Galaxy Evolution Workshop 2018:

A Hard Ionising Spectrum in
z=3-4 Lyman Alpha Emitters
Kimihiko Nakajima (NAOJ)
In collaboration with
R. S. Ellis (ESO/UCL), T. Fletcher (UCL), B. E. Robertson (UCSC),
D. P. Stark (U. Arizona),
I. Iwata (Subaru), A. K. Inoue (Osaka Sangyo U.)

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Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

When and How Cosmic Reionisation occurred?
Recombinationz~1100：

Neutral Universe

Ionised gas
bubbles

z~6：

z=0：

Reionisation
Ionised Universe

credit: Subaru telescope, NAOJ

Page 3Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

Galaxies governed Reionisation process?
Robertson, B. E., Ellis, R. S., Dunlop,Robertson,J. S., McLure,B. E., Ellis,
R. J.R.andS., Stark,
Dunlop,
D.J.P.,S.,
Nature
McLure,468,R.55
J. (2010)
and Stark, D. P., Nature 468, 55 (2010)

History of cosmic star-formation

ρUV

Fraction of ionised hydrogen?

Robertson et al. 2010, Nature 468, 55

Electron scattering
Optical depth

Planck 2016?

BOX 2: Observational Probes of the Reionization EpochThe observed rest-frame UV luminosity density of star forming galaxies, which are the expected photon sourc
reionization, provides the cosmic star formation rate density ρSFR (panel a, circles with 1 s.d. error bars40,41,62,91,92, w
indicating the contribution from Lyman-α emitting galaxies65). Also shown are illustrative model star formation hist
See also Robertson et al. 2015, Faisst 2016
stellar ages of 108 yrs consistent with these observations (green area) based on an extension of the fitting form propo
The models61,94 span from very metal-poor (Z~5 x 10-6 Zsun) stars at the upper boundary to metal-rich (Z~2 Zsun) stabelow). The volume fraction of ionized hydrogen QHII implied by these models is shown in panel b (orange region), whwith the present data, the universe becomes fully reionized (QHII=1) at redshifts z ~ 5.5-8.5. The observed stellar massc, data points, 1 s.d. error bars)30,31,49-51,95 also constrains the process of reionization since the stellar mass should trof the star formation rate density (blue shaded area) if most stars are long-lived. Their relative agreement indicates
III stars may not contribute significantly to the UV luminosity density at z~7. Lastly, the scattering optical depth τe othat polarise the cosmic microwave background (CMB) can also be measured32 (panel d, gray shaded area). The
depth τe (red area) can be calculated from QHII by finding the path length through ionized hydrogen along the lineCMB. Producing the large electron scattering optical depth given the observed star formation rate density may be difevolving initial mass function, contribution from Population III stars, or yet unobserved star formation at higher (z>10) r

Fraction of ionising photons thatEﬃciency of ionising photon production

escape into IGM[We adopt the form ρSFR(z) = [a + b(z/c)h ]/[1 + (z/c)d ] + g with a = 0.009 Msun yr-1 Mpc-3, b = 0.27 Msun yr-1 Mpc-3, an
metal-poor case adopts c = 3.7, d = 7.4, g = 10-3 Msun yr-1 Mpc-3, fesc=0.3 and CHII=2, while the metal rich case uses c == 10-4 Msun yr-1EpochMpc-3, fesc=0.2 and CHII=6.]
ervational Probes
BOX 2: Observationalof the Reionization
ProbesEpochof the Reionization

est-frame UVTheluminosity
observeddensity
rest-frameof star
UVforming
luminosity
galaxies,
densitywhichof star
are forming
the expectedgalaxies,
photonwhichsources
are theforexpectedcausing photon sources for causing

Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

Lyα emitters (LAEs) as Probes of Early galaxies
Fraction of LAEs
in all star-forming galaxies

Stark, Ellis, & Ouchi

EpochofReionisation
345

678

Redshift
Stark et al. 2011, ApJL, 728, L2•Low-mass, metal-poor, young star-forming galaxies•Typical in early universe(computed in bins spanning ∆WLyα,0 = 30 Å) for star-forming galaxies at z ≃ 6 in twoPage 4

Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

Lyα emitters (LAEs) as Probes of Early galaxies
Fraction of LAEs
in all star-forming galaxies

Stark, Ellis, & Ouchi

z=3.1 LAEʼs MOSFIRE K spectrum

EpochofReionisation
345678Redshift
Stark et al.
ApJL, 728, L2Nakajima
et2011,al. 2016
See also Nakajima&Ouchi 2014, Erb+2016, Kojima+2017•Low-mass, metal-poor, young star-forming galaxies•

