extreme population iii starbursts and direct collapse ... · has a quite good ﬁt at slightly...

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Extreme Population III Starbursts and Direct Collapse Black Holes Stimulated by

High Redshift Quasars

Jarrett L. Johnson with

Aycin Aykutalp

Into the Starlight Aspen Center for Physics

March 5, 2019

Los Alamos National Laboratory 11/1/2018 | 9

Population III star formation has been elusive.

Credit: STSci

Searches for Pop III star-forming galaxies Claims of possible Pop III detection

2001 2003 2005 2007 2009 2011 2013 2015 2017 2019

Nagao et al. search for He II 1640 angstrom emission in a high redshift galaxy.

Jimenez & Haiman appeal to Pop III to explain emission from galaxies at z = 3 – 4.

Sobral et al. announce discovery of CR7.

Rydberg et al. find Pop III candidates in the CLASH survey.

Nagao et al. search for He II 1640 angstrom-emitting galaxies.

Cai et al. find an upper limit on Pop III in a galaxy at z = 6.96.

Cassata et al. find evidence for Pop III z = 2 – 4.6.

Malhotra & Rhoads find larger than expected Lyman alpha EWs at z = 4.5.

Kashikawa et al. report a large Lyman alpha EW in a galaxy at z = 6.5

Inoue et al. suggest Pop III could power Lyman ‘bump’ galaxies at z = 3.1

Cai et al. search for He II 1640 angstrom emission from a z ~ 7 galaxy.

Artistic impression of CR7

credit: New York Times

Pop III galaxy signature 9

Fig. 4.— 50′′ × 50′′ image in F160W of the cluster MACS0416.MACS0416-1828 is marked with a circle. As can be seen, there ispossible contamination of light from a diffraction spike originatingin an object to the lower right of MACS0416-1828.

The Lyα-break for MACS0416-1828 (see Figure 7)around F850LP-F105W is not very clear with a 2.7σdetection in F850LP. This is also the object with thelowest photometric redshift estimate (z = 6.8) of the fiveobjects. The object has just one 5σ detection, in thefilter F110W. MACS0416-1828 also has one S/N ≈ 4.98detection in F105W. As can be seen in Figure 6, thefilters F850LP, F105W and F110W have brighter magni-tudes, while the F125W, F140W and F160W filters havefainter magnitudes. This causes a break between F110Wand F125W, which suggests a steep spectral slope. Theobject can also be reproduced with a Lyα-emission lineentering the three filters with lower wavelength, as in thePop III galaxy model. The cross-validation fit to Pop IIIgalaxy models is excellent, as shown in the P(z) graph inFigure 6. The fit to Z > 0 Yggdrasil templates are worsebut not significantly so. The Gissel grid of models havea good fit around z = 6.2, and the CWW, Kinney gridhas a quite good fit at slightly lower redshift.Figure 4 shows an overview of the MACS0416 cluster

with the object’s location marked. As can be seen, thereis possible contamination by light from a diffraction spiketo the lower right in the image. Most of the light fromthe diffraction spike appears to be lower in the imagethan the object, yet there can be some contamination.This could distort the observed colors.

5.1.3. MACS0647-610

This object, even though something can be discerned inthe F105W thumbnail in Figure 7, seem to have the Lyα-break between F105W and F110W. It is also hard to dis-criminate any coherent morphology for the object, espe-cially when comparing F110W and F125W. F110W con-tains several smaller detections spread out while F125Whas one larger detection but offset to the lower in theimage. This raises doubts about the nature of the ob-

Fig. 5.— 50′′ × 50′′ image in F160W of the cluster MACS0647.MACS0647-610 is marked with a circle. There is plausible lightcontamination from a diffraction spike from an object below andslightly to the left of MACS0647-610.

ject. It could even be several smaller objects identifiedas one by SExtractor. Also, Figure 5 shows that theMACS0647-610 object, similar to the MACS0416-1828object, is plausibly contaminated by light from a diffrac-tion spike. The contamination could possibly explainthe morphology as optical artifacts. Examining the im-ages in each filter separately reveals that the diffractionspike in F110W has a completely different angle com-pared to F125W, F140W, and F160W (where it coversthe object). Since this uncontaminated image has a 5σdetection the whole object is not likely to be an arti-fact from the diffraction spike. But closer investigationwould be necessary to determine the complete impact ofthe diffraction spike on the reported fluxes.If, despite these considerations, considering it as one

object, it has two 5σ detections in F110W and F125W.For the best-fitting models there is a huge difference inphotometric redshifts – 8.8 for the Pop III model versus6.1 and 6.3 for CWW, Kinney and Gissel, respectively,and 8.1 for the Yggdrasil Z > 0 grid. The differencecan be understood by investigating the object in Fig-ure 6. The Pop III model has a very strong Lyα-lineentering F105W, F110W and F125W as well as partlyinto F140W (causing the small peak as described in Sec-tion 5.1). This produces a good fit even though it hashardly any continuum emission in F105W and only halfof F110W has continuum flux. The Yggdrasil Z > 0grid, unable to produce a similar peak at z = 8.8, pro-duces its optima at z = 8.1 by having the Lyα-line inF105W, F110W and F125W simultaneously and relyingon a stronger continuum. The other comparison modelsneed to have more continuum emission instead, causinga lower redshift solution to fit better.

5.1.4. MACS1931-777

Rydberg et al. (2015)

– 12 –

Fig. 1.— High resolution images of galaxy IOK-1 in the F125W (left) and the F130N (right)bands, with contours spaced by 1.4 sky rms for the F125W image and 1 sky rms for the

F130N image. The black elliptical aperture is determined by the F130N image. IOK-1 isclearly resolved into two components separated by ∼ 0.′′2. Photometric analysis of the F130N

image reveals a flux density excess of 1.2σ.

Cai et al. (2011)


Future Searches for Population III Galaxies

• The James Webb Space Telescope (JWST) will be launched in 2021.

• The JWST will have 6.25 larger light gathering area than the Hubble Space Telescope.

• Operating in the infrared, it is geared towards detecting the most distant early galaxies.

• First light for the European Extremely Large Telescope (E-ELT) is scheduled for 2025.

• The E-ELT will be the largest optical/IR telescope in the world, at 40 meters.

Credit: STSci

It is critical to make predictions now for how these facilities could be used to find Population III galaxies. Predictions are much more powerful than postdictions!


It is critical to predict which Pop III star formation JWST could find.

• The first stars formed in isolated mini halos at z ~ 20 will be too dim even for the JWST to detect.

• Pop III clusters, even with a top-heavy IMF, may have to be as massive as ~ 106 Msun, in order to be detectable (e.g. Gardner 2006).

• Two characteristics of Pop III star clusters that could make them detectable by JWST:

• Large stellar mass • Low formation redshift

Hirano et al. (2014)

6 Hirano et al.

Fig. 3.— Projected gas density distribution at z = 25 in one of our cosmological simulations. We show five primordial star-formingclouds in a cube of 15 kpc on a side. The circles show the zoom-in to the central 1 pc region of the clouds at the respective formationepoch. The masses of the first stars formed in these clouds are 60, 76, 125, 303, and 343 M⊙, respectively.

Fig. 4.— Expanding Hii regions around the primordial protostar for three in our sample of 110 clouds (the same ones as in Figure 12).We show the structure and the evolution of the accreting gas from left to right. The plotted regions are cubes with 60000 AU on a side.The colors indicate gas temperature and the contours show the density structure. The main accretion takes place through the accretiondisk on the equatorial plane. As the central protostar becomes more massive and the surface temperature increases, the ionizing photonproduction of the central star increases. Hii regions are launched into the polar direction and the opening angles grow with time, eventuallystopping the accretion.


Observational Evidence of Primordial Gas at Low Redshift

• Observations of Lyman limit and damped Lyman alpha (DLA) systems have revealed possibly metal-free gas at:

• z ~ 3 (Fumagalli et al. 2011) • z = 4.4 (Robert et al. 2019) • z ~ 7 (Simcoe et al. 2012)

• This is empirical evidence that there is the potential for Pop III star formation well after reionization.

• Low redshift Pop III star clusters are much more readily detected, as their flux scales as (1+z)-2.

