Cosmological Reionization -- Allahabad, India High-Redshift Galaxies and the Reionization of the Universe: Insight from Recent WFC3/IR Observations Rychard Bouwens (UC Santa Cruz / Leiden) Cosmological Reionization -- Allahabad, India February 17, 2010

Shuttle Servicing Mission SM4 WFC3 UCSC 02/01/10 RJB

Special Thanks to My Collaborators 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

Galaxy Formation & Evolution at z>6 Key Science Interests 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… UCSC 02/01/10 RJB

Galaxy Formation & Evolution at z>6 Key Science Interests 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) UCSC 02/01/10 RJB

What are the implications for What does the new WFC3/IR instrument tell us about galaxy evolution at z>6? What are the implications for reionization?

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

Faint-end Slope of the UV Luminosity Function High Luminosity Galaxies Low Luminosity Shallow Bouwens et al. 2007 Reddy et al. 2008 Need the deepest data to do this well, so use fields like HUDF! Faint-end Slope Steep 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% Bouwens et al. 2007 (see also Beckwith et al. 2006 and Oesch et al. 2007)

Evolution of the UV Luminosity Function Bright Hierarchical Buildup AGN Feedback? Downsizing M*UV Faint Redshift Bouwens, Illingworth, Franx, & Ford 2007 UCSC 02/01/10 RJB

Let us look at quick demonstration of how well WFC3/IR works! 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 NICMOS 72 orbits WFC3/IR 16 orbits Region of the HUDF

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

Exciting Ultradeep WFC3/IR Program Deepest optical data HUDF09 WFC3/IR program CDF-South GOODS 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 Should find 50-100 z>=7 galaxies UCSC 02/01/10 RJB

August 26 - Sept 6, 2009

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-dropout candidates identified previously (Bouwens et al. 2004, 2008; Oesch et al. 2009) Oesch et al. (2010) 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 the real 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 Now, use the z~7 search results to derive constraints on z~7 UV LF UV Luminosity Functions z~7 Old NICMOS z~7 LF (Bouwens et al. 2008; Oesch et al. 2009) z~7 z~4 Log # mag-1 Mpc-3 z~6 Bright Faint Oesch et al. 2010 UCSC 02/01/10 RJB

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 Now, use the z~8 search results to derive constraints on z~8 UV LF UV Luminosity Functions z~8 z~4 Log # mag-1 Mpc-3 z~7 Bright Faint Oesch et al. 2010; Bouwens et al. 2010 UCSC 02/01/10 RJB

Total WFC3/IR Data Set Deepest optical data WFC3/IR ERS HUDF09 WFC3/IR program New WFC3/IR ERS samples ~17 z~7 z-dropouts ~6 z~8 Y-dropouts Second HUDF09 sample CDF-South GOODS ~17 z~7 z-dropouts ~7 z~8 Y-dropouts Total z>=7 WFC3/IR sample ~50 z~7 z-dropouts ~25 z~8 Y-dropouts UCSC 02/01/10 RJB

UV LFs at z~7-8 from Wide area + Ultra-deep Observations with WFC3/IR UV Luminosity Functions Preliminary Log # mag-1 Mpc-3 ~50 z~7 galaxies ~25 z~8 galaxies 50 z~7 galaxies, 25 z~8 galaxies Bright Faint Bouwens et al. 2010 UCSC 02/01/10 RJB

UV Luminosity Functions Wide area + Ultra-deep Observations can be used to more accurately constrain the UV LF at z~7-8 UV Luminosity Functions Preliminary 68% and 95% confidence intervals ϕ* Faint Bright Bouwens et al. 2010 UCSC 02/01/10 RJB

Integrate the UV LFs at z~7 and z~8, one derives the SFR density Bouwens et al. (2010) Star Formation Rate density

