Project ALCATRAZ-2: Archival Lyman-Continuum andTheoretical Reionization Analysis vs. z: Where, When, & HowMuch Does LyC Escape from Galaxies & AGN?

Abstract Project ALCATRAZ will study escaping Lyman continuum (LyC) radiation from galaxies and weak AGN atz=2.3-5, vastly expanding our systematic study of the Early Release Science (ERS) field to include ArchivalUV images in HUDF and GOODS. Each field was imaged in 2-3 WFC3 UV-filters and 6-9 ACS + WFC3/IRfilters. SED-fits provide photo-z, luminosity, stellar mass, age, SFR, and extinction estimates. Paying carefulattention to systematics, stacking 6-15 orbit native depth for 100s of objects will reach UV-depths of 100s-1000s of orbits. ALCATRAZ will reveal where, when, how and how much LyC escapes, and if galaxies startedand AGN maintained cosmic reionization. Its science goals are: 1. HOW MUCH LyC escapes? ERS results from stacking 11-37 galaxies and weak AGN at z=2.3-5.5 suggestm(LyC) ~ 29-30.5 mag (>3-4 sigma). With robust 8-12 filter SEDs, excellent rejection of foregroundinterlopers, and >100 new spectra, ALCATRAZ will improve the statistics 3.5x and depth 2x. 2. HOW does LyC escape? LyC light-profiles suggest it escapes through an ISM that gets more porous at largergalactic radii. We will stack LyC from LBGs, Lya and dusty star-forming galaxies, and AGN with outflows. 3. WHEN did LyC escape? We will constrain how LyC escape fractions evolved with epoch for galaxies &weak AGN, and if f_esc(z) follows the cosmic SFH and SMBH-growth. LyC detections at z>4 will helpconstrain IGM transmission models at z>4. 4. WHERE does LyC escape and for which classes of objects vs. epoch? We will study escaping LyC vs. dustaccumulated over time, age/SFR, luminosity/mass, plus for AGN, and how extinction increasing with timesuppressed escaping LyC.

Scientific Category: UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE

Scientific Keywords: AGN Physics, Dust, Dwarf Galaxies, Hubble Deep Fields, Interstellar AndIntergalactic Medium

Budget Size: Regular

Hubble Space Telescope Cycle 23 AR Proposal 20

Investigators:

Dataset Summary:

Investigator Institution CountryPI& R Windhorst Arizona State University USA/AZ

CoI B Smith Arizona State University USA/AZ

CoI R Jansen Arizona State University USA/AZ

CoI S Cohen Arizona State University USA/AZ

CoI* M Dijkstra University of Oslo NOR

CoI A Inoue Osaka Sangyo University, College of GeneralEducation,

JPN

CoI A Koekemoer Space Telescope Science Institute USA/MD

CoI* R Bielby University of Durham GBR

CoI* C Conselice University of Nottingham GBR

CoI J MacKenty Space Telescope Science Institute USA/MD

Number of investigators: 10* ESA investigators: 3& Phase I contacts: 1

Instrument No. of Datasets Retrieval Method Retrieval PlanACS 3076 FTP FTP at 100 Gb/week or one STScI visit

WFC3 2170 FTP FTP at 100 Gb week or one STScI visit

R Windhorst : Project ALCATRAZ-2: Archival Lyman-Continuum and Theoretical ReionizationAnalysis vs. z: Where, When, & How Much Does LyC Escape from Galaxies & AGN?

Scientific Justification

A. Scientific Background: Cosmic Reionization was the second major phase transition ofhydro-gen in the universe, following recombination. It began at z∼<9–20 (Planck 2015; we useH0 = 68km s−1 Mpc−1, Ωm=0.31,ΩΛ=0.69), and was completed by z≃6–7 (Mesinger & Haiman 2004;Becker+ 2001; Fan+ 2002). Bubbles of ionized hydrogen formed around UV-brightobjects, ex-panded, and merged until the intergalactic medium (IGM) fully ionized. Lyman-continuum (LyC;λ≤912A) photons can be produced by massive stars in star-forming (SF) galaxies, by hot accre-tion disks in Active Galactic Nuclei (AGN), or by more exoticsources. Neutral hydrogen and dustare opaque in the far-UV, so LyC can only escape where the HI column density (NH) and dustextinction (AV ) are low. For a fraction of LyC photons to escape, pathways need to be cleared inthe object’s interstellar medium (ISM), which both SNe winds and AGN outflows can do.

Fig. 1a compares the rest-frame far-UV spectra of QSOs (z≃0.1–5; van den Berk+ 2001) andLBGs (z≃2–4; Shapley+2003; Bielby+ 2013), illustrating that AGN can produce more hard UVradiation than LBGs. LBGs may also by selection have lower LyC escape fractions (fesc). BecauseAGN are much more rare than galaxies and their density decreases at z∼>2.5 (Madau+ 1999; Fan+

2001; Hunt+ 2004; Siana+ 2007), they likely did not reionize the IGM at z∼>3. However, AGNcontributed much of the LyC background from their peak epochat z∼2 until today, maintainingthe current ionization of the IGM (Cowie+ 2009). No significant escaping LyC flux was detectedin rest-frame far-UV data of SF galaxies at 0.5∼<z∼<2 (Siana+ 2007, 2010; Grimes+ 2009; Cowie+