Apparently metal-free gas at z = 4.4 9

Figure 6. Summary of the metallicity distribution of LLSs (squares) andDLAs (circles) in the literature. Upper limits are indicated by arrows. Themetallicity upper limit (95% confidence) for LLS1723 from this work ishighlighted in blue. Upper limits from Fumagalli et al. (2011a) for twoapparently metal-free LLSs, LLS0958B and LLS1134, are shown in black.The lowest metallicity measurement for a LLS from Crighton et al. (2016),LLS1249, is shown in black with its associated 1� error bar. The red squaresand error bars represent the LLS sample of Fumagalli et al. (2016a) and showthe median and 25–75% range of the composite posterior probability densityfunction in redshift bins containing at least 25 LLSs each. The green circlesare DLAs from Cooke et al. (2011), Rafelski et al. (2012) and Jorgensonet al. (2013). The lowest metallicity measurement for a DLA from Cookeet al. (2017), DLA0903, is shown in green with its associated 1� errorbar. The shaded orange region shows the expected metallicity range for gasenriched by PopIII supernovae from the simulations of Wise et al. (2012).

campaign were specifically designed to identify very low metal-licity LLSs. This was clearly successful. However, as discussed inSection 2, our target selection drew on a sample of e�ectively ⇠191LLSs without strong metallicity biases. Therefore, including theother two apparently metal free cases, which were serendipitouslydiscovered, it is clear that LLSs at 3 . zabs . 4.5 with metallicitylog10(Z/Z�) < �4 are rare, but not extremely so: ⇠ 3/191 ⇠ 1.6%of the population. That is, it is currently unclear whether they aresimply the very low metallicity tail of a unimodal LLS distribution,or whether they constitute a second mode. In other words, if the LLSmetallicity distribution is unimodal, it may be that all LLSs have thesame origin, with the common assumption that they arise in the cir-cumgalactic medium (CGM). On the other hand, very metal-poorLLSs constituting a second mode of the metallicity distribution,would mean that they arise in a di�erent environment: for instance,the intergalactic medium (IGM). The remainder of this section isthen dedicated to investigate this question.

In the context of LLSs arising in the CGM, their populationmay include gas ejected from galaxies, cold accretion streams orother, virialised gas located in the CGM. With such a low metallicity,LLS1723 is unlikely to be outflowing gas or virialised, well-mixedCGM gas: these CGM components would be highly enriched withmetals from supernovae in the host galaxy. Indeed, the much highercolumn densities of DLAs make them very likely to arise in theseCGM components (and not, for example, the IGM), and the lowest-metallicity DLA known – the z ⇡ 3.1 absorber discovered by Cooke

et al. (2017) (included in Fig. 4) – has log10(Z/Z�) ⇡ �3.2, consid-erably higher than that our upper limit for LLS1723. This leaves thecold stream component as a likely origin for a LLS like LLS1723in a circumgalactic environment. This agrees with a prediction ofcosmological simulations: the streams of cold gas accreting intogalactic haloes have column densities in the LLS range (e.g. Fu-magalli et al. 2011b; Faucher-Giguère & Kereö 2011; van de Voortet al. 2012), so we expect some LLSs to be very low metallicity or,possibly, completely pristine gas being polluted for the first time byCGM gas at z ⇠ 3–4.5. Therefore, LLS1723 may indeed be part ofa cold accretion stream. We should however note that modelling theCGM in a non-idealised context is di�cult, despite the advancesin numerical simulation over the years. The CGM in such worksis usually under-resolved, and this could impact the ability to re-produce its properties infered through observations. For instance,van de Voort et al. (2018) found that the covering fraction of LLSsincreases with the resolution of the CGM: from 8% to 30% within150 kpc from the galaxy centre.

On the other hand, the current small sample of very metal-poor LLSs might instead arise in a di�erent environment: the IGM.There are several reasons to expect this scenario. The first is theredshift evolution of the number of LLSs per unit redshift, l(z).In Fumagalli et al. (2013), the evolution of l(z) at z > 3.5 cannot be explained with only a contribution from the CGM, i.e. acontribution from the IGM is speculated. Another motivation forthe intergalactic scenario comes from the lowest-metallicity LLSwith detected metals, LLS1249: on the basis of the [C/Si] ratio (i.e.compared to metal-free nucleosynthesis calculations, e.g. Heger& Woosley 2002) and metal-line shifts from the hydrogen lines,Crighton et al. (2016) argued that LLS1249 may be an intergalacticremnant of a PopIII explosion, unpolluted by subsequent genera-tions of stars. However, with only two detected metal species andmetallicity log10(Z/Z�) ⇡ �3.4, the possibility that this system iscircumgalactic, and mainly polluted by PopII/I stars, remains. Fi-nally, previous studies of the chemical abundance of the IGM usingthe Ly↵ forest (e.g. Aguirre et al. 2001; Schaye et al. 2003; Aguirreet al. 2004; Simcoe et al. 2004; Aguirre et al. 2008; Simcoe 2011)suggest that a large fraction of the IGM at high redshift (z & 2)is metal-poor. For instance, Simcoe (2011) estimated that ⇠ 50%of the Ly↵ forest has log10(Z/Z�) �3.6 at z ⇠ 4.3. DespiteLLSs having a higher H � column density than most features in theLy↵ forest (i.e. log10(N� �/cm�2) 15.5), the fact that LLS1723’smetallicity is typical of the IGM is at least consistent with an IGMorigin.

Therefore, an intergalactic environment for the apparentlymetal free LLSs (LLS0958B, LLS1134, LLS1723) is particularlyinteresting to consider: in principle, their extremely low metallici-ties may imply they are either (i) completely metal free gas clouds,(ii) remnants of PopIII explosions, or (iii) clouds polluted by PopII/Idebris at extremely low levels. Given the lack of metal abundanceinformation in such systems, it is di�cult to definitively distinguishbetween these possibilities. However, existing numerical simula-tions can provide a guide to their relative likelihood, and we discussthese below.

Apparently metal free clouds like LLS1723 may be completelypristine, intergalactic gas – surviving vestiges of the early universethat have never entered a large enough overdensity to be pollutedby stellar debris. Cosmological simulations of structure formation,including pollution from PopIII stars, feature a very patchy and inho-mogeneous metal enrichment (e.g. Tornatore et al. 2007; Maio et al.2010; Wise et al. 2012; Jaacks et al. 2018). Highly metal-enrichedregions and pristine regions coexist in the simulation volume, but

MNRAS 000, 1–12 (2018)

Robert et al. (2019)


• In cosmological simulations, metal enrichment does not completely quench Pop III star formation.

• Pop III stars are found to form down to at least z ~ 6 (e.g. Tornatore et al. 2007; Xu et al. 2016; Sarmento et al. 2017; Jaacks et al. 2018; Mebane et al. 2018).

• The Pop III star formation rate is, however, strongly impacted by radiative feedback during reionization (e.g. Ahn et al. 2012). JLJ, Dalla Vecchia, Khochfar (2013)

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA

UNCLASSIFIED

• In cosmological simulations,

metal enrichment does not

completely quench Pop III

star formation.

• Pop III stars are found to

form down to at least z ~ 6 (e.g. Tornatore et al. 2007; Xu et al.

2016; Sarmento et al. 2017; Jaacks

et al. 2018).

• The Pop III star formation

rate is, however, strongly

impacted by radiative

feedback during reionization

(e.g. Ahn et al. 2012).

6 J. L. Johnson, C. Dalla Vecchia and S. Khochfar

2.3.1 SN mechanical feedback

The mechanical feedback from SNe is modelled as a prompt

injection of thermal energy into the ISM surrounding star

particles (which represent individual, evolving stellar clus-

ters), as described in Dalla Vecchia & Schaye (2012). For the

feedback from Pop II SNe, for each SN that occurs 1051

erg

of thermal energy is distributed stochastically to neighbor-

ing SPH particles by instantaneously assigning them a gas

temperature of 107.5

K. As Dalla Vecchia & Schaye (2012)

show, for the resolution of our simulations this prescription

suffices to capture the deposition of mechanical energy into

the ISM reliably well. We use the same technique to model

feedback from Pop III stars but we differentiate between

type II SNe which occur for initial stellar masses 8 <∼

M∗

<∼ 100, and the more powerful PISNe which occur for initial

stellar masses 140 <∼ M∗

<∼ 260 (Heger et al. 2003). For

the former we inject 1051

erg per SN, while for the latter

we inject 3 × 1052

erg per SN which is roughly the average

PISN energy found from the suite of models computed by

Heger & Woosley (2002).

2.3.2 Metal enrichment

We follow the prescription for metal enrichment presented

in Wiersma et al. (2009a), which is similar to that also em-

ployed by Tornatore et al. (2007b). In this implementation,

Pop II star particles continuously release hydrogen, helium,

and metals into the surrounding gas in abundances calcu-

lated according to tabulated yields for types Ia and II SNe,

and from asymptotic giant branch (AGB) stars. The mixing

of this material with the surrounding ISM is modelled by

transferring it to neighboring SPH particles in proportions

weighted by the SPH kernel. We use the same technique to

model metal enrichment from Pop III stars, but we adopt the

appropriate different chemical yields for type II SNe (Heger

& Woosley 2010) and PISNe (Heger & Woosley 2002).

2.4 Reionization in the FiBY

Concurrent with the build-up of the LW background ra-

diation field is the onset of reionization, the process by

which the intergalactic medium becomes heated and ion-

ized at z >∼ 6 (e.g. Ciardi & Ferrara 2005). We adopt a

simple approach to account for the effects of reionization.

