Collaborators: E. Egami, X. Fan, S. Cohen, R. Dave, K. Finlator, N. Kashikawa, M. Mechtley, K. Shimasaku, and R. Windhorst

Outline  Introduction  UV and Lyα properties Rest-frame UV continuum slope Rest-frame Lyα equivalent width (EW) UV luminosity function of Lyα emitters (LAEs) SED modeling LAE vs. LBGs ……  Morphology Rest-frame UV continuum morphology Merging/interacting systems Lyα morphology of LAEs Positional differences between UV continuum and Lyα emission Nonparametric measurements …… (Jiang et al. 2011) z ~ 0 galaxy, 1 min int. with SDSS 4’ 10” 29 hr int. with Subaru (z band) 4 hr int. with Keck/DEIMOS

Epoch of Cosmic Reionization  Cosmic Reionization Neutral IGM ionized by the first luminous objects at 6 < z < 15 Evidence: CMB polarization (Komatsu 2011) + GP troughs (Fan 2006) + … Responsible sources for Reionization? (e.g. Finlator 2011)  High-z galaxies (z ≥ 6) HST + the largest ground-based telescopes A few hundred galaxies or candidates at z ≥ 6; many at z ≥ 8 (e.g. Oesch 2010; Bouwens 2011; Stark 2011; Yan 2011; and more papers in 2012 and 2013) (Robertson+2011) (Robertson 2011)

Galaxies at z ≥ 6  Current studies of galaxies at z ≥ 6 Mostly done with photo-selected Lyman-break galaxies (LBGs) Lack of a large spec-confirmed sample with deep infrared data LBGs found by HST are faint  often no spec-z, no Spitzer detections LBGs or LAEs found by ground-based telescopes are bright, but  do not have deep near-IR (HST) or mid-IR (Spitzer) data  Our sample of spec-confirmed galaxies A total of 67 galaxies, from the Subaru Deep Field (SDF) 22 LAEs at z ≈ 5.7; 16 LBGs at z ≈ 6; 28 LAEs at z ≈ 6.5; 1 LAE at z ≈ 7 3 HST and 2 Spitzer programs (PIs: L. Jiang and E. Egami) First systematic study of spec-confirmed galaxies at z ≥ 6

 Imaging data Optical data from Subaru/Suprime-Cam (PSF≈0.6”) Broad-band data: BVRi ≈ 28.5, z ≈ 27.5, y ≈ 26.5 (AB mag at 3σ) Narrow-band data: NB816, NB921, NB973 Near-IR data: HST/WFC3 F125W (or F110W) and F160W (2 orbits per band) Mid-IR data: Spitzer IRAC 1 and 2 (3 – 7 hrs)

z J H IRAC1 IRAC2

Rest-frame UV and Lyα properties  UV continuum slope β (f λ ~ λ β )  –1.5 ≤ β ≤ –3.5; median β ≈ –2.3  Steeper than LBGs in previous studies (β ≈ –2 ~ –2.1 )  No obvious β – M 1500 relation  LAEs do not have steeper β than LBGs

 Extremely blue galaxies (β ~ –3!)  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 )  To confirm β ~ – 3: new HST observations

Rest-frame Lyα EW EW: 10 ~ 300 Å EW – M relation and selection effect M UV EW

UV luminosity function (LF) of LAEs with EW > 20Å In the brightest end: comparable to the LF of LBGs  a large fraction of LAEs among bright LBGs In the faint end: much lower  faint galaxies with weak Lyα emission could be the dominate contribution to the total ionizing flux at z ~ 6

z ≥ 7 (Oesch 2010) 4’ 4” 2” 1” z<0.1 z=1 z=3 z=6 Morphology and structure  Galaxies at z ≥ 6 are faint and small At higher redshift: size evolution, (1+z) 4 surface brightness dimming At higher redshift: less well developed, more peculiar Galaxies at z ≥ 6: occupy several pixels even in HST images

Galaxy size  Half-light radius r hl r hl ≈ 0.1”–0.28” (0.6–1.6 kpc) Median r hl = 0.16” (1 kpc) Intrinsic r hl,in ≈ 0.05”–0.26” (0.3–1.5 kpc) Median r hl,in = 0.13” (0.8 kpc) Small and compact  Size-luminosity relation Brighter galaxies are larger r hl ~ L 0.14 and r hl,in ~ L 0.20  Comparison with previous work Similar to photo-selected LBGs In particular, LAEs are not smaller

Nonparametric methods  Morphological parameters CAS (Conselice 2003) Gini and M 20 (Lotz 2004,2006)  Our measurements Different locations in parameter space, due to small galaxy sizes  Applicability Correlation between parameters Still applicable, if used with caution?

z=6.96 LAE Interacting/merging galaxies  Merging galaxies Visual identification at M 1500 < –20.5 mag ≥ 2 distinct cores, or, extended with long tails  Merger rate 36% – 48% at M 1500 < –20.5 mag 39% – 56% at M 1500 < –21 mag

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

20” x 20”  No Lyα halos found in z=5.7 and 6.5 LAEs  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.

Lyα–continuum misalignment  Lyα and continuum emission Originated from the same SF regions Lyα affected by resonant scattering  Data UV continuum: HST Lyα: narrow-band images  Results Compact LAEs: no offsets Interacting systems: a variety of positional differences Disturbed ISM distribution

Summary  First systematic study of spec-confirmed galaxies at z ≥ 6  Steep UV continuum slopes  UV continuum LF of LAEs  Galaxy size: mostly small and compact  Large fraction of merging galaxies in the bright end  No diffuse Lyα halos were found around LAEs  Significant positional differences between Lyα and UV continuum  For more information: Jiang et al. 2013a, ApJ submitted (arXiv: ) Jiang et al. 2013b, ApJ submitted (arXiv: ) Voted as No. 1 and 2 by on Monday