

Scientific Motivation for StudiesScientific Motivation for Studies LyLy Emission-Line Galaxy Surveys Emission-Line Galaxy Surveys

Depth, area requirements for large high-redshift Depth, area requirements for large high-redshift samplessamples

Current statusCurrent status Luminosity Functions at z~5.7, z~6.5Luminosity Functions at z~5.7, z~6.5 Line Profiles at z~5.7, z~6.5Line Profiles at z~5.7, z~6.5 Structured Distribution of High-z GalaxiesStructured Distribution of High-z Galaxies Summary ConclusionsSummary Conclusions

Collaborators: Len Cowie, Peter Capak, Yuko Kakazu

Lyman alpha emitters atLyman alpha emitters atz = 5.7 versus z = 6.5z = 5.7 versus z = 6.5

Did the intergalactic hydrogen reionize at z just beyond 6 ?

Or was it earlier?

Can we find galaxies at these redshifts ?

Are there enough of them to ionize the gas?

What can we infer about IGM evolution from these galaxy populations?

Is reionization at z=6 consistent with the galaxy observations?

Question :

H REIONIZATION at z~6.2 ???

Or is it just the natural thickening of the Lyman alpha forest as we move to high redshift?

VERY HARD to tell the difference between an optical depth of 10 and one of 10000!

ALTERNATE TEST: is there a change in the Ly line properties of galaxies across this redshift boundary -- either a change in the luminosity function or in the properties of the lines that might show they were now living in a mostly neutral medium where the Ly line is cut away by the damping wings of the IGM?

High redshift galaxies

We need to develop large well selected samples in the z=5 7 redshift range to answer this question….

And also--

How does initial structure formation and reionization take place?

Is ionization at this redshift produced by high redshift AGN? star-forming galaxies?

What is the history of star formation in the Universe in the z=5 7 range?

How can we find galaxies at these redshifts?

Currently the only method which can turn up large homogeneously selected samples at these redshifts are Ly searches with narrow-band filters or direct spectroscopic techniques (Hu et al 2002, Taniguchi et al. 2004, Ellis et al 2004)

z = 6.6, ~7

Other possibilities are red color selection and targeted observations of X-ray, radio or far infrared selected

sources but there are very few objects so far….

High redshift galaxies

Need many very large fields

Objects are sparse at brighter magnitude

(few hundred per square degree for AB <25.5)

Fields are highly correlated on subdegree scales

Capak et al. 2004, Brodwin et al.2003 (astro-ph/0310038)

Hawaii survey: wide field color and narrow band mapping at z=57

Peter Capak, Esther Hu, Len Cowie, Amy Barger, Richard McMahon, Yuko Kakazu, Wei-Hao Wang, Tomoki Hayashino, Yutaka Komiyama, Ed Fomalont, Niel Brandt, Dave Alexander, Franz Bauer, Gordon Garmire, Mark Bautz, Aaron Steffen, Yuxuan Yang, Richard Mushotzky, Mauro Giavilisco, Mark Dickinson, Dan Stern, S. Okamura, C. Kretchmer, S. Miyazaki

6 Well studied fields: HDF, SSA22, Lockman Hole NW, SSA13, SSA17, A370

Deep X-ray, radio and submillimeter data for most of these

Muliticolor imaging

With Suprime on Subaru

Megaprime on CFHT,

ULBCAM on 2.2m

Spectroscopy with

Deimos on Keck II

HK’, J, Z’, 9130/125, I, 8150/120, R, V, B, U

Total area just over a square degree

(Z=6.6) (Z=5.7)

Spectroscopy of all X-ray and radio sources , all z=5.7 and 6.6 emission line candidates and all red color selected objects together with large magnitude selected field samples

HDF

B,R,Z

SUPRIME

15/ X 15/

Capak

et al. 2004

HST F814W vs SUPRIME 8150 narrow band

HST ‘wide-I’ continuum

NB816 narrowband

Wide-field narrowband exposures comparable in depth to Hubble Deep Field continuum

Filter profile

1% Night Sky

Keck LRIS spectrum

z=6.56 Galaxy Behind A370

NARROW BAND (strong Ly emission) R BAND (no galaxy detected)

N(8150) < 24 samples -- Z=5.7 selection

Continuum break

O II

Red stars

O III

SSA22

Equivalent width

HDF

Composite of Deimos Spectra Hu et al. (2004)R=2700 spectra allow us to easily distinguish OII and OIII emitters

instrument profile

SSA22 field to N(AB)=25.1

19 spectroscopic Ly emitters

Spectroscopicz = 5.7(solid boxes)

Redshift distribution of spectroscopically identified objects in Hawaii fields.

