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Exploring the High-z Frontier — Galaxies at z 6 and beyond Haojing Yan (Carnegie Observatories) Purple Mountain Observatory July 14, 2008 Haojing Yan (Carnegie Observatories) Purple Mountain Observatory July 14, 2008
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Outline UV Luminosity Function of Galaxies at z 6 — LBG LF has a very steep faint-end slope Stellar Masses of Galaxies at z 6 — some high-mass, “old” galaxies already in place Implications for (HI) Reionization — dwarf galaxies did it! Unanswered Questions at z 6 — evolution of LF at the bright-end? Searching for Galaxies at z > 7-8
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Part I LF of Galaxies at z 6 (5.5 z 6.5)
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Reionization might have ended at z 6 (Fan et al. 2006, AJ, 132,117) ~ 1% is sufficient to create a complete GP-trough Practically, H still nearly fully ionized at z 6
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Searching Techniques Lyman- Break Galaxy (LBG) “Dropout” Ly Emitter (LAE)
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Surface Density Expectation Assuming non-evolving M* (- 21.23) & faint-end slope (-1.6) from z=3 Using the z=5.60 galaxy in the HDF-N (Weymann et al. 1999) to fix the normalization Yan et al. 2002, ApJ, 580, 725
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Simple Prediction Seems to Work Well Consistent with all observations up to 2003, including new results from the HST/ACS Different groups emphasized different aspects: Yan et al. (2003) Bouwens et al. (2003) Bunker et al. (2004) Dickinson et al. (2004)
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Source(s) of Reionization Yan & Windhorst 2004, ApJ, 600, L1 Critical value from Madau, Haardt & Rees 1999 Contribution from reionizing sources Galaxies can account for the necessary reionizing photons, if the LF has a steep faint-end slope; dwarf galaxies are important contributors. Galaxies can account for the necessary reionizing photons, if the LF has a steep faint-end slope; dwarf galaxies are important contributors.
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To z<30 mag, 108 i-dropouts found in the HUDF (Yan & Windhorst 2004, ApJ, 612, L93; YW04) Note: ~ 1.5 mag deeper than Bunker et al. (2004; MNRAS, 355, 374)
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By pushing to the very limit of the HUDF, we start to be able to address the LF faint-end slope at z~6.
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i’ z’ z’=29.23 z’=29.97 Detection Reliability at z>28.5 mag Level
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z=5.83; Dickinson et al. (2004) z=5.9; Malhotra et al. (2005)
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ACS Grism Observations of HUDF (GRAPES; Malhotra et al. 2005) z=6.0 z=6.1 z=6.4 GRAPES: i-dropouts success rate of ~ 90% in the HUDF to z~27.5 mag
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Our HUDF z 6 candidate sample supports a very steep UV LF faint-end slope: α = -1.8 to -1.9 Dwarf galaxies can provide sufficient (re)ionizing photons at z 6 YW04 Constrain to the UV LF at z 6
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Recent Result Confirms the Steep Faint-end Slope (Bouwens et al. 2006) 506 i-drops: UDF, UDF-Pars, GOODS But compare to YW04: M* = -21.03, * = 4.6x10 -4 /Mpc 3 4.6x10 -3 M sun /yr/Mpc 3 1.1x10 -2 M sun /yr/Mpc 3 SFR is still uncertain by 2x “Lilly-Madau Diagram”
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Luminosity Function of z 6 LAE LAE : ~ 1/4 of the entire galaxy population (based on results at z~3), but still very important — easier to identify; current redshift record holder is the LAE at z=6.96 (Iye et al. 2006) LAE as probe of the reionization epoch : neutral IGM — Lya line suppressed — LAE number drop (e.g., Marilada-Escude 1998; Malhotra & Rhoads 2001) LAE at z 6 are usually selected at two narrow windows at z=5.7 & 6.5 in order to avoid strong night-sky lines
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Evolution of LAE LF from z=5.7 t0 6.5 Malhotra & Rhoads (2004): no evolution seen; IGM ionized up to z=6.5 Haiman & Cen (2005): not necessarily; local HII bubble permits escape of Lya photons and the suppression is not as large; up to 25%
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Better Statistics from Subaru Deep Field Shimasaku et al. (2006)Kashikawa et al. (2006) Kashikawa et al. (2006): strong evolution from z=5.7 to z=6.5 ! Significant fraction of HI at z=6.5 ?? WMAP z reion ~ 11.4?
