Observational Properties of z~6 Galaxies Rychard J. Bouwens UCSC Special thanks to Roderik Overzier, Mauro Giavalisco, Haojing Yan for helping me prepare this talk The End of the Dark Ages / STScI / March 14, 2005 Collaborators: Garth Illingworth, Ivo Labbe, Marijn Franx, Roderik Overzier, John Blakeslee, Dan Magee

z~6 -- An Exciting Epoch! Mass of ~L* galaxies Springel et al. (2005) Rapid Buildup of L* galaxies z~6 represents a key transition point of change between z~10 and z~3

High Redshift Frontier 1990: z = 3.80 Radio Galaxy (Chambers et al.) 1997: z = 4.92 Lensed Dropout around CL (Franx et al.) 1998: z = 5.34 Lyman-alpha emitting Object (Dey et al.) 1998: z = 5.60 LBG in HDF North (Weymann et al.) 1999: z = 5.74 Lyman-alpha emitter (Hu et al.) 2001: z = 6.28 SDSS quasar (Fan et al.) 2002: z = 6.56 Lyman-alpha emitter (Hu et al.) 2003: z = 6.58 Lyman-alpha emitter (Kodaira et al.) 2004: z ~ 6.6 Lensed Dropout (Kneib et al.) 2005: z = 6.7 Malhotra et al. 2 Highest Redshift Spectroscopically Confirmed Object / Some Mileposts Wasn’t until the 2000s that we crossed the z~6 barrier… Interesting how so many different techniques have been useful in finding the highest redshift objects: * Lyman-alpha emitters, QSOs, Lyman Break Galaxies * gravitational lensing, wide-area surveys, deep HST surveys

Finding Sources at z~6 z~6 Sloan QSOs z = 6.56 Ly  emitter (Hu et al. 2002) (leverages i+z band imaging over very large area) Ly  (leverages narrowband preselection + gravitational lensing) 9120 NR

HST WFPC2 Space has big advantages in searching for high-z objects due to much lower background. However, until 2002, WFPC2 was the only camera in space to use for exploring the z>5 universe. U BVI

HST Advanced Camera for Surveys

Redder, more efficient filters for exploring z > 5.5 universe UBViz i HST ACS UBVI HST WFPC2 Can select dropouts in much redder filter with ACS!

Redder, more efficient filters for exploring z > 5.5 universe UBViz i HST ACS UBVI HST WFPC2 Can select dropouts in much redder filter with ACS! From Stanway et al. (2003) z~6 galaxy cuts off at the boundary beween the i and z filters

Ideally we would do the z~6 i-dropout selection using the familiar two color diagram, i.e., Lyman Break Color Strong Break No Break Continuum Color Blue Red z~6 objects UB V i z

Ideally we would do the z~6 i-dropout selection using the familiar two color diagram, i.e., Lyman Break Color Strong Break No Break Continuum Color Blue Red Unfortunately, you get the continuum color you need deep infrared imaging which is very expensive z~6 objects UB V i z IR

Single color i-dropout selection Lyman Break Color Strong Break i - z > 1.3 selection No Break Redshift Bunker et al. (2004)

Initial Round of Papers on i-dropouts Stanway et al. (2003) Yan et al. (2003) Bouwens et al. (2003) Dickinson et al. (2004) ~ 6 candidates ~ 30 candidates ~ 23 candidates ~ 251 candidates

Finding Real z~6 Galaxies Amongst Possible Contaminants Evolved z~2-3 Sources did not appear to be an important concern Bouwens et al. (2003) Lyman Break Color Strong Break No Break Continuum Color BlueRed All resolved sources here Stellar Locus Size z 850 band mag Stanway et al. (2003) i-dropouts are sufficiently resolved to exclude stellar contaminants Stars Galaxies

Surface Brightness Selection Biases (Incompleteness) U-dropout from HDF-N artificially redshifted to z~6.0 Cosmic Surface Brightness Dimming Substantial Factor of 10 from z~3 to z~6 Did surface brightness selection effects represent an important bias for the SFH? SFR density Redshift Lanzetta et al. (2002) After correction for SB selection effects? Or selection effects not so significant?

