High-Redshift Galaxies at the Epoch of Cosmic Reionization

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1 High-Redshift Galaxies at the Epoch of Cosmic Reionization Linhua Jiang ( 江林华 ) (KIAA, Peking University) 2014 KIAA-PKU Astrophysics Forum Collaborators: F. Bian, B. Clement, S. Cohen, R. Dave, E. Egami, X. Fan, K. Finlator, N. Kashikawa, H. Krug, I. McGreer, M. Mechtley, M. Ouchi, K. Shimasaku, D. Stark, and R. Windhorst

2 Outline Introduction How to find high-redshift galaxies Drop-out technique Narrow-band technique Galaxies and cosmic reionization Evolution of Lyα luminosity function Fraction of line-emitting galaxies Lyα emission halos Clustering Properties of spectroscopically confirmed galaxies at z > 6 Rest-frame UV slope TMT and high-redshift galaxies

3 Introduction: cosmic reionization Cosmic reionization Neutral IGM ionized by the first astrophysical objects at 6 < z < 15 Evidence: CMB polarization + GP troughs in quasars + (By M. Alvarez & T. Abel) (By A. Pontzen)

4 (By X. Fan) z~6 composite Lya Low-z composite NV OI SiIV Lya forest

5 High redshift galaxies High-z galaxies (z 6) HST + the largest ground-based telescopes More than 1000 galaxies or candidates at z 6; some at z 8 (e.g.; Bouwens 2011; Oesch 2012; Ellis 2013; Yan 2013; CANDELS papers, and many more papers) z ~ 0 galaxy, 1 min int. with SDSS 29 hr int. with Subaru (z band) 4 hr int. with Keck/DEIMOS 4 10 (Jiang et al. 2011, ApJ)

6 HST Keck LBT 8.2 m 10 m 8.4 m 2 Magellan MMT 6.5 m 6.5 m

7 How to find high-z galaxies Drop-out technique Lyman break galaxies (LBGs) Narrow-band technique Lyman-α emitters (LAEs) (Steidel 1993) i N816 z

8 Understanding reionization with high-z galaxies Increasing fraction of neutral IGM from low-z to high-z Patchy reionization Lyα luminosity function Lyα halos Enhanced galaxy clustering (Zheng et al. 2010) (McQuinn et al. 2007)

9 Lyα luminosity function 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 >2 from z=6.5 to 7.7 (Jiang et al. 2013a, ApJ)

10 Fraction of galaxies with strong Lyα emission among LBGs This fraction increases from low redshift to z~6 It then decreases from z~6 towards higher redshift This is broadly consistent with previous pictures (Bian, Stark, Fan, Jiang, et al. 2014)

11 Lyα halos around LAEs Diffuse Lyα halos Based on ground-based NB (Lyα) images Detect halos by stacking many images At high redshift: predicted by simulations z = 5.7 LAEs (Zheng 2011)

12 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, ApJ)

13 Enhanced clustering of LAEs So far no enhanced clustering has been found (e.g. Kashikawa 2011). (McQuinn et al. 2007) z~6.5 LAEs in SXDS (1.3 deg^2)

14 A large spectroscopic survey of LAEs at z 6 Team: KIAA + Arizona + Carnegie + PUC Chile Telescope/instrument: Magellan/M2FS + MMT/BinoSpec Fields: COSMOS, UDS, GOODS, SSA22, etc. Will produce the largest (and homogeneous) sample of LAEs and LBGs Will definitely confirm the strong evolution of Lyα LF from z=5.7 to higher z Will detect diffuse Lyα halos around LAEs Will likely detect enhanced LAE clustering Many other scientific topics

15 Rest-frame UV continuum slope of galaxies at z 6 UV continuum slope β (f λ ~ λ β ) Sample: ~60 spectroscopically confirmed galaxies Data: Subaru optical + HST near-ir 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 (Jiang et al. 2013c, ApJ)

16 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. 2013c, ApJ)

17 TMT (IRMS) and high-redshift galaxies Identification of a typical z~7 LAE with min integration Measurement of rest-frame UV properties of z > 6 galaxies Detection of metal-free star formation in the earliest galaxies (Figure from the IRMS website; Model based on Schaerer 2002)

18 Summary Cosmic reionization and the first-generation objects are one of the frontier fields for the next-generation telescopes High-redshift galaxies can be used to study cosmic reionization Rapid evolution of the Lyα LF from z=5.7 to higher redshifts Fraction of line-emitting galaxies among LBGs changes with redshift No diffuse Lyα halos around LAEs have been found yet No enhanced LAE clustering has been found yet We are planning an extensive survey of LAEs at z 6 Spec-confirmed galaxies at z 6 have very steep UV slopes TMT: a powerful telescope to study the high-redshift universe