2009; Bridge+ 2010). Ground-based spectra yielded evidence for escapingLyC in SF galax-ies at 3∼<z∼<4 (fesc≃1–16%; Shapley+ 2006; Cooke+ 2014), and images indicatefesc≃2–24%(Iwata+ 2009; Nestor+ 2011; Vanzella+ 2010, 2012; Boutsia+ 2011; Mostardi+ 2013; Borthakur+

2014), despite the higher IGM opacity at higher z (Haardt & Madau 1996, 2012). HST UV spec-tra (Bridge+ 2010) detected one AGN with significantfesc≃15% at z≃0.7. Siana+ (2015) andVanzella+ (2015) give a careful assessment of the contribution of contaminating flux to LyC de-tections in previous work. Because AGN activity peaked lateand galaxies outnumber AGN, thecombined far-UV output from (dwarf) galaxies may have started reionization at z∼>8, completedand then maintained it at z∼<6, until AGN started to dominate at z∼<2–3.Using the best ArchivalHST UV data and ∼>100 new ground-based spectra, Project ALCATRAZ will study where,when, how & how much LyC flux escapes from galaxies and weak AGNat 2.3∼<z∼<5.

B. Available Data for Project ALCATRAZ, Assessing & Correcting SystematicsSmith+ (2015; S15) analyzed WFC3/UVIS UV-images in the Early ReleaseScience field (ERS;Windhorst+ 2011; W11) plus ACS/WFC images from GOODS (Giavalisco+ 2004). The F225W,F275W, F336W, and F435W filters can capture LyC emission atz∼>2.26, z∼>2.47, z∼>3.08, andz∼>4.35 (Fig. 1a). The higher IGM opacity at z∼>4.5 makes it more difficult to detect LyC invisible images (Fig. 1b). Inoue+ (2014) suggest that the IGM transmission at z∼5 could still be∼12%, so we include ACS/WFC F435W in our analysis. Through SED-fitting, GOODS, ERS, andHUDF (Teplitz+ 2013) 8–12 band object catalogs yielded photo-z’s (zphot; if zspec unknown), with∆z/(1 + z) accurate to∼<4% (Coe+ 2006; Dahlen+ 2013), and luminosity/stellar mass, age, star-formation rate (SFR) and history (SFH), and extinction (AV ) for each object.S15 showed that, bycarefully correcting for systematics (§D), stacking images with a native 2-orbit depth for 133objects can reach sensitivities equivalent to 100s of UV orbits. ALCATRAZ will expand thisto stacking 6–15 orbit images for 460 objects, equivalent toLyC depths of 1000s of orbits.

1

Fig. 1a: Composite rest-frame spectra of SDSS QSOs atz≃1.3 (van den Berk+ 2001 [blue]) and of LBGs atz≃2–4 (Bielby+ 2013 [greenand

orange]; Shapley+ 2003 [red]). The F225W, F275W, F336W and F435W (not shown) transmission curves capture LyC (λ<912A) at z≥2.26,

z≥2.47,z≥3.08, andz≥4.35. An average QSO produces a stronger LyC signal than an average LBG.Fig. 1b: Inoue+ (2014) IGM transmission

model used forfesc calculations. Red is the median and grey the 68% range, based on a Monte Carlo (MC) simulation of IGM attenuation vs.

redshift. ALCATRAZ will use LyC detections at z∼>3.5 to help improve IGM transmission models (Table 1).

C. Science Goals of Project ALCATRAZ

Goal 1. HOW MUCH?: What level of LyC escape can we measure reliably?The WFC3 ERS dataof S15 (Fig. 2–5; Table 1) suggest that in each of four redshifts bins from z≃2.3 to z≃5, LyC fluxis detected atmAB≃29–30.5 mag (∼>3–4σ) in images stacked over 11–37 galaxies, and for someweak AGN (Fig. 3). Cen & Kimm (2015) showed thatfesc will converge to more reliable valueswhen averaged over many dozen, compared to N∼<10, because a better average is obtained whenstacking LyC flux (and IGM transmission) over larger samples. ALCATRAZ will increase currentstatistics∼3.5×, and add ground-based spectra (Fig. 2) for∼>100 new object with 2.3∼<zphot∼<5to AB∼<24.5 mag. Using accurate 8–12 filter photo-z’s (Fig. 4b &§D), we will mask-out allforeground interlopers (Fig. 3).ALCATRAZ will significantly improve upon LyC detectionswith more rigorous treatment of low level systematics in theWFC3 UVIS stacks (see§D), andget∼>100 new spectroscopic redshifts with LBT, MMT, Magellan and VLT.

Goal 2. HOW?: What is the radial dependence of escaping LyC radiation?Fig. 3 shows 51 (118)galaxies in the spectroscopic “Gold” (“Gold+Silver”) samples of S15 (§D.2a). Their weightedaverage LyC emission isnot centrally concentrated, perhaps vaguely resembling a “ring”. Fig. 4ashows that the stacked LyC profiles are extended with respectto the PSFs (S15),andmuch flatterthan non-ionizing UV-continuum (UVC; 1500A) profiles for r∼<0.′′7, beyond which sky-subtractionerrors become substantial. This holds clues as to how ionizing photons may escape along a fewrandom sight-lines through a porous ISM and surrounding gaseous or dusty material. With at mosta few clear sight-lines per galaxy, the likeliest LyC escapepaths may be on averagesomewhatoffsetfrom a galaxy center. This could arise naturally in a porous ISM in which the covering factorof neutral gas decreases with increasing galacto-centric radius. To illustrate this quantitatively, weconsider the transfer of UV and LyC continuum photons through simplified models with a multi-phase ISM (Dijkstra & Kramer 2012), adapted for LyC scattering. Assuming that the coveringfactor decreases asfcov(r) = N exp−(r/rs)

x, a normalization constantN ≃0.075,x ≃0.54,andrs ≃10 kpc match the observed F275W LyC-profile at〈z〉≃2.67 (light-blue dotted curve inFig. 4a). ALCATRAZ will carefully model the LyC light-profiles of LBG’s, Ly-α selectedgalaxies, dusty star-forming galaxies, and AGN with outflows from ∼3.5×larger samples.