High Redshift Size Evolution Sizes Redshift Ferguson et al. (2004) did not plot a point at z~6 since surface brightness selection biases were still very important in the data used to construct this plot. Ferguson et al. (2004) Standard ruler H(z) -1 ~ (1+z) -1.5 H(z) -2/3 ~ (1+z) -1 Data appear to be in good agreement with the scalings expected from this simple theory High redshift galaxies are expected to be smaller because their halos collapse earlier and therefore more concentrated

Extending Size Measurements to z~6 Size vs. redshift The sizes of i-dropouts are in good agreement with size-redshift trends found in Ferguson et al. (2004) Sizes Bouwens et al. (2004) This suggests z>7 galaxies are likely to have half-light radii of ~0.1” Size vs. magnitude Sizes ~0.14”-0.15” UDF i-dropouts are small (~0.15”) Bouwens et al. (2006); see also Bunker et al. (2004)

z~6 observations versus z~3 Volume Density Rest-frame UV Continuum Luminosity Function z~3 (Steidel et al. 1999) Rest frame UV 1350 Å

z~6 observations versus z~3 Volume Density Rest-frame UV Continuum Luminosity Function z~3 (Steidel et al. 1999) Yan (2003) Rest frame UV 1350 Å

z~6 observations versus z~3 Volume Density Rest-frame UV Continuum Luminosity Function z~3 (Steidel et al. 1999) Yan (2003) Stanway (2003) 6x Rest frame UV 1350 Å

z~6 observations versus z~3 Volume Density Rest-frame UV Continuum Luminosity Function z~3 (Steidel et al. 1999) Yan (2003) Stanway (2003) Bouwens (2003) 6x Rest frame UV 1350 Å

z~6 observations versus z~3 Volume Density Rest-frame UV Continuum Luminosity Function z~3 (Steidel et al. 1999) Yan (2003) Stanway (2003) Bouwens (2003) 6x Dickinson (2004) Rest frame UV 1350 Å

z~6 observations versus z~3 Volume Density Rest-frame UV Continuum Luminosity Function z~3 (Steidel et al. 1999) Yan (2003) Stanway (2003) Bouwens (2003) 6x Dickinson (2004) Rest frame UV 1350 Å

z~6 observations versus z~3 Volume Density Rest-frame UV Continuum Luminosity Function z~3 (Steidel et al. 1999) Stanway (2003) Bouwens (2003) 6x Dickinson (2004) Rest frame UV 1350 Å

z~6 observations versus z~3 Volume Density Rest-frame UV Continuum Luminosity Function z~3 (Steidel et al. 1999) Stanway (2003) Bouwens (2003) 6x Dickinson (2004) Disagree? Rest frame UV 1350 Å

The two GOODS fields (~150 arcmin 2 each) were key search areas in the earlier work.

Overall approach: UDF UDF-IR Hubble Ultra-Deep Field UDFUDF-IR ACS and NICMOS 5  limit: in UDF is ~30-31 AB mag in BViz; in UDF-IR ~27.5 AB mag in JH

Images of z~6 Galaxies >100 i-dropouts in the UDF Credit: Image by Zolt Levay Yan & Windhorst (2005); Bouwens et al. (2006) see also Bunker et al. (2004) (vs. much smaller numbers in the other fields)

Message from HUDF was that there are many faint galaxies Surface Density of i-dropouts z-band magnitude No-evolution (NE) predictions from z~3 At bright mags: z~6 observations are much lower than NE z~3 predictions At faint mags: z~6 observations nearly equal to NE z~3 predictions Bouwens et al. (2006) BrightFaint Observed surface density of z~6 galaxies (uses UDF + shallower datasets)

Early work by Dickinson et al. (2004) before HUDF suggested there were more faint galaxies than bright ones. Message from HUDF was that there are many faint galaxies No-evolution (NE) Predictions From z~3 Corrected i-dropout counts Surface Density z-band magnitude BrightFaint Many fewer bright z~6 objects found predicted from z~3 assuming NE

