Spectroscopy of Lyman-alpha Emitters in the Reionization Era - - PowerPoint PPT Presentation

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spectroscopy of lyman alpha emitters in the reionization
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Spectroscopy of Lyman-alpha Emitters in the Reionization Era - - PowerPoint PPT Presentation

May 18, 2023 237 likes •506 views

Spectroscopy of Lyman-alpha Emitters in the Reionization Era credit: B. Robertson/UDF12 Dan Stark (University of Arizona) with Ramesh Mainali, Mengtao Tang (Arizona), Stphane Charlot (IAP), Jacopo Chevallard (IAP), Alba Vidal Garcia (IAP),

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SLIDE 1

Spectroscopy of Lyman-alpha Emitters in the Reionization Era

Dan Stark (University of Arizona)

with Ramesh Mainali, Mengtao Tang (Arizona), Stéphane Charlot (IAP), Jacopo Chevallard (IAP), Alba Vidal Garcia (IAP), Anna Feltre (CRAL/Lyon) Johan Richard (CRAL/Lyon), Richard Ellis (UCL), Nicolas LaPorte (UCL)

credit: B. Robertson/UDF12

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SLIDE 2

4 5 6 7 8 Redshift 0.0 0.2 0.4 0.6 0.8 xLyα, 25 MUV > -20.25 MUV < -20.25 Stark et al. (2011) This work

Lyman-alpha Disappearance at z~7-8

(see also Fontana et al. 2010, Vanzella et al. 2011, Ono et al. 2012, Pentericci et al. 2011, 2014, Treu et al 2012, 2013, Tilvi et al. 2014, Caruana et al. 2014, Bian et al. 2014, Schmidt et al. 2015, Furusawa et al 2016).

  • Lyman-alpha emission is much less

common among z>7 star forming galaxies than it is at z~5-6.

  • Lyman-alpha emitter fractions are

~10% in UV-bright galaxies at z~7.

Stark 2016 ARAA, Schenker+2014

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SLIDE 3

credit: Wise, Cen, and Abel

  • Most models suggest neutral

hydrogen must fill 40-60% of z~7 IGM to explain Lyman-alpha results (i.e., Mason+17).

  • Lyman-alpha emitters we observe

expected to trace early ionized bubbles in significantly neutral IGM.

Late Reionization Implied by Lyman-alpha

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SLIDE 4

Lyman-alpha Properties of Massive z~7-9 Galaxies with Extremely Large EW Optical Line Emission

Roberts-Borsani+16

Ideal spectroscopic targets for Lyman-alpha visibility test! Selected to have extremely large EW [OIII]+Hβ. Four very bright (H~25) z~7-8 galaxies, stellar masses of 1010 M☉.

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SLIDE 5

Discovery of Lyman-alpha at z~8-9

Oesch+15 Zitrin+15

z=7.73 z=8.68

First two galaxies from this sample revealed record breaking Lyman- alpha detections:

  • z=7.73 (Oesch et al. 2015)
  • z=8.68 (Zitrin et al. 2015)
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SLIDE 6

0.980 0.985 0.990 0.995 1.000 1.005 Observed Wavelength (µm) −2 2 4 Fλ (10−18 erg cm−2 s−1Å−1)

COSY−0237 zLyα=7.151

1.025 1.030 1.035 Observed Wavelength (µm) −1.0 −0.5 0.0 0.5 1.0 1.5 2.0 Fλ (10−18 erg cm−2 s−1Å−1)

EGS−zs8−2 zLyα=7.477

Large Lyman-alpha fraction in Strong [OIII] +Hβ Emitters at z~7-9

Stark+17

Next two objects also showed Lyman-alpha emission:

  • z=7.48 (Roberts-Borsani+16, Stark+17)
  • z=7.15 (Stark+17).

100% Lyman-alpha emission fraction in massive sample at z~7-9

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SLIDE 7

What Regulates Detectability of Ly𝛃 Emission at z=8-9?

Robertson et al. 2015 Fraction

  • f HI in

IGM Redshift range of Roberts- Borsani sample

Why do we see a 100% Lyman- alpha fraction in this new sample while it is so strongly attenuated in most other systems? Lyman-alpha fractions in luminous galaxies tend to be below 10% at z~8.

