Physical Properties of Spectroscopically Confirmed Galaxies at Redshift ≥ 6

1. Physical Properties of Spectroscopically Confirmed Galaxies at Redshift ≥ 6 Linhua Jiang (Arizona State University ) Collaborators: E. Egami, X. Fan, S. Cohen, R. Dave, K. Finlator, N. Kashikawa, M. Mechtley, K. Shimasaku, and R. Windhorst Hubble Fellow Symposium 2013

2. z ~ 0 galaxy, 1 min int. with SDSS Outline • Introduction • UV and Lyαproperties • 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 • …… 4’ 29 hr int. with Subaru (z band) 4hr int. with Keck/DEIMOS 10” (Jiang et al. 2011)

3. Note: • See Dan Stark’s talk for EoR 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; Stark2011; Yan 2011; and more papers in 2012 and 2013) (Robertson+2011) (Robertson 2011)

4. 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 • See Chun Ly’s talk for the SDF • Note: • LAEs: found by the narrow-band (NB) technique • LBGs: found by the dropout technique

5. 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)

6. z J H IRAC1 IRAC2

7. Rest-frame UV and Lyα properties • UV continuum slope β (fλ~ λβ) • –1.5 ≤ β ≤ –3.5; median β ≈ –2.3 • Steeper than LBGs in previous studies (β ≈ –2 ~ –2.1 ) • No obvious β – M1500relation • LAEs do not have steeper β than LBGs

8. 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

9. Rest-frame Lyα EW • EW: 10 ~ 300 Å • EW – M relation and selection effect EW MUV

10. 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

11. Morphologyand 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 z<0.1 z ≥ 7 (Oesch 2010) z=1 z=3 z=6 4’ 4” 2” 1”

12. Galaxy size • Half-light radius rhl • rhl ≈ 0.1”–0.28” (0.6–1.6 kpc) • Median rhl= 0.16” (1 kpc) • Intrinsic rhl,in ≈ 0.05”–0.26” (0.3–1.5 kpc) • Median rhl,in= 0.13” (0.8 kpc) • Small and compact • Size-luminosity relation • Brighter galaxies are larger • rhl ~ L0.14 and rhl,in ~ L0.20 • Comparison with previous work • Similar to photo-selected LBGs • In particular, LAEs are not smaller

13. Nonparametric methods • Morphological parameters • CAS (Conselice 2003) • Gini and M20(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?

14. Interacting/merging galaxies • Merging galaxies • Visual identification at M1500 < –20.5 mag • ≥ 2 distinct cores, or,extended with long tails • Merger rate • 36% – 48% at M1500< –20.5 mag • 39% – 56% at M1500< –21 mag z=6.96 LAE

15. 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)

16. 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. 20” x 20”

17. 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

18. 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: 1303.0024) • Jiang et al. 2013b, ApJ submitted (arXiv: 1303.0027) • Voted as No. 1 and 2 by on Monday