High-Redshift Quasars and Galaxies at
the Epoch of Cosmic Reionization
Linhua Jiang
(Arizona State University)
Hubble Fellow
Symposium 2014
Collaborators: F. Bian, Z. Cai, B. Clement, S.H. Cohen, R. Dave,
E. Egami, X. Fan, K. Finlator, N. Kashikawa, H.B. Krug, I.D. McGreer,
M. Mechtley, M. Ouchi, K. Shimasaku, M.A. Strauss, D.P. Stark,
R. Wang, R.A. Windhorst, and others
Cosmic reionization and high-z objects
 Cosmic reionization
• Neutral IGM ionized by the first astrophysical objects at 6 < z < 15
• Evidence: CMB polarization + GP troughs in quasars + …
 High-z (z ≥ 6) objects
• Quasars and galaxies
• SNe and gamma-ray bursts
• Responsible sources for reionization
(Robertson 2011)
Outline
 High-z galaxies
• A large sample of spectroscopically-confirmed galaxies at z ≥ 6
• UV continuum slopes
• Galaxy morphology
• Lyα luminosity function (LF) at z > 5.7 and implication for reionization
 High-z quasars
• Surveys of z ≥ 6 quasars using the SDSS data
• Quasar LF and implication for reionization
Part I. High-Redshift Galaxies
 Current studies
• HST + the largest ground-based telescopes
• A few hundred galaxies or candidates at z ≥ 6; many at z ≥ 8 (e.g.; Bouwens
2011; Oesch 2012; Ellis 2013; and many more papers)
 One issue
• Mostly done with photometrically-selected LBGs with decent IR data
(e.g., several HST ultra/deep fields)
• Lack of a large spectroscopically-confirmed sample with deep IR data
(HST + Spitzer)
 A simple idea
• HST and Spitzer imaging of spectroscopically-confirmed galaxies in the
Subaru Deep Field (SDF) and Subaru-XMM Deep Field (SXDS)
• The largest sample of spec-confirmed galaxies at z ≥ 6
A study of spectroscopically-confirmed galaxies at z ≥ 6
 Our galaxy sample
• About 70 galaxies from z = 5.6 to 7.0, including LBGs and LAEs
• Three HST programs and two Spitzer programs (PIs: Jiang and Egami)
 Our imaging data
• Optical data from Subaru
Suprime-Cam (PSF ≈ 0.6−0.7”)
• Broad-band data (AB mag at 3σ):
BVRi ≈ 28.5, z ≈ 27.5, y ≈ 26.5
• Narrow-band data (26 mag):
NB816 and NB921, NB973 (25 mag)
• HST near-IR data (~2 orbits per band):
WFC3 F125W (or F110W) and F160W
• Spitzer mid-IR data (3 ~ 7 hrs):
IRAC 1 and 2
A new large Spitzer program (PI: Jiang)
just approved last year (total 132 hrs).
Rest-frame UV continuum slope
 UV continuum slope β (fλ ~ λβ)
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–1.5 ≤ β ≤ –3.5; median β ≈ –2.3
Slightly steeper than LBGs in previous studies (β ≈ –2 ~ –2.1)
The β – M1500 relation is weak at the bright end
LAEs do not have steeper β than LBGs
(Jiang et al. 2013a)
 Extremely blue galaxies
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Statistically significant excess of galaxies with β ~ –3
Nearly zero dust and metallicity + extremely young + …
Current simulations cannot produce β ≤ –3 (Finlator 2011)
How to: top-heavy IMF, high escape fraction, etc. (e.g. Bouwens 2010)
(Jiang et al. 2013a)
Lyα morphology in LAEs
 Diffuse Lyα halos
2<z<3
(Steidel 2011)
 Based on ground-based NB (Lyα) images
 At low redshift: controversial
 At high redshift: predicted by simulations
z = 3.1 LAEs
(Matsuda 2012)
z = 3.1 LAEs
(Feldmeier 2013)
z = 5.7 LAEs
(Zheng 2011)
 No Lyα halos found at z=5.7 and 6.5
 Stack 43 LAEs at z=5.7 and 40 LAEs at z=6.5
 Stacked images: resolved but not very extended
 Possible reasons: dust, halo distribution, or no halos, etc.
