HST Observations of LyC Radiation from Galaxies & weak 5 ... · HST Observations of LyC Radiation...

HST Observations of LyC Radiation from Galaxies & weak

AGN at 2.3<∼z<∼5: (How) Did they Reionize the Universe?

Rogier Windhorst (ASU) — JWST Interdisciplinary Scientist

Brent Smith, S. Cohen, R. Jansen, L. Jiang, M. Dijkstra, A. Inoue,

A. Koekemoer, R. Bielby, J. MacKenty, R. O’Connell, & J. Silk

Talk at the Centre for Extragalactic Theory Workshop on “Reionization: A Multi-wavelength Approach”

(Kruger Gate, South Africa; Thursday June 4, 2015)

Outline

• (1) HST WFC3 Data & Spectroscopic Sample Selection

• (2) WFC3 & ACS Lyman Continuum Stacking, Systematics, & Fluxes

• (3) Stacked Lyman-Continuum and UV-Continuum Light-Profiles

• (4) SED-fitting & Dust-distribution AV (z)

• (5) LyC Escape Fractions vs. z for Faint Galaxies & Weak AGN

• (6) What critical aspects will JWST add to LyC Escape studies?

• (7) Summary and ConclusionsSponsored by NASA/HST & JWST

Talk is on: http://www.asu.edu/clas/hst/www/jwst/jwsttalks/za15reion_hstlyc.pdf

http://www.asu.edu/clas/hst/www/jwst/jwsttalks/za15reion_hstlyc.pdf

A dim ultraviolet surface brightness is best seen against a dark background ...

The LyC SB-signals we see are very dim and very flat (i.e., non-Sersic!).

(1a) Hubble WFC3 Data: The Early Release Science (ERS) field.

10 filters with HST/WFC3 & ACS reaching AB=26.5-27.0 mag (10-σ)over 40 arcmin2 at 0.07–0.15” FWHM from 0.2–1.7µm (UVUBVizYJH).

(JWST adds 0.05–0.2” FWHM imaging to AB≃31.5 mag (1 nJy) at 1–5µm + 0.2–1.2” FWHM at 5–29µm, tracing young+old SEDs & dust).

WFC3/UVIS channel unprecedented UV–blue throughput & areal coverage:

• QE>∼70%, 4k×4k array of 0′′.04 pixel, FOV ≃ 2′.67 × 2′.67.

WFC3/IR channel unprecedented near–IR throughput & areal coverage:

• QE>∼70%, 1k×1k array of 0′′.13 pixel, FOV ≃ 2′.25 ×2′.25.

WFC3 filters designed for star-formation and galaxy assembly at z≃1–8.

Early Release Science (ERS) field covers 40 arcm2, 0.2-2µm in 10 filters.

[LEFT] Composite rest-frame far-UV spectra of:SDSS QSOs at z≃1.3 (van den Berk et al. 2001);LBGs at z≃3 (Shapley et al. 2003); [see also J. Cooke’s talk, this Conf.]LBGs at z≃2–4 (Bielby et al. 2013, Lyα emitters, & absorbers).

• WFC3/UVIS F225W, F275W, F336W, and ACS/WFC F435W filters cancapture LyC (λ<912A) at z≥2.26, z≥2.47, z≥3.08, and z≥4.35.

• Lower z-bounds: no λ>912A below filter’s red-edge (≡0.5% of peak).

[RIGHT] Total observed throughput curves, designed to maximize through-put and minimize red-leak, which is <∼0.6% of actual LyC signal.

• Filter red-leak wing (λ>∼3648A) is <∼3×10−5 of peak transmission.

[LEFT] Cen & Kimm (2015): PDFs of mean fesc over “Nstack” objects:high-mass (top) & low-mass (bottom) at z=4 (left) & z=6 (right).

• Mean fesc from weighted number of photons mimics SED stacking ofgalaxy LyC data with true mean fesc listed. ERS has Nstack=11–37.

[RIGHT] Inoue et al. (2014): IGM transmission models for fesc calcula-tions: Red is the median and grey the 68% range, based on MC simulationsof IGM attenuation vs. z. (See other talks this Conf., e.g., G. Becker).

Uses updated absorber function + available data on Lyα forest, DampedLyman Alpha (DLA) & Lyman Limit Systems (LLS) mean-free paths.

• We do stack z∼5 samples: (z∼5) AGN have more LyC than galaxies.

