Unveiling the nature of bright z ~ 7 galaxies with HST and JWST

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1 Unveiling the nature of bright z ~ 7 galaxies with HST and JWST Rebecca Bowler Hintze Fellow, University of Oxford Nicholas Kurti Junior Fellow, Brasenose College with Jim Dunlop, Ross McLure, Derek McLeod, Matt Jarvis, Elizabeth Stanway, JJ Eldridge, and the UltraVISTA and VIDEO teams

2 high-redshift galaxies with HST Hubble Ultra-Deep Field Hubble Frontier Fields

3 Bright galaxies into the EoR CANDELS 0.2 deg

4 Bright galaxies into the EoR CANDELS is not enough to find the very brightest galaxies Hubble Ultra Deep Field CANDELS GOODS North and South CANDELS EGS CANDELS COSMOS CANDELS UDS Ground-based near-infrared data from: UltraVISTA* in COSMOS, UKIDSS and VIDEO* in the UDS Total area = 1.7 sq. deg UltraVISTA Survey / COSMOS field UKIDSS Ultra Deep Survey / Subaru XMM-Newton Deep Survey *ESO Public Surveys

5 Bright galaxies into the EoR Lyman-break galaxies as bright as mab = 24, without lensing ~ few per sq. degree for the brightest LBGs Hubble Ultra Deep Field CANDELS GOODS North and South CANDELS EGS CANDELS COSMOS CANDELS UDS UltraVISTA Survey / COSMOS field UKIDSS Ultra Deep Survey / Subaru XMM-Newton Deep Survey HST surveys e.g. CANDELS, UDF+ Ground-based

6 Bright galaxies into the EoR Such galaxies are unlikely to be found in JWST surveys e.g. NIRCam/NIRSpec GTO surveys Deep ~ tens sq. arcmin Wide 400 sq. arcmin (< CANDELS) Hubble Ultra Deep Field CANDELS GOODS North and South CANDELS EGS CANDELS COSMOS CANDELS UDS UltraVISTA Survey / COSMOS field UKIDSS Ultra Deep Survey / Subaru XMM-Newton Deep Survey Bright z > 6 LBGs provide a unique probe of galaxy properties during the EoR: accessible by JWST, ALMA, ELTs

7 HST/WFC3 imaging of bright z ~ 7 LBGs S/N > 20 Ground-based HST/WFC3 Targeted follow-up: one object per orbit 17 galaxies z > 6.5, reaching Muv ~ -23

8 HST/WFC3 imaging of bright z ~ 7 LBGs 3 /16kpc Ground-based HST/WFC3

9 HST/WFC3 imaging of bright z ~ 7 LBGs 3 /16kpc Himiko Ouchi et al. 2009, 2013 CR7 Sobral et al. 2015

10 Bright galaxies in the most ionized regions? Fraction of LBGs with Lyα Faint Bright Curtis-Lake et al Oesch et al e.g. Schenker et al Stark et al. 2015, 2017, Zitrin et al Roberts-Borsani et al Lyα can escape the brightest galaxies at z > 7 - ionised bubbles? Also see other rest-frame UV lines, CIV, CIII] To study the Lyα escape will require wide-area (CANDELS+) surveys and targeted follow-up of the brightest sources

11 Bright LBGs : the view from JWST 1) Spectroscopy of rest-frame UV and optical nebular emission lines Maseda et al Wuyts et al ) Resolved imaging of the rest-frame optical

12 Bright LBGs : the view from JWST 1) Spectroscopy of rest-frame UV and optical nebular emission lines R =100, t ~ 8 min R=1000, t < 1hr [OII] [OIII] Hα Hβ [NII] c/o Marijn Franx NIRSpec will clearly detect these lines + the continuum Metallicity, Ionisation parameter, temperature indicators Balmer break measured directly Also access to rest-frame UV lines

13 1) Spectroscopy of rest-frame UV/optical nebular emission

14 1) Spectroscopy: Pop III/DCBH signatures in z = 6.6? [Direct collapse black hole] CR7 is extreme z = 6.6 in COSMOS He II 1640 line observed EW0 = 80±20A He II is strong and narrow, no metal lines. Sobral et al. 2015

