Exploring the High-z Frontier — Galaxies at z  6 and beyond Haojing Yan (Carnegie Observatories) CCAPP/OSU Seminar April 8, 2008

Outline 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 — evolution of LF at the bright-end? Searching for Galaxies at z > 7-8

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

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

Searching Techniques Lyman-Break Galaxy (LGB) “Dropout” Ly  Emitter (LAE)

Surface Density Expectation Assuming non-evolving M* ( ) & faint-end slope  (-1.6) from z= Using the z=5.60 galaxy in the HDF-N (Weymann et al. 1999) to fix the normalization Comparing to Simulation of Weinberg et al. (2002) Yan et al. 2002, ApJ, 580, 725

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)

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)

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 an important 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

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 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

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)

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

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?

Part IV Searching for Galaxies at z > 7-8 and beyond

Deep Space-based IR Imaging for LBG Bouwens & Illingworth (2006); Bouwens et al. (2008)

Space-based IR Imaging around Lensing Clusters for LBG Bradley et al. (2008) Abell 1689

Direct Slit-Spectroscopy around Lensing Clusters for LAE Stark et al. (2007)

Another Line of Thought There might be a much more luminous population at z>7; surface density as high as /arcmin 2 From Yan et al. (2006)

Wide-field near-IR Survey with WIRCam at CFHT PIs. Lihwai Lin & Luc Simard

CFHT WIRCam J, 26 hrs Candidates to be observed by NICMOS in Cy-16 soon (PI. Yan)

LBT Can Play an Important Role in the Study of the High-z Universe

MODS: efficient identification & detailed study of large samples of LBG candidates from z = 3 to 6 LBC: large-field surveys along many sight-lines to overcome the bias caused by “cosmic variance”; deep Y-band imaging to look for z  7 galaxies LUCIFER: identification of the luminous z>7 candidates found in the on-going wide-field IR surveys

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 — there might be a luminous population, detectable at ~24.5mag