F225W F275W F336W

The first & hardest part was to get the WFC3 astrometry right:

• Pre-flight 2009 ERS geo-distortion had <∼0′′.45 offsets at image borderscompared to GOODS v2.0 (Windhorst et al. 2011 ApJS, 193, 27).

• In-flight 2013 geo-distortion correction yielded excellent registration ofall WFC3/UVIS tiles to the ACS F435W mosaics (Kozhurina et al. 2014).

• Compared to GOODS, all offsets are now <∼0′′.02 ±0.06 (rms) in all LyCfilters (Smith et al. 2015) — this no longer blurs any LyC signal!

• Any LyC signal can now be measured and stacked, including removal of allforeground interlopers (AB<∼27.5), and measurement of LyC light-profiles.

Residual sky-background levels in the drizzled WFC3/UVIS ERS mosaics:

• Black lines: Best fit to the 2009 ERS v0.7 mosaics of Windhorst et al.(2011), which used pre-flight thermal vacuum flat-fields.

• Red lines: Current mosaics (ERS v2.0; Smith et al. 2015), using bestavailable on-orbit calibrations.

• Global residual sky-background levels (in ADU/sec) remaining after driz-zling the ERS mosaics are ∼30.29, 29.99, and 28.15 mag arcsec−2 .

• Removed in 3 stages: globally during drizzling (zodi≃25.5 mag/”2),locally before stacking, and again locally after stacking (to do photometry).

This is absolutely critical for optimal LyC stacking.

• Final 71×71 pix (6′′.39×6′′.39) LyC stacks allow residual local sky-subtraction to <∼32.3 mag arcsec−2 .

(1b) Hubble WFC3 ERS — Spectroscopic Sample Selection

Comparison of redshift reliability (spectrum quality) assessments, from best(0.0) to poorest (2.0), by five co-authors [BS, RAW, SHC, RAJ, and LJ]:

• Measuring LyC escape fractions of fesc ≃6.0% at >∼3σ requires low

interloper fraction (Siana+ 2015; Vanzella+ 2015).

• Mask-out all interlopers from 10-band ERS mosaics to AB<∼27.5 mag.

• Use all VLT, Keck, & HST grism spectra to get most reliable samples:

• “Gold” sample: highest fidelity (grades=0–0.63): zsp’s very likely correct.

• “Silver” sample: next highest fidelity (0.64–1.33), with z’s likely correct.

Absolute and apparent WFC3/IR F125W (J -band) magnitude distributionsof the Gold and combined Gold + Silver samples:

• The F125W filter samples rest-frame near-UV emission at 2.26<∼z<∼5.

Serves as proxy for restframe MAB (1650A) for flat spectrum objects.

• The blue dotted curve indicates the faint-end power-law slope of 0.16dex/mag of the galaxy number counts of Windhorst+ (2011).

• Sample incompleteness for AB>∼24, or MAB (1650)>∼–21 mag.

• Any LyC AB-fluxes & fesc -values are only valid for these luminosities!

• Galaxies with weak AGN have same N(MAB) as galaxies without AGN.

