Spectroscopically Confirmed Galaxies at z >= 6
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Transcript Spectroscopically Confirmed Galaxies at z >= 6
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)
•
•
•
•
–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
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
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