62 objects

14 objects

z=3.4 Ly LFZ=5.7 Ly LF

(Approx 1 solar mass per year: no extinction case B)

Ly Luminosity Function at z=3.4 & z=5.7

z=3.4 LySample(Cowie & Hu

1998)

Incompleteness correctedZ = 5.7

Raw Ly

selected

Steidel et al,z = 3

z = 4

UV continuum luminosity function of Ly-selected objects

Z=3.4 Ly LF

Z=6.5 Ly LF

Z=5.7 Ly LF

(Approx 1 solar mass per year: no extinction case B)

Lyman alpha luminosity function with z=6.5 points

Z= 5.7 Ly emitters in SSA 22 & HDF

SUPRIME fields

Hu et al. 2004

(no spectroscopy)

HDF

SSA 22

Z= 5.7 Ly Z= 5.7 Ly emitters in SSA 22 & HDF emitters in SSA 22 & HDF

SSA 22HDF

Colored symbols show selected redshift regions (about 1/4 of filter bandpass)

Z= 6.5 Ly emitters in HDF & A 370 (Hu et al. 2005)

A370 and the Subaru

Deep field (Taniguchi

et al. 2004) are rich compared to the HDF and SSA22 (Hu et al.2004).

HDF

A 370

Cosmic Variance is a Problem for High-z Studies

Composite line profiles at 5.7 and 6.5 (Virtually identical!)

Instrument resolution

EW(5.7)=56Å

EW(6.5)=50Å

FWHM(5.7)

=1.1Å

FWHM(6.5)=

0.8Å

Does this mean conditions are Does this mean conditions are the same in the IGM at 5.7 and the same in the IGM at 5.7 and

6.5?6.5? Maybe not:: (Madau, Haiman, Loeb, Gnedin, etc….)Maybe not:: (Madau, Haiman, Loeb, Gnedin, etc….)

More luminous objects may self shield themselves by ionizing More luminous objects may self shield themselves by ionizing the gas aroundthe gas around

them. them.

Even for lower luminosity objects:Even for lower luminosity objects:

Clustered or neighboring objects mayClustered or neighboring objects may also ionize the region around the object.also ionize the region around the object.

Preferred (low density) lines of sight mayPreferred (low density) lines of sight may be ionized and we may have strong selection bias in our be ionized and we may have strong selection bias in our

object sample.object sample.

H II region

Neutral IGM

Can we see such an emitter prior to reionization?

(Haiman 2002, Madau 2002)

Galaxy

Maybe --- if the galaxy is bright enough

IGM scatteringDamping wing

Intrinsic profile

Final profile

Small residualfrom red wing

Stacked profileOf 19 Ly emitters in SSA22

Input profileInput profileGaussian (200 km/s) Gaussian (200 km/s) truncated by IGM truncated by IGM scatteringscattering

HST (ACS) 6000, 8000 andHST (ACS) 6000, 8000 and9000 Å images of the z=5.79000 Å images of the z=5.7

LyLy emitters in the GOODS-N field emitters in the GOODS-N field

F606W, F775W, F850LP: only 2 of 6 are resolved by ACS

12”

Comparison of stacked colors Comparison of stacked colors ofof

z=5.7 emitters with z=5.7 z=5.7 emitters with z=5.7 quasarquasar

SED of Galaxies consistent with Ly Forest Absorption in Quasar Spectrum

Summary---

Large samples of z=5.7 and 6.5 objects can now be obtained.

Ly and continuum luminosity functions at z = 5.7 seem similar to those at lower redshifts --- (galaxies are the dominant ionizers rather than AGN)

Ly luminosity function and Ly line shape are similar at z=6.6 and z =5.7

We may be able to make 3 dimensional maps of the cosmic web at these redshifts!

Composite line profiles of z=6.5 emitters

compared with SDSS 1148+5251

Summary--- (ctd.)

H reionization at z~6.2 ? Probably not…..

Dark gaps may be a genuine Gunn-Peterson effect but could be just line blanketing of the increasing neutral hydrogen density

Presence of residual flux in 1148 is strong evidence against

the GP interpretation.