2

Fig. 2a: Absolute and apparent WFC3/IR F125W magnitude distributions of the Gold and Gold+Silver samples of spectroscopic redshifts (S15),

sampling rest-frame near-UV at 2.26∼< z∼

< 5. The blue dotted curve indicates the faint-end power-law slope of 0.16 dex/mag of the galaxy counts of

W11, suggesting sample incompleteness for AB∼> 24 mag. [2b] Same, for galaxies hosting aweakAGN, which have〈MAB〉≃–21.5±1 mag. [2c]

Same, for galaxies without AGN.ALCATRAZ will add∼>100 new spectra for ERS objects at 2.3

∼< z

∼< 5 selected by 10-band photo-z’s.

Goal 3. WHEN?: How exactly does the LyC escape fraction evolve with redshiftfor galaxiesand weak AGN? Doesfesc follow the cosmic SF and SMBH-formation history?Estimating theescape fraction of LyC photons from galaxies,fesc, is non-trivial as it requires modeling intrinsicLyC flux, f int

LyC, and the wavelength-dependent fraction of LyC photons transmitted through theIGM, T LyC

IGM(λ, z), for a galaxy at redshiftz. In Fig. 5a, we summarize publishedfesc-values asblue triangles. These came from different data sets (including both spectra and imaging; see§A),with different object selection, reduction techniques, assessment of systematics, and treatment ofthe estimated corrections for IGM absorption. With SED-fitting of the UVC longwards of Lya,the observed LyC fluxes of S15 correspond toaveragerelative LyC escape fractions that seemto rapidly increase fromfesc≃7% at〈z〉≃2.37–2.67 to∼50±30% at〈z〉≃3.5, and to∼100% at〈z〉≃5.1, where we do see some LyC flux at the∼>3σ level, although its interpretation is muchharder due to the considerable IGM opacity-correction at z∼>5. Fig. 5ab plot thesefesc-valuesfrom Table 1, and from MC simulations of our ERS data through IGM transmission models (Fig.1b). Several authors (Inoue+ 2006; Kuhlen & Faucher-Giguere 2012; Finlator+ 2012; Becker &Bolton 2013; Dijkstra+ 2014) have suggested thatfesc may increase significantly with redshift,possibly as steeply as∝(1+z)3. The combined data in Fig. 5a suggest a trend in thefesc-valuesof galaxies with redshift that may not be a simple power-law in (1+z). The violet-shaded regionis bounded by:fesc ≃ (0.02 ± 0.01) × (1 + z)1.0±0.5, which assumesno dependence offesc onMAB. About 2/3 of the 21 independent data points in Fig. 5a deviates bymore than1σ from eitherone of the three power-laws, so thatno single (1+z)-regression fits all thefesc-data for galaxies.Therefore, we suggest thata more sudden increase offesc with redshiftmay instead have occurred:log(fesc) ≃ log(fesc,0) + F0 · tanh [(log((1 + z) − log(1 + z0))/Z0)].

Each of the four free parameters in this tanh-fit has a straightforward meaning. For galaxies,the steepest drop infesc occurs atz0 ≃2.9 — i.e., right around the peak in the cosmic star-formationhistory — over an interval less than±1 Gyr in cosmic time [i.e.,Z0≡∆log(1 + z)≃0.07]. Thepivot point for galaxies atz0 ≃2.9 occurs atfesc,0≃11%, andfesc may have dropped by a factorof ∼30 [i.e.,F0≡∆logf≃(log 30)/2] from∼60% at z≃5 to ∼2% at z≃0–1. For “Galaxies withweak AGN” these parameters are very poorly constrained, butif we assume that their UVC SEDsare still dominated by their stellar population [〈MAB〉≃–21.5±1 mag in Fig. 2b], and that thefesc-values of weak AGN dropped similarly fast over±1 Gyr in cosmic time — but aroundz0 ≃2.4during the peak in the QSO epoch — then theirfesc-values may have dropped fromfesc∼90% atz≃5 to fesc≃15% at z≃0–1, i.e., only by factor a of∼6 over most of cosmic time.Multiplyingby their numbers in Table 1, galaxies would then dominate thereionizing flux at z∼>3, whileAGN take over at z∼<3. ALCATRAZ will address this with ∼3.5× better statistics.

