Rychard Bouwens(UC Santa Cruz / Leiden)

Cosmological Reionization -- Allahabad, IndiaFebruary 17, 2010

High-Redshift Galaxies and the Reionization of the Universe:

Insight from RecentWFC3/IR Observations

WFC3

UCSC 02/01/10 RJB

Shuttle Servicing Mission SM4

With a Special Thanks to: Garth Illingworth, Marijn Franx, John Blakeslee, Holland Ford, Rodger Thompson, Louis E. Bergeron, Massimo Stiavelli, Dan Magee, Ivo Labbe, Pieter van Dokkum, Dan Coe, Larry Bradley, Valentino Gonzalez

ACS GTO team: Holland Ford, Garth Illingworth, Mark Clampin, George Hartig, Txitxo Benitez, John Blakeslee, Rychard Bouwens, Marijn Franx, Gerhardt Meurer, Marc Postman, Piero Rosati, Rick White, Brad Holden, Dan Magee + many other team members

UDF-IR team: Rodger Thompson, Garth Illingworth, Rychard Bouwens, Mark Dickinson, Pieter van Dokkum, Dan Eisenstein, Xiaohui Fan, Marijn Franx, Marcia Rieke, Adam Riess

HUDF09 WFC3 IR team: Garth Illingworth, Rychard Bouwens, Marijn Franx, Pieter van Dokkum, Massimo Stiavelli, Ivo Labbe, Michele Trenti, Marcella Carollo, Pascal Oesch, Dan Magee

Special Thanks to My Collaborators

1) Galaxies as possible reionization sources-- This follows from evidence from z~6 SDSS quasars and 7-year

WMAP optical depth measurements that the universe was likely reionized between z~6 and 11…

Key Science Interests

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Galaxy Formation & Evolution at z>6

1) Galaxies as possible reionization sources-- This follows from evidence from z~6 SDSS quasars and 7-year

WMAP optical depth measurements that the universe was likely reionized between z~6 and 11…

2) The luminosity and masses of galaxies at these epoches are likely to build up very rapidly to z~3.

3) Galaxies at these epochs are likely to show unique and very interesting stellar populations (new IMFs, zero metallicities,

and no dust)

Key Science Interests

UCSC 02/01/10 RJB

Galaxy Formation & Evolution at z>6

What does the new WFC3/IR instrument tell us about galaxy

evolution at z>6?

What are the implications forreionization?

But first let me remind you about results from LF studies at z~4-6?

Faint-end Slope of the UV Luminosity Function

Bouwens et al. 2007

Bouwens et al. 2007Reddy et al. 2008

Steep

Shallow

Faint-end Slope

For such steep faint end slopes, the volume density of lower luminosity galaxies is substantial: 50% of the UV luminosity density is below 0.06 L* 50% 50%

Need the deepest data to do this well, so use fields like HUDF!

(see also Beckwith et al. 2006and Oesch et al. 2007)

High LuminosityGalaxies

Low LuminosityGalaxies

Evolution of the UV Luminosity Function

Bright

Faint

Redshift

M*UV

Bouwens, Illingworth, Franx, & Ford 2007

Hierarchical Buildup

AGN Feedback?

Downsizing

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What does the new WFC3/IR instrument tell us about galaxy

evolution at z>6?

Let us look at quick demonstration of how well WFC3/IR works!

Demonstrating Performance of WFC3/IR

Region of the HUDF

NICMOS 72 orbitsWFC3/IR 16 orbits

Let us talk about some of the early science results...

Exciting Ultradeep WFC3/IR Program

HUDF09 WFC3/IR program

CDF-South GOODS

Should find 50-100 z>=7 galaxies

Deepestoptical data

HUDF09 WFC3 IR team: Garth Illingworth, Rychard Bouwens, Marijn Franx, Pieter van Dokkum, Massimo Stiavelli, Ivo Labbe, Michele Trenti, Marcella Carollo, Pascal Oesch, Dan Magee

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August 26 - Sept 6, 2009

Oesch et al. (2010)

16 z~7 z-dropouts from our 4.7 arcmin2

HUDF09 observations over the HUDF(Oesch et al. 2009)

Excellent S/N

As an example, here are the z-dropoutcandidates identified previously (Bouwens et al. 2004, 2008; Oesch et al. 2009)

but see also McLure et al.; Bunker et al.; Yan et al; Finkelstein et al.

