1. Redshift sox:The beginning of an STScI softball team?
Sangeeta Malhotra
Contact Andy Fruchter

2. 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…)
Collaborators, mention James, Nor, Chun prominently, Lexi, Emanuele, Yan.
Beckwith, Stiavelli, Ferguson, Koekemor, Sosey and Bergeron and the UDF imaging team
LALA: Junxian Wang, Dawson, Norman, Heckman, Livio
GLARE: Glazebrook
New stuff: surface brightness (SFRD), volume argument?, EW for the z=5.7 sample, luminosity function evolution
Of both lyman-alpha and LBGs
Dark gap statistics
Spitzer observations of lyman-alpha galaxies

3. 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…)
Collaborators, mention James, Nor, Chun prominently, Lexi, Emanuele, Yan.
Beckwith, Stiavelli, Ferguson, Koekemor, Sosey and Bergeron and the UDF imaging team
LALA: Junxian Wang, Dawson, Norman, Heckman, Livio
GLARE: Glazebrook
New stuff: surface brightness (SFRD), volume argument?, EW for the z=5.7 sample, luminosity function evolution
Of both lyman-alpha and LBGs
Dark gap statistics
Spitzer observations of lyman-alpha galaxies

4. Reionization: What: When: Who: Sources of reionization.
Clustering of sources of ionization.
When:
CMB
Gunn Peterson
Lyman-alpha galaxies

6. 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: lionization reinsertion reanimation lionizations realization renunciation rhinestone reignitions reinsertions reanimations
also plural sox /'säks/ : a knitted or woven covering for the foot usually extending above the ankle and sometimes to the knee

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

9. The Gunn-Peterson Test

10. 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 )

11. The Renaissance after the Dark Ages
Ultra Deep Field
“Dark
Ages”
Hubble Deep Field
primordial
galaxy
Here
Now S1
Big Bang
(re) combination
normal
galaxy
This schematic drawing by Mike Fall shows the development of the universe since the time of the Big Bang.
The era of recombination, leading to the Cosmic Microwave Background, occurs at redshifts around 1000.
The era of galaxy formation occurs between redshifts of about 20 (max) and 1, with the re-ionization of the universe occuring around z~6 as the number of hot, young stars becomes large enough to ionize the neutral gas.
The “Dark Ages” occurred between the time of recombination (z=1000) and the time of re-ionization (z~6) and currently represents an interesting but unobserved phase of the evolution of structure in the universe.
The Hubble Deep Field got us to a time when galaxy buildup was active but still not at the “edge” of the dark ages.
The Hubble Ultra Deep Field should take us right up to the edge, to a time before starlight was kept the electrons and protons apart and the universe transparent. It should get us to the boundary of the “dark ages.”
HST will be able to probe out to about z~6 with its instruments after SM4. With more powerful instruments, it could conceivably push even farther into the “Dark Ages;” otherwise, we will await NGST.
H I
H II
z ~ 6-10
z ~ ∞
TIGM ~ 104 K
TIGM ~ 4z K
z ~ 103 t z
Mike Fall

12. 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.
Yan & Windhorst 2004
Need to go red:
Because of redshifting of the spectra and the IGM absorption.

13. H U D F

14. 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

15. GRism ACS Program for Extragalactic Science (GRAPES)
Deepest Unbiased Spectroscopy yet. I(AB) < 27.5
To match the deepest imaging (Hubble Ultra Deep Field)
The goal of this project is to find primitive galaxies at very high redshifts and thereby directly study early galaxy and star formation. (could comment on the line as a good indicator of the unevolved population if present)
Team: S. Malhotra, James Rhoads, Nor Pirzkal, Chun Xu
A. 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

16. 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:

17. 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

18. GRAPES sample (A nice science free slide)
This is a typical GRAPES ACS UDF observation, containing thousands of spectra on the left
Extracted spectra of emission line objects are shown on the right.
This looks easy, but.... it is not.
If only slitless extraction was that easy...

19. Complications
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.

20. Solutions and Improvements
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

21. A Spiral galaxy at z=0.3
Direct image | Dispersed image

22. 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.

