Exploring the High-z Frontier — Galaxies at z 6 and beyond Haojing Yan (Carnegie Observatories)...
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Transcript of Exploring the High-z Frontier — Galaxies at z 6 and beyond Haojing Yan (Carnegie Observatories)...
Exploring the High-z Frontier
— Galaxies at z 6 and beyond
Haojing Yan (Carnegie Observatories)
CCAPP/OSU SeminarApril 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)
• <XHI> ~ 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* (-21.23) & 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 ofWeinberg 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 ReionizationYan & Windhorst 2004, ApJ, 600, L1
Critical value fromMadau, Haardt & Rees 1999
Contribution from reionizing sources
• Galaxies can account for the necessary reionizing photons, if the LF has a Galaxies can account for the necessary reionizing photons, if the LF has a steep faint-end slope; dwarf galaxies are important contributors.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* = -21.03, * = 4.6x10-4/Mpc3
4.6x10-3
Msun/yr/Mpc3
1.1x10-2
Msun/yr/Mpc3
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; <XHI> 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 zreion ~ 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
3.6μm 4.5μm
5.6μm 8.0μm
z =5.83 galaxy
IRAC Sees z ~ 6 Galaxies in HUDF
z=5.83
z=5.9
zp~5.9
Three i-drops in HUDF securely detected by IRAC
Yan et al. 2005, ApJ, 634, 109
• Some high-mass (a few x 1010Msun) galaxies were already in place by z6 (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, 3.6μm HDFN, 3.6μm
Extending to Entire GOODS(Yan et al. 2006, ApJ, 651, 24)
IRAC-detected i-dropouts
CDFS, 3.6μm HDFN, 3.6μm
IRAC-invisible i-dropouts
Difficulty: no photometric info between z’ and IRAC 3.6μm
Have to take a different, simplified approach
(z’-3.6μm) 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
Mrep: 0.09 ~ 7.0x1010Msun (median 9.5x109Msun)
Trep: 50 ~ 400 Myr (median 290 Myr)
• IRAC-invisible Sample, using 3.6m upper limit
Upper-limit of Mmax (median 4.9x109Msun)
IRAC-invisible sample stack Random stack
3.6μm
3.6μm mag = 27.44median z’ mag = 27.00
Mmin = 1.5x108
Mrep = 2.0x108 Msun
Mmax = 5.9x109
Stacking of IRAC-invisible i-dropouts
Models courtesy of K. Nagamine;based on simulationsof 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 106MsunMpc-3
Implications (III): Source of Reionization• Critical SFR based on
Madau et al. (1999)
• Progenitors of all IRAC-detected z6 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-deg2 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 deg2); reducing cosmic variance with limited telescope time
•Survey depth (5-) AB=25.0 mag (2.4510-17 erg/s/cm2 for pure-line sources; 7-810-18 erg/s/cm2 for continuum-detected sources)
•Aiming at bright-end of the luminosity function
6.46 — 6.62
6.91 — 7.07
~ 400 Mpc3/arcmin2
(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. 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
COSMOSCFHTLS-D4
1.48o
1.48o
1o
1o
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)
Kashikawaet al. 2006(in SubaruDeep 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 0.01-0.05/arcmin2
From Yan et al. (2006)
Wide-field near-IR Surveywith 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 z7 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