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SLIDE 8

Classical Explanation: Accelerated Reionization around Massive Galaxies

Image credit: Barkana

  • Trace overdense regions

that ionize their surroundings early.

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SLIDE 9

Additional Explanations May Be Required

Image credit: Barkana

ξion Lyman-alpha emitters trace systems with hard ionizing spectra (AGN, very hot metal poor stars)?

  • Enhanced production rate of

Lyman continuum photons.

  • Efficiently ionize/heat surroundings.
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SLIDE 10

Additional Explanations May Be Required

Image credit: Barkana

ξion Lyman-alpha emitters trace systems with hard ionizing spectra (AGN, very hot metal poor stars)?

  • Enhanced production rate of

Lyman continuum photons.

Massive sources may have larger velocity offsets. Δv

  • Reduced attenuation from IGM.
  • Efficiently ionize/heat surroundings.
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SLIDE 11

Lyman-alpha Emitters at z>7 Have Extreme Optical Line Emission

Roberts-Borsani et al. 2016, ApJ, 823, 143

Inferred [OIII] equivalent widths

  • f z>7 sources with Lyman-

alpha tend to be ~2x larger than average. Do these more extreme EW [OIII] emitters produce more LyC radiation?

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SLIDE 12

Measuring the LyC Production Efficiency in z~2 galaxies with Extreme [OIII] Emission

Tang+2018 (see Mengtao Tang’s poster)

  • Large near-IR spectroscopic survey of z~2 galaxies with similarly

large [OIII] EW as z>7 Lyman-alpha emitters.

  • Measure production efficiency of LyC photons (ξion) as function of

[OIII] EW.

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SLIDE 13

70 100 200 400 700 1000 2000 EW([OIII]λ5007) (˚ A) 24.4 24.8 25.2 25.6 26.0 log[ξion erg−1 Hz]

Typical EW at z > 7 Hyper-extreme [OIII]λ5007 EW Tang et al. 2018 z > 7; Stark et al. 2017

−1

Production Efficiency of Lyman Continuum Photons is Enhanced in EELGs at z~2

z~2

  • Extreme [OIII] emitters at z~2

have largest ξion.

  • Produce more LyC radiation

per UV luminosity, likely implying enhanced Ly𝛃 production rates.

  • Largest EW [OIII] emitters are

likely to be more easily detected in Ly𝛃.

Tang+2018 (see Mengtao Tang’s poster)

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SLIDE 14

CIII] HeII OIII] Lyα

z~3 composite of ~900 LBGs WCIII] = 1.7 Å WHeII = 1.3 Å WOIII]λ1661+1666 = 0.2 Å

  • If galaxies similar to z~3, they will

be undetectable (≲ 7x10-19 erg cm-2 s-1) in z>7 galaxies.

Shapley et al. 2003

CIV

Can we learn more about radiation field of z>7 Lyman-alpha emitters?

  • If radiation field more extreme,

expect larger EW nebular emission, appearance of high ionization lines (NV, CIV, He II).

z~3

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SLIDE 15
  • Measure strength of far-UV lines in bright (24<H<26) galaxies at z~6-9.
  • Test for presence of extreme radiation fields in z>6 systems with

Lyman-alpha emission.

Characterizing the Far-UV Spectra of Reionization Era Galaxies

Stark et al. 2015a, 2015b, 2017, Mainali et al. 2017, 2018, Laporte+2017

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SLIDE 16

Oesch+15

z=7.73

Massive Lyman-alpha Emitter at z=7.73

z=7.730 galaxy in EGS, confirmed in Oesch+15

  • H=25.0
  • WLyα,0 = 21 Å
  • W[OIII]+Hβ ~ 900 Å
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SLIDE 17

− −

λ − − − −

α

− −

α

1.650 1.655 1.660 1.665 1.670 1.675 Observed Wavelength (µm) −0.4 −0.2 0.0 0.2 0.4 0.6 0.8 Fλ (10−18 erg cm−2 s−1Å−1) [CIII] CIII]

z=7.73

CIII] doublet detected with total EW~22Å.