20” x 20”
(Jiang et al. 2013b)
Deep spectroscopy of a z=7.7 LAE candidate
 Observations
 Target: brightest z=7.7 LAE candidate from Krug et al. (2012)
 Instrument: LUCI on the 2×8.4m LBT; tint = 7.5 hrs, with good conditions
 Results: non-detection  not a LAE at z=7.7 (confirmed by Faisst 2014)
Acquisition star
(J=15)
Reference star
Reference star
(J=18.5)
LAEz7p7
E
N
LAEz7p7
Faint galaxy
(J=22.6)
Faint galaxy
 Observed Lyα LF at z ≥ 5.7
 Rapid evolution from z = 5.7 to 6.5
based on a large sample of LAEs
 A z=7 LAE and a z=7.2 LAE
suggest such a trend towards higher
redshift
 The upper limit at z=7.7 is >5 times
lower than the z=6.5 LF
 Explanations:
• Not likely by intrinsic evolution
• Likely by neutral IGM
• Lyα reduced by a factor of two
(Jiang et al. 2013c)
Part II. High-Redshift Quasars
Quasars are boring: z ~ 6 quasars look similar to z ~ 0 quasars
z~6 composite Lya
Low-z composite
z = 7.08
NV
OI SiIV
Lya forest
(Mortlock 2011)
(Jiang et al. 2007)
zAB < 20 AB mag in the SDSS
 Surveys of z ≥ 6 quasars
 The first z~6 quasars found by the SDSS main survey (Fan 2000−2006)
 Followed by the SDSS deep survey (Jiang 2008,2009), the CFHTQS
(Willott 2005−2010), the UKIDSS (Venemans 2007, Mortlock 2009,2011),
the Pan-STARRS1 (Morganson 2012, Banados 2014), and the VISTA VIKING
(Venemans 2014)
 More than 60 quasars have been found so far, half of them found by the SDSS
 The most distant one at z = 7.08 (Mortlock 2011)
 Three quasars at z > 6.5 (Venemans 2014)
Surveys of high-z quasars
 Quasars (z ~ 6) in the SDSS
• High-z quasars in the SDSS main survey
• High-z quasars in the SDSS deep survey (Stripe 82)
• High-z quasars in the SDSS overlap regions
 Quasars in the SDSS main survey
• A total of 14555 deg2 of unique sky area (Ahn 2012)
• Completed: 8500 deg2 (Fan 2000−2006); zAB < 20 mag
• To do: >4000 deg2
 Quasars in the SDSS deep survey
• Stripe 82: a total of ~300 deg2
• −60° (20h) < RA < 60° (4h)
• −1.26° < Dec < 1.26°
• Repeatedly scanned 70-90 times by the SDSS
• Two mag deeper than single-epoch data
• Depth-optimized co-adds by Jiang et al. (2014a)
• Current survey status: almost completed;
12 quasars published; 1 to be published
−60°
0°
60°
(Jiang et al. 2014a)
zAB < 21 mag
zAB < 22 mag
 Quasars in the SDSS overlap regions
• SDSS: drift scan along great circles
• Adjacent runs overlap
• A total of >3000 deg2
• Allow selection of quasars ~0.5 mag fainter
(Jiang et al. 2014b)
 Quasar luminosity function at z ~ 6
SDSS main+deep
(Jiang et al. 2009, AJ, 138, 305)
SDSS + CFHTQS
(Willott et al. 2010, AJ, 139, 906)
Quasar contribution to the UV background:
 Double power-law QLF
ϕ(M1450) = ϕ* / (100.4(α+1)(M1450-M1450*) + 100.4(β+1)(M1450-M1450*) )
 β = −3
 α = [−2.2, −1.2]
 M1450* = [−25, −21]
Results:
 Not sensitive to α, but
strongly depends on M* and
clumping factor C
 Quasar/AGN population can
provide enough photons only
if the IGM is very
homogeneous and the break
luminosity is very low
 Search for z>6.5 quasars in Stripe 82
• Stripe 82 data + VISTA VHS J and K-band data
• Need Y-band imaging data
g
r
i
z
J
K
 Brand new: Close companions to z ~ 6 quasars in HST images
Summary
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A systematic study of spectroscopically-confirmed galaxies at z ≥ 6
Steep UV continuum slopes
No diffuse Lyα halos were found around LAEs
Rapid evolution of Lyα LF from z=5.7 to 7.7 caused by the IGM
Surveys of z~6 quasars using the SDSS data
Quasar luminosity function and its implication
Future search for z>6.5 quasars in the SDSS stripe 82
Quasar close companions