Message from HUDF was that there are many faint galaxies Yan & Windhorst (2004): Used UDF to argue faint-end slope of z~6 LF was very steep,  =  1.8 z~6 LF Faint-end slope  at z~6 BrightFaint Malhotra et al. (2005): Best fit to z~6 galaxies (HUDF) had a fainter characteristic luminosity than at z~3 (compare to  = -1.6 at z=3) BrightFaint

Galaxies at z~6 (i-dropouts): Bouwens et al 2006 Wide Deep z 850,AB ~ 27.1 (10  ) (vers: 1.0) UDF-Parallels UDF z 850,AB ~ 28.4 (10  ) z 850,AB ~ 29.2 (10  ) 506 z~6 i-dropouts! 17 arcmin 2 11 arcmin arcmin 2 GOODS CDF-S HDF-N Since original GOODS program, a significant amount of SNe search data has been taken over the GOODS fields.

z~6 UV Luminosity Function  Applied a well-tested i-z > 1.3 criterion to select i- dropouts in all fields.  Used detailed degradation experiments on our deeper fields to perform completeness and flux corrections.  Carefully matched up surface densities of all fields to remove field-to-field variations (35% effect)  Accounted for blending with foreground objects (5-10% effect)  Determined contamination level (5-10% effect):  Intrinsically-red objects  Photometric scatter  Stars  Spurious sources  Selection function determined by using best estimates of UV colors and sizes of z~6 objects. Rigorous i-dropout luminosity function determination

z~6 UV Luminosity Function Bouwens et al 2006 Rest frame UV 1350 Å Log # mag -1 Mpc -3 z~6 BrightFaint

z~6 UV Luminosity Function Bouwens et al 2006 Rest frame UV 1350 Å Log # mag -1 Mpc -3 z~6 z~3 LF at z~6: goes ~3 mag below L* BrightFaint

z~6 UV Luminosity Function Bouwens et al 2006 Rest frame UV 1350 Å Luminosity evolution provides the best fit - not density evolution Log # mag -1 Mpc -3 z~6 z~3 Luminosity Evolution Provides a good fit BrightFaint

z~6 UV Luminosity Function Bouwens et al 2006 Rest frame UV 1350 Å z~6 Faint-end Slope The characteristic luminosity at z~6 (L* UV,z~6 ) is ~50% of (L* UV,z~3 ) at z~3. Faint Bright

z~6 UV Luminosity Function Bouwens et al 2006 Rest frame UV 1350 Å z~6 Faint-end Slope The characteristic luminosity at z~6 (L* UV,z~6 ) is ~50% of (L* UV,z~3 ) at z~3. Faint Bright Weak constraints on faint-end slope 

Star Formation History Luminosity Density (Star Formation Rate Density - no extinction) Log 10 M  yr -1 Mpc -3 Star Formation History -- z ~ z~6 result Brighter Flux Limit Fainter Flux Limit Evolution in SFR density is much more dramatic to brighter flux limits Bouwens et al. 2006

Star Formation History Luminosity Density (Star Formation Rate Density - no extinction) Star Formation History -- z ~ Shimasaku et al Bright (z R <25.4) wide-area i-dropout search with Subaru Fainter i-dropout search (Bouwens et al. 2004) SFR density to bright limit SFR density to fainter limit

Evolution of the UV LF Hierarchical Buildup AGN Feedback? Gas Exhaustion? Transition between Hot/Cold Cooling Flows? Bright Faint

z~6 observations versus z~3 Volume Density Rest-frame UV Continuum Luminosity Function z~3 (Steidel et al. 1999) Stanway (2003) Bouwens (2003) 6x Dickinson (2004) Disagree? Rest frame UV 1350 Å

z~6 observations versus z~3 Volume Density Rest-frame UV Continuum Luminosity Function Rest frame UV 1350 Å z~3 (Steidel et al. 1999) Dickinson (2004) Bouwens (2003) Stanway (2003) 6x ?