In particular, we assume that reionization takes place uni-

formly throughout our simulation volume starting at z =

12, roughly consistent with range of redshifts inferred for

instantaneous reionization by WMAP (e.g. Komatsu et al.

2011) and also with the limit of ∆z > 0.06 for the extent of

reionization reported by Bowman & Rogers (2010).

In practice, to model the effects of reionization, at z =

12 we switch from the collisional to photoionization equilib-

rium cooling tables, which account for heating by the ion-

izing background radiation field given by Haardt & Madau

(2001). This results in a gradual heating of the IGM to ∼

104K. To account for the shielding of dense gas from the

ionizing radiation, we adopt a maximum density threshold

nshield,ion below which the gas is subjected to the full ra-

diative flux; following Nagamine et al. (2010) we choose

nshield,ion = 0.01 cm−3

. At densities above nshield,ion the

Figure 1. Top panel: The comoving formation rate density ofPop III stars (dashed lines) and of all stars (solid lines), in oursimulations with (red) and without (yellow) LW feedback, as afunction of redshift z. Also plotted here (gray points) are thestar formation rate densities inferred from data on high-z galax-ies, compiled from Hopkins & Beacom (2006), Mannucci et al.(2007), and Bouwens et al. (2008). Bottom panel: The level ofthe cosmological background LW flux in our simulation with LWfeedback, in units of 10−21 erg s−1 cm−2 Hz−1 sr−1, due to PopII stars (dashed green line), Pop III stars (dashed red line), andboth populations together (solid yellow line).

flux is decreased from the unattentuated value by a frac-

tion (n/nshield,ion)−2

, which is proportional to the recombi-

nation rate and allows for a continuous transition betwee the

shielded and unshielded regimes. The cooling rates are then

derived by interpolation between the collisional equilibrium

and photoionization equilibrium tables.

3 RESULTS

Here we report the results of our two simulations, one in-

cluding the effects of LW feedback (in dissociating H2 and

c⃝ 2012 RAS, MNRAS 000, 000–000

6 J. L. Johnson, C. Dalla Vecchia and S. Khochfar

2.3.1 SN mechanical feedback

The mechanical feedback from SNe is modelled as a prompt

injection of thermal energy into the ISM surrounding star

particles (which represent individual, evolving stellar clus-

ters), as described in Dalla Vecchia & Schaye (2012). For the

feedback from Pop II SNe, for each SN that occurs 1051

erg

of thermal energy is distributed stochastically to neighbor-

ing SPH particles by instantaneously assigning them a gas

temperature of 107.5

K. As Dalla Vecchia & Schaye (2012)

show, for the resolution of our simulations this prescription

suffices to capture the deposition of mechanical energy into

the ISM reliably well. We use the same technique to model

feedback from Pop III stars but we differentiate between

type II SNe which occur for initial stellar masses 8 <∼

M∗

<∼ 100, and the more powerful PISNe which occur for initial

stellar masses 140 <∼ M∗

<∼ 260 (Heger et al. 2003). For

the former we inject 1051

erg per SN, while for the latter

we inject 3 × 1052

erg per SN which is roughly the average

PISN energy found from the suite of models computed by

Heger & Woosley (2002).

2.3.2 Metal enrichment

We follow the prescription for metal enrichment presented

in Wiersma et al. (2009a), which is similar to that also em-

ployed by Tornatore et al. (2007b). In this implementation,

Pop II star particles continuously release hydrogen, helium,

and metals into the surrounding gas in abundances calcu-

lated according to tabulated yields for types Ia and II SNe,

and from asymptotic giant branch (AGB) stars. The mixing

of this material with the surrounding ISM is modelled by

transferring it to neighboring SPH particles in proportions

weighted by the SPH kernel. We use the same technique to

model metal enrichment from Pop III stars, but we adopt the

appropriate different chemical yields for type II SNe (Heger

& Woosley 2010) and PISNe (Heger & Woosley 2002).

2.4 Reionization in the FiBY

Concurrent with the build-up of the LW background ra-

diation field is the onset of reionization, the process by

which the intergalactic medium becomes heated and ion-

ized at z >∼ 6 (e.g. Ciardi & Ferrara 2005). We adopt a

simple approach to account for the effects of reionization.

In particular, we assume that reionization takes place uni-

formly throughout our simulation volume starting at z =

12, roughly consistent with range of redshifts inferred for

instantaneous reionization by WMAP (e.g. Komatsu et al.

2011) and also with the limit of ∆z > 0.06 for the extent of

reionization reported by Bowman & Rogers (2010).

In practice, to model the effects of reionization, at z =

12 we switch from the collisional to photoionization equilib-

rium cooling tables, which account for heating by the ion-

izing background radiation field given by Haardt & Madau

(2001). This results in a gradual heating of the IGM to ∼

104K. To account for the shielding of dense gas from the

ionizing radiation, we adopt a maximum density threshold

nshield,ion below which the gas is subjected to the full ra-

diative flux; following Nagamine et al. (2010) we choose

nshield,ion = 0.01 cm−3

. At densities above nshield,ion the

Figure 1. Top panel: The comoving formation rate density ofPop III stars (dashed lines) and of all stars (solid lines), in oursimulations with (red) and without (yellow) LW feedback, as afunction of redshift z. Also plotted here (gray points) are thestar formation rate densities inferred from data on high-z galax-ies, compiled from Hopkins & Beacom (2006), Mannucci et al.(2007), and Bouwens et al. (2008). Bottom panel: The level ofthe cosmological background LW flux in our simulation with LWfeedback, in units of 10−21 erg s−1 cm−2 Hz−1 sr−1, due to PopII stars (dashed green line), Pop III stars (dashed red line), andboth populations together (solid yellow line).

flux is decreased from the unattentuated value by a frac-

tion (n/nshield,ion)−2

, which is proportional to the recombi-

nation rate and allows for a continuous transition betwee the

shielded and unshielded regimes. The cooling rates are then

derived by interpolation between the collisional equilibrium

and photoionization equilibrium tables.

3 RESULTS

Here we report the results of our two simulations, one in-

cluding the effects of LW feedback (in dissociating H2 and

c⃝ 2012 RAS, MNRAS 000, 000–000

JLJ, Dalla Vecchia, Khochfar (2013)

The Extended Epoch of the First Stars and GalaxiesTheoretical Evidence of Population III Star Formation through Reionization


Primordial haloes subjected to strong ionizing radiation collapse at mass scales up to Mhalo ~ 109 Msun (Trenti et al. 2009; JLJ 2010; Visbal et al. 2016, 2017; Yajima & Khochfar 2017; also talk by Kulkarni).

This may set stage for the formation of a Pop III starburst.

Collapsing photo-heated gas

JLJ (2010) JLJ et al. (2014)

Massive Pop III clusters are expected to form from photo-heated gas.


!8

▪ If Pop III galaxies do form in massive halos due to photoheating of the IGM, then the most massive Pop III galaxies likely form in halos exposed to the most intense photo-heating.

▪ The highest temperatures (~ 106 K) could be achieved by X-ray heating in the vicinity of high-z quasars.

▪ In such an environment Pop III stars would form in halos with virial temperatures in the range, with masses of order 1010 Msun.

Smidt et al. (2018)

IGM heating by a quasar at z = 7

This implies that the most massive Pop III clusters may be at least ~ 106 Msun — detectable by JWST!

Extreme Pop III Starbursts from the Hottest Photo-heated Gas

5

10-3 10-2 10-1 1 10radius (Mpc)

102

103

104

105

106

107

T (

K)

Fig. 4.— Left: metallicity slice through the center of the host galaxy of the quasar at z = 7.1. Distance scales are in comoving Mpc.Right: Spherically averaged temperature profile of the H II region of the quasar at z = 7.1. The vertical line marks the approximateboundary of gas at > 104 K at ⇠ 2 Mpc, the observed radius of the ionized near zone of ULAS J1120+0641.

