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Observational Properties of z~6 Galaxies

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

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Observational Properties of z~6 Galaxies

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  1. Observational Properties of z~6 Galaxies Rychard J. Bouwens UCSC Collaborators: Garth Illingworth, Ivo Labbe, Marijn Franx, Roderik Overzier, John Blakeslee, Dan Magee 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

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

  3. High Redshift Frontier Highest Redshift Spectroscopically Confirmed Object / Some Mileposts 1990: z = 3.80 Radio Galaxy (Chambers et al.)1997: z = 4.92 Lensed Dropout around CL1358+62 (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 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

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

  5. 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. B V I U

  6. HST Advanced Camera for Surveys

  7. Redder, more efficient filters for exploring z > 5.5 universe HST WFPC2 i U B V I HST ACS U B V i z Can select dropouts in much redder filter with ACS!

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

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

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

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

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

  13. Finding Real z~6 Galaxies Amongst Possible Contaminants Evolved z~2-3 Sources did not appear to be an important concern i-dropouts are sufficiently resolved to exclude stellar contaminants Strong Break Stars Galaxies Lyman Break Color z850bandmag No Break Blue Red Size All resolved sources here Continuum Color Stellar Locus Bouwens et al. (2003) Stanway et al. (2003)

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

  15. High Redshift Size Evolution High redshift galaxies are expected to be smaller because their halos collapse earlier and therefore more concentrated Ferguson et al. (2004) Data appear to be in good agreement with the scalings expected from this simple theory Sizes H(z)-1 ~ (1+z)-1.5 H(z)-2/3 ~ (1+z)-1 Standard ruler 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.

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

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

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

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

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

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

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

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

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

  25. The two GOODS fields (~150 arcmin2 each) were key search areas in the earlier work.

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

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

  28. Message from HUDF was that there are many faint galaxies Bouwens et al. (2006) No-evolution (NE) predictions from z~3 Surface Density of i-dropouts Observedsurface density of z~6 galaxies (uses UDF + shallower datasets) Bright Faint z-band magnitude 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

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

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

  31. Galaxies at z~6 (i-dropouts): Wide Deep GOODS HDF-N UDF-Parallels CDF-S UDF z850,AB~ 28.4 (10) z850,AB~ 29.2 (10) 17 arcmin2 11 arcmin2 506 z~6 i-dropouts! z850,AB~ 27.1 (10) (vers: 1.0) 27.5 1.9 Since original GOODS program, a significant amount of SNe search data has been taken over the GOODS fields. 316 arcmin2 Bouwens et al 2006

  32. z~6 UV Luminosity Function Rigorous i-dropout luminosity function determination • 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.

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

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

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

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

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

  38. Star Formation History -- z ~ 0 - 6 Star Formation History Brighter Flux Limit Evolution in SFR density is much more dramatic to brighter flux limits Luminosity Density (Star Formation Rate Density - no extinction) z~6 result Log10 Myr-1Mpc-3 Fainter Flux Limit z~6 result Bouwens et al. 2006

  39. Star Formation History -- z ~ 0 - 6 Star Formation History SFR density to fainter limit Fainter i-dropout search (Bouwens et al. 2004) Luminosity Density (Star Formation Rate Density - no extinction) Bright (zR<25.4) wide-area i-dropout search with Subaru SFR density to bright limit Shimasaku et al. 2005

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

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

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

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

  44. 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. Dickinson (2004) 6x Rest frame UV 1350 Å

  45. Field-to-field variations can be significant # of i-dropouts / field at same depth 44 UDF First ACS parallel to UDF NICMOS field 50 ~35% RMS variations for single ACS fields (Bouwens et al. 2006; see also Bunker et al. 2004) Second ACS parallel to UDF NICMOS field 18

  46. Large Scale Structure significantly limits our ability to determine M*,  Ignoring LSS uncertainties Surface Density of i-dropouts from GOODS + UDF-Ps + UDF UDF + UDF-Ps Including LSS uncertainties GOODS Significant Poisson Noise 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

  47. Large Scale Structure significantly limits our ability to determine M*,  Ignoring LSS uncertainties Surface Density of i-dropouts from GOODS + UDF-Ps + UDF ==> Need more deep fields UDF + UDF-Ps Including LSS uncertainties GOODS Significant Poisson Noise 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

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

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

  50. Ground Based Spectroscopy Keck VLT Gemini Subaru

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