Typical in early universe•

Intense nebular lines, e.g. [OIII]5007,4959(computed in bins spanning ∆WLyα,0 = 30 Å) for star-forming galaxies at z ≃ 6 in two

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Page 6Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

Lyα emitters (LAEs) as Probes of Early galaxies
Stark, Ellis, & Ouchi

Fraction of LAEs
in all star-forming galaxies

Roberts-Borsani et al. 2016

z=3.1 LAEʼs MOSFIRE K spectrum

EpochofReionisation
345678Redshift
Stark et al.
ApJL, 728, L2Nakajima
et2011,al. 2016

See also Smit+2014,2015

Fig. 4.— Left: Best-fit SED models (blue line) to the observed HST + Sp
See also Nakajima&Ouchi 2014, Erb+2016, Kojima+2017bars) for the 4 especially bright (H160,AB < 25.5) z ≥ 7 galaxies selected u
included on the figure is the redshift estimate for the best-fit model SED prfor the same 4 candidate z ≥ 7 galaxies, as derived by EAZY. The impa
distributions should be close.

•

Low-mass, metal-poor, young star-forming galaxies•

Typical in early universe•

Intense nebular lines, e.g. [OIII]5007,4959(computed in bins spanning ∆WLyα,0 = 30 Å) for star-forming galaxies at z ≃ 6 in two

Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

LAEs present Hard Ionising Spectrum ..?
z=3.1 LAEʼs MOSFIRE K spectrum

Eﬃciency of ionising photon production

Nakajima et al. 2016

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Page 8Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

LAEs present Hard Ionising Spectrum ..?
z=3.1 LAEʼs MOSFIRE K spectrum

Eﬃciency of ionising photon production
ξion Based on Hydrogen recombination lines

LBGs(Bouwens et al. 2016)

Nakajima et al. 2016
Refer also to Poster by M. Hilmi

LAEs

More eﬃcient productionof ionising photons

Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

Number of photons
emitted above energy E

Nature of Ionising Spectrum Examined by
UV Emission lines

Nakajima et al. 2018a (A&A) in collaboration with VUDSHarderSofterPage 9Page 10

Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

UV line diagnostics of ξion
Flux(CIII])
Nion(>24.4eV)
EW(CIII]) = --------------- ∝ ------------------ = f(Z,U,ξion(age))
fλ,1909
LUV

1Myr

10Myr
Age

100MyrSmaller ξion

Nakajima et al. 2018a (A&A) in collaboration with VUDS
See also Stark+2014, Gutkin+2016

Page 11Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

VLT/VIMOS (11hrs) Observation
Identifying Lyα from ~70 Faint z=3 LAEs
z=3 LBGs (Shapley+03)z⇠2 LAEs (Stark+14)

N o (Shapley + 03 only)350

z=2-3 LAEs (Erb+14)
z=3.1 LAEs (This Work)

300
250

LBGs

200

35
30

Our targetLAEs(Shapely et al. 2003)

40

25
20

150

15100

1050

5026-26

24-24

22-22

20

18-20
MUV -18
MUV

16-16

14-14

No

400

0Nakajima et al. 2018b (MNRAS)

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Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

VLT/VIMOS (11hrs) Observation
Identifying Lyα from ~70 Faint z=3 LAEs
z=3 LBGs (Shapley+03)z⇠2 LAEs (Stark+14)

N o (Shapley + 03 only)350

z=2-3 LAEs (Erb+14)
z=3.1 LAEs (This Work)

300
250

LBGs

200

3530

Our target
LAEs(Shapely et al. 2003)

40

25
20150

15100

1050

5026-26

24-24

22-22

20

18-20
MUV -18
MUV

16-16

14-14

No

400

0Nakajima et al. 2018b (MNRAS)

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Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

VLT/VIMOS (11hrs) Observation
Identifying Lyα from ~70 Faint z=3 LAEs
z=3 LBGs (Shapley+03)z⇠2 LAEs (Stark+14)

N o (Shapley + 03 only)350

z=2-3 LAEs (Erb+14)
z=3.1 LAEs (This Work)

300
250

LBGs

200

3530

Our targetLAEs(Shapely et al. 2003)

40

25
20

150

15100

1050

5026-26

24-24

22-22

20

18-20
MUV -18
MUV

16-16

14-14

No

400

0

Nakajima et al. 2018b (MNRAS)

Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

Page 14Flux density (cgs per A)

VLT/VIMOS (11hrs) Observation
Identifying rest UV lines in Stacks of 70 z=3 LAEs

Rest Wavelength (A)Nakajima et al. 2018bPage 15

Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

Strong CIII] Associated with Strong Lyα

EW(Lyα) large
UV faintBluer βEW(Lyα) small
UV brightRedder βNakajima et al. 2018b

Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

Page 16

Stronger LAEs Characterised by lower metallicity

Nakajima et al. 2018b

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Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

ionization state

Stronger LAEs Characterised by lower metallicity

Gas metallicity

Nakajima et al. 2018b

Nakajima et al. 2018aStronger LAEs: Z = 0.05 – 0.2 Zsun
Weaker LAEs:

Z = 0.1 – 0.5 Zsun

Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

Page 18LAEsʼ Hard ξion Conﬁrmed with UV line analysis@ 1MyrNakajima et al. 2018b

Stronger LAEs: log ξion = 25.68±0.13
Weaker LAEs:

log ξion = 25.54±0.09

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Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

LAEsʼ Hard ξion Conﬁrmed with UV line analysis

Stronger LAEs
Weaker LAEs

LBGs

(Bouwens et al. 2016)

Nakajima et al. 2018b

Stronger LAEs: log ξion = 25.68±0.13
Weaker LAEs:log ξion = 25.54±0.09

LAEs(Nakajimaet al. 2016)

Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

Page 20

ξion as functions of UV luminosity, redshift and Lyα(Nakajima+16)

Nakajima et al. 2018b
Refer to Talk by Y. Harikane; Poster by M. Hilmi

LBGs: Uniform ξion (~25.2--25.4), independent of MUV, zLAEs: Larger ξion (~25.5--25.7), particularly for faintest LAEs
→ Analogous to Galaxies in EoRPage 21

Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

LymAn Continuum Escape Survey (LACES):UV Imaging of z=3 LAEs
Deep (20orbits x3) HST/F336W imaging of 54 z=3 LAEs

Rest wavelength (A)Spectrum of z=3.1 LAEs

Obs. wavelength (A)Fletcher, KN+ 2018 (arXiv:1806.01741)
See also Mostardi+15, Siana+15, Steidel+18, etc.

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Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

LymAn Continuum Escape Survey (LACES):
LymAn Continuum
EscapeSurvey(LACES):UV Imagingof z~3LAEs
UVz=3LAEs
Deep (20 orbits)
F336WImaging
imaging of 51 Escapez~3ofLAEs;
80% have[O III] + Lyα(LACES):
redshifts
LymAnContinuum
SurveyHigh success rate in securing significant F336W detections (~35% )Deep HST(20orbitsx3)
HST/F336W
of 51
z=3 LAEs
localisationsuggests
minimal (<2%)imaging
foregroundcontamination
UV
Imagingof z~3LAEs
Deep (20F336W
of 51 z~3LAEs; 80% have
[O III] +detections
Lyα redshifts (~30%)
Lyαorbits)
F160W
High successratein imaging
securing
signiﬁcantF336WF336W

High success rate in securing significant F336W detections (~35% )HSTforeground
localisation suggests
minimal (<2%) foreground contamination
Minimalcontamination

F336W NB497
F160W
F336W
Lyα
F160W

BPASS fit (NoIGM absorption)

LyC

Lyα

StellarWith IGM
absorption
BPASS fit (NoIGM absorption)

With IGM
absorption

fesc=15 ± 3%

fesc~7±2%

f=15 ± 3%

Predict LyC flux using BPASS +esc
nebular emission(calibrated with MOSFIRE [O III]/Hβ fluxes)
Lineof sightvariation
IGM absorption
Predict
LyC flux
using inBPASS+ nebular critical:
emission
Adopt
Inoueetal(2014)
τdistribution
to get fesc likelihood.
with MOSFIREIGM[O III]/Hβ fluxes)
For (calibrateddetections:Improvement over Madau (1995) with updated HI absorberstatistics
includinglimitabsorption&from
DLAs ~2-80%
Line of sightin IGM
critical:Individualfvariation
esc Lyman
rangesAdopt Inoue et al (2014) τIGM distribution to get fesc likelihood.

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Galaxy Evolution Workshop, Ehime on Jun 8, 2018 – Kimihiko Nakajima

SummaryLAEs are ideal analogs of sources
in Reionization era
Low-mass, Low-metallicity, Young
Intense [OIII]5007,4959
Hard Ionizing Spectrum

LymAn ContUV
Deep (20 orbits)
F336W
LymAnContHigh success rate in sec
HST localisation sugges
UVF336W

Galaxies like LAEs could dominate
Reionization process
Hard Ionizing Spectrum
High Escape Fraction?
→ Being examined by LACES

Deep (20F336W
Lyαorbits)
F160W
High success rate in sec
HST localisation sugges

F336W
Lyα
F160W
F336W NB497
F160W

LyC

Lyα

Stellar