Galaxy Formation and Evolution at z>6: New Results From HST WFC3/IR

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1 Galaxy Formation and Evolution at z>6: New Results From HST WFC3/IR Rychard Bouwens (UC Santa Cruz / Leiden) The Origin of Galaxies: Lessons from the Distant Universe Obergurgl, Austria December 14, 2009

2 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 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 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

3 Shuttle Servicing Mission SM4 WFC3 Obergurgl 12/14/09 RJB

4 Demonstrating Performance of WFC3/IR NICMOS WFC3/IR orbits orbits Region of the HUDF

5 Lyman Break Galaxies at z~7 Unattenuated Spectrum Attenuated Spectrum z~7.4 V i z J H No Detection Blue Continuum

6 16 z~7 z-dropouts from our 4.7 arcmin 2 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. (2009)

7 5 z~8 Y-dropouts from our 4.7 arcmin 2 HUDF09 observations over the HUDF (Bouwens et al. 2009)

8 New WFC3/IR Observations HUDF09 WFC3/IR program WFC3/IR ERS Deepest optical data CDF-South GOODS Field Area Bands Depth HUDF 5 arcmin 2 YJH 28.8 AB mag HUDF arcmin 2 YJH 28.6 AB mag ERS 39 arcmin 2 YJH 27.5 AB mag Obergurgl 12/14/09 RJB

9 New WFC3/IR Observations HUDF09 WFC3/IR program WFC3/IR ERS CDF-South GOODS Deepest optical data New z~7 z-dropout samples ~25 (ERS) ~35 (HUDF+HUDF05-1) New z~8 Y-dropout samples ~3-5 (ERS) ~25 (HUDF+HUDF05-1) Obergurgl 12/14/09 RJB

10 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%

11 Now, use the z~7 search results to derive constraints on z~7 UV LF UV Luminosity Functions z~4 Log # mag -1 Mpc -3 z~6 z~7 Old NICMOS z~7 LF (Bouwens et al. 2008; Oesch et al. 2009) Oesch et al Bright Faint Obergurgl 12/14/09 RJB

12 Now, use the z~8 search results to derive constraints on z~8 UV LF UV Luminosity Functions z~4 Log # mag -1 Mpc -3 z~8 z~7 Bright Oesch et al. 2009; Bouwens et al Faint Obergurgl 12/14/09 RJB

13 Evolution of the UV LF at High Redshift using new WFC3 results NEW Assuming DM Halos M/L = (1+z) -1 Assuming that phi* = Mpc -3, α=-1.7 Oesch et al Obergurgl 12/14/09 RJB

14 M/L ratio of dark matter halos at high redshift One of many different scaling relations How might they scale? galaxies L M that seem to be at work in high redshift f b τdyn ρ 1/2 (1+z) 3/2 or M (1+z) -3/2 L which seems consistent with what we find given the uncertainties M (1+z) -1 L

15 Integrate the UV LFs at z~7 and z~8, one derives the SFR density Bouwens et al. (2009)

16 However, Yan et al. (2009) isolated a sample of 15 purported z~8 candidates and 20 purported z~9-10 candidates Purported Upturn in SFR density Yan et al. (2009)

17 However, most of the Yan et al z~9-10 J-dropout candidates are very close to extended foreground galaxies e.g., Yan et al. (2009) z~9-10 Candidates We decided to test this hypothesis: Plot distance of dropouts to closest extended galaxy Clear association of Yan et al z~9-10 sample with foreground galaxies at % confidence Suggests that their sample suffers from significant contamination concerns Yan z~9-10 sample Yan et al z~8 sample also shows this association with foreground galaxies at 99.2% confidence Our z~7 sample But expect no association between z~9-10 J-dropouts and extended foreground galaxies Distribution of distances to extended sources for blank area on image

18 Where does this leave us with the SFR density? perhaps not? Yan et al. (2009)

19 Galaxies at z>6: How large are they in physical size?

20 Physical Sizes of High Redshift Galaxies Half-light radii vs. z Scaling law again! Star Forming Galaxies Scale as (1+z) same as at z~0-3 Oesch et al Bouwens et al 2004 See also Ferguson et al 2004

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

22 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 The power law slope of UV continuum: fλ ~ λ β UV-continuum slope β most sensitive to changes in dust content

23 Galaxies at z>6: What type of colors do they have in the UV-continuum? red more dusty UV slope blue more dustfree dust free not fit with standard stellar population models bright Luminosity faint

24 Galaxies at z>6: What is the stellar mass density of z~7-8 galaxies? Valentino Gonzalez

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

26 Galaxies at z>6: What is the relationship between their stellar masses and their SFRs? From z~0 --> z~1 Given that the relatively tight relationship between SFR and stellar mass Specific SFR = SFR / Stellar Mass [SSFR] Noeske et al. (2007) / AEGIS Team

27 How does the specific star formation rate evolve at high redshift? Labbe et al Possible Scaling law! Gonzalez et al Not Very Sensitive to Mass Obergurgl 2009 RJB

28 Simple Consequence SFR / Stellar Mass = Constant SFR Stellar Mass (Factor) Some Mass Dependence and the time scale ~ 0.5 Gyr (independent of cosmic time) Gonzalez et al. 2009; Stark et al. 2009; Labbe et al Obergurgl 2009 RJB

29 Stellar Mass Density Labbe et al. 09b New WFC3/IR Results Gonzalez et al Obergurgl 2009 RJB

30 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 60 z~7 z-dropouts and ~30 z~8 Y-dropout galaxies in the new observations The number of galaxies we find at z~7 and z~8 are consistent with what we expect extrapolating the UV LF from z~4-6 to higher redshift The SFR density continues to decrease towards higher redshift to our search limits The UV-continuum slopes beta we measure at z~7 are very blue, particularly towards very low luminosities and suggest minimal dust extinction there. 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 >~50% of the bright z~7 and z~8 galaxy candidates are detected in the deep IRAC data -- while the faint z~7 galaxy candidates are detected in the IRAC data when stacked. Stellar mass measurements can be used to estimate stellar mass densities at z~7 and z~8 Observations and modelling of galaxies at z~7-8 and at z~3-6 suggest little evolution in specific star formation rate for the first 4 Gyr of cosmic time... i.e., that the SFR in galaxies is proportional to the stellar mass density. Obergurgl 2009 RJB