(2) WFC3 & ACS Lyman Continuum Stacking, Systematics, & Fluxes

med=1.59e-05avg=1.69e-05mod=-4.87e-05

med=3.64e-06avg=4.47e-06mod=-6.34e-05

med=6.47e-06avg=6.00e-06mod=-6.09e-05

med=1.25e-05avg=1.39e-05mod=-4.19e-05

med=1.24e-05avg=1.60e-05mod=-1.54e-04 med=2.20e-06

avg=3.52e-06mod=-6.90e-05

med=1.17e-05avg=1.26e-05mod=-6.00e-05

med=1.27e-05avg=1.37e-05mod=-5.37e-05

med=4.42e-06avg=4.25e-06mod=-5.51e-05

stack1 avgtot =9.39e-06 medtot =8.91e-06modetot =-5.73e-05 σavg=5.02e-06

med=1.66e-05avg=1.61e-05mod=-6.35e-05

med=1.79e-05avg=1.85e-05mod=-6.08e-05

med=5.17e-06avg=4.54e-06mod=-6.87e-05

med=3.64e-06avg=4.32e-06mod=-8.02e-05


avg=2.58e-06mod=-8.96e-05

med=2.53e-07avg=-2.95e-07mod=-8.27e-05

med=5.51e-06avg=4.76e-06mod=-7.43e-05

med=-3.68e-06avg=-3.67e-06mod=-8.95e-05


med=4.57e-05avg=4.59e-05mod=-8.40e-05

med=3.53e-05avg=3.45e-05mod=-9.33e-05

med=4.70e-05avg=4.97e-05mod=-8.60e-05

med=4.11e-05avg=3.70e-05mod=-1.14e-04


avg=4.66e-05mod=-8.54e-05

med=3.12e-05avg=3.36e-05mod=-1.06e-04

med=3.35e-05avg=3.20e-05mod=-1.12e-04

med=4.23e-05avg=4.53e-05mod=-5.35e-05


med=1.70e-03avg=1.69e-03mod=3.71e-06

med=1.58e-03avg=1.62e-03mod=-1.89e-04

med=1.51e-03avg=1.50e-03mod=-1.25e-04

med=1.69e-03avg=1.71e-03mod=1.71e-04


avg=1.60e-03mod=5.36e-05

med=1.52e-03avg=1.51e-03mod=-1.78e-04

med=1.59e-03avg=1.60e-03mod=2.62e-05

med=1.59e-03avg=1.61e-03mod=-1.02e-04


med=3.19e-03avg=3.15e-03mod=1.08e-03

med=3.22e-03avg=3.18e-03mod=1.06e-03

med=3.26e-03avg=3.33e-03mod=1.65e-03

med=3.23e-03avg=3.21e-03mod=1.31e-03

med=4.44e-03avg=4.60e-03mod=1.81e-03

med=3.02e-03avg=3.05e-03mod=1.01e-03

med=3.13e-03avg=3.19e-03mod=1.06e-03

med=3.33e-03avg=3.30e-03mod=1.34e-03

med=3.02e-03avg=3.00e-03mod=1.10e-03

stack1uv avgtot =3.18e-03 medtot =3.17e-03modetot =1.17e-03 σavg=1.04e-04

med=3.06e-03avg=3.00e-03mod=6.83e-04

med=3.10e-03avg=3.12e-03mod=9.85e-04

med=3.19e-03avg=3.19e-03mod=9.68e-04

med=3.17e-03avg=3.24e-03mod=1.07e-03

med=4.44e-03avg=4.49e-03mod=2.26e-03

med=3.09e-03avg=3.10e-03mod=9.06e-04

med=3.13e-03avg=3.10e-03mod=1.08e-03

med=3.09e-03avg=3.09e-03mod=7.97e-04

med=3.19e-03avg=3.27e-03mod=1.06e-03


med=3.25e-03avg=3.24e-03mod=1.44e-03

med=3.41e-03avg=3.39e-03mod=1.67e-03

med=3.61e-03avg=3.56e-03mod=2.19e-03

med=3.25e-03avg=3.26e-03mod=1.66e-03

med=4.06e-03avg=4.06e-03mod=2.44e-03

med=3.35e-03avg=3.29e-03mod=1.70e-03

med=3.25e-03avg=3.19e-03mod=1.61e-03

med=3.33e-03avg=3.36e-03mod=1.60e-03

med=3.48e-03avg=3.49e-03mod=1.88e-03


med=2.85e-03avg=2.84e-03mod=1.44e-03

med=2.85e-03avg=2.81e-03mod=1.15e-03

med=2.91e-03avg=2.87e-03mod=1.27e-03

med=2.69e-03avg=2.70e-03mod=1.58e-03

med=3.04e-03avg=3.01e-03mod=1.38e-03

med=2.70e-03avg=2.67e-03mod=1.03e-03

med=2.87e-03avg=2.87e-03mod=1.52e-03

med=2.69e-03avg=2.73e-03mod=1.26e-03

med=2.46e-03avg=2.47e-03mod=9.84e-04


“Tic-tac-toe” sky-background analysis of 71×71 pixel (6′′.39×6′′.39) stacks:

LyC [left 4 panels] and UVC [right 4 panels].

• Large-scale gradients in residual sky-background left in drizzled images5–40× fainter than global remaining sky residuals in previous Figure.

• Residual UV sky-gradients on 71×71 pixel scales are fainter than ∼32.3mag arcsec−2 across the “tic-tac-toe” apertures.

• This is fainter than the LyC SB-signal where this can be measured, &imposes a (fundamental?) limit to how many images can be stacked.

<~ <~z2.3 6 RAJ

a) F225W

g)

c) d) e) f)F275Wb) F336W F435W

h) i) j) k) l)

LyC

LyCLyC

LyC

Gold

Gold+Silver

N=51

Gold+Silver (smoothed)

Gold (smoothed) N=51

N=118

N=118F225W F275W F336W F435W

Galaxies without AGN,

z=2.26–2.47 z=2.47–3.08 z=3.08–4.35 z=4.35-6 WEIGHTED ALL: z=2.26–6.

