Table Of ContentMon.Not.R.Astron.Soc.000,000–000 (0000) Printed27January2012 (MNLATEXstylefilev2.2)
Infra-red emission line tomography of the intergalactic
medium during the Epoch of Reionization
Koki Kakiichi, Avery Meiksin, Eric Tittley
2
1 SUPA⋆, Institute forAstronomy, Universityof Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
0
2
27January2012
n
a
J
ABSTRACT
6
The first majorstar-forminggalaxiesand Active Galactic Nuclei will produce Balmer
2
and higher order extended haloes during the Epoch of Reionization throughthe scat-
] tering of Lyman resonance line photons off the surrounding neutral intergalactic gas.
O Theopticaldepthdependenceofthescatteringrateswillproduceasignalsensitiveto
C both the density and velocity fluctuations of the gas, offering the possibility of prob-
ing the ionization region and flow field surrounding young star-forming galaxies. The
.
h requirements for detecting the haloes in the infra-red using a space-based telescope
p
arediscussed,alongwithanassessmentofthepossibilityofdetectingthehaloesusing
-
o the Tunable Filter Imager on the James Webb Space Telescope.
r
t Key words: atomic processess – cosmology: theory – line: formation – radiative
s
transfer – infrared: general – scattering
a
[
1
v
9 1 INTRODUCTION Higherenergyphotonsemittedbythecontinuumofthe
9 sourceswillscatteraswellastheyredshiftintolocalLyman
The breaking of the redshift z =7 barrier in the campaign
4 resonancefrequencies.Radiativecascadesfollowingthescat-
5 todiscover high redshift galaxies is closing in on theEpoch teringofhighorderLymanseriesphotonswillproduceradi-
. of Reionization (EoR), when sufficient stars, with a possi-
1 ationfromhigherorderhydrogensequencesliketheBalmer
blecontributionfromActiveGalacticNuclei(AGN),formed
0 andPaschenseries(Meiksin2010).Thehaloeswillbehighly
to reionize the hydrogen produced in the Big Bang follow-
2 extendedbecause ofthedistances overwhich higherenergy
ing the Recombination Era. In addition to the handful of
1 photons may travel before scattering. The Hα signal from
: sources with spectroscopically confirmed redshifts z > 7 within the inner 1 arcminute of the halo could, as for the
v
(Vanzella et al.2011;Onoet al.2012;Schenkeret al.2012),
i Lyα signal, be detected by an infra-red detector in space.
X severalplausiblecandidateshavebeenidentifiedwithhigher
The Balmer haloes, however, have the advantages over the
photometricredshifts extendinguptoz ∼< 9(McLure et al.
r Lyα haloes of being both more extended and comprised of
a 2011),andpossiblyashighasz ≃10(Bouwens et al.2011).
multiple orders. Combining the images for the different re-
MeasurementsoftheCosmicMicrowaveBackground(CMB)
solvableorderscouldsubstantially reducetherequiredinte-
by the Wilkinson Microwave Anisotropy Probe (WMAP)
gration times for a given source.
confine the EoR, if a sudden event, to z =10.4±1.2 (1σ)
r Since the identical structures would give rise to
(Larson et al. 2011). Thusthe highest redshift galaxies dis-
a 21cm signature around a source (Madau et al. 1997;
covered may havealready entered theEoR.
Pritchard & Loeb 2011), correlating the images with ra-
In addition to ionizing the IGM, high redshift galaxies
diodetections using an instrumentlike theLOw Frequency
willilluminatestillneutralintergalactichydrogenbeforethe
ARray (LOFAR)1 or the Square-Kilometre Array (SKA)2
EoR has ended. The Lyα radiation escaping high redshift
would further enhance the detections and probe the struc-
sourceswill scatterinthevicinityofthesources,producing
ture of the underlying IGM as well as the ionization geom-
Lyα haloes with a characteristic core radius of 70 kpc at
etry produced by thesource (Tozzi et al. 2000).
z = 10 (Loeb & Rybicki 1999). These haloes would be ob-
The purpose of this paper is to compute the expected
servable in the nearinfra-red, with characteristic diameters
Balmer signals allowing for thestructureof theIGM. Since
of 30 arcsecs. The sources will be overwhelmed by zodiacal
the scattering rate depends on the optical depth from the
light,butadedicatedspace-basedfacilitywithnarrowband
source to Lyman resonance line photons, the signal will
imaging could plausibly detect a halo surrounding a very
bright source.