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Part II Stellar Masses of Galaxies at z 6
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Stellar Mass Assembly History in Early Universe Stellar mass density & SFR density: = ∫ SFR dt Need measurements at rest-frame optical (and beyond) to reduce biases caused by dust extinction and short-lived stars when converting light to mass Study at high-z made possible by Spitzer IRAC GOODS Spitzer Legacy Program has played an important role
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HST Chandra Spitzer GOODS: Great Observatories Origins Deep Survey
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Chandra Deep Field SouthChandra Deep Field North (HDF-N) 24’ 28’ (2 Million Seconds)(1 Million Seconds) GOODS Fields
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CDF-SHDF-N 10’ 16.5’ 10’ 16.5’ (PI. Mauro Giavalisco) HST Treasury Program: ACS B, V, i, z (0.5 to 0.9μm) to near-HDF depth
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CDF-S HDF-N (PI. Mark Dickinson) Spitzer Legacy Program: Deepest IRAC 3.6 – 8.0μm & MIPS 24μm
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Extensive Supporting Observations
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3.6, 5.8, 4.5, 8.0µm 256x256 array 1.2”/pixel 5.12’x5.12’
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3.6 μ m4.5 μ m 5.6 μ m8.0 μ m z =5.83 galaxy IRAC Sees z ~ 6 Galaxies in HUDF
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z=5.83 z=5.9 z p ~5.9 Three i-drops in HUDF securely detected by IRAC Yan et al. 2005, ApJ, 634, 109
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Some high-mass (a few x 10 10 M sun ) galaxies were already in place by z 6 (age of Universe < 1.0 Gyr) A few hundred Myr old (formed at z>>6) Number density consistent with CDM simulation from Nagamine et al. (2004) Some Major Conclusions from SED Fitting See also Eyles et al. (2005)
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CDFS, 3.6 μ mHDFN, 3.6 μ m Extending to Entire GOODS (Yan et al. 2006, ApJ, 651, 24) IRAC-detected i-dropouts
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CDFS, 3.6 μ m HDFN, 3.6 μ m IRAC-invisible i-dropouts
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274 i’-drops selected by GOODS ACS data (~12 spec-id’ed) Rejecting low-z contaminators --- IRAC-selected Extremely Red Objects (IEROs; Yan et al. 2004): ~17% among the non-blended i’-drops CDF-S HDF-N Sum detected 34 19 53 (“IRAC- detected”) invisible 45 34 79 (“IRAC- invisible”) blended 54 64 118 x 83% 98 (“Blended”) additional contamination due to photometric error 3/13~23% based on HUDF results Basic Statistics
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Difficulty: no photometric info between z’ and IRAC 3.6 μ m Have to take a different, simplified approach (z’-3.6 μ m) color age for a given SFH M/L for a given SFH at this age stellar mass; repeat for all SFH in the set, and take min, max, median
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Stellar Mass Estimates Summarized IRAC-detected Sample M rep : 0.09 ~ 7.0x10 10 M sun (median 9.5x10 9 M sun ) T rep : 50 ~ 400 Myr (median 290 Myr) IRAC-invisible Sample, using 3.6 m upper limit Upper-limit of M max (median 4.9x10 9 M sun )
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IRAC-invisible sample stackRandom stack 3.6 μ m 3.6 μ m mag = 27.44 median z’ mag = 27.00 M min = 1.5x10 8 M rep = 2.0x10 8 M sun M max = 5.9x10 9 Stacking of IRAC-invisible i-dropouts
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Models courtesy of K. Nagamine; based on simulations of Nagamine et al. (2004) and Night et al. (2006) Implications (I): compare to simulation ΛCDM models seem to be capable of producing such high-mass galaxies by z 6
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Implications (II): Global Stellar Mass Density Lower limit at z ~ 6: (1.0, 1.6, 6.5) x 10 6 M sun Mpc -3
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Implications (III): Source of Reionization Critical SFR based on Madau et al. (1999) Progenitors of all IRAC- detected z 6 galaxies formed simultaneously with the same e-SFH: SFR e -t/ The progenitors of high-mass galaxies alone CANNOT provide sufficient ionizing photons to sustain the reionization Dwarf (low-mass, low- luminosity) galaxies, which could be more numerous, must have played an important role
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Part III Bright-end of LF at z 6
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L* & Bright-end of LBG LF Bouwens et al. (2006): L*(z=6) = 0.6L*(z=3) Effect of large-scale structure ( “cosmic variance”)??