z~6 observations versus z~3 Volume Density Rest-frame UV Continuum Luminosity Function z~3 (Steidel et al. 1999) Stanway (2003) Bouwens (2003) 6x Dickinson (2004) Evolution Factor is Luminosity Dependent Don’t Disagree! Rest frame UV 1350 Å

Implications for Reionization Using the standard Madau description, we find that the number of I-dropouts at z~6 appears to be approximately consistent with the numbers necessary to reionize the universe, assuming an escape fraction of 0.5 and clumping factor of 30. 6x Dickinson (2004) Rest frame UV 1350 Å

Field-to-field variations can be significant # of i-dropouts / field at same depth UDF First ACS parallel to UDF NICMOS field Second ACS parallel to UDF NICMOS field ~35% RMS variations for single ACS fields (Bouwens et al. 2006; see also Bunker et al. 2004)

Large Scale Structure significantly limits our ability to determine M*,  Surface Density of i-dropouts from GOODS + UDF-Ps + UDF Significant Poisson Noise UDF + UDF-Ps GOODS Relative normalization of bright + faint probes uncertain due to large- scale structure ~ L* z=6 Unfortunately, L* is just at the edge of what can be probed with the wide-area GOODS fields Including LSS uncertainties Ignoring LSS uncertainties

Large Scale Structure significantly limits our ability to determine M*,  Surface Density of i-dropouts from GOODS + UDF-Ps + UDF Significant Poisson Noise UDF + UDF-Ps GOODS Relative normalization of bright + faint probes uncertain due to large- scale structure ~ L* z=6 Unfortunately, L* is just at the edge of what can be probed with the wide-area GOODS fields Including LSS uncertainties Ignoring LSS uncertainties ==> Need more deep fields

Deep i-dropout Search Fields ACS Parallels to the UDF NICMOS data UDF CDF South

Deep i-dropout Search Fields ACS Parallels to the UDF NICMOS data UDF UDF05 (PI: Stiavelli) CDF South Key New Data

Ground Based Spectroscopy Keck GeminiVLT Subaru

z~6 spectroscopic samples Malhotra et al GRAPES 23 objects Dow-Hygelund et al objects UCSC/Keck GOODS Team GLARE/Exeter ~20 objects + 80(?) more from the PEARS program => ~100 z~6 objects spectroscopically confirmed! 47 objects Vanzella et al. 2005, 2006; Stern et al., in prep; Dawson et al (also includes a few redshifts from GRAPES here)

Spectroscopy on z~6 galaxies Bunker et al z=5.78 Vanzella et al. 2006, in prep z=5.52 Dow-Hygelund et al Some noteworthy examples of z~6 spectra Stack of 25 emission line galaxies

Composition of z~6 spectroscopic samples ~30% of i-dropouts show Ly  emission (EW: >20 A) vs. 25% of U-dropouts at z~3 (Dow-Hygelund et al. 2006) Contamination rates for current I-dropout selections appears to very low.

Red UV continuum slope Blue Dust Properties (important for calculating unobscured star formation rate) ()() UV Low Dust extinction High Dust extinction

Red UV continuum slope Blue Most Light Absorbed By Dust First Infrared Light UV Light Most Light Escapes Without Absorption Dust Properties (important for calculating unobscured star formation rate) Correction Factor (Meurer et al. 1999) ()() UV Low Dust extinction High Dust extinction

Evolution in UV Continuum Slope UV continuum slope vs. z Bouwens et al. 2004, 2006b,c; See also Stanway et al. 2005; Lehnert et al. 2003; Yan et al Red UV continuum slope Blue Dusty Dust Free Galaxies appear to become less dusty at high redshift

Significant Dust at z~6.5? Chary et al. (2005) HCM6A Abell 370 Hu et al. (2002) z = 6.56 Anomalous jump in the flux density at ~6000 A rest- frame Is this due to H  emission? If so, suggests significant dust extinction ?