1 www.lofar.org
⋆ ScottishUniversitiesPhysicsAlliance 2 www.skatelescope.org
(cid:13)c 0000RAS
2 K. Kakiichi, A. Meiksin, E. Tittley
depend on the density, temperature and peculiar velocity lution of the IGM will be negligible before the photon is
structure of the IGM. The influence of inhomogeneities in destroyed.
thesequantitiesiscomputedusingacosmological numerical Includingphotonsproducedincascadesfromhigheror-
simulation. ders, thenet scattering rate of Lynphotons is
The paper is structured as follows: the next section
1 nmax
smuomdmela.rAisepsrtehseenmtaetciohnanoifsmthoefrtehseuletffinegctimanadgetshfeolsliomwusl.atTiohne Pn = 1−pn,n "Pn(1)+nX′>npn′,nPn′#, (3)
observationalrequirementsfordetectingthesignalarethen
foramaximumordern ofdirectly scatteredLymanres-
discussed, followed by ourconclusions. onancelinephotons,whmearxeP(1) isthedirectscatteringrate
n
P(1) =Pinc(0)S , (4)
n n n
2 THE PRODUCTION OF BALMER HALOES with Pninc(0) = σnLνn(4πrL2hνn) the scattering rate at the
luminosity distance r from a source of specific luminos-
L
2.1 The Lyn scattering rate ity L assuming no intergalactic attenuation
νn(1+zs)/(1+z)
(Meiksin 2010). Here, S accounts for the intergalactic at-
ThelocalLynradiationfieldwithinagasparcelarisesfrom n
two contributions, the direct UV photons emitted from the tenuation and pn′,n is the probability that a Lyn′ photon
convertsto a Lynphoton perscatter.
central radiating source redshifted to the local Lyn reso-
The scattering rate may be expressed more succinctly
nancefrequency by thecosmological expansion and anyra-
in terms of thedirect scattering rates as
dial peculiar velocity v of the gas, and the photons pro-
r
ducedinradiativecascadesfollowingthescatteringofhigher 1 nmax
orderLyman series photons. Theeffect of redshifting limits Pn = 1−p Cn′,nPn(′1), (5)
the distance freely streaming photons from a source may n,n nX′=n
travel before scattering. From the perspective of a gas par- where the scattering cascade matrix Cn′,n has been defined
cel at redshift z, only sources within theLyman horizon according to
v 1−(n+1)−2 n′
1+znhorizon =(1+z) 1− cr 1−n−2 . (1) Cn′,n = Cn′,n′′ηn′′,n, (6)
are able to excite a h(cid:16)ydrogen(cid:17)atom into an electronic state nX′′>n
with principal quantum numbern (Barkana & Loeb 2005). with Cn,n = 1, Cn′,n = 0 for n >n′ and ηn′,n = pn′,n/(1−
Higher energy photons will have passed through a higher pn′,n′).
The suppression factor S is given by
order Lyman resonance. As a result, the maximim possible n
distance of sources able to produce a direct scatter of Lyn ∞
S = dνϕ (a ,ν−ν )e−τn(ν,z;zs), (7)
photonsdecreases with increasing n. n νn n n
Z0
Higher order Lyman photons will scatter within the
whereϕ (a ,ν−ν )=(∆ν )−1φ(x)istheVoigt profile
Doppler core3. The mean free path of Lyn photon within νn n n D,n
with x = (ν −ν )/∆ν and a is the ratio between the
theDoppler core is n D,n n
damping width and Doppler width for Lyn photons. The
π1/2∆ν optical depth is given by
λmfp(z) = D,n (2)
n nH(z)σn τ (ν,z;z ) = σ zsdz′ dl n (z′) (8)
≃ 0.101(1+z)−3T1/2n(n2−1)pc n s n dz′ H
Zz
1−v′/c1+z′
where nH(z) is the hydrogen number density, ∆νD,n = ×ϕνn an(T′),ν1−vr/c 1+z .