Fig. 5.— Stellar mass of the host galaxy of the quasar at z = 7.1. Left panel: number of star particles binned by log mass. Right panel:cumulative stellar mass as a function of star particle mass.

peak into the keV range (Done et al. 2012). The averagephoton energy of these spectra ranges from 2.0 keV at105 M� to 0.3 keV at 109 M�, so our choice of 1 keV isan appropriate average for this interval in BH mass.That said, lower-energy photons in actual SMBH spec-

tra may have a measurable e↵ect on the evolution of thequasar because they have larger cross sections to ion-ization in H, He and some metal ions. But this e↵ectappears to be modest at lower BH masses. Smidt et al.(2016) evolved a DCBH over two decades in mass withboth monoenergetic X-ray and multigroup spectra thatincluded ionizing UV and found little change in its evo-lution. Radiation pressure from IR on dust in the hostgalaxy of the BH may also drive strong but short-livedoutflows (Bieri et al. 2017; Costa et al. 2018a,b), althoughsuch outflows have only been observed in a fraction ofquasars at z > 6. The softer components of SMBH spec-tra may also quench their images at 21 cm in emission

because they ionize rather than heat the IGM. The ef-fects of evolving BH spectra on the growth of the firstquasars will be examined in future simulations.While our models trace metal production due to star

formation, they do not include dust formation and cool-ing or opacity due to dust and metals in the radiationtransport. Dust cooling would promote star formationin environments in which radiation does not destroy itfirst, and both metals and dust would enhance X-rayheating in the galaxy by absorbing more photons. Howthese processes would o↵set each other and other factorsgoverning star formation and the growth of the BH willbe explored in future studies.X-ray and SF feedback limit accretion to 0.2 - 0.8 mEdd

in our models, rates at which quasars are not observedto have jets, so we do not include them in our models.Steady jets are observed in active galactic nuclei (AGNe)at L . 0.01LEdd and intermittent jets are seen in quasars

H II region

2

nel, cooling and collapsing gas and creating more stars(e.g., Glover & Abel 2008). On the other hand, radiationfrom the BH can also evaporate star-forming clouds andglobal LW backgrounds can destroy H2, quenching starformation.To model the formation of primordial quasars, simu-

lations must resolve all these processes deep in the hostgalaxy of the BH and in cold streams in the intergalac-tic medium (IGM). We have now bridged these scaleswith new simulations that include X-rays from the BHand winds, ionizing UV and SNe from star-forming re-gions, and have evolved a quasar in cold flows from birthat z = 19 down to z = 6. We describe these modelsin Section 2 and examine the evolution of the BH andits host galaxy in Section 3, where we also compare itsproperties with those observed for J1120. We discuss ourresults and conclude in Section 4.

2. NUMERICAL METHOD

We use the Enzo adaptive mesh refinement (AMR) cos-mology code (Bryan et al. 2014) with the MORAY ra-diation transport package (Wise & Abel 2011) to modelthe quasar in this study. X-ray and ionizing UV trans-port in MORAY includes radiation pressure on gas dueto photoionizations and is self-consistently coupled to hy-drodynamics and nine-species nonequilibrium primordialgas chemistry in Enzo. Secondary ionizations due to en-ergetic photoelectrons and Compton heating by X-raysare taken into account in the chemistry and energy equa-tions along with the usual primordial gas cooling pro-cesses: collisional excitational and ionizational coolingby H and He, recombinational cooling, bremsstrahlungcooling, H2 cooling, and inverse Compton cooling by thecosmic microwave background.The BH is represented by a modified star particle

whose X-ray luminosity, Lr, is ✏rmBHc2, where ✏r is themean radiative e�ciency, taken to be 0.1, and mBH is theaccretion rate. This luminosity is all in the form of 1 keVphotons to maximize the heating of gas because at higherenergies they have smaller ionization cross sections andat lower energies they deposit less energy per ionization(Xu et al. 2014; Hummel et al. 2016). This energy is alsoconsistent with new observations showing 90% of the X-ray flux of J1120 to be at 0.5 - 2 keV (Nanni et al. 2017).Our simulations do not resolve the accretion disk of theBH, which is ⇠ 1 pc in diameter, so we use an alpha diskmodel to compute accretion rates to approximate angu-lar momentum transport out of the disk on subgrid scales(DeBuhr et al. 2010). We also approximate a disk windby depositing 10�4 Lr as thermal energy above and be-low the midplane of the BH perpendicular to its angularmomentum vector (Ciotti et al. 2009).We use a stochastic prescription for star formation that

is based on Cen & Ostriker (1992) (hereafter CO92) butis slightly modified to accommodate a minimum star par-ticle mass to avoid having too many low-mass particles(section 8.2.2 of Bryan et al. 2014). The algorithm tal-lies the mass accumulated in a region until it exceeds theminimum star particle mass, at which point it creates astar particle there if the conditions for SF in CO92 havealso been met. This accumulated mass exceeds the min-imum mass at random times so particles are formed spo-radically. Furthermore, the particles will have a range ofmasses because the CO92 criteria might not be satisfied

Fig. 1.— Density slice of the halo at z = 7.1. Cold accretionstreams intersecting the host galaxy of the quasar are clearly visi-ble. Distances are in comoving Mpc. The cold streams have tem-peratures of ⇠ 500 K due to H2 cooling.

when the accumulated mass in a region exceeds the min-imum mass, so it will grow in mass until they are met.We adopt a minimum star particle mass of 107 M�.Star particles are assigned a Salpeter initial mass func-

tion (IMF) for simplicity and are tagged as sources ofionizing UV photons, which are propagated throughoutthe simulation box by MORAY. Each particle emits pho-tons at four energies: 12.6 eV (LW photons), 21.62 eV(the average energy of UV photons from massive, low-metallicity stars), 30 eV (He I ionizing photons), and 60eV (He II ionizing photons). The relative numbers ofphotons apportioned to these bins are determined fromthe fits for the Z = 0, no mass-loss tracks in Table 6 ofSchaerer (2002). The particles also deposit momentumand metals from stellar winds into the ISM over their life-times. SN feedback is modeled as thermal energy, with1051 erg deposited per explosion assuming one SN per200 M� of stars formed. Cooling by metals from SNeis included with rates from Glover & Jappsen (2007),assuming solar yields that are consistent with our cho-sen IMF. Our models also have a uniform Lyman-Wernerbackground due to early stars that evolves with redshift.Our simulation box is 100 h�1 Mpc on a side, with

a 2563 root grid and three nested 25 h�1 Mpc gridsthat are centered on the host halo for an e↵ective res-olution of 20483. These grids yield initial dark mat-ter and baryon mass resolutions of 8.41 ⇥ 106 h�1 M�and 1.57 ⇥ 106 h�1 M�, respectively. The grid is ini-tialized with gaussian primordial density fluctuations atz = 200 with MUSIC (Hahn & Abel 2011) with cos-mological parameters from the second-year Planck bestfit lowP+lensing+BAO+JLA+H0: ⌦M = 0.308, ⌦⇤ =0.691, ⌦b = 0.0223, h = 0.677, �8 = 0.816, and n = 0.968(Planck Collaboration et al. 2016). We use a maximumrefinement level l = 10 and refine the grid on baryon over-densities of 3 ⇥ 2�0.2l to obtain a maximum resolutionof 35 pc (comoving). We also refine on a dark matteroverdensity of 3 and resolve the local Jeans length withat least 32 zones at all times to avoid artificial fragmen-


• No Lyman alpha emitters (LAEs) are found within several Mpc of a quasar at z = 6.4 (Goto et al. 2017; see also Simpson et al. 2014; Ota et al. 2018; Uchiyama et al. 2019).

• This indicates that star formation is suppressed in halos with masses < 1010 Msun.

• If the gas remains metal-free, a Pop III starburst is expected when halos exceed this mass scale (Tvir ~ 105 K).

Goto et al. (2017)

Upper limit in vicinity of quasar CFHQS J2329−0301

LAE luminosity functions at z > 6

Observational Evidence Delayed Star Formation Near Quasars4 Goto

Figure 6. LAE LF. One σ upper limit from our work with NB906 is shown

with the red arrow. Note the bin size is 1 dex. The black and purple lines

show results from Ouchi et al. (2010) and Matthee et al. (2015) at z=6.6.

The black small dots are results from five different sub-fields in Ouchi et al.

(2010).

not in the redshift range of NB906 (6.4 < z < 6.5), or they are butwithout a strong Lyα emission. Because their broad-band coloursare still very red (i′ − z′ > 1.9, and z′ − zR > 0.3), they are likelyto be at z > 5.8. Previous observations reported the fraction ofbright LBGs with a strong Lyα emission is small at z> 6. For ex-ample, Stark et al. (2011); Pentericci et al. (2011); Schenker et al.(2014) reported the fraction of bright LBGs (EW>25A, MUV <-20.25) with a Lyα emission is ∼20% at z∼6, and ∼10% at z∼7.Our LBGs are even brighter with MUV =−22.2∼ −21.7. The frac-tion would be even smaller. It is not too surprising if none of the sixLBGs had a strong Lyα emission. Further conclusions need spec-troscopic confirmation of these LBGs.

4.2 Comparison to previous work

In previous work investigating the environment of QSOs, there ex-ist both positive and negative results on the detection of overden-sity of galaxies around QSOs. At lower redshift, QSOs’ duty cy-cles become relatively shorter compared with the age of the Uni-verse. There are increasing chances that surrounding galaxies mayhave formed before the central QSO did. In addition, LBGs andLAEs are different in their mass, and thus, physical effects from thecentral QSOs might be also different (e.g., Kashikawa et al. 2007).Therefore, to simplify the discussion, below we compare with re-sults at higher-z (z>4), which used LAEs to investigate the QSOenvironment.