[Top Row ]: All galaxies in combined Gold Galaxy sample: N=51;

[Bottom Row ]: All galaxies in combined Gold+Silver sample: N=118.

[Right 2×2 panels]: Weighted “stack-of-stacks” over all 4 LyC filters: bestvisualizes LyC of galaxies at z≃2.3–5.5. Formal detection S/N -ratios:

>∼6.8σ (∼√51×1.0σ above sky), and >∼13σ (∼√

118×1.2σ).

Equivalent to 22–236 orbit stacks with HST, respectively.

Circles: r=8 (0′′.72), 13 pix (1′′.17), centered on the UVC emission.

RAJGalaxies without AGN, Gold sample

a) F225W LyC b) F275W c) F336W d) F435W

e) F606W f) F606W g) F775W h) F850LP

LyC LyC LyC

UVC UVC UVC UVC

z=2.26–2.47 z=2.47–3.08 z=3.08–4.35 z=4.35-6.

Galaxies without AGN in Gold sample.

Top row: Ly-Continuum stacks, Bottom Row: UV-Continuum stacks.

Blue: SExtractor LyC apertures, >∼1σ in >∼4 connected pixels.

Green: SExtractor MAG AUTO apertures using UVC centroids+apertures.

RAJGalaxies with AGN, Gold sample


e) F606W f) F606W g) F775W h) F850LP

LyC LyC

UVC UVC UVC

LyC

UVC

z=2.26–2.47 z=2.47–3.08 z=3.08–4.35 z=4.35-6.

Galaxies hosting weak AGN in Gold sample.

[Lower Left]: N=1 AGN with background objects shown before masking-out.

RAJAll galaxies, Gold sample

a) LyC b) F275W c) F336W d) F435W

e) F606W f) F606W g) F775W h) F850LP

LyC LyC LyC

UVC UVC UVC UVC

F225W

z=2.26–2.47 z=2.47–3.08 z=3.08–4.35 z=4.35-6.

All Objects (Galaxies + Weak AGN) in Gold sample.

RAJAll Galaxies, Gold+Silver sample


e) F606W f) F606W g) F775W h) F850LP

LyC LyC LyC

UVC UVC UVC UVC

z=2.26–2.47 z=2.47–3.08 z=3.08–4.35 z=4.35-6.

All Objects (Galaxies + Weak AGN) in Gold+Silver sample.

(3) Stacked LyC Light-Profiles, & Weighted “Stack-of-Stacks”<~ <~z2.3 6 RAJ

a) F225W

g)

c) d) e) f)F275Wb) F336W F435W

h) i) j) k) l)

LyC

LyCLyC

LyC

Gold

Gold+Silver

N=51

Gold+Silver (smoothed)

Gold (smoothed) N=51

N=118

N=118F225W F275W F336W F435W

Galaxies without AGN,

z=2.26–2.47 z=2.47–3.08 z=3.08–4.35 z=4.35-6 WEIGHTED ALL: z=2.26–6.

[Top Row ]: All galaxies in combined Gold Galaxy sample: N=51;

[Bottom Row ]: All galaxies in combined Gold+Silver sample: N=118.

The faint LyC emission has a very flat SB-distribution with radius:

• Not centrally concentrated, with few clear sight-lines per galaxy.

• On average escapes along few random sight-lines through a porous ISM?

• Likeliest escape paths may be somewhat offset from galaxy center.

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Isophotal Semi-Major Axis (arcsec)

22

24

26

28

30

32

Surfac

e Brig

htne

ss (m

agAB arcse

c−2)

F435W PSFF275W PSF

Model (z=2.65)

F225W (<z>=2.38)

F275W (<z>=2.68)

F336W (<z>=3.47)

F435W (<z>=5.02)

[Top Curves]: Radial SB-profiles of non-ionizing UVC (solid).

[Bottom Curves]: Radial SB-profiles of LyC signal (dashed):

• All LyC SB-profiles are extended compared to the PSFs (dotted).

• Horizontal black dashed line is the 1σ SB-limit of ∼32 mag arcsec−2 .

Light-blue dot-dash: Dijkstra’s z=2.68 UVC-scattering model with ISMporosity + escaping LyC increasing as: fcov(r)=N exp{−(r/10 kpc)x}.

(4) Spectral Energy Distribution (SED)-fitting & Dust (AV )-distribution

1 2 3 4 5 6 7 8 92 10

0

1

2

3

[LEFT]: Best-fit AV from 10-band SEDs for all ERS galaxies (black dots).