νnb/c is the Doppler width with Doppler parameter (cid:20) r (cid:21)
b = (2kT/m )1/2 for gas temperature T, and σ =
H n
(πe2/mec)f1nforoscillatorstrengthf1n(Meiksin2009).The 2.2 The halo emissivities
approximation f ≃ 1.56n−3 was used, accurate to bet-
1n
The emissivities depend on the populations n of the ex-
ter than 10 per cent. for n > 4. The mean free path is n,l
much smaller than the Jeans length λ =c (π/Gρ )1/2 ≃ cited states, where the subscripts indicate the principal
J s M
16(1+z)−3/2T1/2 kpcforasoundspeedc andcosmicmass quantum number and orbital angular momentum, respec-
s
tively,ofagivenfine-structurestateofan excitedhydrogen
density ρ over which the physical properties of the IGM
M
atom. The equations governing the populations are, for the
will benearlyuniform. Theredistribution ofphoton energy
ground state n ,
from scatters may thus be considered to occur locally, con- 1
finedwithinahomogeneousmedium.Ahigherorderphoton dn nmax nmax
willscatteronlyafewtimesbeforedecayingintoaloweror- dt1 = nn,1An1,10−n1 Pn, (9)
der photon, with a survival probability of ∼0.8 per scatter nX=2 nX=2
(Hirata 2006; Pritchard & Furlanetto 2006), so that the ef- and for excited states,
fectsofspatialandfrequencydiffusion,redshiftingandevo- dn nmax
dnt,l = n1Pnδl,1+ nn′,l′An′l′,nl (10)
n′X=n+1l′X=l±1
3 At z = 8, for an IGM temperature T > 10 K (100 K), Lyδ n−1
(Lyγ)andhigherorderLymanresonancelinephotons scatter in −nn,l Anl,n′l′,
theDopplercore(Meiksin2010). nX′=1l′X=l±1
(cid:13)c 0000RAS,MNRAS000,000–000
Infra-redemissionline tomographyofthe intergalactic mediumduringthe Epoch ofReionization 3
where δl,l′ = 1 for l = l′ and vanishes otherwise. Here,
Anl,n′l′ isthespontaneousdecayratefrom leveln,ltolevel
n′,l′.
The level populations will establish their steady-state
values on the timescales P−1. The system of steady-state
n
equations is solved by
nn,l =nnX′m=enxn1Pn′ nn−′=11 Cln′=′1l,±nl1Anl,n′l′, (11)
whereCn′l′,nl isthPecascaPdematrixexpressingtheprobabil-
itythat anupperstaten′,l′ cascades downtoalower state
n,l via all possible transition routes. It is given by
′
n
Cn′1,nl = Cn′1,n′′l′′αn′′l′′,nl, (12)
n′′X=n+1l′′X=l±1
with Cnl′,nl = δl,l′, where αn′l′,nl =
′
An′l′,nl/ nn′′−=11 l′′=l′±1An′l′,n′′l′′ is the branching
ratio from leveln′l′ tolevelnl (cf. Osterbrock (1989)).The
P P
transition rates An′l′,nl are computed as in Meiksin (2010).
Theresultingemissivityduetoalltransitionsfromnto Figure1.(Clockwisefromthetopleft)Thetemperature,tangen-
n′ with mean frequency νnn′ is tial(singlecomponent) peculiarvelocity, radialpeculiarvelocity
anddensityfieldsofIGMaroundaradiatingsourceattheorigin.
ǫnn′ = hν4nπn′ nn,lAnl,n′l′ (13) (Distanceunitsareproper.)
