1. 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

2. 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)

3. 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

4. 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 (Robertson+2011)

5. 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).

6. (Jiang et al. 2013a) Rest-frame UV continuum slope  UV continuum slope β (f λ ~ λ β ) –1.5 ≤ β ≤ –3.5; median β ≈ –2.3 Slightly steeper than LBGs in previous studies (β ≈ –2 ~ –2.1) The β – M 1500 relation is weak at the bright end LAEs do not have steeper β than LBGs

7.  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)

8. Lyα morphology in LAEs  Diffuse Lyα halos  Based on ground-based NB (Lyα) images  At low redshift: controversial  At high redshift: predicted by simulations 2 < z < 3 (Steidel 2011) z = 3.1 LAEs (Matsuda 2012) z = 3.1 LAEs (Feldmeier 2013) z = 5.7 LAEs (Zheng 2011)

9. 20” x 20”  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. (Jiang et al. 2013b)

10. 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; t int = 7.5 hrs, with good conditions  Results: non-detection  not a LAE at z=7.7 (confirmed by Faisst 2014)

11. (Jiang et al. 2013c)  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

12. Part II. High-Redshift Quasars Quasars are boring: z ~ 6 quasars look similar to z ~ 0 quasars Lya NV OI SiIV Lya forest z~6 composite Low-z composite (Jiang et al. 2007) (Mortlock 2011) z = 7.08

13. z AB < 20 AB mag in the SDSS

14.  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)

15. 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 deg 2 of unique sky area (Ahn 2012) Completed: 8500 deg 2 (Fan 2000−2006); z AB < 20 mag To do: >4000 deg 2

16. (Jiang et al. 2014a) −60° 0° 60°  Quasars in the SDSS deep survey Stripe 82: a total of ~300 deg 2 −60° (20 h ) < RA < 60° (4 h ) −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

17. z AB < 21 mag z AB < 22 mag

18.  Quasars in the SDSS overlap regions SDSS: drift scan along great circles Adjacent runs overlap A total of >3000 deg 2 Allow selection of quasars ~0.5 mag fainter (Jiang et al. 2014b)

19. SDSS main+deep (Jiang et al. 2009, AJ, 138, 305) SDSS + CFHTQS (Willott et al. 2010, AJ, 139, 906)  Quasar luminosity function at z ~ 6

20. Quasar contribution to the UV background:  Double power-law QLF ϕ (M 1450 ) = ϕ * / (10 0.4(α+1)(M 1450 -M 1450 *) + 10 0.4(β+1)(M 1450 -M 1450 *) )  β = −3  α = [−2.2, −1.2]  M 1450 * = [−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

21.  Search for z>6.5 quasars in Stripe 82 Stripe 82 data + VISTA VHS J and K-band data Need Y-band imaging data

22. g r i z J K

23.  Brand new: Close companions to z ~ 6 quasars in HST images

24. 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