In previous work, Kashikawa et al. (2007) found that LBGswithout Lyα emission form a filamentary structure near QSO SDSSJ0211−0009 at z=4.87, while Lyα emitters are distributed around2

but avoid QSO within a distance of ∼770 pkpc. Swinbank et al.(2012) used the Taurus Tunable Filter to find a significantgalaxy overdensity around a QSO at z=4.528 over 35 arcmin2.

2 Note that De Rosa et al. (2011) used MgII line to measure the redshift

of J0210−0009 to be z=4.894. If so, Lyα emissions could be out of the

NB711 filter.

Mazzucchelli et al. (2017) and Banados et al. (2013) investigatedthe environment of two z=5.7 quasars to find no enhancement ofLAEs in comparison with blank fields. Kikuta et al. (2017) ob-served environments of LAEs around two QSOs at z∼4.9 usinga narrow-band filter. They found that two QSOs are located nearlocal density peaks (< 2σ), but the number densities of LAEs ina larger spatial scale are not significantly different from those inblank fields.

While results of the previous studies vary, we would like tohighlight differences in our work. Our QSO is at the highest redshiftof z=6.4. At a higher redshift, the age of the Universe is younger.With less time available for halo formation, the effect of the QSOUV radiation would be clearer. This could be a reason why wefound the number density of LAEs is even smaller than the gen-eral field by 3 σ. It is an important future task to investigate QSOluminosity dependence of LAE distribution using multiple QSOsat similar or higher redshifts.

Also previous work at z∼5.7 could not rule out the QSO envi-ronment could be overdense at large scale (∼10 pMpc) because oftheir smaller field of view (∼200 cMpc2 at most). Our larger areacoverage of ∼5400 cMpc2, for the first time at z∼6, ruled this outby finding the lower density of LAEs is over a large scale of ∼10pMpc across.

4.3 Physical interpretation

By finding the lack of LBGs near the QSO, Utsumi et al. (2010)discussed the strong UV radiation may have suppressed the for-mation of galaxies in the vicinity of the QSO. The QSO is associ-ated with a giant Lyα nebulae (Goto et al. 2009, 2011), reflecting astrong UV radiation from the QSO. In this work, we found the lackof LAE not just in the QSO vicinity but in the whole field.

Kashikawa et al. (2007) quantitatively estimated how muchQSO’s UV radiation can suppress such galaxy formation. QSOCFHQS J2329−0301’s absolute magnitude is M

1450A=-25.2

(Willott et al. 2007), which is about 1.2 magnitude fainter that inKashikawa et al. (2007) at z=4.87 (M

1450A=-26.4). Following their

arguments, within 770 pkpc, J21 ∼ 24. The QSO can suppress star-formation (SF) in halos with Mvir < 10

10M⊙, while halos withMvir > 10

11M⊙ are almost unaffected (see their Fig.8). How-ever, at the edge of the field (∼5pMpc away), J21 is ∼ 0.6. OnlySF in halos with Mvir < 10

9M⊙ can be suppressed. Previousestimates of halo mass of typical LAEs (LLyα ∼ 10

42erg/s) are

around Mvir ∼ 1010M⊙ (Gawiser et al. 2007; Ouchi et al. 2010;

Garel et al. 2015). If so, the SF can be suppressed in halos near theQSOs, but it remains to be explained why LAEs are not detectedaround the edge of the field, where UV radiation is weaker.

There are several notable sources of uncertainty on the dis-cussion. On the theoretical side, it was assumed that stars form atthe centre of a spherical halo. If star formation takes place after adisk-like collapse or in substructures, the impact of photoionizationwill be greater and the inferred mass of the host halo can be larger.For example, some evidence was found that high-z sub-millimetergalaxies are rotationally-supported (e.g., Goto & Toft 2015).

On the observational side, we should note that halo mass es-timates of LAEs depends on the age of the stellar population,and thus there remains uncertainty. If the halo mass of LAEs areMvir < 10

9M⊙, the lack of LAEs in our QSO field is consistentwith the suppression scenario.

The suppression scenario could explain the detection of LBGsin Utsumi et al. (2010). LBGs are thought to have older stel-lar population, and thus more massive than LAEs (Overzier et al.

c⃝ 2009 RAS, MNRAS 000, 1–5


Our calculations include: •A one-zone dynamical model assuming gas is in free-fall collapse (e.g. Omukai 2005) •Monoenergetic quasar X-ray heating and ionization (e.g. Nanni et al. 2017) •Lyman-Werner (LW) H2 dissociating UV radiation (e.g. Haiman 2001; Ahn et al. 2009)

•H- photodetaching radiation from stars in quasar host galaxy (e.g. Agarwal et al. 2016) •Lyα−enhanced H- photodetachment in collapsing halo (JLJ & Dijkstra 2017)

•Gas cooling, including by H2 and HD (e.g. JLJ & Bromm 2006; Wolcott-Green & Haiman 2011)

Infalling X-ray heated primordial gas

High z quasar

X-rays

LW radiation

Optical+infrared

JLJ & Aykutalp (submitted)

Calculating the Evolution of Quasar-irradiated Primordial Gas2

FIG. 1.— Schematic of the scenario we consider, the evolution of collapsing primordial gas (right) under the influence of X-rays, LW and optical/infraredradiation from a quasar (left) composed of an acceting black hole and stars in its host galaxy at redshift z ! 6. The intense X-ray heating of the primordial gasprevents its collapse into its host halo until the halo mass exceeds ∼ 1010 M⊙ (see Figure 2), resulting in the formation of a massive cluster of Population IIIstars or a direct collapse black hole.

ing supports the tantalizing possibility that the strong radiativefeedback from high redshift quasars may delay primordial starformation until extremely massive haloes are assembled, sug-gesting that the conditions for the brightest Pop III starburstsmay indeed occur in the neighborhoods of bright high redshiftquasars.

Here we study the evolution of primordial gas irradiated bya luminous quasar at high redshift, in order to predict the na-ture of the primordial objects formed during its collapse. InSection 2 we lay out the methodology of our calculations. InSection 3 we present our basic results illustrating the evolu-tion of irradiated gas, while in Section 4 we explore the na-ture of the objects that are formed in its collapse. In Section5 we demonstrate the validity of this model, as it depends onthe suppression of star formation in haloes neighboring highredshift quasars during their full growth history. Finally, weconclude in Section 6 with a brief summary of our findings.

2. METHODOLOGY

The basic scenario that we consider is illustrated schemat-ically in Figure 1. On the left, a quasar at high redshift (e.g.z ! 6) emits radiation in three distinct wavebands that impactthe evolution of the primordial gas collapsing into the massiveDM halo, on the right, that sits at a distance d from the quasar.A portion of this radiation is emitted during the accretion pro-cess of the central black hole and a portion is from the stellarpopulation in the quasar host halo. In addition, some fractionof the metals produced by the stars inhabiting the host halo areassumed to be entrained in a galactic wind driving an outflow.

The accreting black hole powering the quasar emits highenergy X-ray radiation, most of which escapes its host galaxy,although a small portion is converted into Lyman-Werner(LW) H2-dissociating radiation that escapes the host galaxy.Here we assume that the X-rays which escape the host galaxyare monoenergetic at 1 keV, which is in the range in whichmost X-ray energy has been observed to escape from high-zquasars (e.g. Nanni et al. 2017).4 For the flux of LW radiationJ21,BH at the location of the target primordial halo that is pro-

high redshift quasars this could also explain the observed trend (but see e.g.Balmaverde et al. 2017; Ginolfi et al. 2018).

4 We also note that Smidt et al. (2018) find good agreement with the avail-

duced due to reprocessing of the radiative energy emitted inthe accretion process, as well as due to diffuse emission in thehost galaxy, we assume a simple scaling that has been derivedfrom post-processing of cosmological radiation hydrodynam-ics calculations (Barrow et al. 2018):

J21,BH = 80

!

MBH

108 M⊙

"!

fEdd

1

"!

d

1Mpc

"

−2

, (1)

where d is the distance between the quasar and the target pri-mordial halo (as shown in Figure 1), MBH is the mass of theblack hole powering the quasar, and fEdd is the ratio of the X-ray luminosity to the Eddington luminosity. Finally, the unitsof J21,BH are the standard 10−21 erg s−1 cm−2 Hz−1 sr−1. TheX-ray energy that escapes the quasar host halo propagates intothe IGM, where it heats the primordial gas to high tempera-tures. This is shown in Figure 2, which illustrates schemat-ically the impact of radiation emitted from a high redshiftquasar on the primordial gas in the surrounding IGM.

The stellar population in the quasar host galaxy is assumedto contribute to the LW flux impinging on the target primor-dial halo, as well as to a flux of optical and infrared radiationat energies ≥ 0.75 eV that can destroy H−, an important pre-cursor to the formation of H2 in the primordial gas. The LWflux J21,∗ produced by the stellar population is expressed interms of the stellar mass M∗ in the quasar host halo, as fol-lows (Johnson et al. 2013):

J21,∗ = 60

!