Xl l′X=l±1
= hν4nπn′n1 βnlαnl,n′l′,
Xl l′X=l±1
whereβnl = nnm′=anxPn′Cn′1,nl.Theobservedspecificinten- Ωuumm=en0e.2rg3y6,aΩndv =ba0ry.7o6n4icamndatΩtebr=de0n.0si4t1yfpoarrtahmeemteartst,ear,Hvuabc--
sity is then
P ble constant H0 =100hkm s−1 Mpc−1 with h=0.73, and
jν ≃ ∞dzddlzp (1+z)−3ǫnn′(lp) (14) tthoeσini=tial0.B7B4,KgSenpeorwalelryscpoencstirsutmentwiwthithnC=M0.B95flnuocrtmuaatliiosends
Z0 8
×ϕνnn′ ν 1+ vck (1+z)−νnn′ , a(Lsamrseoansuertedal.by20t1h1e)W. TilhkeinssiomnuMlaitcioronwwavaesArunnisointroapyvoPlurombee
foremissionalonhgt(cid:16)heline-o(cid:17)f-sightpathl wiithline-of-sight 10h−1Mpc on a side with 2563 cells and 5123 dark matter
p
velocity v . particles. The volume was evolved from an initial redshift
k
of z = 530 to z = 10. The initial mean temperature is set
i
2
to 550K 1+zi ≃ 3800K, and evolves to T ≃ 2K by
1+200
3 INFRA-RED EMISSION TOMOGRAPHY z = 10. R(cid:16)adiativ(cid:17)e cooling permits collapse of gas in halos,
but thereis no feedback from star formation.
The optical depth is sensitive to the density, temperature A source was assigned to the highest gas density peak
and peculiar velocity fields. As a consequence, fluctuations within the simulation volume at z =10, as recorded on the
in these quantities between the source and a given gas par- gasgridwithcellsofsize10/256Mpc h−1 ≃40kpch−1 per
cel will produce fluctuations in the scattering rate through sidecomoving.Thecorrespondingdensity,temperatureand
Eqs. (4) and (5). These in turn will produce fluctuationsin peculiar velocity fields in a quadrant around the source are
theemissivityoftheresultingcascaderadiation,openingup shown for a slice in Fig. 1, with representative line-of-sight
the opportunity to measure the density, temperature and valuesshown in Fig. 2.
peculiarvelocityfieldsonsmallscalessurroundingasource. The source is modelled as a starburst galaxy with a
specific intensity approximated as flat at the relevant fre-
quencies, so that the source intensity a luminosity distance
3.1 Numerical simulation r away is
L
Inorder toestimate themagnitude of theeffect of thefluc- L
tuations on the received intensity, we use a numerical cos- Sν = (4π)ν2Lr2 (15)
mological ΛCDM simulation of the IGM to compute the L
signalpredictedfromthesurroundingsofasourceplacedin where L is the luminosity at the Lyman edge frequency
νL
the simulation volume. The simulation was run using ver- ν .Acontinuousstarformationrate10M yr−1 isassumed,
L ⊙
sion 1.0.1 of enzo4 with the cosmological parameter values with a Salpeter initial mass function for the range 1 <
M < 100M and a metallicity Z = 0.05Z , corresponding
⊙ ⊙
to L = 3.8×1021Js−1Hz−1 after 107yr (Leitherer et al.
νL
4 Availablefromhttp://lca.ucsd.edu. 1999).
(cid:13)c 0000RAS,MNRAS000,000–000
4 K. Kakiichi, A. Meiksin, E. Tittley
-1-3-1εmissivity [Jsmsr]n2 1111100000-----3333354321 Hα homogenous eδxρp,a δδδnρTρdδ iaaanρnnng dodd gn δδδalTyvvs Hβ homogenous eδxρp,a δδδnρTρdδ iaaanρnnng dodd gn δδδalTyvvs
E
10-36
-1-3-1εmissivity [Jsmsr]n2 1111100000-----3333354321 Hγ homogenous eδxρp,a δδδnρTρdδ iaaanρnnng dodd gn δδδalTyvvs Hδ homogenous eδxρp,a δδδnρTρdδ iaaanρnnng dodd gn δδδalTyvvs
E
10-36
0 0.1 0.2 0.3 0.4 0.5 0.6 0 0.1 0.2 0.3 0.4 0.5 0.6
Figure 2. (Clockwise from the top left) Representative line-of- r [Mpc] r [Mpc]
sightvariationsinthetemperature,peculiarvelocity,totalveloc-
Figure4.TherelativedifferencebetweentheHnemissivityalong
ity(includingHubbleflow)anddensityofIGMaroundaradiating
therayinFig.2andthecorrespondingrateassumingahomoge-
source atthe origin.The dotted lines arethe corresponding val-
neousexpandingmedium.
ues for a homogeneous expanding medium. (Distance units are
proper.)
