Redshift sox:The beginning of an STScI softball team?

Sangeeta Malhotra

Contact Andy Fruchter

Redshift six: the beginning of the universe as we know it?

Reionization or a phase transition at z~6

GRAPES/PEARS: James Rhoads, Nor Pirzkal, Chun Xu, Anton Koekemoer, Kailash Sahu, Nino Panagia, Rachel Somerville, Lexi Moustakas, Mark Dickinson, John Gardner, Gerhard Meurer, Caryl Gronwall, Zlatan Tsvetanov, Tamas Budavri,

LALA: James Rhoads, Junxian Wang,Katarina Kovac, Elizabeth Barker, Colin Norman, Tim Heckman, Mario Livio.

UDF team: Steve Beckwith, Harry Ferguson, Anton Koekemoer, Massimi Stiavelli & Roberto, Shardha Jogee, Megan Sosey, Eddie Bergeron….

OPO: Ann Feild, Skip Westphal, John Bedke, Cheryl Gundy, Zolt Levay, Ray Villard

Archives: Karen Levay, Inga Kamp…

GLARE: Karl Glazebrook

(Apologies to the forgotten collaborator…)

Redshift six: the beginning of the universe as we know it?

Sangeeta Malhotra

GRAPES/PEARS: James Rhoads, Nor Pirzkal, Chun Xu, Anton Koekemoer, Kailash Sahu, Nino Panagia, Rachel Somerville, Lexi Moustakas, Mark Dickinson, John Gardner, Gerhard Meurer, Caryl Gronwall, Zlatan Tsvetanov, Tamas Budavri, A. Cimatti, E. Daddi, I. Ferreras, Z. Haiman, M. Kuemmel, A. Pasquali, S. di Serego Aligheri, J. Vernet, J. Walsh, R. Windhorst, H.J. Yan

LALA: James Rhoads, Junxian Wang,Katarina Kovac, Elizabeth Barker, Colin Norman, Tim Heckman, Mario Livio, Steve Dawson, Dan Stern, Arjun Dey, Buell Jannuzi, Hy Spinrad.

UDF team: Steve Beckwith, Harry Ferguson, Anton Koekemoer, Massimi Stiavelli & Roberto, Shardha Jogee, Megan Sosey, Eddie Bergeron….

OPO: Ann Feild, Skip Westphal, John Bedke, Cheryl Gundy, Zolt Levay, Ray Villard

Archives: Karen Levay, Inga Kamp…

GLARE: Karl Glazebrook, Stanway, Bunker, Abraham et al.

(Apologies to the forgotten collaborator…)

Reionization:• What:• Who:

– Sources of reionization.– Clustering of sources of ionization.

• When: – CMB– Gunn Peterson– Lyman-alpha galaxies

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I. Reionization: what is it?

The word you've entered isn't in the dictionary. Click on a spelling suggestion below or try again using the search box to the right.Suggestions for reionization: 1. lionization 2. reinsertion 3. reanimation 4. lionizations 5. realization 6. renunciation 7. rhinestone 8. reignitions 9. reinsertions 10. reanimations

also plural sox /'säks/ : a knitted or woven covering for the foot usually extending above the ankle and sometimes to the knee

The Gunn-Peterson effect: (Gunn & Peterson 1965)

The Gunn-Peterson Test

Detection of G-P trough.• The detection of Gunn-

Peterson trough(s) in z ~ 6 quasars show the late stages of H reionization (Becker et al. 2001, Fan et al. 2002.)

The Renaissance after the Dark Ages

H II

z ~

6-1

0

“Dark Ages”

TIGM ~ 4z K

z ~

10

3

z ~

∞

Big

Ban

g

(re)

com

bin

ati

on

tz

H I

TIGM ~ 104 K

normal galaxy

S1Here Now

primordial galaxy

Hubble Deep Field

Ultra Deep Field

Mike Fall

Need to go faint:•GO back to redshift z > 6 and account for photons needed for reionization

•See ordinary galaxies, i.e. fainter than L*, because they make up most of the photons needed.

Need to go red:

Because of redshifting of the spectra and the IGM absorption.

Yan & Windhorst 2004

H U D F

Reionization Results from the HUDF images:

• Bunker et al : count galaxies to magnitude 28.5 mag. (WYSIWYG) and fall short by a factor of 3.

• Yan & Windhorst: Go fainter (30.5 mag) and attempt correction for incompleteness. Enough photons.

• See also Bouwens et al. 2004ab

Residual uncertainty: reliability and completeness of I-drop sample

GRism ACS Program for Extragalactic Science (GRAPES)

Team: S. Malhotra, James Rhoads, Nor Pirzkal, Chun XuA. Cimatti, E. Daddi, H. Ferguson, J. Gardner, C. Gronwall, Z. Haiman, A.