15 1) Spectroscopy: Pop III/DCBH signatures in z = 6.6? CR7 is extreme z = 6.6 in COSMOS He II 1640 line observed EW0 = 80±20A He II is strong and narrow, no metal lines. Sobral et al Sobral et al Visbal et al Pop III? DCBH? other? Bowler et al. 2017b Pallottini et al Hartwig et al Agarwal et al Smidt et al Smith et al Dijkstra et al Pacucci et al Agarwal et al. 2017

16 1) Spectroscopy: Pop III/DCBH signatures in z = 6.6? CR7 is extreme z = 6.6 in COSMOS He II 1640 line observed EW0 = 80±20A He II is strong and narrow, no metal lines. Sobral et al Pop III? DCBH? other? Bowler et al. 2017b Sobral et al Visbal et al Pallottini et al Hartwig et al Agarwal et al Smidt et al Smith et al Dijkstra et al Pacucci et al Agarwal et al. 2017

17 1) Spectroscopy: Pop III/DCBH signatures in z = 6.6? UltraVISTA DR3 + deconfused Spitzer SPLASH data Sobral et al Bowler et al. 2017b

18 1) Spectroscopy: Pop III/DCBH signatures in z = 6.6? Hβ [OIII] 4959, 5007 UltraVISTA DR3 + deconfused Spitzer SPLASH data Lower HeII EW = 40±30A Hα Sobral et al Bowler et al. 2017b

19 1) Spectroscopy: Pop III/DCBH signatures in z = 6.6? Pop III DCBH Pop III? DCBH? other? Normal stellar populations or an AGN, with strong [OIII] 5007 emission can reproduce the colours

20 1) Spectroscopy: Pop III/DCBH signatures in z = 6.6? IRAC colour of CR7 is exactly what you expect for contamination of ch1 by [OIII] (as in other z ~ 6-8 LBGs) Pacucci et al. 2017, also Agarwal et al CR7 He II 1640 emission is still a puzzle. Could be AGN (as supported by line ratios in the UV + point-like core) Or young stellar population with binary populations (e.g. BPASS models) More objects with rest UV/optical spectroscopy will be key: JWST

21 1) Spectroscopy: bright galaxies or faint quasars? Bowler et al Galaxies Quasars z ~ 6 quasar search by Matsuoka et al Potential region of overlap

22 1) Spectroscopy: combination with far-ir measurements Measured with ALMA e.g. the dusty normal galaxy at z = 7.5 from Watson et al. (2015) bluer Bowler+ in prep. ALMA band 6 imaging of six bright LBGs at z ~ 7 redder Balmer decrement and β measured by NIRSpec can be directly compared to ALMA results

23 2) Resolved imaging of the rest-frame optical Rest-frame UV Rest-frame optical SF galaxies at z ~ 1 Wuyts et al The brightest LBGs into the EoR, are they: Merging galaxies or clumpy galaxies? Merging could explain high SFRs Clumps are expected in gas rich high-z galaxies

24 2) Resolved imaging of the rest-frame optical z = 2-3 SF galaxies Elmegreen et al Guo et al. (2015) Rest-frame UV `chain `clump-cluster double-core galaxies Rest-frame optical NIRCam will reveal the underlying rest-frame optical profile WFC3 FWHM ~ 0.2, NIRCam <~ 0.1 S/N ~ 50 for < 10 min

25 2) Resolved imaging of the rest-frame optical Deep data required below the break to confirm that the clumps are at high-z: e.g HST/ACS imaging at z ~ 6 [regime where Hα is covered by NIRSpec] Lower redshift galaxies along the line-of-sight to high-z galaxy (centre)

26 2) Resolved imaging of the rest-frame optical Size-luminosity relation at z ~ 7 from the rest-frame UV (HST/WFC3)

27 2) Resolved imaging of the rest-frame optical Size-luminosity relation at z ~ 7 from the rest-frame UV (HST/WFC3) Large range of sizes for the brightest galaxies, driven by clumpy morphology Is there a smoother underlying older population: mergers or clumps?

28 Summary Using ground-based data from the UltraVISTA + UDS we now have samples of extremely bright star-forming galaxies at z = 7 The sample is ideal for detailed follow-up with HST, ALMA, and JWST HST reveals a clumpy, extended morphology, deep F814W essential CR7 - inferred [OIII] emission argues against Pop III or DCBH interpretation With JWST: Rest-frame optical emission lines Test of PopIII/DCBH nature of CR7- like objects Detection of faint quasars? The impact of dust at z > 6 Underly morphology of the rest-frame optical A more robust measure of galaxy size at early times