0.8 homogenous expanding gas homogenous expanding gas
0.6 Hα δρδ aρn do nδlTy Hβ δρδ aρn do nδlTy
1.5 0.4 δρ, δδTρ aanndd δδvv δρ, δδTρ aanndd δδvv
0 .15 Lyβ Lyγ δεn2 0 .02
-0.2
δPn 0 -0.4
-0.5 homogenous expanding gas homogenous expanding gas -0.6
δρ only δρ only
-1-.15 δρ, δδδρTρ aaannnddd δδδTvv δρ, δδδρTρ aaannnddd δδδTvv 00..68 Hγ homogenous expaδnρdδ ianρng do gnδalTys Hδ homogenous expaδnρdδ ianρng do gnδalTys
1.5 0.4 δρ, δδTρ aanndd δδvv δρ, δδTρ aanndd δδvv
0 .15 Lyδ Lyε δεn2 0 .02
-0.2
δPn 0 -0.4
-0.5 homogenous expanding gas homogenous expanding gas -0.6
δρ only δρ only
-1 δδρρ aanndd δδTv δδρρ aanndd δδTv 0 0.1 0.2 0.3 0.4 0.5 0.6 0 0.1 0.2 0.3 0.4 0.5 0.6
-1.5 δρ, δT and δv δρ, δT and δv r [Mpc] r [Mpc]
0 0.1 0.2 0.3 0.4 0.5 0.6 0 0.1 0.2 0.3 0.4 0.5 0.6 Figure 5.HnemissivityalongtherayinFig.2.
r [Mpc] r [Mpc]
Figure 3. The relative difference between the Lyn scattering
ratealongtherayinFig.2andthecorrespondingrateassuming
ahomogeneous expanding medium. beseenbycomparingthefluctuationsinthescatteringrate
in Fig. 3 with the slope in the total velocity shown in the
lower right panel of Fig. 2.
The Balmer emissivity profiles for Hα through Hδ are
3.2 Emission line haloes
showninFig.4fortherayshowninFig.2.Thefluctuations
TheresultingscatteringratesofLynphotonsdiffersubstan- follow those in the Lyn scattering rates, but are somewhat
tially from those for a homogeneous expanding medium, as suppressed in magnitude, as shown in Fig. 5. This is be-
shown in Fig. 3. Thecontributions duetothedensity,tem- cause, while the emissivity is proportional to the local gas
peratureand velocity departuresfrom themean are broken density,sothatfluctuationsintheemissivityincludealinear
down in the figure. While the differences are primarily due dependence on the density fluctuations, the scattering rate
to the density fluctuations, fluctuations in the temperature fluctuates oppositely to the density fluctuations because of
andexpansionvelocitycontributenon-negligibly.Inparticu- the effect of the optical depth variations. The sum of the
lar,thescatteringratebecomesincreasinglysensitivetothe contributionstotherelativefluctuationsintheemissivityis
peculiar velocity field towards the higher orders, for which thus reduced compared with the magnitude of the relative
scattering in the Doppler core dominates increasingly over density fluctuations.
Lorentzwingscattering.Astheopticaldepthincreaseswith The derivation of the surface brightness is computa-
decreasing total velocity gradient, regions with a peculiar tionally intensive, as the cascade equations must be solved
velocity gradient dv/dr<0tendtohavea suppressedscat- separately within each simulation cell. For this reason the
teringratecomparedwithregionswithdv/dr>0.Thismay computation is restricted to a plane perpendicular to the
(cid:13)c 0000RAS,MNRAS000,000–000
Infra-redemissionline tomographyofthe intergalactic mediumduringthe Epoch ofReionization 5
Figure 6. Differential Balmer surface brightness fluctuations Figure 8. Differential Balmer surface brightness fluctuations
compared with the homogeneous expanding IGM case allowing compared with the homogeneous expanding IGM case allowing
onlyforthedensityfluctuationcontribution. onlyforthedensityandvelocityfluctuation contributions.
