Galaxies as Sources of Reionization Haojing Yan (Carnegie Observatories) Reionization Workshop at KIAA July 10, 2008 Haojing Yan (Carnegie Observatories) Reionization Workshop at KIAA July 10, 2008

Outline Luminosity Function of Galaxies at z  6 — UV LF has a very steep faint-end slope Stellar Masses of Galaxies at z  6 — some high-mass, “old” galaxies already in place; but they are not likely the dominant reionzation sources. Implications for (HI) Reionization — dwarf galaxies did it! An Unanswered Question at z  6 — evolution of LF at the bright-end?

Part I LF of Galaxies at z  6 (5.5  z  6.5)

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.

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)

By pushing to the very limit of the HUDF, we start to be able to address the LF faint-end slope at z~6.

i’ z’ z’=29.23 z’=29.97 Detection Reliability at z>28.5 mag Level

z=5.83; Dickinson et al. (2004) z=5.9; Malhotra et al. (2005)

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

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

Recent Result Confirms the Steep Faint-end Slope (Bouwens et al. 2006) 506 i-drops: UDF, UDF-Pars, GOODS But compare to YW04: M* = ,  * = 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”

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

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%

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?

Part II Stellar Masses of Galaxies at z  6

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 a critical role

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

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

Some high-mass (a few x 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)

CDFS, 3.6 μ mHDFN, 3.6 μ m Extending to Entire GOODS (Yan et al. 2006, ApJ, 651, 24) IRAC-detected i-dropouts

CDFS, 3.6 μ m HDFN, 3.6 μ m IRAC-invisible i-dropouts

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 (“IRAC- detected”) invisible (“IRAC- invisible”) blended x 83% 98 (“Blended”) additional contamination due to photometric error 3/13~23% based on HUDF results Basic Statistics

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

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 )

IRAC-invisible sample stackRandom stack 3.6 μ m 3.6 μ m mag = median z’ mag = M min = 1.5x10 8 M rep = 2.0x10 8 M sun M max = 5.9x10 9 Stacking of IRAC-invisible i-dropouts

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

Implications (II): Global Stellar Mass Density Lower limit at z ~ 6: (1.0, 1.6, 6.5) x 10 6 M sun Mpc -3

Implications (III): Source of Reionization Critical SFRD 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

Part III Bright-end of LF at z  6

L* & Bright-end of LBG LF Bouwens et al. (2006): L*(z=6) = 0.6L*(z=3) Effect of large-scale structure ( “cosmic variance”)??

Need Degree-sized Surveys to Minimize Impact of “Cosmic Variance” at Bright-end (Millennium Simulation slice at z=5.7)

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)

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

D1 D2 D3 D4 z’< ≤z’< ≤z’< Total % Yan & Windhorst 04: Bouwens et al. 06: /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

Magellan High-z LAE Survey Yan, McCarthy & Windhorst

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  erg/s/cm 2 for pure-line sources; 7-8  erg/s/cm 2 for continuum-detected sources) Aiming at bright-end of the luminosity function

6.46 — — 7.07 ~ 400 Mpc 3 /arcmin 2 (Before upgrading, SITe CCDs) o(917nm)p(971nm) Survey Design: Filters

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

Survey Status 1-night in Feb 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

COSMOS CFHTLS-D o 1o1o 1o1o

5-  source counts CFHTLSD4NW, 20hr in o

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’

3 candidates invisible in continuum o=23.88 o=24.39 o=25.49? (Now seeking time do spectroscopic identification)

Kashikawa et al (in Subaru Deep Field) Rapid Evolution from z=5.7 to 6.6 or not?

Summary UV Luminosity Function of Galaxies at z  6 — a very steep faint-end slope (lots of dwarf galaxies …) Stellar Masses of Galaxies at z  6 — some high-mass, “old” galaxies in place; but not enough Implications for (HI) Reionization — dwarf galaxies did it! Unanswered questions at z  6: Bright-end of LF (LBG/LAE) should tell a lot — degree-sized surveys needed to reduce “cosmic variance”