Koekemoer, L. Moustakas, A. Pasquali, N. Panagia, L. Petro, M. Stiavelli, S. di Serego Aligheri, Z. Tsvetanov, J. Vernet, J. Walsh, R. Windhorst, H.J. Yan

Deepest Unbiased Spectroscopy yet. I(AB) < 27.5

To match the deepest imaging (Hubble Ultra Deep Field)

40 orbits of UDF observations with the ACS grism

• Spectra for every source in the field.• Good S/N continuum detections to I(AB) ~

27.5 – 10 times deeper than ground-based : Keck,

Gemini, VLT

• about 15% of UDF sources ~ 1500 spectra with good s/n

• Spectral identification of every z=4-7 object to I(AB)=27.5

• Moderate redshift ellipticals z~1-2• Emission line galaxies• Reduced spectra available from HST

archives: http://archive.stsci.edu/prepds/udf/udf_hlsp.html

Advantages of HST/ACS combination:

•Low sky background from space

•Red sensitivity of the ACS

•High redshift galaxies are compact, spatial resolution of HST helps.

•Contiguous wavelength/redshift coverage, unlike ground based instruments.

Improvements in data reduction

GRAPES sample(A nice science free slide)

If only slitless extraction was that easy...

•Each pixel has all of the sky and about 1/100th of the object flux.

•3-D flat field; sky is a different color.

•High chance of overlap of spectra.

Complications

•Made a supersky and subtract that first.

•Flatfield after extracting each spectra from each exposure, then combine: first 1-D then 2-D

•Minimize contamination with 2-4 orient angles 90 degrees apart.

•Estimate contamination from broad-band colors of neighbouring objects

•Optimal extraction.

•All improvements in the new aXe extraction software aXe 1.5, thanks to our colleagues at ST-ECF: Jeremy Walsh and Martin Kuemmel.

aXe 1.7 will write ApJ letters after extracting the spectra

Solutions and Improvements

A Spiral galaxy at z=0.3

Direct image | Dispersed image

Experimental design (Pirzkal et al. 2004)

Four orients: 0, 8, 90, 98 degrees orient to disentangle overlapping spectra.

The agreement between the four orients in wavelength and flux demonstrate accurate flat-fielding and wavelength calibration.

Spectroscopically identified objects:

from 600 to 6.7x1010 pc

Salient results from GRAPES1. Too few white dwarfs: < 10% of the DM halo (Pirzkal et al. 2004b)2. Ellipticals at z~1 much like z~0 (Pasquali et al. 2005)3. Too many Ellipticals at z~2 (Daddi et al. 2005)4. Unusually large/interacting object at z=5.5 (Rhoads et al. 2004)5. Unusually difficult data set to reduce (Pirzkal et al. 2004a)6. Catalog of line emitters at z~1 (Xu et al. 2005)7. Luminosity function of [OII] emitters at z~1 (Gronwall et al. in prep)8. Line emitters are small, high surface brightness objects (Pirzkal et al. 2005)9. z~5 galaxies are not pop-III dominated (Rhoads et al, in prep.)10. Large scale clustering at z~6 (Malhotra et al. 2005)

Enough photons locally to reionize the intergalactic gas

Quantitative statements: need more than one field:

(Esp. in view of the large scale structure that we see)

PEARS

High redshift galaxiesz=5.5, z=26.9

z=6.4, z=27.8

z=5.8, z=25.1

With GRAPES we can spectroscopically confirm LBGs to z’(AB)=27-28 depending on the redshift.

Reliability of (i-z) selection • 80% for (i-z) > 0.9

• 96% for (i-z) > 1.3

Completeness: color-redshift plot

• The (i-z’) generally follows the expected color but there are some blue galaxies: all can be explained by a moderately strong lyman-alpha emission.

• Incompleteness implied is about 4/23~20%

A spike in the Redshift distribution (Malhotra et al. 2005)

Comparison of observed redshift distribution (histogram) vs. expected numbers

The spike at z~6 is at least a factor of two over-dense.

Deep probe vs. Flat-wide probe

• Ly-alpha emitters at z=5.7-5.77 observed with mosaic at CTIO– (36’x36’ = 13x13 Mpc)

(Wang, Malhotra & Rhoads 2004)

• Inhomogeneous distribution– UDF is at the edge of it

Luminosity function at the overdensity

• Star-formation rate density for this over-dense region is 2-4x10-2

MO/Mpc3/year

• This is enough to drive re-ionization in this “local” over-density.

Reionization : when• When was reionization?

– Gunn-Peterson effect z~6– WMAP polarization z~17

• How fast was it?• How homogeneous?• We need to agree of a definition of reionization!

Lyman- galaxy test: local, scaleable relevant at neutral fractions of <f(HI)>~0.5

The Lyman- ReionizationTest

To

Observer

Ionized IGM

Young starburst

Lyman- photons

Continuum Photons

The Lyman- Test

To

Observer

Neutral IGM

Young starburst

Lyman- photons

Continuum Photons

(Miralda-Escude 1998; Miralda-Escude & Rees 1998;

Haiman & Spaans 1999; Loeb & Rybicki 1999)

To

Observer

Neutral IGM

Young starburst

Lyman- photons

Continuum Photons H II

region

(Madau & Rees 1999; Rhoads & Malhotra 2001;

Haiman 2002)

The Lyman- Test, First Order Concerns: HII Regions

theorists!Ly- lines were expected to be invisible in a neutral IGM until Hu

et al. 2002 found a source at z=6.6.