3

<~ <~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,

Fig. 3 [Top Row]: All galaxies in the spectroscopic Gold sample of S15 (see§D.2a); [Bottom Row]: All galaxies in their Gold+Silver sample

(images are 6.′′4×6.′′4); (a, g)F225W stacks at〈z〉=2.37;(b, h) F275W stacks at〈z〉=2.67;(c, i) F336W stacks at〈z〉=3.45;(d, j) F435W stacks at

〈z〉=5.1;(e, k) Weighted “stack-of-stacks” averaged overall four LyC filters, containing 51 Gold Galaxies, and 118 Gold + Silver Galaxies. These

best visualize the accumulated LyC signal of galaxies without AGN for z≃2.3–5.5; and(f, l) Same as (e, k), but after smoothing the “stack-of-

stacks” with a Gaussian kernel withσ=1 pixel. Blue and green circles have radii of 8 and 13 pixels (0.′′72 and 1.′′17), and yield S/N≃7–13 for the

“stack-of-stacks”. (Each individual panel is the effective sum of 11–118 fluctuations of 1.3–1.5σ each, on average!). The exceedingly faint LyC

emission from the average of 51 (118) galaxies in(f, l) has a rather flat distribution, perhaps vaguely resembling a “ring”. These LyC-stacks are

equivalent in depth to 22–236 HST orbits. ALCATRAZ will incr ease these samples∼3.5× with ∼2× the current stacking S/N.

The transition from galaxy–dominated to weak-AGN–dominated reionization may have occurredat z∼<2.5–3, i.e., after the peak in the cosmic SFR (Madau+ 1995), where the universe transitionedfrom infall- and SF-driven to more passively evolving galaxies. This may result in dust and gasrapidly accumulating in the central bulges and disks of forming galaxies, combined with a SN-ratethat has progressively less impact on removing gas from galaxies which are steadily growing inmass over time. This could cause thefesc-fraction torapidly drop over a relatively narrow intervalof cosmic time. When AGN-outflows started to ramp up after the peak in the cosmic SFH at z∼3(Hopkins+ 2006), their outflows may have cleared enough paths in the ISMof host galaxies toenhance the fraction of escaping LyC radiation, resulting in AGN starting to dominate reionizationat z∼<2.5–3.ALCATRAZ will confirm this with ∼3.5× better LyC statistics.

Goal 4. WHERE and WHY?: For which classes of objects does LyC escape?We will subdividethe new data in Table 1 into large enough sub-samples tostack escaping LyC flux vs. redshift, accu-mulated dust content (Fig. 4b), SED-age, SFR, or luminosity/mass. We will do the same for (weak)AGNselected from deep Chandra X-ray data (Xue+ 2011), E-VLA radio images (Miller+ 2013),variability, or emission-line spectra (e.g., Cohen+ 2006; Windhorst & Cohen 2010). The currentsamples are very small, and clearly need confirmation through much largerfesc-samples for bothgalaxies and weak AGN, both through analyzing wider HST fields and additional spectroscopy ofH-band selected objects with LBT, MMT, Magellan or VLT. Fig.4b shows that AV -values (Calzetti2000) of our LyC sample as a function of spectroscopic redshift are consistent with those in theentire ERS sample of 6900 galaxies to AB∼<27 mag with accurate 10-band photo-z’s and SEDs(W11). The median dust extinction of galaxies appears to increase with redshift, and our directfesc-error calculations will incorporate that. ALCATRAZ will estimate the gradual increasein extinction towards lower redshifts for all classes of objects, AV (z), when the stellar popu-lations have aged and produced more dust, and constrain how much of the strongly decliningfesc(z)-evolution is due to the increasing dust content at lowerredshift.

4

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

Surfa

ce 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)

1 2 3 4 5 6 7 8 92 10

0

1

2

3

Fig. 4a: Radial surface brightness (SB) profiles of the non-ionizing UVC signal (solid curves) and of the LyC signal (dashed curves) detected in

the stacks for the combined spectroscopic Gold sample of S15, color-coded according to their mean redshift. The horizontaldashed line indicates

the 1σ SB-limit for stacked LyC profiles. All four UVC SB-profiles areextended with respect to the PSFs (dotted purple and cyan curves). The LyC

SB-profiles (dashed) are also clearly extended,and flatterthan the UVC profiles (solid), as predicted by our scattering model (light-blue dot-dashed

curves for z≃2.68). Fig. 4b: Distribution of dust extinction AV -values from best-fit SEDs for all 6900 galaxies in the 10-band ERS data (W11;

small black dots), compared to the LyC samples used for the stacks in the four indicated redshift bins (colored open circles and asterisks for galaxies

and AGN, resp.).ALCATRAZ will address with 3.5 × better statistics how dust accumulating over cosmic time has shut downfesc(z).

Other work (see text)

Other work (see text)

Fig. 5a: Relativeescape fractions for various galaxy samples vs. redshift. Orange filled circles indicate WFC3+ACS ERS data for the spectroscopic

Gold galaxy, and grey filled circles for the Gold+Silver galaxy samples of S15. Orange triangles connected by thin lines indicate the modal–

median–averagefesc-values plus their±1σ-range for Gold galaxies, derived from MC simulations with the Inoue+ (2014) code. Blue triangles are

published data (§A), some of which have different sample selection. The violet-shaded region is bounded by:fesc≃(0.02±0.01)×(1+z)1.0±0.5.

The combined galaxy samples suggests a trend offesc with redshift, although it may not be a simple power-law in (1+z). Hence, we also plot a

simple tanh[log(1+z)] relation (green curve), which captures the possibly rather sudden change infesc with redshift around z∼>3 from fesc≃2%

at z≃0–1 tofesc∼>60% at z

∼>5, implying that galaxies may have had high enoughfesc-values, and so produced sufficient LyC flux, to complete

reionization byz≃6. Fig. 5b: Same as Fig. 5a, but for weak AGN in the S15 sample, plus one fromBridge+ (2010).fesc-values were calculated

under theassumptionthat the UVC-SED of weak AGN is dominated by star-light and notQSO light. For (weak) AGN,fesc-values may have

increased fromfesc≃15% at z≃0–1 tofesc≃90% at z∼>5 (purple curve). The object-weighted ratio of these tanh-curves suggests that galaxies

dominated reionization for z∼> 3, while AGN took over at z∼

< 3. ALCATRAZ is essential to confirm these results with∼3.5× better LyC

statistics in HST UV-fields and∼>2× the depth, plus spectra for

∼>100 new objects with 2.3

∼<zphot ∼

<5 to AB∼<24 mag.