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Need Degree-sized Surveys to Minimize Impact of “Cosmic Variance” at Bright-end (Millennium Simulation slice at z=5.7)
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D1(2h-4d) (overlap SWIRE) D2 (10h+2d) (w/COSMOS) D3 D4 16.5’x10’ GOODS- Size Area Bright i-drops in 4-deg 2 CFHTLS Yan et al. (in prep)
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u’ g’ r’ i’ z’ 3.6µm 4.5µm 5.8µm 8.0µm u’ g’ r’ i’ z’ 3.6µm 4.5µm 5.8µm 8.0µm z’-ch1≥3.25; IRAC-selected ERO (IERO; Yan et al. 2004); “red & dead” galaxies at z~2-3 IRAC to Screen Out Interlopers
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D1 D2 D3 D4 z’<24.0 12 50 12 34 24.0≤z’<24.5 18 36 19 37 24.5≤z’<25.0 54 67 42 75 Total 72 103 61 112 75% 54 77 46 84 Yan & Windhorst 04: Bouwens et al. 06: 17.81 1.53 96.21 26.72 114/deg 2 28/deg 2 Much closer to YW04 prediction; the agreement is even better after counting the incompleteness correction at AB~25. Sample Statistics
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Magellan High-z LAE Survey Yan, McCarthy & Windhorst
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Survey Highlights Narrow-band imaging in 917nm & 971nm OH- free windows to search for LAE at z ≈ 6.5 & 7.0 Four IMACS f/2 fields (~ 0.9 deg 2 ); reducing cosmic variance with limited telescope time Survey depth (5- ) AB=25.0 mag (2.45 10 -17 erg/s/cm 2 for pure-line sources; 7-8 10 -18 erg/s/cm 2 for continuum-detected sources) Aiming at bright-end of the luminosity function
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6.46 — 6.62 6.91 — 7.07 ~ 400 Mpc 3 /arcmin 2 (Before upgrading, SITe CCDs) o(917nm)p(971nm) Survey Design: Filters
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Survey Design: Fields Use fields that have public, deep continuum images in multi-bands (especially in z’-band) Accessibility from Las Campanas CFHTLS Deep D1, D2 & D4 spreading out in RA
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Survey Status 1-night in Feb. 2007 + 2-night in Mar. 2008, 1 IMACS pointing in COSMOS field (CFHTLS- D2), 20hr in o(917nm) 3-night in Jul. 2007, 1 IMACS pointing in CFHTLS-D4, 20 hr in o(917nm) Achieved desired depth
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COSMOS CFHTLS-D4 1.48 o 1o1o 1o1o
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5- source counts CFHTLSD4NW, 20hr in o
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LAE Candidate Selection Continuum images from the T0003 release of CFHTLS-D4 z’-o>0.44 (f lin /f con >1.5) i’-z’>1.3 if detected in z’ non-detection in u’,g’ and r’ For now only discussing candidates invisible in z’
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3 candidates invisible in continuum o=23.88 o=24.39 o=25.49? (Now seeking time do spectroscopic identification)
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Kashikawa et al. 2006 (in Subaru Deep Field) Rapid Evolution from z=5.7 to 6.6 or not?
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Part IV Searching for Galaxies at z > 7-8 and beyond
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Deep Space-based IR Imaging for LBG Bouwens & Illingworth (2006); Bouwens et al. (2008)
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Space-based IR Imaging around Lensing Clusters for LBG Bradley et al. (2008) Abell 1689
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Direct Slit-Spectroscopy around Lensing Clusters for LAE Stark et al. (2007)
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Another Line of Thought There might be a much more luminous population at z>7; surface density as high as 0.01-0.05/arcmin 2 From Yan et al. (2006)
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Wide-field near-IR Survey with WIRCam at CFHT PIs. Lihwai Lin & Luc Simard
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CFHT WIRCam J, 26 hrs Candidates to be observed by NICMOS in Cy-16 soon (PI. Yan)
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WFC3/HST Will Play a Critical Role in the Study of the High-z Universe
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Programs with various depths & coverage WFC3 IR FOV 4.6 arcmin2 Ultra-deep program (HUDF- like) to probe the faint-end Wide program (GOODS-like) to probe the L* level Different sight-lines to beat down the cosmic variance — 200-orbit parallel program approved in Cycle- 17 (PI. Yan)
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Summary UV Luminosity Function of Galaxies at z 6 — a very steep faint-end slope Stellar Masses of Galaxies at z 6 — some high-mass, “old” galaxies already in place Implications for (HI) Reionization — dwarf galaxies did it! Unanswered Questions at z 6: Bright-end of LF (LBG/LAE) — degree-sized surveys needed to reduce “cosmic variance” Searching for Galaxies at z > 7-8 — very wide-field IR survey from the ground and deep surveys from the space (wait for WFC3!)
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