The Evolution of the SFR density Bouwens et al SFR density True SFR density SFR density (not counting for dust) Correcting for dust extinction accentuates the size of SFR density peak at z~1-3

X-ray Properties Chandra

Independent Method: SFR density from X-ray emission Lehnert et al 2005A Recent stack of a larger ~400 object i-dropout sample from GOODS is undetected in x-ray Lehnert et al 2006, private communication - There is a known incidence of high mass x-ray binaries in SF regions - X-ray light is much less affected by dust than UV light

Spitzer Space Telescope

(Measuring Stellar Masses) UV Optical Rest-frame Size of break tells us how many old stars there are Age NIR Observed IRAC Rest-optical & -IR at z~6

Kneib et al. (2004) lensed object at z~6.6 J H z~6.6 source 3.6  4.5  Stellar Mass = ~10 9 M sol Best Fit  (e-decay) = 100 Myr z~6.6 source IRAC Imaging Egami et al. (2005)

Stellar Masses in select GOODS/UDF i-dropouts ch2, 4.5  m rest =6600A Yan et al. (2005); see also Eyles et al. (2005) Major results: Very massive galaxies (M>10 10 M sun ) existed at z ~ 6 A few hundred million years old (must form well before z ~ 6) Modest reddening (best-fits all have zero reddening) IRAC 3.6  J 110 z 850 z 850 (zoomed) SED fitting using Bruzual & Charlot (2003) models with exponentially decay star formation histories

Significantly Larger z~6 Samples Yan et al (to be submitted) 12’ 53 i-dropouts from GOODS with firm IRAC detections 79 i-dropouts are invisible in their individual IRAC exposures Move to complete samples of i-dropouts over the GOODS fields (~200 objects) To make statistically significant statements:

z IRAC 3.6  colors for ~170 i-dropouts Yan et al (to be submitted) Balmer Break z 850 -band magnitude i-dropouts detected in 3.6  IRAC imaging i-dropouts undetected in 3.6  IRAC imaging Old Young BrightFaint Control Stack of I-dropouts which are undetected individually

Implications Yan et al (to be submitted) AB = 1.33 Detected with IRAC (~40% of the sample) Individually undetected with IRAC (~60% of the sample) AB =  0.4 Constant SFR Simple Stellar Population  >100 Myr old => 1 Gyr of constant SF is not enough

Stellar mass density lower limits based on full-epoch GOODS results Yan et al (to be submitted) Stellar Mass Density Integral of SFR History Diagram 1 + Redshift New Point

None, or at least very few, of these objects appear to have solar masses as large as the Mobasher et al. (2005) JD2 object or the Wiklind et al. (2006) objects.

Clustering of i-dropouts 181 i-dropouts CDF South GOODS Overzier et al. (2006) HDF North GOODS 151 i-dropouts Bouwens et al. (2006) sample of i-dropouts Based upon original GOODS v1.0 data + SNe search data (twice as deep) Useful for learning about the halo masses

Clustering of i-dropouts Clustering w(  ) Angular Separation (“) Clustering significant at 99.9% confidence Overzier et al. (2006) It is true that better statistics would be ideal, but larger samples are unlikely to be available soon

Invert using Limber’s Equation Overzier et al. (2006) Redshift Distribution Angular Correlation Function Limber’s Equation Real Space Correlation Function

Results in Real Space Overzier et al. (2006) Correlation Lengths More luminous i-dropouts appear to be more clustered than the faint ones. Bright Correlation Length Strongly clustered Weakly clustered Faint Similar to findings at z~3-5 (Giavalisco & Dickinson 2001; Ouchi et al. 2004; Lee et al. 2006) Suggests that the most luminous starbursts live in the most massive halos. i-dropouts z~6 z~4 z~5