Figure 7. Differential Balmer surface brightness fluctuations Figure 9. Differential Balmer surface brightness fluctuations
compared with the homogeneous expanding IGM case allowing compared with the homogeneous expanding IGM case allowing
onlyforthedensityandtemperaturefluctuation contributions. fortheeffects ofdensity,temperatureandvelocityfluctuations.
line-of-sight. A narrow-band filter would include contribu- Theeffectsofthedensity,temperatureandvelocityfluc-
tions from the nearby foreground and background regions tuations on the Balmer surface brightnesses are illustrated
as well. Modelling a specific filter arrangement would re- in the differential maps shown in Figs. 6, 7, 8 and 9. The
quire further layers to be included for a realistic estimate, mapsshowthedifferencesfrom thecase for ahomogeneous
whichwouldtendtoblurtheimageifthefilterwidthcorre- expanding IGM. The differential map allowing only for the
spondedtoalengthscalethatexceedsthecoherencescaleof densityfluctuations shows thesuppression bytheincreased
the inhomogeneities. The results shown here are thus only optical depth in dense regions, as in Fig. 5. Adding in the
representative of the magnitude of the effects that should contribution of the temperature fluctuations substantially
arise from inhomogeneities in the density, temperature and enhances the structures. Adding the peculiar velocity con-
peculiar velocity fields. tributiontothedensityemphasizesdifferentialsinthestruc-
(cid:13)c 0000RAS,MNRAS000,000–000
6 K. Kakiichi, A. Meiksin, E. Tittley
with a field of view of FOV = 2×2 arcmin2. Imaging
fid
using a narrow-band filter of resolution R=λ/∆λ=100 is
assumed.
Estimates for the zodiacal light background5 based on
the model of Wright (1998) are converted to count rates in
Table1.Theintensityofzodiacallightdependsontheposi-
tionandpointingdirectionofasatellite.Thelowerestimates
are quoted here.
Lyman Break Galaxies and Lyα emitters at z >
6 suggest star formation rates of up to 30M yr−1
⊙
(Gonz´alez et al. 2011; McLure et al. 2011). Much higher
star formation rates are known in the lower redshift Uni-
verse, reaching values of 500−1000M yr−1, but these are
⊙
associated with ultra-luminousinfra-red galaxies (ULIRGs)
in dusty environments, which severely attenuate the ultra-
violet radiation (Kennicutt 1998). On the other hand, by
z = 1−2 ULIRGs are found to be much more transparent
to UV radiation (Daddiet al. 2007). Accordingly, our esti-
matesarenormalizedtoasourcewithastarformation rate
of 100M yr−1.
⊙
The resulting lower order Balmer fluxes are shown in
Figure 10. Balmer surface brightnesses including the effects of Table 1, based on the estimates in Meiksin (2010). The
density,temperatureandvelocityfluctuations. correspondingsignal-to-noiseratios (SNR)afterintegrating
over a time t are provided in the last row of the table. The
SNR is nearly independent of the Balmer order. Increasing
Source Hα Hβ Hγ Hδ the resolution to R=500 would be adequate for capturing
5.91µm 4.38µm 3.91µm 3.69µm the emitting flux while minimizing the zodiacal light back-
ground. A starburst as great as 700M yr−1 would still be
⊙
Zodiacal 4.7×104 7.7×103 3.5×103 2.6×103 requiredtoachievea3σ detectionin2×104 s.Allowingfor
the stacking of multiple bands in an instrument that split
Halo 0.048 0.018 0.011 0.0089
the beam into a range of bands tuned to correspond to the
SNR/M˙100 0.16t14/2 0.15t14/2 0.14t14/2 0.13t14/2 different Balmer series, would reduce the required star for-
mation rate for detection by the square-root of the number
of bandsstacked.