Circles: galaxies; Asterisks: AGN at: z=2.37, z=2.68, z=3.45, z=5.1.

[RIGHT]: Adopted distributions N(AV ) for total Gold + Silver LyC sample(top), and also for each of the four redshift bins:

Median AV increases from ∼0.2m at z=5.1–3.5 to ∼0.6m at z=2.67–2.37.

1 2 3 4 5 6 7 8 92 10

0

1

2

3

missing for

most SMGs

Best-fit AV from 10-band SEDs for all ERS galaxies (black dots).

• Galaxies+AGN with zspec =2.37–2.68 represent N(AV ) distribution.

• Spectroscopically selected galaxies + AGN at z=3.45–5.1 miss ∼45% ofdusty (AV

>∼1 mag) objects at z>∼3.

• Our fesc -value calculations vs. redshift will correct for this.

(5) LyC Escape Fractions vs. z for Faint Galaxies & Weak AGN

PDFs of absolute [left] & relative [right] fesc -values (Inoue+ 2014 MC),folding LyC fluxes ± their 1σ errors through 109 random LOS of IGMtransmission.

• Filled triangles indicate the resulting modal and circles the average fesc

-values in each PDF. Tick-marks show the ±1σ-range.

T=tanh[(log(1+z)-0.59)/0.07]

Other work (see text)

T=tanh[(log(1+z)-0.53)/0.07]

T=tanh[(log(1+z)-0.59)/0.07]

Other work (see text)

[Left]: Relative fesc -z: Published + ERS Gold & Gold+Silver samples.

Shaded bounded by: fesc ≃(0.02±0.01)·(1+z)1.0±0.5 does not fit well.

Simple tanh[log(1+z)] captures more sudden fesc -increase at z>∼2.5–3.[Dashed: Same, corrected for ∼45% missing SMGs(AV >1) at z>∼3.1].

[Right]: Same for 12 AGN in ERS (+Bridge+ 2010) available thus far.

Object-weighted ratio of tanh-curves suggests fesc (galaxies) high enoughto dominate reionization at z>∼3, while weak AGN may dominate at z<∼2.5.

(6) What critical aspects will JWST add to HST’s LyC Escape studies?

NIRSpec: JWST’s short-wavelength (0.6–5.0µm) spectrograph:

• Can do 100’s of simultaneous faint-object spectra to AB<∼27–28 mag:

JWST FGS+NIRCam: R≃150 1–5.0µm grism spectra to AB<∼28-29:

• Larger & fainter zspec -samples for LyC candidates in HST UV fields.

We hope the HST and JWST TAC’s will allow field to do what’s needed:

• HST WFC3/UVIS: More LyC images, before this becomes impossible.

• JWST NIRSpec, FGS, NIRCam: 1000’s of zspec’s for faint LyC objects.

(7) Summary and Conclusions

(1) HST can measure LyC for galaxies + weak AGN at z≃2.26–5.5.• WFC3 and ACS filters designed with low-enough redleak to enable this.

• Samples of sufficient size (N=11–118) need to be stacked to see LyC signal, preferably many dozen.

• Astrometry/registration and sky-background subtraction must be carefully done in various stages.

• Subtle residual sky-gradients and other systematics ultimate limitation to LyC stacking (at >

∼32.3 mag arcsec−2 ).

• Deepest 10-band images at HST resolution critical to mask-out all foreground interlopers to AB<

∼27.5 mag.

• Careful spectroscopic redshift selection critical for reliable samples.

• Must correct results for MAB and AV -biases that result from the necessary spectroscopic selection.

(2) LyC signal detected in sub-samples of N=11–37 objects at z=2.26–5.5.• Detections of AB(LyC) generally better than >

∼3–4σ (AB≃29.5–31 mag).

• Weak AGN have ∼1 mag brighter AB(LyC), but are 4–10× less numerous than galaxies.

• Stacked LyC SB-profiles are on average much flatter than the UV-continuum Sersic-profile.

• LyC may escape along few random sight-lines, offset from the average galaxy center.

• Non-Sersic LyC SB-profiles may indicate that the ISM porosity increases with r.

(3) Resulting fesc -values show rapid “tanh[log(1+z)]” increase at z>∼2.5.• Dust-corrected SED-fits and MC simulations are essential to interpret this sudden drop in fesc (z).

• Best-fit 10-band ERS SEDs suggests AV increases from z∼6 to z≃2.3.