M∗

1010 M⊙

"!

d

1Mpc

"

−2

. (2)

This rate has been chosen to correspond to an effective stellartemperature of T∗ = 3 × 104 K, in line with the cosmologi-cal average stellar properties at z ∼ 6 presented in Agarwal& Khochfar (2015). Also following these authors, we haveadopted this effective stellar temperature in evaluating the rateof H− destruction by optical and infrared radiation, although

able data on the Mortlock et al. (2011) quasar at z = 7.1 by adopting sucha monoenergetic X-ray spectrum in a fully cosmological radiation hydrody-namics calculation.

11/1/2018 | 9

Pop III star clusters or DCBHs may form around high-z quasars.

• Within a characteristic distance from a high-z quasar, the gas remains hot enough during its collapse to form a direct collapse black hole (DCBH):

6

TABLE 2MAXIMUM DISTANCE OF DCBHS FROM QUASARS

Stellar to BH mass ratio

BH mass [M⊙] 1 10 100

108 10 20 50109 30 70 2001010 100 200 500

NOTE. — Maximum distance dDCBH (in kpc) from host quasarspowered by black holes with masses MBH in which DCBH can form,for various ratios of the stellar to black hole mass (M∗/MBH) in thequasar host halo. Eddington accretion is assumed for the BH inthe source quasar in all cases shown here, as is an effective stellartemperature of T∗ = 3 × 104 K.

FIG. 7.— Temperature of the gas (Tgas) surrounding a canonical high red-

shift quasar powered by a BH that grows to a mass of MBH = 109 M⊙ by z= 7 via Eddington-limited accretion, as a function of the distance d from thequasar, at three epochs of its growth (solid): z = 19 (yellow), 11 (green) and 7(red); at these times the BH mass is 105, 107 and 109 M⊙, respectively. Alsoshown is the virial temperature (Tvir) of a 2σ halo (dashed), correspondingto a massive (1010 M⊙) potential Pop III star forming halo at z ∼ 6, at thesame three epochs. Star formation would be suppressed in the 2σ halo up toz = 7 within ≃ 100 kpc, as the gas temperature remains higher than its virialtemperature.

may be the most frequently occurring primordial objects inthe vicinity of high-z quasars.

5. SUPPRESSION OF STAR FORMATION

In our picture of bright Pop III starburst and/or DCBH for-mation, it is critical that the massive haloes in which theseobjects may form remain metal-free, as even small amountsof heavy elements will prevent Pop III star formation andwill likely also preclude DCBH formation (e.g. Omukai et al.2008). This implies that star formation must be suppressed inthem throughout their growth until they reach mass scales ofup to ! 1010 M⊙, by z ≃ 6. Here we consider the growth his-tory of a typical such halo, which corresponds to a ≃ 2σ over-density in the cosmological dark matter field (e.g. Barkana& Loeb 2001). We also model the growth of the photoheatedregion surrounding a high redshift quasar with a mass that isconsistent with that of the highest redshift quasars found todate (Mortlock et al. 2011; Bañados et al. 2017).

Figure 7 shows the virial temperature of a 2σ halo, corre-sponding to a halo with mass 1010 M⊙ at z = 6, at three repre-sentative redshifts (z = 19, 11 and 7) during its growth. Also

FIG. 8.— Graphical representation of our findings presented in Table 2 forthe maximum distance dDCBH from a high redshift quasar at which a DCBHcan form in a collapsing primordial halo, as it depends on the mass MBH of theblack hole powering the quasar and on the stellar mass M∗ in the quasar hostgalaxy. In general, DCBH formation can occur farther away from quasarspowered by more rapidly accreting black holes, as it can also from quasarhost galaxies containing a larger mass in stars. See equation (3) for a formulaproviding a rough fit to these results.

shown are the temperature profiles of the gas in the vicinityof a growing BH powering the high redshift quasars that aremodeled in the cosmological radiation hydrodynamics simu-lations of Smidt et al. (2018), at these same three represen-tative redshifts. At early times, the gas is too hot to collapseinto the 2σ target halo (i.e. Tgas > Tvir; see e.g. Okamoto etal. 2008), unless it is farther from the quasar than ∼ 100 kpcby z = 7. Thus, haloes with masses of ∼ 1010 M⊙ will notform stars in the vicinity of such high redshift quasars, unlessthey lie farther than ∼ 100 kpc away by z ≃ 7. Cosmologicaldark matter simulations predict that there are expected to behaloes within this mass range that lie at distances d < 100 kpcof the ∼ 1012 M⊙ haloes inferred to host the highest redshiftquasars (see e.g. Poole et al. 2017; Poulton et al. 2018). Thisimplies that star formation in these haloes may in fact be sup-pressed as they grow, setting the stage for a Pop III starburstor DCBH to form as we have explored here. Farther awayfrom the quasar, it may only be lower mass (e.g. 108 - 109

M⊙) haloes in which star formation is suppressed; these ob-jects may still host DCBHs or Pop III starbursts (e.g. Trentiet al. 2009; Johnson et al. 2010; Visbal et al. 2017), althoughthey would likely be less luminous than those hosted by moremassive haloes.

6. SUMMARY

We have explored the evolution of the primordial gas as it isexposed to the extreme radiation emitted from high-z quasarspowered by rapidly accreting supermassive black holes andby their host stellar population. As shown in Figure 2, weconfirm that the temperature of the gas is raised to values ofup to ∼ 106 K due to the intense X-ray flux, with the implica-tion that the gas will only collapse once it has been incorpo-rated in DM haloes with masses up to ∼ 1011 M⊙. Such largehaloes would provide extremely large mass reservoirs of gasfrom which Pop III stars could form, setting the stage for thebrightest primordial starbursts in the early Universe.

The possible final outcomes of the collapse of the gas thatwe find are shown schematically in Figure 8. The intense LWradiation that is emitted from quasar host galaxies suppresses


!"#$% = 200kpc & '()*+,.⨀

0+.2& '∗*++.()

0+.4


Metal enrichment is not expected to preclude Pop III star formation.

• Metal enrichment is observed to extend out to only ~ 30 kpc from high redshift quasars (Cicone et al. 2015; also e.g. Fujimoto et al. 2019).

• This length scale is also found in recent cosmological simulations (Smidt et al. 2018; Ni et al. 2018).

• We find that both Pop III clusters and DCBH can form at larger distances.

5

10-3 10-2 10-1 1 10radius (Mpc)

102

103

104

105

106

107

T (

K)

Fig. 4.— Left: metallicity slice through the center of the host galaxy of the quasar at z = 7.1. Distance scales are in comoving Mpc.Right: Spherically averaged temperature profile of the H II region of the quasar at z = 7.1. The vertical line marks the approximateboundary of gas at > 104 K at ⇠ 2 Mpc, the observed radius of the ionized near zone of ULAS J1120+0641.

Fig. 5.— Stellar mass of the host galaxy of the quasar at z = 7.1. Left panel: number of star particles binned by log mass. Right panel:cumulative stellar mass as a function of star particle mass.

peak into the keV range (Done et al. 2012). The averagephoton energy of these spectra ranges from 2.0 keV at105 M� to 0.3 keV at 109 M�, so our choice of 1 keV isan appropriate average for this interval in BH mass.That said, lower-energy photons in actual SMBH spec-

tra may have a measurable e↵ect on the evolution of thequasar because they have larger cross sections to ion-ization in H, He and some metal ions. But this e↵ectappears to be modest at lower BH masses. Smidt et al.(2016) evolved a DCBH over two decades in mass withboth monoenergetic X-ray and multigroup spectra thatincluded ionizing UV and found little change in its evo-lution. Radiation pressure from IR on dust in the hostgalaxy of the BH may also drive strong but short-livedoutflows (Bieri et al. 2017; Costa et al. 2018a,b), althoughsuch outflows have only been observed in a fraction ofquasars at z > 6. The softer components of SMBH spec-tra may also quench their images at 21 cm in emission

because they ionize rather than heat the IGM. The ef-fects of evolving BH spectra on the growth of the firstquasars will be examined in future simulations.While our models trace metal production due to star

formation, they do not include dust formation and cool-ing or opacity due to dust and metals in the radiationtransport. Dust cooling would promote star formationin environments in which radiation does not destroy itfirst, and both metals and dust would enhance X-rayheating in the galaxy by absorbing more photons. Howthese processes would o↵set each other and other factorsgoverning star formation and the growth of the BH willbe explored in future studies.X-ray and SF feedback limit accretion to 0.2 - 0.8 mEdd

in our models, rates at which quasars are not observedto have jets, so we do not include them in our models.Steady jets are observed in active galactic nuclei (AGNe)at L . 0.01LEdd and intermittent jets are seen in quasars

Smidt, Whalen, JLJ, et al. (2018)

Metal enrichment by a quasar at z = 7


It may only be around high-z quasars that JWST could find Pop III clusters.