⦗ ???? What does this mean for reionization? Change in ionization state Recombination Rate Ionization Rate dQHII dnion/dt QHII = − ⦗ nH dt trec QSO + Galaxy + Annihilating DM(?) ~3% unknown ???? trec = (0.6 Gyr) C3 ((1+z)/7)3

What fraction of universe do galaxies reionize? Fraction of HI ionized ~100% ~54% ~28% ~14% z~6 z~7 z~8 z~9 Clumping Factor ~3 (Bolton et al. 2005; Pawlik et al. 2009) Escape Fraction ~20% see also Oesch et al. 2009

What does such a LF evolution mean for reionization? Fraction of HI ionized QHII ~100% ~54% ~28% ~14% z~6 z~7 z~8 z~9 Thompson optical depth τ ~ 0.05 vs. WMAP-7 τ ~ 0.087 +/- 0.014 see also Oesch et al. 2009

Purported Upturn in SFR density 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

We decided to test this hypothesis: However, most of the Yan et al. 2010 z~9-10 J-dropout candidates are very close to extended foreground galaxies We decided to test this hypothesis: Plot distance of dropouts to closest extended galaxy Our z~7 sample Distribution of distances to extended sources for blank area on image e.g., Yan et al. (2009) z~9-10 Candidates 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 z~9-10 sample 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 But expect no association between z~9-10 J-dropouts and extended foreground galaxies

Where does this leave us with the SFR density? Yan et al. (2010) Bouwens et al. (2010)

IRAC What can we learn about reionization from Stellar Mass Estimates? IRAC images IRAC rest-frame optical at z~7 Stellar Mass Valentino Gonzalez

Stellar Masses of z~7 Galaxies z~7 SED Fit z~2 SED Fit (bad fit) Flux 1030 ergs s-1 cm-1 Hz-1 Mass = 4.2 x 109 Msol Age = 398 Myr Gonzalez et al. 2009 UCSC 2010 RJB

Total WFC3/IR z~7-8 samples of use for stellar mass density estimates WFC3/IR ERS HUDF09 WFC3/IR program HUDF09 sample ~17 z~7 z-dropouts ~7 z~8 Y-dropouts New WFC3/IR ERS samples ~17 z~7 z-dropouts ~6 z~8 Y-dropouts CDF-South GOODS UCSC 02/01/10 RJB

Stellar Mass Density Divide by cosmic time... Implies higher value of SFR density... and hence higher thompson optical depth, but still does not match τ ~ 0.087 +/- 0.014 WMAP-7 value... New WFC3/IR Results Labbe et al. 09b Gonzalez et al. 2009 UCSC 2010 RJB

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

fλ ~ λβ Galaxies at z>6: What type of colors do they have in the UV-continuum? 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 The power law slope of UV continuum: fλ ~ λβ UCSC 2010 RJB

not fit with standard stellar population models z~7 galaxies from ultra-deep WFC3/IR observations of the HUDF: What about their UV colors? red “more dusty” Bouwens et al. 2009 UV slope dust free not fit with standard stellar population models blue “more dust-free” bright Luminosity faint Bouwens et al. 2010 UCSC 2010 RJB

not fit with standard stellar population models What about their UV colors? versus redshift red “more dusty” Lower UV Luminosities (~0.1 L*) UV slope blue dust free not fit with standard stellar population models “more dust-free” Redshift Bouwens et al. 2010 UCSC 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 To produce very blue β’s (i.e., −3) we require hot, young stars... Very Hot Stars β ~ −3 (blue) Emitted Light 1. Lyman-Continuum Escape Fraction Large (>~ 30%) β ~ −3 Ionized Gas (from hot stars) β ~ −1.7 (red) Total (Hot Stars + Ionized Gas) β ~ −2.3 → Nebular Continuum Emission Keeps Us from producing very blue β’s Possible Solutions? 2. Models overpredict nebular continuum emission (?) Bouwens et al. 2010 Aspen 2010 RJB

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 redshift SFR density continues to decrease towards higher redshift to our search limits Implies 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. UCSC 2010 RJB