Then everyone rushed to explain why we could see Ly- even in a neutral IGM: ionized bubbles, winds …

But hard to avoid attenuation of factors of 2-3 (Santos 2004)

How do you know that any individual object was not intrinsically brighter?

Statistical test on the population

Lyman- Luminosity Functions• Luminosity function fits on all

available data at z=5.7 and 6.5– Santos et al. 2004, Taniguchi et al.

2004, Rhoads et al. 2004, Kurk et al. 2004, Tran et al. 2004, Hu et al. 2002, Hu et al. 2004, Ajiki et al. 2004, Rhoads et al. 2003, Rhoads & Malhotra 2001 (few tens of nights on large telescopes)

• z = 6.5 plot shows two hypotheses:

– z = 5.7 LF, or– z = 5.7 LF reduced by a factor

of 3 in luminosity to approximate IGM absorption.

• No evidence for neutral IGM!

Charting ReionizationThere is no contradiction between the GP effect at z=6.2 and

the Ly test at z=6.5; remarkable agreement with the dark gap tests (Fan et al. 2005)

MR99

MR03

1st order concern 1.Cosmic variance in samples

Monte Carlo simulations to account for cosmic variance: All observed densities allowed to vary by factor of 2.– Circles: z = 5.7

– Triangles: z = 6.5

– Squares: z = 5.7 with L* divided by 3.

1st order concern 2.Picket fence effect

Suppose you obliterate some fraction of the sources completely, and the other half remains untouched in luminosity.

Then phi* should decrease

- it is seen to increase slightly at z=6.5 compared to z=5.7

Concern 3: redshift evolution:

none! LALA Lum Fn at z=4.5

(Dawson et al. 2005)

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LALA Lum fn at z=4.5

4. Bright end of luminosity function

• Biggest changes expected at the bright end of the luminosity function!

• See Haiman & Cen 2005, for luminosity dependent attenuation: the conclusions do not change significantly.

• Furlanetto et al. 2005, conclude that neutral fraction is 50% compared to ~30% as in MR04.

Concern 5: Clustering around Ly-a sources

1. What about clustering and Stromgren spheres created by unseen sources around Lyman-alpha emitters at z=6.5?

• Need to boost the ionizing flux by a factor of 10: possible in simulations: Wyithe & Loeb 2004, Furlanetto et al. 2004:

• deep ACS imaging around one z=6.5 source shows no dramatic overdensity (Rhoads et al. in prep.) Stiavelli et al. 2005 see an overdensity at z=5.9 around a Sloan quasar at z=6.2

Agnostic about this possibility

Mapping Ionized and Neutral Gas with Lyman Alpha Galaxies

• We can map the distribution of Lyman alpha galaxies over large scales…

• This may map out bubbles of ionized gas in the overlap phase of reionization.

Mapping Ionized and Neutral Gas with Lyman Alpha Galaxies

• A control sample of Lyman break selected galaxies will be useful (green dots, below).

Topology of Reionization from Lyman Alpha Galaxies

• The overlap phase is a topological change in the ionized gas distribution.

• Use topological statistics-- the Genus number

Figure after Gott, Weinberg, & Melott 1987

Galaxies at z~5-6

Malhotra et al. 2005, Pirzkal et al. 2006.

First and Last word about Pop-III=> Spectral slopes of UDF faint galaxies

(Rhoads et al. 2005)

The composite spectrum of z=4-5 objects in the UDF is shown by the white line. The Lyman break sample (Shapley et al.) at z=3 is shown in yellow for comparison and one of the bluest nearby galaxies NGC 1705 is shown in blue.

Old Stellar populations at z~6: Spitzer

GOODS data: Yan et al. 2005, also Eyles et al. 2005,

Egami et al. 2005.

Star-formation at z>10

Need to quantify this!

Old Stars and Dust? Spitzer weighs in

(Mobasher et al, 2005):

Edge of the Universe or Edge of technology ?

Summary• Are there enough photons to reionize at z=6? Depends on where you look. • Ly-a luminosity function test at z=6.5 implies neutral fraction <50% at

z=6.5• Space density of observed Ly-a implies a volume fraction of ionized gas

V(I) > 23%. • Limits on V(I) can be improved by going fainter and finding more galaxies:

JWST.• Can go to higher redshifts and track the evolution of reionization as a

function of z: WFPC3, JWST (No fighting 10^6 foregrounds!)• Higher order information: eg. topology of ionized bubbles, can tell us

when, how fast and how inhomogenous reionization was: – Large format IR camera from the ground, WFPC3, JWSTOld stellar populations at

z=5-7…Spitzer today and detailed studies with JWST next week!

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