Bias / Halo Mass Lee et al. (2006); Overzier et al. (2006) Galaxies at z~3-4 live in ~10 12 M sol halos z~6 z~4 z~5 Bias However, galaxies at z~5-6 appear to live in ~10 11 M sol halos This suggests star formation is much more efficient at z>5 than it is at z~3-4 in producing UV photons May be partially due to an evolution in dust content: i.e., more dust at z~3-4 => less UV photons escaping M 1700 < -20.0

Bias / Halo Mass Lee et al. (2006); Overzier et al. (2006) Galaxies at z~3-4 live in ~10 12 M sol halos z~6 z~4 z~5 Bias However, galaxies at z~5-6 appear to live in ~10 11 M sol halos This suggests star formation is much more efficient at z>5 than it is at z~3-4 in producing UV photons May be partially due to an evolution in dust content: i.e., more dust at z~3-4 => less UV photons escaping M 1700 < -20.0

Change in Efficiency can Explain Slow Evolution in LF from z~6 to z~3 Mass of ~L* galaxies Springel et al. (2005) Evolution of Mass Function ~10x increase in number of M sol halos from z~6 to z~3 z=6 z=3

Change in Efficiency can Explain Slow Evolution in LF from z~6 to z~3 Mass of ~L* galaxies Springel et al. (2005) Evolution of Mass Function But the efficiency of star formation changes from z~6 to z~3 Compare M sol halos at z~6 z=6 z=3 with M sol halos at z~3

Change in Efficiency can Explain Slow Evolution in LF from z~6 to z~3 Springel et al. (2005) Evolution of Mass Function Compare M sol halos at z~6 z=6 z=3 with M sol halos at z~3 Now measure increase differently Change between z~6 and z~3 much less

Star Formation History Luminosity Density (Star Formation Rate Density - no extinction) 2006 End of Dark Ages 03/14/06 RJB Log 10 M  yr -1 Mpc -3 z~6 result Star Formation History -- z > 6

Star Formation History Luminosity Density (Star Formation Rate Density - no extinction) Log 10 M  yr -1 Mpc -3 UDF z~7-8 sample z~6 result Star Formation History -- Previous Results 2006 End of Dark Ages 03/14/06 RJB

Star Formation History Previous J-dropout search Luminosity Density (Star Formation Rate Density - no extinction) Log 10 M  yr -1 Mpc -3 UDF z~7-8 sample z~6 result Star Formation History -- Previous Results 2006 End of Dark Ages 03/14/06 RJB

Luminosity Density (Star Formation Rate Density - no extinction) Log 10 M  yr -1 Mpc -3 z~6 result Star Formation History 2006 End of Dark Ages 03/14/06 RJB

 Samples of >500 galaxies are now available at z~6 from HST data.  z~6 UV LF rigorously determined to ~3 magnitudes below L*.  Substantial evolution occurs at the bright end of the UV LF from z~6 to z~3. The characteristic luminosity at z~6 (L* UV ) is 2  smaller than what it is at z~3.  z~6 galaxies appear to be less dusty on average than galaxies at lower redshift. This accentuates the rise in SFR density from z~6 to z~3.  ~ z~6 objects have now been spectroscopically confirmed. Observational Properties of z~6 Galaxies Conclusions

 A small fraction z~6 objects has solar masses in excess of M solar. 40% appear to be at least 100 Myr old.  L* objects at z~6 appear to predominantly live in solar mass halos. This is smaller than at z~3, suggesting there is an increase in the SF efficiency from z~6 to z~3.  Our improved knowledge of the z~6 universe puts us in an ideal position to interpret the z>6 universe.

Determining the z~6 UV LF But, to determine the LF, we need to divide the numbers by the volume, i.e., Surface Density of i-dropouts with magnitude z 850,AB GOODS UDF-Ps UDF After many corrections

Estimating the Selection Volume Probability of Selecting a galaxy with magnitude z 850 and redshift z as an i-dropout Too faint to be detected How to calculate? 1. Create artificial galaxies 2. Add these galaxies to real images 3. Reapply Selection Procedure

z~6 UV Luminosity Function Bouwens et al 2006 Rest frame UV 1350 Å Log # mag -1 Mpc -3 z~6