5

Abbreviated References:Avila R+ ACS Handbook (STScI)Baggett S+ 2006 SPIE 6265 626532Balestra I+ 2010 A&A 512 A12Becker G. D+ 2013 MNRAS 436 1023Becker R. H+ 2001 AJ 122 2850Bertin Arnouts 1996 A&ApS 117 393Bielby R+ 2013 MNRAS 430 425Borthakur S+ 2014 Science 346 216Boutsia K+ 2011 ApJ 736 41Bouwens R+ 2012 ApJ 752 L5Bridge C+ 2010 ApJ 720 465Bruzual+ 2003 MN 344 1000Calzetti D+ 2000 ApJ 533 682Cen & Kimm 2015 ApJL 801 L25Coe D+ 2006 AJ 132 926Cohen S+ 2006 ApJ 639 731Cooke J+ 2014 MNRAS 837 51Cowie L. L+ 2009 ApJ 692 1476Cristiani S+ 2000 A&A 359 489Dahlen T+ 2013 ApJ 775 93Dijkstra, Kramer 2012 MN 424 1672Dijkstra M+ 2004 ApJ 613 646Dijkstra M+ 2014 MNRAS 440 3309Dressel L. WFC3 Handbook (STScI)

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Siana B+ 2010 ApJ 723 241Siana B+ 2015 arXiv:1502.06978Silverman J+ 2010 ApJS 191 124Smith B+ astro-ph/1504. (S15)Springel V+ 2005 ApJ 620 79Stark D+ 2010 Mnras 408 1628Steidel C+ 2001 ApJ 546 665Steidel C+ 2010 ApJ 717 289Sternberg A+ 2002 ApJS 143 419Szokoly G. P+ 2004 ApJS 155 271Teplitz H+ 2013 AJ 146 159Vanden Berk D. E+ 2001 AJ 122 549Vanzella E+ 2008 A&A 478 83Vanzella E+ 2010 MNRAS 404 1672Vanzella E+ 2012 ApJ 751 70Vanzella E+ 2015 arXiv:1502.04708Voyer E+ 2012 ApJ 736 80Windhorst R+ 1998 ApJ 494 L27Windhorst, Cohen 2010 AIP 1291 225Windhorst+ 2011 ApJS 193 27 (W11)Wolf C+ 2004 A&A 421 913Worseck G+ 2014MN 445 1745Wuyts S+ 2009 ApJ 706 885Xue S+ 2011 ApJS 195 10

Table 1. Summary of LyC Stacking thus far, and Proposed New UV-Samples to be AnalyzedFilter z-range 〈z〉 Nobj mLyC SNLyC mUV C SNUV C f1500/fLyC AV med < TIGM > frel

esc,700 frelesc(MC)

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)

ERS GALAXIES WITH AGN (SMITH+ 2015)+ 16 new AGN spectra:F225W 2.291–2.291 2.291 1+3 ∼

> 30.12 ∼< 2.34 27.90 7.85 3.44+0.13

−0.10 0.90+0.14−0.14 0.297+0.081

−0.083 ∼>100% —

F275W 2.470–3.008 2.697 7+5 28.92 8.77 25.00 156.9 2.98+0.08−0.07 1.23+1.14

−1.13 0.247+0.085−0.085 33+24

−22% —F336W 3.217–3.474 3.349 3+4 29.69 3.58 24.45 118.2 11.4+0.20

−0.14 0.10+0.14−0.10 0.112+0.049

−0.049 82+50−50% —

F435W 4.760–4.823 4.792 2+4 28.58 4.48 24.66 79.0 3.55+0.37−0.26 1.90+0.50

−0.50 0.0011+0.0012−0.0010 ∼100% —

ERS GOLD GALAXIES WITHOUT AGN (SMITH+ 2015):F225W 2.302–2.450 2.380 14 29.98 5.64 24.43 237.5 3.44+0.13

−0.10 0.55+0.70−0.44 0.297+0.081

−0.083 7.0+5.3−5.3% 0.76+15

−0.4%F275W 2.559–3.076 2.682 11 30.09 5.71 24.51 192.2 2.98+0.08

−0.07 0.58+0.89−0.40 0.247+0.085

−0.085 7.1+6.0−6.0% 3.22+35

−1.1%F336W 3.132–3.917 3.472 11 30.66 4.48 24.88 101.9 11.4+0.20

−0.14 0.18+0.64−0.12 0.112+0.049

−0.049 50+31−31% 34+63

−16%F435W 4.414–5.786 5.015 15 30.37 3.28 26.12 70.3 3.55+0.37

−0.26 0.17+0.67−0.12 0.0011+0.0012

−0.0010 ∼100% ∼100%ERS GOLD + SILVER GALAXIES WITHOUT AGN (SMITH+ 2015)+ 100 new Galaxy spectra:F225W 2.262–2.450 2.362 31+30 29.79 9.46 24.56 303.6 3.74+0.12