Widths of lines would change…

A370 z=6.5 emitter probably only consistent if it lies in a highly ionized hole produced by a neighbor object of by clusters of fainter objects.

Deimos Spectrum Hu et al. 2003

Pre scattering spectrum(schematic).

Sharp edge

SHARP EDGE

Spatially resolved about4 independent positions

No sharp cutoff

GOODS-S continuum objects from Stanway, Bunker et al

GOODS-N from Spinrad et al, Weyman et al., Barger et al

EmissionLine window

z~5.7 Lyz~5.7 Ly Emitters in Emitters in GOODS-NGOODS-N

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Stacked z~5.7 Galaxy Stacked z~5.7 Galaxy PropertiesProperties

Compare the Compare the composite composite colors of the colors of the high-z high-z LyLygalaxiegalaxies with the s with the spectra of spectra of bright bright quasars at quasars at the same the same redshiftredshift

Color-color plot: Ly Galaxies can be distinguished from [OIII] and [OII] emitters and red objects

Ly

[OIII]

[OII]

Narrowband Ly Images of z~5.7 Candidates (30”x30”)

R-band Thumbnails of z~5.7 Candidates (30”x30”)

Galaxy Colors and Quasar Galaxy Colors and Quasar SpectrumSpectrum

The first stars and galaxies The first stars and galaxies formform

in the densest regions:in the densest regions:

Yellow colors show

the forming stars

Searching for these first Searching for these first galaxiesgalaxies

How do we find these small distant How do we find these small distant galaxies?galaxies?

Can we do it from the ground or Can we do it from the ground or mustmust

we wait for the James Webb spacewe wait for the James Webb space

telescope (the successor to Hubble)telescope (the successor to Hubble)

YES!YES!

We can do it from Mauna KeaWe can do it from Mauna Kea

with its wonderful large telescopes….with its wonderful large telescopes….

The Japanese Subaru (Pleiades) The Japanese Subaru (Pleiades) TelescopeTelescope

on Mauna Kea in Hawaiion Mauna Kea in Hawaii

The largest telescope in the world The largest telescope in the world with a wide-field prime-focus with a wide-field prime-focus imaging cameraimaging camera

Collecting area (8.3 m Collecting area (8.3 m diameter)diameter)

Field of view (0.5 deg on a side)Field of view (0.5 deg on a side)

Optical Image:

50,000 galaxies in 600 squarearcminutes

And much larger than the images from HST

The Hubble deep field is a small part

of this Subaru image which

lies just above the big

dipper on the sky.

Hubble Space Telescope and Hubble Space Telescope and Subaru Subaru

Subaru can reach the depth ofSubaru can reach the depth ofHST though not quite the HST though not quite the

resolutionresolution HST gives sharper images which HST gives sharper images which

allow allow

us to see more of the structure of us to see more of the structure of the galaxies.the galaxies.

How do wefind the smallearly galaxiesamid this seaof objects?

Most of whatwe see in thisoptical imageis relativelynearby.

There are onlya small numberof very distantgalaxies in theimage.

Here is what Here is what a similar areaa similar area

of the sky of the sky might look might look

like at a time like at a time when the when the

universe was universe was a tenth it a tenth it

present age present age based on based on

simulations. simulations. The little The little yellow yellow

patches show patches show the galaxies.the galaxies.

Theory PredictionsTheory Predictions

First galaxies should be faint, because they are smallFirst galaxies should be faint, because they are small and distant. and distant.

Problem: how do you choose your candidates without examining Problem: how do you choose your candidates without examining the faint galaxies one by one?the faint galaxies one by one?

POSSIBLE SOLUTIONS:POSSIBLE SOLUTIONS:

Early star formation should produce strong emission from Early star formation should produce strong emission from Hydrogen – easiest way to find these galaxies is to look for Lyman Hydrogen – easiest way to find these galaxies is to look for Lyman (1216 (1216 ÅÅ): the strongest emission line produced by the Hydrogen ): the strongest emission line produced by the Hydrogen atom.atom.

