Rychard Bouwens (UC Santa Cruz / Leiden)

1. 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

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

3. With a Special Thanks to: 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 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

4. 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

5. 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

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

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

8. Faint-end Slope of the UV Luminosity Function 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* High Luminosity Galaxies 50% 50% Low Luminosity Galaxies 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 Bouwens et al. 2007 (see also Beckwith et al. 2006 and Oesch et al. 2007)

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

10. 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!

11. NICMOS 72 orbits WFC3/IR 16 orbits Demonstrating Performance of WFC3/IR Region of the HUDF

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

13. Exciting Ultradeep WFC3/IR Program HUDF09 WFC3/IR program Deepest optical data 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

14. August 26 - Sept 6, 2009

15. Excellent S/N As an example, here are the z-dropout candidates identified previously (Bouwens et al. 2004, 2008; Oesch et al. 2009) 16 z~7 z-dropouts from our 4.7 arcmin2 HUDF09 observations over the HUDF (Oesch et al. 2009) Oesch et al. (2010) but see also McLure et al.; Bunker et al.; Yan et al; Finkelstein et al.

16. 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%

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

18. 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%

19. 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

20. Total WFC3/IR Data Set HUDF09 WFC3/IR program WFC3/IR ERS Deepest optical data 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

21. 50 z~7 galaxies, 25 z~8 galaxies ~50 z~7 galaxies ~25 z~8 galaxies Preliminary UV LFs at z~7-8 from Wide area + Ultra-deep Observations with WFC3/IR UV Luminosity Functions Log # mag-1 Mpc-3 Bright Faint Bouwens et al. 2010 UCSC 02/01/10 RJB

22. Preliminary 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 ϕ* Faint Bright Bouwens et al. 2010 UCSC 02/01/10 RJB

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

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

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

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

27. Purported Upturn in SFR density Yan et al. (2010) 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....

28. Clear association of Yan et al. 2010 z~9-10 sample with foreground galaxies at 99.99995% confidence e.g., Yan et al. (2009) z~9-10 Candidates Yan et al. 2009 z~8 sample also shows this association with foreground galaxies at 99.2% confidence Plot distance of dropouts to closest extended galaxy Suggests their sample is not reliable and likely full of contaminants Suggests their sample is not reliable and likely full of contaminants Yan z~9-10 sample Our z~7 sample Distribution of distances to extended sources for blank area on image 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: But expect no association between z~9-10 J-dropouts and extended foreground galaxies

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

30. Stellar Mass rest-frame optical at z~7 ~4μm IRAC images IRAC Valentino Gonzalez What can we learn about reionization from Stellar Mass Estimates?

31. 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

32. Total WFC3/IR z~7-8 samples of use for stellar mass density estimates HUDF09 WFC3/IR program WFC3/IR ERS 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

33. 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... Stellar Mass Density New WFC3/IR Results Labbe et al. 09b Gonzalez et al. 2009 UCSC 2010 RJB

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

35. Galaxies at z>6: What type of colors do they have in the UV-continuum? What is the UV slopeβ? 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

36. dust free 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 blue “more dust-free” bright Luminosity faint Bouwens et al. 2010 UCSC 2010 RJB

37. not fit with standard stellar population models dust free What about their UV colors? versus redshift red Lower UV Luminosities (~0.1 L*) “more dusty” UV slope blue “more dust-free” Redshift Bouwens et al. 2010 UCSC 2010 RJB

38. Total (Hot Stars + Ionized Gas) β ~ −2.3 To produce very blue β’s (i.e., −3) we require hot, young stars... Emitted Light β ~ −3 Very Hot Stars β ~ −3 (blue) 1. Lyman-Continuum Escape Fraction Large (>~ 30%) 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) → 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

39. 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