−0.10 0.55+0.70−0.44 0.306+0.055

−0.055 9.9+7.0−7.0% 1.76+15

−0.7%F275W 2.481–3.076 2.692 26+25 29.46 11.9 24.76 229.6 3.25+0.06

−0.06 0.58+0.89−0.40 0.249+0.052

−0.054 17+9.7−11 % 6.2+27

−2.1%F336W 3.110–4.149 3.524 24+25 29.96 6.85 24.73 164.9 4.33+0.34

−0.30 0.18+0.64−0.12 0.089+0.027

−0.027 39+18−21% 6.5+25

−3.1%F435W 4.414–6.277 5.312 37+20 30.35 5.79 26.72 92.7 2.97+0.13

−0.15 0.17+0.67−0.12 0.0002+0.0015

−0.0015 ∼100% 87+113−55 %

PROPOSED HUDF-UV Galaxies + weak AGN for analysis, including newspectra (estimated):F225W 2.26–2.47 2.37 12+3 ∼29.8 ∼

> 9 ∼24.5 ∼> 1100 3.74+0.12

−0.10 0.5+0.7−0.4 0.306+0.055

−0.055 10+7−7%? 10+15

−0.7%?F275W 2.47–3.08 2.68 15+3 ∼29.5 ∼

> 12 ∼24.6 ∼> 900 3.25+0.06

−0.06 0.6+0.9−0.4 0.249+0.052

−0.054 20+10−11%? 20+27

−2 %?F336W 3.08–4.35 3.52 20+5 ∼30.0 ∼

> 9 ∼24.7 ∼> 1250 4.33+0.34

−0.34 0.2+0.6−0.1 0.089+0.027

−0.027 40+20−20%? 40+25

−3 %?F435W 4.35–6 5.2 20+5 ∼30.0 ∼

> 20 ∼26.0 ∼> 620 2.97+0.13

−0.13 0.2+0.7−0.1 0.0005+0.0010

−0.0010 80+20−40%? ∼

> 80%?PROPOSED GOODS-N+S–UV Galaxies + weak AGN for analysis, including new spectra (estimated):F275W 2.47–3.08 2.68 75+7 ∼29.5 ∼

> 20 ∼24.6 ∼> 360 3.25+0.06

−0.06 0.6+0.9−0.4 0.249+0.052

−0.054 20+5−5%? 20+14

−1 %?F336W 3.08–4.35 3.52 75+7 ∼30.0 ∼

> 12 ∼24.7 ∼> 290 4.33+0.34

−0.34 0.2+0.6−0.1 0.089+0.027

−0.027 40+10−10%? 40+13

−1.5%?F435W 4.35–6 5.2 90+6 ∼30.0 ∼

> 9 ∼26.0 ∼> 145 2.97+0.13

−0.13 0.2+0.7−0.1 0.0005+0.0010

−0.0010 80+20−20%? ∼

> 80%?TOTAL New objects: 2.3–5 ∼460

Table columns:(1) WFC3 or ACS filter; (2) Redshift range used in LyC/UVC stacks; Each lower redshift bound samplesno light atλ>912A below the filter’s red edge(defined at 0.5% of the filter’s peak transmission; see S15). (3) Average redshift of stack; (4) Number of galaxies with reliable spectroscopic redshifts used in stack; (5)Observed total AB magnitude in LyC stack (using SEXTRACTORMAG AUTO); (6) S/N ratio of LyC stack; (7) Observed total AB magnitude in UVC stack; (8) S/Nratio of UVC stack; (9) Averageintrinsic model flux ratiof1500/fLyC and its±1σ error; (10) Median dust extinction AV and its±1σ error from the 10-band SEDBC03-model fits; (11) Average IGM transmission〈TIGM〉 and its±1σ range, derived from the Inoue+ (2014) models for the sample of actual redshifts; (12) Inferredrelative escape fraction of LyC photons in percent and its±1σ range, assuming a constantintrinsic LyC flux density overλ=700–900A. (13) Modal relativefesc-valuesderived from our Monte Carlo test of the IGM transmission using the code of Inoue+ (2014) plus their±1σ ranges, usingfabs

esc ≡ fLyC,obs/fLyC,⋆. These ERSUV-stacks are equivalent in depth to 22–236 HST orbits.ALCATRAZ will increase these samples∼3.5× with ∼2× the current stacking depth. All the proposednumbers of new objects are indicated in violet.For the HUDF and GOODS-UV, the corresponding numbers in blackare the expected resulting values from ALCATRAZ.

=========================================================================================================Table 2: -----GOODS-N+S Fields Data----- ---------HUDF Data---------- ----------ERS Data---------------Instrum Nfilt*NexpxNfld Nexp Norb Nfilt*Nepoch*Nexp Nexp Norb Nfilt*NexpxNfld=Nexp Norb Nexptot---------------------------------------------------------------------------------------------------------WFC3 UVIS: 2*(6x8+6x8)+(9x5+8x5)= 277 181 3*2*(2x15) = 180 090 4x8+4x8+3x8 = 88 40 545ACS/WFC: (6+10+10+20)*(3x3x2) = 828 234 164+286+460+362+700=1972 494 (6+10+10+20)x6 =276 78 3076WFC3 IR: 3*4*(2x5)x(2x2) = 480 240 248+289+122+366 =1025 254 3*4*(2x5) =120 60 1625Grand Tot 1585 655 3177 838 484 178 5246---------------------------------------------------------------------------------------------------------

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D. Analysis Plan

(0) Building/Reducing Database: Table 2 shows a total of 2170 WFC3 images and 3076 ACSimages. We already have the full ERS data set. At∼128–164 Mb per image, there are∼>280 Gbof WFC3 and 400 Gb of ACS data, a total of 680 Gb. To resolve remaining astrometric and subtlebias level (DC) and flat-field systematics (see below), we may also need to retrieve the individualdata frames. A student will retrieve these from MAST at the rate of 50-100 Gb a day, which willtake 1–2 weeks. The student may re-drizzle the 90 orbit HUDF UV and the GOODS UV data, ifneeded. All raw data are public, as are the v1 HUDF mosaics as of Apr. 2014.