Are these sources really redshift z~7 galaxies?

The properties of these sources are: 1) Very strong z-Y break 2) Very blue Y-J colors redward of the break 3) Non-detection at optical wavelengths

Very unusual properties for sources found in thereal universe

Typical contaminants tend to be low-mass stars, but in a multi-color space (z-Y, Y-J, J-H), there is a nice separation between z~7 star-forming galaxies and low-mass stars.

Contamination from Photometric Scatter: Simulations give contamination rates <= 1%

UV Luminosity Functions

Bright Faint

Log # mag-1 Mpc-3

Oesch et al. 2010 UCSC 02/01/10 RJB

z~6z~7

z~4

Old NICMOS z~7 LF (Bouwens et al. 2008;Oesch et al. 2009)z~7

Now, use the z~7 search results to derive constraints on z~7 UV LF

5 z~8 Y-dropouts from our 4.7 arcmin2

HUDF09 observations over the HUDF(Bouwens et al. 2009)

Are these sources really redshift z~8 galaxies?

Extended, so not low-mass stars...Contamination from photometric scatter < 1%

UV Luminosity Functions

Bright Faint

Log # mag-1 Mpc-3

Oesch et al. 2010; Bouwens et al. 2010 UCSC 02/01/10 RJB

Now, use the z~8 search results to derive constraints on z~8 UV LF

z~8

z~7

z~4

Total WFC3/IR Data Set

HUDF09 WFC3/IR program

CDF-South GOODS

Deepestoptical data

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WFC3/IR ERS

New WFC3/IR ERS samples~17 z~7 z-dropouts~6 z~8 Y-dropouts

Total z>=7 WFC3/IR sample~50 z~7 z-dropouts~25 z~8 Y-dropouts

Second HUDF09 sample~17 z~7 z-dropouts~7 z~8 Y-dropouts

Bright Faint

Log # mag-1 Mpc-3

Bouwens et al. 2010

UV LFs at z~7-8 from Wide area + Ultra-deep Observations with WFC3/IR

UV Luminosity Functions

Prelimi

nary

~50 z~7 galaxies ~25 z~8 galaxies50 z~7 galaxies,25 z~8 galaxies

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Bright Faint

ϕ*

Bouwens et al. 2010

Wide area + Ultra-deep Observations can be used to more accurately constrain the UV LF at z~7-8

UV Luminosity Functions

68% and 95% confidence intervals

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Prelimi

nary

Integrate the UV LFs at z~7 and z~8, one derives theSFR density

Bouwens et al. (2010)

Star FormationRate density

What does this mean for reionization?

dQHII

dt= dndnion/dt/dt

nH− QHII

trec

Recombination RateIonization Rate

Change in ionizationstate

trec = (0.6 Gyr) C3 ((1+z)/7)3

⦗QSO + Galaxy + Annihilating DM(?)

~3% unknown

????

What fraction of universe do galaxies reionize?

see also Oesch et al. 2009

Fraction of HI ionized~100%

~54%~28%~14%

z~6

z~7z~8z~9

Clumping Factor ~3

(Bolton et al. 2005; Pawlik et al. 2009)

Escape Fraction ~20%

What does such a LF evolution mean for reionization?

see also Oesch et al. 2009

Fraction of HI ionized~100%

~54%~28%~14%

z~6

z~7z~8z~9

Thompson optical depth

τ ~ 0.05

QHII

vs. WMAP-7τ ~ 0.087 +/- 0.014

One other solution to reionization of the universe was proposed by Yan et al. 2010...

based upon 15 purported z~8 galaxies and 20 z~9-10 candidates....

Yan et al. (2010)

Purported Upturn in SFR density

However, most of the Yan et al. 2010 z~9-10 J-dropout

candidates are very close to extended foreground galaxiese.g.,

Yan et al. (2009) z~9-10 Candidates

But expect no association between z~9-10 J-dropouts and extended

foreground galaxies

We decided to test this hypothesis:

Plot distance of dropouts toclosest extended galaxy

Our z~7 sample

Distribution of distances to extended sources for blank area on image

Yan z~9-10 sample

Clear association of Yan et al. 2010 z~9-10 sample with foreground galaxies at

99.99995% confidence

Suggests their sample is not reliable and likely full of contaminants

Yan et al. 2009 z~8 sample also shows this association with foreground galaxies at

99.2% confidence

Suggests their sample is not reliable and likely full of contaminants

Yan et al. (2010)

Bouwens et al. (2010)

Where does this leave us with the SFR density?