Table 1. Estimated photon flux (photonsm−2s−1) from low-
The haloes could plausibly be detected by the James
level zodiacal light and the integrated halo flux within one ar-
WebbSpaceTelescope(JWST)usingtheTunableFilterIm-
cmin of a starburst at z = 8, through an aperture of solid an-
gle 4 arcmin2 and narrow-band filter with resolution λ/∆λ = ager for a sufficiently bright source. The narrowest filter
width, with resolution6 R ≃ 100, is sub-optimal, as it is
100. The starburst is normalised to a star formation rate of
100M˙100M⊙yr−1.Thelastrowprovidesthesignal-to-noiseratio broaderthantheemissionfeature,andthusletsinanexces-
afteranintegrationtimet4inunitsof104 sforfluxincidentona sive amount of background light compared with the signal.
mirroranddetectorwitheffectivecollectingarea50m2.AnIGM The wavelength range of the detector would also miss Hα
temperatureT =10Kisassumed. for a source at redshift z > 6.6, however it would capture
S
thehigherorders.Themirrorhasacollectingareaof25m2.
Allowing for a photon throughput of 50 per cent., a 5σ de-
tures,allowingthepossibilityoftracingthepeculiarvelocity
tection of Hβ for a 1000 M yr−1 source would require an
field around forming galaxies on small scales. ⊙
integration time of 4.7×105 s.
The combined map is shown in Fig. 10. The rippling
effectoftheIGMisclearlydiscernable.Theinfluenceofthe
peculiar velocity becomes increasingly strong for thehigher
orders,wherethedominantscatteringproducingthesignals 5 CONCLUSIONS
moves from theVoigt wings to theDoppler core.
Thesearchforthehighestredshiftgalaxiesmayhaveidenti-
fiedforming galaxies responsible at least for alarge compo-
nentofthereionization of theintergalactic medium.Estab-
4 DETECTION OF INFRA-RED EMISSION
lishingthattheIGMwasactuallyneutral,however,requires
HALOES
directdetectionoftheneutralmedium.Amajorgoal ofex-
The Balmer emission lines produced in the diffuse IGM by isting and planned radio facilities is to detect the neutral
galaxies during the Epoch of Reionization will redshift to IGM 21cm signal from the Epoch of Reionization. A com-
the infrared. In this section, an estimate is made for the plementarypathistodiscovertheUVlightfromthesources
requirementstodetectthehaloes.Itisassumedthedetector
is limited by photon noise, which will be dominated by the
IR background, primarily zodiacal light for a telescope in 5 Athttp://jwstetc.stsci.edu/etcstatic/users guide/t8 background.html.
space. A fiducial collecting area of Afid =50 m2 is adopted 6 Athttp://www.stsci.edu/jwst/doc-archive/handbooks/JWST Primerv20.pdf.
(cid:13)c 0000RAS,MNRAS000,000–000
Infra-redemissionline tomographyofthe intergalactic mediumduringthe Epoch ofReionization 7
re-radiated by theIGM and received as infra-red radiation. Kennicutt Jr. R. C., 1998, ARA&A,36, 189
Rescattered Lyα photonsofferone possibility, although the Larson D., Dunkley J., Hinshaw G., Komatsu E., Nolta
emission isrestrictedbythespatialdiffusionofthephotons M. R., Bennett C. L., Gold B., Halpern M., Hill R. S.,
to the vicinity of the source. Higher energy photons will Jarosik N.,Kogut A., Limon M., 2011, ApJS,192, 16
redshiftintolocalhigherorderLymanseriesphotons,excit- Leitherer C., Schaerer D., Goldader J. D., Gonz´alez Del-
ing extended Balmer and higher order emission line haloes gadoR.M.,RobertC.,KuneD.F.,deMelloD.F.,Devost
through electron cascades following Lyman photon scatter- D.,Heckman T. M., 1999, ApJS,123, 3
ing. Loeb A., RybickiG. B., 1999, ApJ,524, 527