(1) Assess UVIS mosaic quality:We will make a rigorous assessment of the GOODS and HUDFUV images that goes well beyond the normal use of these data toAB≃26–29 mag for point sourcedetection. Our ERS study thus far (S15) has shown some very low-level systematics in the WFC3UVIS image stacks that we must address first. These are:

(1a) Remaining astrometric offsets:The 2009 calibration of the WFC3 ERS mosaics had as-trometric offsets∼>5 pixels (W11), which have been addressed with new geometrical distortioncorrections (GDCs; Kozhurina-Platais 2013) to within〈∆(X,Y )〉∼<0.′′017±.′′05 (0.19±0.56 pix).For accurate UV-stacking of all data in Table 2, we must remove these across all mosaicsat thesub-pixel level, by cross-correlating the UVIS images with the deepestχ2-images.(1b) CTE effects and their correction: The 2 orbit WFC3 ERS images (W11) taken in Sept.2009 do not suffer significantly from Charge Transfer Efficiency (CTE) losses compared to the2012 HUDF (2×15 orbits per UV-filter) or GOODS-UV (2–9 orbits per UV-filter) data. The latterwere post-flashed with∼6–12e− to fill in CCD-traps that accumulated over time. Following S15,we will verify that LyC fluxes are not affected by CTE-degradation by sub-dividing all images inone-half closer to the A/D converters (i.e., suffered less CTE-degradation), and one-half furtheraway. The LyC photometry between the two data-halves differs by∼<1.4σ for the ERS (S15).

(1c) Subtle DC or Dark-Current Offsets, Residual Sky-Gradients, and Sky-Subtraction Er-rors: Some subtle DC offsets are seen in the 22–236 orbit LyC stacksin the ERS in Fig. 3. Thesemay be due to subtle variations in the dark-current between exposures, residual flat-field errors,or the way sky-subtraction was done in each image during drizzling. The original WFC3/UVISthermal vacuum flat-fields (Sabbi 2009) left residual gradients of 5–10% on top of Zodi sky (whichitself is AB∼25.5 mag arcsec−2 ; W11). This has significantly improved with on-orbit “delta-flats”(Mack+ 2013), reducing residual gradients in the sky to∼3% of Zodi (S15). Such dim gradientsare very hard to remove, but they appear to be linear across the entire CCD. Following S15, subtleDC offsets and these residual flat-field gradients amount to alocal sky-subtraction errorof ∼32.3mag arcsec−2 across our 6.′′39×6.′′39 LyC boxes (Fig. 3). We will map any low-level residualgradients across all images in Table 2 as a 2D-surface, and subtract them from the individual im-ages after super-darkframe subtraction, and if needed again after flat-fielding and before drizzling.This may require an additional step where all cosmic-rays (CRs) and objects are first identified andmasked-out in each image to stabilize the 2D surface-fits.(1d) Red-Leak and Filter-Pinhole Corrections:Fig. 1a and S15 predict the LyC red-leak fractionfor LBGs at z≃2–6 relative to their UVC flux as 0.0030%–0.0001%, in line with the red-leak wingsof these four filters. Redleak fractions are thus very small compared to our relativefesc-values.

(2) Panchromatic SED fitting: We will use panchromatic SED-fitting (Coe+ 2006; Dahlen+

2013) to estimate the following galaxy properties: zphot, total flux, & luminosity, stellar mass,