Stark+17

  • ~10x greater EW than in

composite of z~1-3 galaxies (Shapley+03, Du+2016, 2018).

Intense CIII] emission at z=7.73

  • Extreme radiation field, either

from AGN (Nakajima+17) or metal poor stars (Stark+17).

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SLIDE 18

Massive Lyman-alpha Emitter at z=8.68

z=8.68

Zitrin+2015

  • z=8.68 galaxy with strong [OIII]

confirmed in Zitrin+15

  • H=25.3
  • WLyα,0 = 28 Å
  • W[OIII]+Hβ ~ 895 Å
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SLIDE 19

1.175 1.180 1.185 1.190 1.195 1.200 1.205 Observed Wavelength (µm) −2 −1 1 2 3 Fλ (10−18 erg cm−2 s−1Å−1)

EGSY8p7

zLyα=8.683 2D

NV Emission in Lyman-alpha Emitter at z=8.68

− −

λ − − − −

α

rum

SNR

unsmoothed smoothed

Mainali+18

  • Requires >77eV photons,

likely powered by AGN.

  • NV detected in Y-band

spectrum, no CIV or OIII] in H-band spectrum.

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SLIDE 20

Massive z=7.154 Lyman-alpha Emitter

0.980 0.985 0.990 0.995 1.000 1.005 Observed Wavelength (µm) −2 2 4 Fλ (10−18 erg cm−2 s−1Å−1)

COSY−0237 zLyα=7.151

z=7.151 galaxy in COSMOS, confirmed in Stark+17

  • H=25.1
  • WLyα,0 = 28 Å
  • W[OIII]+Hβ ~ 1900 Å

Stark+17 (see also Pentericci+17)

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SLIDE 21

Detection of NV and He II Emission

LaPorte +17 NV Lya

  • Nebular NV and He II emission detected in 10 hr X-Shooter
  • exposure. Another AGN?

Massive galaxies at z>7 with Lyman-alpha often have extreme radiation fields that may be effective at ionizing surrounding ISM/ CGM, contributing to visibility of strong Lyman-alpha.

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SLIDE 22

−200 200 400 600 800 1000 Vel (km s−1) −500 500 1000 1500 2000 2500 3000 Fλ (10−20 erg cm−2 s−1 Å−1)

FWHM=175 km/s Ly! velocity profile

Stark et al. 2015a

Ly𝛃 Velocity Offsets at z>6

CIII] systemic redshift

  • UV metal lines (CIII], OIII]) and far-IR

lines ([CII], [OIII]) now providing systemic redshifts at z>6.

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SLIDE 23
  • Lyα velocity offsets small (<200 km/

s) in low mass galaxies.

Mainali+17

Ly𝛃 Velocity Offsets in Low Mass Galaxies

  • Small velocity offsets in dwarf

galaxies may lead to stronger IGM attenuation of Lyman-alpha than in systems with large offsets.

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SLIDE 24
  • Ly𝛃 velocity offsets (and FWHM)

much larger in these massive galaxies.

Lyman-alpha velocity offsets large in massive galaxies at z>6

  • 2/4 Roberts-Borsani+16 z>7 LAEs

have systemic redshift measurements.

  • Enhances transmission of Lyman-

alpha through IGM.

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SLIDE 25

Factors regulating Lyman-alpha visibility in massive galaxies at z>7

  • Massive galaxies have large

Lyman-alpha velocity offsets at z>7, boosting transmission.

Δv

Lyα

Image credit: Barkana

  • Massive galaxies trace
  • verdense regions with largest

ionized bubbles.

  • Extreme radiation fields: large

Ly𝛃 output and enhanced transmission. ξion

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SLIDE 26

Summary and Outlook

  • Rest-UV spectroscopy is already providing improved

understanding of systematics (velocity offsets, LyC production rate) which are being included in inferences of XHI (i.e., Mason+17).

  • Variations in galaxy properties (radiation field, velocity
  • ffsets) play significant role in Lyman-alpha visibility at z>7,

and must be controlled for in inferences of XHI .

  • JWST will not only provide Ly𝛃 EW distributions at z>7, but it will

deliver constraints on ξion and ΔvLya, improving mapping between Ly𝛃 and XHI.