• Basic predictions for the luminosities and spectral signatures of Pop III clusters and DCBHs can be made now.

• The large mass budget implies galaxies potentially more luminous than previously considered, even under conservative assumptions: • Collapse fraction = 0.1 (e.g.

Dijkstra et al. 2004) • Star formation efficiency =

0.002 (e.g. Xu et al. 2016; Barrow et al. 2018)

• Here we show flux limits for 3 sigma detection in 2x105 sec.

Pop III fluxes vs. JWST detection limits


https://jwst.stsci.edu/instrumentation/nircam


DCBH-powered Pop III starbursts may be more easily detectable by JWST.

• DCBH accretion power leads to enhanced luminosity and X-rays trigger a Pop III starburst (Barrow et al. 2018).

• DCBH-powered Pop III starbursts would be brighter, due to reprocessed emission from accretion.

• Could be detected by JWST with shorter exposure times than pure Pop III starburts.

JWST Detectability of DCBH-powered Starbursts

Barrow, Aykutalp & Wise (2018)

Figure 5: Exposure time needed to confirm a a DCBH observation with a S/N of 5. The existence

of a DCBH in this scenario can be confirmed with J277w and either J200w(blue) or J210m(green).

We can distinguish between the recovery and other phases with the addition of J277w(purple) and

we can use J150w to confirm the epoch (black). Each line includes the preceding contributions. The

purple and black lines assume the use of J200w and approximately overlap due to the log scaling.

Exposure times are based on the JWST Exposure Time Calculator 31.

15


Surveys with NIRCam could be carried out with one pointing per quasar.

5.1

arcm

in

2.2 arcmin

300 kpc at z = 6

Predicted region of brightest

Pop III clusters

JWST NIRCam FOV

Figure 6: (Extended Data Figure 2)

20

Figure 6: (Extended Data Figure 2)

20

10 a

rcse

c

Wu et al. (2015)

• One huge advantage to searching around high-z quasars is that we already know where to look — they are bright targets!

• Measurements of stellar and BH mass can be used to estimate where DCBH and Pop III clusters may form around individual quasars.

https://jwst.stsci.edu/instrumentation/nircam


Population III stars should be sought around high-z quasars!

• Current observational constraints support the possibility that the brightest Pop III clusters form in massive halos around high-z quasars.

• It may only be around quasars that Pop III clusters are bright enough to be found by JWST.

• Single pointings toward high-z quasars by JWST would allow to test predictions tailored to individual quasars.

6



BH mass [M⊙] 1 10 100

108 10 20 50109 30 70 2001010 100 200 500











6. SUMMARY




Backup Slides


We recover the expected IGM temperature profiles around high-z quasars.

• Applying our one-zone model for X-ray irradiation to the IGM at z = 6 produces the expected temperature profile around quasars powered by BHs accreting at the Eddington rate (e.g. Mortlock et al. 2011; Smidt et al. 2018).

• The H II region surrounding the quasar is larger and hotter for more massive BHs .

• The gas temperature is high enough to suppress star formation in halos in the observed mass range of up to 1010 Msun.

3

FIG. 2.— Temperature of the primordial gas (left axis), as a function ofdistance d from quasars powered by Eddington accretion onto black holesof three distinct masses: 108, 109 and 1010 M⊙. The gas is assumed tobe at the cosmic mean density at z = 6. The kinks in the curves are dueto recombination of helium and hydrogen ions and the additional coolingthat they provide. Also shown is the minimum halo mass required for theprimordial gas to collapse (right axis) to form either stars or a DCBH.

in Section 3 we explore the impact on our results of assum-ing either older (cooler) or younger (hotter) stellar populations(e.g. Shang et al. 2010).

To model the evolution of the primordial gas as it collapsesinto the massive primordial target halo (shown at right in Fig-ure 1), we use these radiative fluxes in the one-zone primor-dial chemistry code adopted in Johnson & Dijkstra (2017). Toproperly incorporate the effects of X-rays in this model, wehave made the following four modifications. (1) We calcu-late the rate of photoionization of both hydrogen and heliumspecies, using the cross sections presented in Osterbrock &Ferland (2006). (2) We account for the partitioning of pho-toelectron energy into secondary ionizations and collisionalheating, as described by Shull & van Steenberg (1985). (3)We adopt an approximate treatment for the local attenuationof the X-ray flux in the target primordial halo, following John-son et al (2014). (4) We account for Compton heating of theprimordial gas due to X-rays.

It is important to note that this treatment is appropriate forprimordial gas that starts at the low densities characterizingthe high-z IGM, as has been extensively studied (e.g. Dijkstraet al. 2004; Okamoto et al. 2008; Johnson et al. 2014; Chon& Latif 2017). This is distinct from the situation in which gasis pre-collapsed in haloes and is photoevaporated by ionizingphotons, as studied in detail by e.g. Iliev et al. (2005). Weemphasize, however, that the impact of X-rays in potentiallystimulating primordial gas cooling through the creation of freeelectrons that catalyze H2 formation is included in our one-zone model (as also in e.g. Inayoshi & Omukai 2011).

As we show in the next Section, our results are in basicagreement with those gleaned from the similar frameworkpresented in Inayoshi & Omukai (2011) and in the cosmolog-ical calculations presented in Regan et al. (2016), although inmany cases the X-ray fluxes that we consider are much higherthan those considered by these authors.

3. EVOLUTION OF STRONGLY IRRADIATED PRIMORDIAL GAS

Given the extreme radiative environment in the vicinity ofa luminous quasar in the early Universe, the evolution of theprimordial gas exposed to this radiation is strongly dependenton its proximity to the quasar. In addition, the chemistry ofthe primordial gas is impacted in a complex manner by the

various types of radiation that are emitted from the accret-ing black hole and its surrounding host galaxy. In particu-lar, while the LW radiation and the optical/infrared radiationgenerally act to suppress the abundance of the key molecularcoolant H2, the intense X-ray radiation acts to produce freeelectrons which stimulate its formation (e.g. Glover 2003;Aykutalp et al. 2014).

Figure 3 shows the evolution of the primordial gas as itcollapses to high density in a massive primordial DM haloexposed to the radiation produced by a quasar powered byEddington accretion onto a 108 M⊙ supermassive black holewithin a host galaxy containing 1010 M⊙ in stars. While thegas is initially at very high temperatures when it is at the den-sity of the IGM prior to its collapse, as shown in Figure 2,once it is bound in a sufficiently massive DM halo it is able tocollapse to high density and its temperature then drops to the∼ 104 K floor set by atomic hydrogen cooling. Then, depend-ing on its distance from the quasar, the temperature drops byup to another two orders of magnitude due to molecular cool-ing by H2. There are two competing processes which dictatethe degree to which H2 cooling affects the evolution of theprimordial gas. While the free electron fraction is elevateddue to photoionization of hydrogen and helium species by theX-rays, leading to the catalyzed formation of H2 molecules,the LW and optical/infrared radiation emitted from the quasarhost galaxy also strongly suppress the H2 fraction. The resultis that, closer to the quasar source, the gas remains hotter atthe highest densities than it is farther away.

The net impact of the X-ray flux on the thermal evolutionof the gas is shown in Figure 4, where the solid lines showthe temperature of the gas with the X-ray flux included in thecalculation and the dashed lines show it with them excluded.It is clear that while they strongly heat the gas at low densi-ties, the X-rays also have the impact of enhancing molecularcooling at high densities (e.g. Aykutalp et al. 2014; Inayoshi& Tanaka 2015; Latif et al. 2015; Glover 2016). Their ef-fect is strongest closest to the quasar source, where in theirabsence the gas temperature remains elevated at ≃ 104 K at adistance of 100 kpc, signifying a very strong suppression ofH2 formation.

At larger distances from the quasar source, where the gasis able to cool due to the radiation from H2 molecules, it isalso possible for the coolant HD to play a role in the thermalevolution of the gas, as shown in Figure 5. As the gas temper-ature drops to lower values with increasing distance from thequasar source, HD cooling becomes stronger, as reflected inthe higher HD fractions at larger distances in the bottom-rightpanel of Figure 3. This is consistent with previous work show-ing that HD cooling can be triggered in primordial gas withan elevated free electron fraction (e.g. Nagakura & Omukai2005; Johnson & Bromm 2006; Nakauchi et al. 2014). Dueto the lower temperatures to which the gas is able to cool, inpart due to HD cooling, farther from the quasar source, thefragmentation scale in the primordial gas is likely smaller andthe characteristic initial mass function of stars that form maybe shifted to lower masses (e.g. Uehara & Inutsuka 2000; Ri-pamonti 2007; McGreer & Bryan 2008).