23. Spectroscopically identified objects:
from 600 to 6.7x1010 pc

24. Salient results from GRAPES
Too few white dwarfs: < 10% of the DM halo (Pirzkal et al. 2004b)
Ellipticals at z~1 much like z~0 (Pasquali et al. 2005)
Too many Ellipticals at z~2 (Daddi et al. 2005)
Unusually large/interacting object at z=5.5 (Rhoads et al. 2004)
Unusually difficult data set to reduce (Pirzkal et al. 2004a)
Catalog of line emitters at z~1 (Xu et al. 2005)
Luminosity function of [OII] emitters at z~1 (Gronwall et al. in prep)
Line emitters are small, high surface brightness objects (Pirzkal et al )
z~5 galaxies are not pop-III dominated (Rhoads et al, in prep.)
Large scale clustering at z~6 (Malhotra et al. 2005)
Enough photons locally to reionize the intergalactic gas
PEARS
Quantitative statements: need more than one field:
(Esp. in view of the large scale structure that we see)

25. High redshift galaxies
With GRAPES we can spectroscopically confirm LBGs to z’(AB)=27-28 depending on the redshift.
z=5.5, z=26.9
z=5.8, z=25.1
As you can see we have approximately doubled the well-observed redshift range of the Hubble diagram.
6 of the 7 highest redshift known
z=6.4, z=27.8

26. Reliability of (i-z) selection
80% for (i-z) > 0.9
96% for (i-z) > 1.3

27. 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%

28. 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.

29. Deep probe vs. Flat-wide probe
Ly-alpha emitters at z= observed with mosaic at CTIO
(36’x36’ = 13x13 Mpc)
(Wang, Malhotra & Rhoads 2004)
Inhomogeneous distribution
UDF is at the edge of it

30. 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.

31. Reionization : when When was reionization? How fast was it?
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

32. The Lyman- ReionizationTest
Ionized IGM
Continuum Photons To
Young starburst
Observer
Lyman- photons

33. The Lyman- Test Continuum Photons Lyman- photons
Neutral IGM
Continuum Photons To
Young starburst
Observer
Lyman- photons
(Miralda-Escude 1998; Miralda-Escude & Rees 1998;
Haiman & Spaans 1999; Loeb & Rybicki 1999)

34. The Lyman- Test, First Order Concerns: HII Regions
Neutral IGM
Continuum Photons
H II
region To
Young starburst
Observer
Lyman- photons
(Madau & Rees 1999; Rhoads & Malhotra 2001;
Haiman 2002)

35. Statistical test on the population
theorists!
Ly- lines were expected to be invisible in a neutral IGM until Hu et al 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

36. 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!

37. Charting Reionization
There 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

38. 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.

39. 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

40. Concern 3: redshift evolution: none!
LALA Lum Fn at z=4.5
LALA Lum fn at z=4.5
(Dawson et al. 2005)

41. 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.

42. Concern 5: Clustering around Ly-a sources
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 see an overdensity at z=5.9 around a Sloan quasar at z=6.2
Agnostic about this possibility

43. 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.

44. Mapping Ionized and Neutral Gas with Lyman Alpha Galaxies
A control sample of Lyman break selected galaxies will be useful (green dots, below).

45. 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

46. 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
The 3D Genus number quantifies whether a two phase medium is dominated by islands of one phase embedded in a sea of the other, or whether both phases percolate.
2D version exists too.
Useful for HI as well as Lyman-.
(Rhoads+, 2005)
Figure after Gott, Weinberg, & Melott 1987

47. Extension to redshifts z > 7
Windows in the atmospheric OH spectrum continue into the J and H bands, though narrower.
Newest NIR cameras have A sufficient for plausible Ly- searches.
Several efforts under way…
Horton et al 2004 (DAzLE project): VLT + DAzLE) z ~ 7.7
Smith et al (see Barton et al 2004): Gemini + NIRI, z ~ 8.2
Willis et al (“ZEN” project): VLT +ISAAC, z ~ 8.8
Cuby et al: VLT +ISAAC, z ~ 8.8
… and I don’t think I’ll miss this chance either!

48. Galaxies at z~5-6

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

50. First and Last word about Pop-III=>
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.

51. Old Stellar populations at z~6: Spitzer
GOODS data: Yan et al. 2005, also Eyles et al. 2005,
Egami et al
Star-formation at z>10
Need to quantify this!

52. Old Stars and Dust? Spitzer weighs in
(Mobasher et al, 2005):

53. Edge of the Universe or Edge of technology ?

54. 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!