• Spectroscopic selection at z=2.37–2.68 follows field galaxy AV , but at z=3.45–5.1 misses ∼45% of dusty objects.

• This explains part but not all of sudden fesc -increase at z>

∼2.5: Accumulating HI+AV (t) may shut down fesc (z<

∼3).

• Object-weighted ratio of tanh-curves suggests fesc (galaxies) high enoughto dominate reionization at z>∼3, while weak AGN may take over at z<∼2.5.

Time for some (picky?) questions ...

Picture: Sunday May 31 (Ehlanzeni water hole; Kruger Park, South Africa)

SPARE CHARTS

References and other sources of material shown:

http://www.jwst.nasa.gov/ & http://www.stsci.edu/jwst/

http://ircamera.as.arizona.edu/nircam/

http://ircamera.as.arizona.edu/MIRI/

http://www.stsci.edu/jwst/instruments/nirspec/

http://www.stsci.edu/jwst/instruments/fgs

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http://www.jwst.nasa.gov/

http://www.stsci.edu/jwst/

http://ircamera.as.arizona.edu/nircam/

http://ircamera.as.arizona.edu/MIRI/

http://www.stsci.edu/jwst/instruments/nirspec/

http://www.stsci.edu/jwst/instruments/fgs

Example of SED fits used for fesc (MC) etc, using λ>∼1216 A and z≡zspec.

RAJ

a) b) c) d)

e) f) g) h)

Stacking Tests, Gold sample

F225W F275W F336W F435W

i) j) k) l)

original

rotation tests

split halves − subset 1

n) o) p)m) split halves − subset 2

blank sky tests r) s) t)q)

z=2.37, z=2.68, z=3.45,z=5.1 Gold stacks;

Same Gold stacks af-ter random 90◦ rotation;

First independent datahalves Gold stacks;

Second independentdata halves Gold stacks;

Random sky-stacksto verify null-signal.

RAJ

a) b) c) d)

e) f) g) h)

Stacking Tests, Gold+Silver sample

F225W F275W F336W F435W

i) j) k) l)

original

rotation tests

split halves − subset 1

n) o) p)m) split halves − subset 2

blank sky tests r) s) t)q)

z=2.37, z=2.68, z=3.45,z=5.1 Silver stacks;

Same Silver stacks afterrandom 90◦ rotation;

First independent datahalves Silver stacks;

Second independentdata halves Silver stacks;

Random sky-stacksto verify null-signal.

a) b)

Detector location of “high-CTE” and “low-CTE” sub-samples: [LEFT]:WFC3/UVIS F225W, F275W, F336W. [RIGHT]: ACS/WFC F435W.

Green regions are closest to parallel read-out amplifier. Red regions arefurthest from amplifiers, and may suffer more from CTE-degradation.

• Filled circles show marginal LyC signal in individual objects:

• These are fairly uniformly distributed across individual CCDs.

Average stacked LyC diff: ∆(Lower-CTE–High-CTE) ≃ 0.5±0.35 mag.

=⇒ Less than four months after WFC3’s launch, CTE-induced systematicsare not yet larger than the random errors in the LyC signal.

WFC3 ERS 10-band redshift estimates accurate to <∼4% with small sys-tematic errors (Hathi et al. 2010, 2013), resulting in a reliable N(z).

• Measure masses of faint galaxies to AB=26.5 mag, tracing the processof galaxy assembly: downsizing, merging, (& weak AGN growth?).

⇒ Median redshift in (medium-)deep fields is zmed ≃1.5–2.

• HUDF showed WFC3 z≃7–9 capabilities (Bouwens+ 2014; Yan+ 2010).

• JWST will trace mass assembly and dust content <∼5 mag deeper fromz≃1–12, with nanoJy sensitivity from 0.7–5µm.

(6b) Can JWST see most of the Reionizing sources?

?

1.6µm counts (Windhorst+2011). [F150W, F225W, F275W, F336W, F435W, F606W, F775W, F850LP, F105W, F125W, F140W not shown].

• Faint-end near-IR count-slope≃0.16±0.02 dex/mag ⇐⇒Faint-end LF-slope α(zmed ∼1.6)≃–1.4 ⇒ reach MAB≃–14 mag.

• 800-hr WUDF can see AB<∼32 objects: MAB ≃–15 (LMCs) at z≃11!

• Lensing will change the landscape for JWST observing strategies (WUDFF).

HST Observations of LyC Radiation from Galaxies & weak 5 ... · HST Observations of LyC Radiation...

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