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stellar population age, star-formation rate (SFR), and extinction (AV , e.g., Windhorst+ 2010).(2a) Spectroscopic Redshifts, Sample Selection, Reliability & Completeness: Spectroscopicredshifts (zspec) will be used wherever available, resulting in smaller but more reliable samples.To detect a 4% escape fraction at 4σ, the interloper fraction must be∼<1%. We will inspect allavailable spectra, and assign a fidelity grade to each redshift, ranging from 1 (Gold or “highlyreliable”), 1 (Silver or “likely reliable”) to 2 (“indeterminable”). We will obtain new spectra toAB∼<24.5 mag for∼>100 objects with 2.3∼<photo-z∼<5.5 using LBT, MMT, Magellan and VLT.(2b) Photometric Redshifts and Removal of Interlopers:To get larger and deeper samples, wewill use the 8-12 filter P(zphot) distribution to maximize the probability that each photo-z objectbelongs to the LyC candidate to be stacked. The galaxy countsshow∼<5.2×105 galaxiesdeg2 toJAB∼<27.5 mag (W11), so the fraction of contaminating objects in r≃0.′′99 LyC apertures is∼<12%.All such contaminating neighbors visible in the deepest 8–12-filter χ2-stacks will be masked outin the LyC apertures and surrounding sky using SEXTRACTOR “segmentation” maps (see Fig. 3).This worked well for UVC stacking of HUDF objects at z≃4–6 (Hathi+ 2008).(3) LyC Stacks and Quality Checks:We will perform various quality checks (see S15), verifyingthat the LyC flux remains present (within the errors in Table 1) when the images are rotated byrandom multiples of 90, or when the first and second independent data-halves are stacked. Wewill also verify that no spurious fluxis seen when stacking an equal number ofrandom emptysky-boxeswithout known objects, verifying the point-source and SB-sensitivity limits in Table 1.(4a) Theoretical Modeling — Scattering Models:Dijkstra will predict LyC SB-profiles for a gridof wind model parameters, and investigate what constraintscan be placed from either detectionsand/or upper limits. He will perform full MC simulations of asub-set of models to account formultiple scattering events, and to test the accuracy of analytic models.(4b) Theoretical Modeling — Improved Constraints on IGM Tran smission Models:Inoue willinvestigate if significant z≃4.35–5 LyC detections require updates of IGM transmission models,which predicts very lowTIGM values (Table 1). The Inoue+ (2014) model is based on the redshift(dn/dz) and column density distributions from LAF, LLS, andDLAs, and best reproduces Lymanlimit mean-free-path (MFP) measurements at z∼<5 by Worseck+ (2014), which averages over∼50QSO-sightlines, but leaving room for a∼0.3 dex systematic between estimation methods. We willuse our z∼>3.5 LyC detections to constrain IGM transmission models (Fig, 1b; Col. 11 of Table 1).

Management PlanWe have the following personnel: Grad Student Assistant (GS; Mr. Brent Smith); Windhorst(RAW); Cohen (SHC); Jansen (RAJ); Koekemoer (AMK); MacKenty (JM); Dijkstra (MD); Inoue(AI); Bielby (RB), Conselice (CC). Steps (0)–(5) require as FTEs: (0) Database+Reduction:3.0mo GS + 0.5 mo AMK +0.5 mo JM;(1) UVIS CTE/gradient-removal/quality: 3.0 mo GS +1.0 mo RAJ/SHC/RAW; (2) SED fitting and photo-z’s: 1.0 mo GS + 0.5 mo SHC;(2a) Newspectra and redshifts:2.0 mo GS + 1.0 mo RB+CC;(2b) Contamination correction: 1.0 moGS + 0.25 mo RAW;(3) LyC stacking + checks:2.0 mo GS + 1 mo RAJ + 0.25 mo RAW;(4) Theoretical modeling:2.0 mo MD & AI (funded by Norway & Japan);(5) Team papers (1Method, 1 Results, 1 Theory):3.0 mo GS + 1 mo RAW, helped by co-I’s. In summary: we need15 mo GS. RAW, RAJ and SHC will spend 1–2 months each of their academic or research time.

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Past HST Usage

Note that the description of past HST usage DOES NOT count against the 9-page limits.

GO-12500, Cycle 19: PI: S. Kaviraj (Oxford): “ High-res WFC3 UV studies of SAURON galax-ies ” — WFC3 observations started in Fall 2011, data fully 6 papers published. Project took 10%of Windhorst’s time, and finished in fall 2014.

GO-12974, Cycle 20: PI: M. Mechtley (ASU):“WFC3 IR Imaging of z=6 QSO Host Galaxies”— Cycle 20 observations continuing through summer 2013. Datareduced and analyzed. Led toDr. M. Mechtley’s PhD Dissertation; ASU; Jan. 2014, see ASU link below). One paper publishedin ApJL, 2 more papers submitted in Spring 2015. Program took20% of Windhorst’s time, andwill finish in Spring 2015.

AR-13241, Cycle 21: PI: Cohen (ASU):“Pixel-by-pixel Resolved Stellar Populations” — Archivalpixel-by-pixel analysis of of resolved stellar populations in nearby galaxies compared with inter-mediate redshift galaxies (z∼<1.5). Analysis underway, program takes∼<10% of Windhorst’s time,and will finish in summer 2015, including two papers currently in preparation.

AR-13877, Cycle 22 PI: Windhorst (ASU):“Project ALCATRAZ: Archival Lyman-Continuumand Theoretical Reionization Analysis vs. z: Where, When, How& How Much does LyC Es-cape?” — Archival analysis of all F225W, F275, and F336W images in the 8 WFC3 tiles of theEarly Release Science (ERS) survey, as well as in the 15 ACS tiles in F435W in GOODS-S forthe purpose of reliably identifying the escaping LyC radiation at z≃2.3–5. All analysis completed,some reported here in this proposal, and reported in detail in first Dissertation paper by ASU grad-uate student Brent Smith+, submitted to ApJS and astro-ph. Program takes∼<30% of Windhorst’stime, and will finish in summer 2015, including one more paperin preparation.The currently pro-posed sequel project ALCATRAZ-2 will vastly expand on this, and improve the current statistics by3.5×.

GO-13779, Cycle 22 PI: Malhotra (ASU):“Faint Infrared Grism Survey (FIGS)” — WFC3 G102grism spectra were started in Fall 2014, and program will continue through 2015. Analysis inprogress by entire FIGS team, and first papers expected to be submitted later spring 2015. Projecttakes∼<10% of Windhorst’s time.

Dissertations by ASU students using HST data are on:

http://www.asu.edu/clas/hst/www/ASUdissertations/

PI Publications based on Past HST Observations (over 140 since 1991) are on:

http://adsabs.harvard.edu/abstract_service.html

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