What can we learn about reionization

from

Stellar Mass Estimates?~4μmIRAC

images

IRAC

rest-frameoptical at

z~7

StellarMass

Valentino Gonzalez

Stellar Masses of z~7 Galaxies

Flux1030 ergs s-1

cm-1 Hz-1

Gonzalez et al. 2009

Mass = 4.2 x 109 Msol

Age = 398 Myr

z~7 SED Fit

z~2 SED Fit(bad fit)

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Total WFC3/IR z~7-8 samples of use for stellar mass density estimates

HUDF09 WFC3/IR program

CDF-South GOODS

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WFC3/IR ERS

New WFC3/IR ERS samples~17 z~7 z-dropouts~6 z~8 Y-dropouts

HUDF09 sample~17 z~7 z-dropouts~7 z~8 Y-dropouts

Stellar Mass Density

Gonzalez et al. 2009 UCSC 2010 RJB

Labbe et al. 09bNew WFC3/IR Results

Divide by cosmic time...

Implies higher value of SFR density...

and hence higher thompson optical depth, butstill does not match τ ~ 0.087 +/- 0.014 WMAP-

7 value...

What can learn from the UV colors of z>~7 galaxies?

Galaxies at z>6: What type of colors do theyhave in the UV-continuum?

The power law slope of UV continuum:

fλ ~ λβ

What is the UV slope β?UV-continuum slope β depends

upon the age, metallicity, and dust content of a star-forming

population

UV-continuum slope β most sensitive to changes in dust

content

UCSC 2010 RJB

UV slope

Luminosity

red

blue

bright faint

“more dusty”

“more dust-free”

z~7 galaxies from ultra-deep WFC3/IR observations of the HUDF:What about their UV colors?

Bouwens et al. 2010

dust free

not fit with standard stellar population

models

Bouwens et al. 2009

UCSC 2010 RJB

UV slope

Redshift

red

blue

“more dusty”

“more dust-free”

What about their UV colors?versus redshift

Bouwens et al. 2010

dust free

not fit with standard stellar population models

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Lower UV Luminosities (~0.1 L*)

Possible Solutions?

Aspen 2010 RJB

What might a UV slope β ~ −3 imply?

--> (Lyman-Continuum Escape Fraction May be > 30%...) Nebular Continuum Emission Must Not Be That Important

Ionized Gas (from hot stars) β ~ −1.7 (red)

To produce very blue β’s (i.e., −3) we require hot, young stars...

Very Hot Stars β ~ −3 (blue)

Emitted Light

Total (Hot Stars + Ionized Gas) β ~ −2.3

→ Nebular Continuum Emission Keeps Us from producing very blue β’s

2. Models overpredict nebular continuum emission (?)

Bouwens et al. 2010

1. Lyman-Continuum Escape Fraction Large (>~ 30%)

β ~ −3

What can we learn about galaxy formation and evolution from observations of very high redshift galaxies

WFC3/IR allows us to very efficiently identify galaxies at high redshift. We identify 50 z~7 z-dropouts and ~25 z~8 Y-dropout galaxies in the new observations

The UV LF at z~7-8 is quite consistent with the extrapolation from lower redshiftSFR density continues to decrease towards higher redshift to our search limitsImplies steady decrease in ionized fraction QHII towards high redshift, i.e., ~56% at z~7, ~28% at z~8, 14% at z~9, ... with tau ~ 0.05 The UV-continuum slopes beta we measure at z~7 are very blue, particularly

towards very low luminosities and may suggest modest Lyman-Continuum Escape Fractions, i.e., > 30%.

We can use the deep IRAC data -- in combination with the near-IR data -- to do stellar population modelling for z~7 and z~8 sources and estimate stellar masses and hence SFR densities.

These estimated SFR densities also allow us to estimate the number of reionizing photons at high-redshift... Again there is a tension with the WMAP-7 measurement.

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