We have shown that the fluctuations in the signal are Madau P., Meiksin A.,Rees M. J., 1997, ApJ,475, 429
sensitive not only to the density fluctuations in the sur- McLureR.J.,DunlopJ.S.,deRavelL.,CirasuoloM.,Ellis
rounding gas through the mean free path of the scattered R. S., Schenker M., Robertson B. E., Koekemoer A. M.,
Lymanphotons,butofthevelocityfieldaswell. Thisoffers Stark D.P., Bowler R.A. A.,2011, MNRAS,418, 2074
the possibility of mapping out both the ionization struc- Meiksin A., 2010, MNRAS,402, 1780
ture and the peculiar velocity field, produced by inflows or Meiksin A.A.,2009, ReviewsofModern Physics, 81, 1405
wind-driven outflows, surroundingthe earliest major radia- OnoY.,OuchiM.,MobasherB.,DickinsonM.,PennerK.,
tion sources, whethergalaxies or AGN. Shimasaku K., Weiner B. J., Kartaltepe J. S., Nakajima
The principle obstacle to the detection of the infra-red K.,NayyeriH.,SternD.,KashikawaN.,SpinradH.,2012,
haloesisthezodiacal lightbackground.Theidealobserving ApJ,744, 83
instrumentwouldbeaspacetelescopewithaneffectivecol- Osterbrock D. E., 1989, Astrophysics of gaseous nebulae
lecting area of 50 m2, a field of view of a few to several and activegalactic nuclei. University ScienceBooks, Mill
square arcminutes, and a detector sensitive to the wave- Valley,CA
length range 1–7 µm with the capability of simultaneous PritchardJ.R.,FurlanettoS.R.,2006,MNRAS,367,1057
imaging in several narrow tunable bands with a resolution Pritchard J. R., Loeb A., 2011, ArXiv e-prints, 1109.6012
of R≃500. Basing an estimate on apointingtoa region of SchenkerM. A., Stark D. P., Ellis R. S., Robertson B. E.,
sky with a low-level of zodiacal light background,we find a DunlopJ.S.,McLureR.J.,KneibJ.-P.,RichardJ.,2012,
700 M yr−1 starburst galaxy could be detected at the 3σ ApJ,744, 179
⊙
level in a single band in a 2×104 s integration, or a star- Tozzi P., Madau P., Meiksin A., Rees M. J., 2000, ApJ,
burstofhalfthestrengthifobservedsimultaneously infour 528, 597
bands. VanzellaE.,PentericciL.,FontanaA.,GrazianA.,Castel-
Although sub-optimal in design for this purpose, the lano M., Boutsia K., Cristiani S., Dickinson M., Gallozzi
Tunable Filter Imager on JWST could detect a z = 8 S., Giallongo E., Giavalisco M., Maiolino R., Moorwood
1000 M yr−1 starburst galaxy at the 5σ level in Hβ in a A.,Paris D., SantiniP., 2011, ApJ, 730, L35
⊙
5×105 s integration. While a major resource investment, Wright E. L., 1998, ApJ, 496, 1
it is half the time allocated to the Hubble Space Telescope
Ultra-Deep Field and would offer the prize of a definitive
detection of the Epoch of Reionization.
ACKNOWLEDGMENTS
K.K. acknowledges support from the Mie Prefecture of
Japan for a Study-abroad Scholarship, and thanks the
RobertCormackBequestforanUndergraduateSummerVa-
cationResearchScholarship.E.T.issupportedbyanSTFC
Rolling Grant.
REFERENCES
Barkana R., Loeb A., 2005, ApJ,626, 1
Bouwens R. J., Illingworth G. D., Labbe I., Oesch P. A.,
Trenti M., Carollo C. M., van Dokkum P. G., Franx M.,
Stiavelli M., Gonz´alez V., Magee D., Bradley L., 2011,
Nature,469, 504
Daddi E., Dickinson M., Morrison G., Chary R., Cimatti
A., Elbaz D., Frayer D., Renzini A., Pope A., Alexander
D. M., Bauer F. E., Giavalisco M., Huynh M., Kurk J.,
Mignoli M., 2007, ApJ, 670, 156
Gonz´alezV.,Labb´eI.,BouwensR.J.,IllingworthG.,Franx
M., Kriek M., 2011, ApJ, 735, L34
Hirata C. M., 2006, MNRAS,367, 259
(cid:13)c 0000RAS,MNRAS000,000–000