While we have assumed a cosmological average stellar pop-ulation for the quasar host galaxy in our results presented thusfar, in Figure 6 we show the thermal evolution of the gas ir-radiated by both an older and a younger stellar population,corresponding to characteristic stellar radiation temperaturesof T∗ = 104 and 105 K, respectively. Principally due to the el-

IGM heating by quasars at z = 6



Star formation even in early minihalos can be suppressed by quasars.

• Dark matter halos with masses of 1012 Msun expected for high redshift quasars are found to have near neighbor galaxies within ~ 100 kpc at the 2 sigma mass level (Poole et al. 2017; Poulton et al. 2018).

• This makes them correspond to the 1010 Msun halos that may host Pop III or DCBHs.

• Radiative feedback from the quasar, going back to its possible birth as a DCBH, could suppress star formation in such close halos down to at least z = 7.

6



BH mass [M⊙] 1 10 100

108 10 20 50109 30 70 2001010 100 200 500











6. SUMMARY




Heating of the IGM throughout the life of a high-z quasar


Intense radiation across wavelengths leads to complex gas chemistry.

• Applying our model to collapsing irradiated produces the expected enhanced H2 fraction due to X-ray ionization (e.g. Inayoshi & Omukai 2011).

• With X-ray heating, the gas is hotter at low density but then cools to lower temperatures as it collapses.

• The gas cools to lower temperatures the further it is from the quasar.

5

FIG. 4.— Like the top-left panel in Figure 3, but now showing the evolutionof the collapsing gas with (solid) and without (dashed) the quasar source X-ray flux.

FIG. 5.— Like the top-left panel in Figure 3, but now showing the evolutionof the collapsing gas with (solid) and without (dashed) HD cooling included.

FIG. 6.— Like the top-left panel in Figure 3, but now showing the evolutionof the collapsing gas under the influence of LW and optical/infrared radiationfrom a stellar population with a characteristic temperature of 104 K (solid)and 105 K (dashed).


Stellar temperature [K]

BH mass [M⊙] 104 3 × 104 105

108 300 50 20109 1000 200 701010 3000 500 200

NOTE. — Maximum distance dDCBH (in kpc) from host quasarspowered by black holes with masses MBH in which DCBH can form,for various values of the effective temperature T∗ of the stellar pop-ulation in the quasar host halo. Eddington accretion is assumed forthe BH in the source quasar in all cases shown here, as is a stellar toblack hole mass ratio of M∗/MBH = 100.

for the earliest stages of growth of high-z quasars, the centralblack hole mass can be even larger relative to that of the stel-lar population (e.g. Agarwal et al. 2013). Table 2 shows thevalues of dDCBH that we find for various ratios of the stellarto black hole mass in the quasar host halo. In general, giventhe contribution that the stellar component makes to the pro-duction of H2-dissociating LW radiation, we find that DCBHformation can occur out to larger distances for a larger stellarpopulation, at a given value of the central black hole mass.The results shown in Table 2 are captured well by a single fit-ting formula which expresses dDCBH in terms of the black holemass MBH and stellar mass M∗ in the quasar host halo:

dDCBH ≃ 30kpc

!

MBH

109 M⊙

"0.5!M∗

MBH

"0.4

, (3)

where this is valid under the assumption of Eddington accre-tion onto the black hole and given our fiducial case of a z ∼ 6cosmological average stellar population with a characteristictemperature of T∗ = 3 × 104 K. Outside of dDCBH we expectthat the gas will cool to sufficiently low temperatures that acluster of Pop III stars is likely to form, instead of a DCBH.

While the radiation emitted from high-z quasars may pro-vide the conditions for the formation of these objects, suchquasars are also known to emit metal-enriched ouflows whichpollute the IGM, as shown schematically in Figure 8. Thesemetals, if mixed with the collapsing primordial gas, will actto preclude the formation of Pop III stars and DCBHs. At anaverage velocity of 100 km s−1 (e.g. Girichidis et al. 2016),the outflow would progress at most ≃ 100 kpc within the ageof the Universe at z = 6. This is, in fact, broadly consistentwith the results of a cosmological radiation hydrodynamicssimulation (Smidt et al. 2018) of the formation of a z = 7.1quasar matching the observable properties of the Mortlock etal. (2011) quasar, in which the metal-enriched region extendsout to ≃ 50 kpc from the compact quasar host galaxy.5 Inaddition, this is also in line with the ≃ 30 kpc extent of theoutflow inferred for a bright z = 6.4 quasar by Cicone et al.(2015). As these distances are comparable to those we find fordDCBH around quasars powered by relatively small black holesand with low stellar to black hole mass ratios, it appears thatthe rate of DCBH formation around high-z quasars is likelyto be somewhat reduced due to metal enrichment of the pri-mordial IGM in their vicinity. Given this, the Pop III galax-ies which we expect to form farther out (i.e. at d > dDCBH)

5 We note that a similar extent of ≃ 50 kpc for metal-enriched outflowsfrom quasar host galaxies at z ≃ 7.5 is also found in other recent cosmologicalsimulations (e.g. Ni et al. 2018).


Thermal evolution of collapsing irradiated gas


The Impact of the Stellar Population in the Quasar Host Galaxy

• Varying the stellar component of the quasar spectrum produces the expected drop in H2 cooling due to photodissociation of H- (e.g. Chuzhoy et al. 2007; Shang et al. 2010; Latif et al. 2015; Agarwal et al. 2018).

• The gas cools to lower temperatures when the stellar spectrum is harder.

• If the gas remains at ~ 104 K, a direct collapse black hole (DCBH) is expected to form.

5






BH mass [M⊙] 104 3 × 104 105

108 300 50 20109 1000 200 701010 3000 500 200



dDCBH ≃ 30kpc

!

MBH

109 M⊙

"0.5!M∗

MBH

"0.4

, (3)




Thermal evolution of collapsing irradiated gas



Direct collapse black holes may form in close proximity to high-z quasars.

• When the primordial gas remains at ~ 104 K, the outcome of its collapse is expected to be a direct collapse black hole (DCBH) (e.g. Volonteri 2012; JLJ & Haardt 2016; Latif & Ferrara 2016; Valiante et al. 2017).

• We find that DCBH are expected to form in collapsing primordial halos that are sufficiently close to high-z quasars.

• How close depends on the star/BH mass ratio and on the age of the stellar population.

6



BH mass [M⊙] 1 10 100

108 10 20 50109 30 70 2001010 100 200 500











6. SUMMARY



5






BH mass [M⊙] 104 3 × 104 105

108 300 50 20109 1000 200 701010 3000 500 200



dDCBH ≃ 30kpc

!

MBH

109 M⊙

"0.5!M∗

MBH

"0.4

, (3)






Next generation simulations are required for detailed predictions.

• Need high resolution to track minihalos and to resolve BH accretion and feedback

• Need large simulation volume to find a bright quasar at high redshift

• Must resolve LW, X-rays from BH, stellar UV and its impact on primordial halos

• Need to track star formation, supernova feedback and metal enrichment

• Smidt et al. (2018) begin to approach this, and match observations of Mortlock et al. (2011) quasar well.

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA

UNCLASSIFIED

Our Simulations Match a Broad Suite of DataOur Enzo simulation ALMA Data

[C II] emission

Quantity Data SimulationBHmass[109Msun] 2+1.5-0.7 2.2

BHacretionrate[Msunyr-1] ~40 11+20-10Starformationrate[Msunyr-1] 105--340 245RadiusofHIIregion[Mpc] 2.1+0.1-0.1 2

Metallicity[Zsun] ~1 1--2Dynamicalmass[109Msun] 43+9-9 40

• We find broad agreement with the available data on one of the earliest known quasars, at z = 7.1 (Mortlock et al. 2011):

• BH mass • BH accretion rate• Metallicity of the host

galaxy• Host galaxy star

formation rate• Dynamical mass of

the host galaxy

• This implies that on-the-fly X-ray feedback is key to understanding early quasar formation.

5 kpc

H2 fraction

30 kpc

Data from Mortlock et al. (2011), Dunlop (2013), Barnett (2015) and Venemans et al. (2017)

Venemans et al. (2017)

Smidt, Whalen, JLJ & Li (2017)Smidt, Whalen, JLJ, et al. (2018)

Nevertheless, it is critical to make what predictions we can now, before next generation observations are carried out (e.g. by JWST).


Formation Sites of Population III Stars and GalaxiesH

alo

mas

s [M

sun]

z

Population III stars are expected to form in increasingly massive halos in which previous star formation has suppressed by increasingly strong radiative feedback.

1011

1010

109

108

107

106

5 10 15 20

Quasar photoheating Tvir ~ 106 K

Stellar photoheating Tvir ~ 5 x 104 K

H2 photodissociation Tvir ~ 104 K

H2-cooled gas Tvir ~ 103 K

First stars

Most massive potential Pop III galaxies

First galaxies

Pop III galaxies in reionized regions

extreme population iii starbursts and direct collapse ... · has a quite good ﬁt at slightly...

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