Intergalactic gas along the line of sight to the galaxy also Intergalactic gas along the line of sight to the galaxy also suppresses the spectrum at wavelengths below this line, so we can suppresses the spectrum at wavelengths below this line, so we can pick these galaxies out by their colours (colour selection works well pick these galaxies out by their colours (colour selection works well at lower redshifts)at lower redshifts)

Lyman alpha line:

Strategy 1Strategy 1

Observe blank regions of sky using Observe blank regions of sky using broadband filters and look for objects broadband filters and look for objects with the right colourswith the right colours

Check whether the colour-selected Check whether the colour-selected objects are high-redshift galaxies by objects are high-redshift galaxies by taking their optical spectrataking their optical spectra

Works well at lower redshifts but doesn’t Works well at lower redshifts but doesn’t havehave

the sensitivity for the galaxies at very the sensitivity for the galaxies at very early times.early times.

Strategy 2Strategy 2

Observe blank regions of sky using a Observe blank regions of sky using a narrow-band filter centered on the narrow-band filter centered on the Lyman Lyman emission at the redshift of emission at the redshift of interestinterest

Check whether emission-line objects Check whether emission-line objects detected by the filter are high-detected by the filter are high-redshift galaxies by taking their redshift galaxies by taking their optical spectraoptical spectra

8185/105 I z’

R V B

z=5.74 Galaxy (SSA22-HCM1)

Optical-Infrared SED SSA22-Optical-Infrared SED SSA22-HCM1HCM1

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Consistent with no dust reddening

z=5.74 galaxy spectroscopicallyz=5.74 galaxy spectroscopicallyconfirmed with theconfirmed with the

Keck 10 metre telescopes onKeck 10 metre telescopes onMauna Kea in HawaiiMauna Kea in Hawaii

Keck LRIS spectrum

Filter profile

1% Night Sky

Z=5.7 L alpha emitters in Z=5.7 L alpha emitters in SSA22 and the HDFSSA22 and the HDF

We can map the filamentsWe can map the filamentsof the web the numerical of the web the numerical

models predict.models predict.

To get evenTo get evenmore more

sensitivitysensitivitywe can add awe can add a

second second cosmiccosmic

telescope totelescope toour groundour groundtelescope:telescope:

GravitationaGravitational lensing by l lensing by

an an intervening intervening

massive massive clustercluster

of galaxies of galaxies will magnify will magnify the distant the distant galaxies, galaxies, making making

them easier them easier to detectto detect

This technique was used byThis technique was used byour group here at Hawaiiour group here at Hawaii

led by Esther Hu to find an led by Esther Hu to find an even more distant and younger even more distant and younger

galaxy:galaxy:

There are now very slightlyThere are now very slightlymore distant objects butmore distant objects but

this is still the state of the art.this is still the state of the art.

z=6.56 Galaxy behind the cluster A370

Narrow-band image

(strong Lyemission)

R-band image

(no galaxy detected)

Submillimetre data

Submillimetre data

OPTICAL, 20cm DATA

Star formation history: the formation rate of stars per unit volume of space as a function of time

(1+z)2

(1+z)0.8

billion years 10 billion years

Future Future

Finding high-redshift samples in large numbers:Finding high-redshift samples in large numbers:

There are now about 50-100 known galaxies There are now about 50-100 known galaxies at z=5-6 and perhaps 20 in the z=6-7 range at z=5-6 and perhaps 20 in the z=6-7 range (in the two years since the first one was (in the two years since the first one was found)found)

With large samples of these objects we shouldWith large samples of these objects we should

be able to map the filamentary structure ofbe able to map the filamentary structure of

the universe at these redshifts.the universe at these redshifts.

Future Future

Studying their star-formation rates:Studying their star-formation rates:

Extending the star formation history to yetExtending the star formation history to yet greater distances.greater distances.

Going further requires giant new infrared Going further requires giant new infrared camerascameras

which the U of Hawaii (Don Hall and Klaus which the U of Hawaii (Don Hall and Klaus Hodapp)Hodapp)

are working to develop.are working to develop.

Looking ahead to the James Webb Space TelescopeLooking ahead to the James Webb Space Telescope

The James Webb space The James Webb space telescopetelescope

6 meter infraredoptimized telescope.

Launch aboutthe end of

the decade.

Should be ableTo detect thesmallest and most distant

galaxies!

Star formation historyWilson et al. 2002 and Barger, Cowie and Richards 2000

ALL SCUBA

SCUBA ABOVE 6 mJy

OPTICAL, 20cm DATA

(1+z)^2

(1+z)^0.8