the sad story of the cosmic EUV backgroundThe Universe in a Nutshell Wednesday, November 27, 13. The...

the sad story of the cosmic EUV background

Matthew McQuinnUC Berkeley

arxiv:1306.4985 with Gabor Worseckarxiv:1101.1964 with Peng Oh and C.-A. Faucher-Giguere

work nearing completion with Yookyung Noh

Wednesday, November 27, 13

Focus of this talk

We understand this!

err...Ωcrab =10-25

Slightly more nonlinear.Much of structure can be

related to cosmological ICs

Getting more nonlinear. Can we model this from

knowledge of ICs?ΩIGM ~ 1

ΩGalaxy ~ 0.005

The Universe in a Nutshell


The picture of the intergalactic HI-ionizing radiation field

1000 c-Mpc

source at z=1

m.f.p

e.g., Haardt & Madau ’96


m.f.p



1000 c-Mpc

source at z=2



m.f.p


1000 c-Mpc

source at z=3


m.f.p



1000 c-Mpc

source at z=5


credit: Marcello AlvarezWednesday, November 27, 13

the post-reionization ionizing background is largely uniform

• λmfp= 400 [𝝼13.6eV]1.5 [(1+z)/4]-3 comoving Mpc at 2<~z<~5

• Fraction of volume where background enhanced by factor of 2 over mean equals

or ~0.1 % for quasars, ~0.01 % for galaxies at z=3.

fproximity

= (6p⇡)�1 n�1/2 ��3/2

mfp


Digression: The Lyα Forest


A uniform background is assumed to measure cosmological and other parameters from the Lyα forest.

figure from Weinberg et al ’03

Faucher-Giguere et al 2008Historic references: Miralda-Escude, Cen, Ostriker & Rauch

’96; Hernquist Katz, Weinberg, Miralda-Escude ’96 Wednesday, November 27, 13

Background is adjusted until mean absorption agrees w/ observations; e.g., Rauch et al ‘97

In fact, the amplitude of the “uniform” radiation background is the first thing

measured in the Lyα forest


Constraints on amplitude of 1 Rydberg radiation background

Fan et al 2006Bolton & Becker 2013

0.1 H(z)-1

Phot

oion

izat

ion

Rat

e


Jν = mean free path x emissivity

What sets the mean free path?

• Systems with NHI ~ 1016-1018 cm-2

• After the Lyα forest (which probes NHI ~1012.5-1014.5 cm-2) these are the next most dense systems that are relatively easy to observe.


How are Lyman-limits identified?

z=3.8

Method 1:

Method 2:

Prochaska, Worseck, O’Meara 2012


Are Lyman-limit systems captured in

cosmological simulations?


Lyman-limits in simulations• simple estimate (if absorbers are Jeans’ length)

is that they reside outside virial radius at z>4

• These densities may or may not be impacted by poorly understood feedback processes.

• Halos where gas is not multiphase dominate σ.

• Previous studies from early 2000s found that the abundance in simulations was way off.

�b = 102✓1 + z

5

◆�3 ✓ NHI

1017cm�2

�HI

10�12 s�1

◆2/3 ✓ T

104 K

◆0.17

where �b ⌘ ⇢/h⇢i � 1 e.g. Schaye 2001


Cosmological simulations agree well with Lyα forest observations (probing 𝛅b ≲ 3). How

well do they fare at 𝛅b ~ 100 ?


Method


What self-shielding systems look like (z=4)

log10NHI

~0.5 cM

pc

15 16 17 18 19 20 21


Comparison w/ Observations at z=4

Simulations able to (approximately) reproduce gas at outskirts of galactic halos. They should do better with increasing redshift.

HI C

olum

n de

nsity

dis

trib

utio

n

Highlighted regions are observational

constraints derived/compiled in Prochaska,

Omeara, Worseck (2010)

MM, Oh, Faucher-giguere, ’11

(also see Altay++ ’11)

Most importantfor mean free path.

Disks where I would not trust simulations.

[cm-2]


Comparison w/ Observations at z=4

Simulations able to (approximately) reproduce gas at outskirts of galactic halos. They should do better with increasing redshift.

HI C

olum

n de

nsity

dis

trib

utio

n

Highlighted regions are observational

constraints derived/compiled in Prochaska,

Omeara, Worseck (2010)

Very Steepβ ≥ 1.7

MM, Oh, Faucher-giguere, ’11

(also see Altay++ ’11)

Most importantfor mean free path.

Disks where I would not trust simulations.

[cm-2]


Let’s assume the simulations are

capturing high-redshift Lyman-limit systems


How many photons do sources emit?(emissions balance recombinations)

MM, Oh, Faucher-Giguere ’11ph

oton

s ba

ryon

-1 G

yr-1

1

10

Kuhlen &Faucher-Giguere ’12see also Mirald-Escude ’03 and

Bolton & Heahnelt ’07


1 Rydberg radiation background evolves rapidly at z~6

Fan et al 2006

0.1 H(z)-1

This fast change cannot be evolution in sources’ emissivity!Wednesday, November 27, 13

It’s not obvious that this is overlap phase of reionization results in rapid evolution in ΓHI

Prediction: Mean free path is shorter than bubble size: e.g., Furlanetto & Oh ’05

RT simulations have not

addressed this as they have not

resolved well the Lyman-limits.

140

com

ovin

g M

pc

IONIZED

NEUTRAL

Simulation of reionization


Intensity = (mean free path) x (source emissivity)



Measured from Ly-alpha

forest




forest

Distance betweendense self-shielding

systems




forest


systems

# of Recombinations(clumpiness of dense

systems)




forest


systems


systems)

~ emissivity(2α-1)/(2α-3) (assumes power-law density profile w/ index α)

~ emissivity1/(2 -β) (β is slope of HI column density distribution)

Observations find β~1.7 at z=3




forest


systems


systems)

≈ emissivityn

• At z=4, n=2.2 and simulations predict a factor of 1.2 change in emissivity results in factor of 1.5 change in intensity.

• At z=6, n=4.5 and simulations predict a factor of 1.2 change in emissivity can result in factor of 2.3 change in intensity. May explain rapid 𝝉eff,Lyα evolution seen in Fan et al (2006).


Inhomogeneities in the ionizing background


Constraining the properties of the EUV ionizing background directly

• Can do this by comparing HeII abundance to HI abundance, which for primordial gas:

• 𝛕HeII and 𝛕HI are observables in the HI Lyα and HeII Lyα forests

• Fluctuations dominated by ΓHeII as mfp=100cMpc

⌘ ⌘ 4⌧HeII

⌧HI⇡ nHeII

nHI= 0.4

�HI

�HeII


the HeII Lyα Forest

Source Frame: 400 A 540 A 670 A 810 A

HS1700+6416 (z=2.72)

Reimers et al ’92

HeII forest

visible in 1% of

sightlines

Flux


The HeII Lyα Forest


HE2347-4342: Previous measurements of 𝜂 ratios

Recent COS HST measurement, 20 hr

Previous FUSE measurement, 140 hr

Shull et al ‘04, see also Zheng et al ‘04, Fechner & Reimers ’07

⌘ ⌘ 4⌧HeII

⌧HI⇡ 0.4

�HI

�HeII

Shull et al 2010


Concerns about previous 𝜂 measurements

• Most studies used estimator

• S/N of FUSE was ~5. One can only measure 𝜂 with standard estimator in pixels where THeII > (S/N)-1. Assuming 𝜂 = 100, this works out to

𝝉HI < 0.05 ln([S/N]/5).

• for COS pixels are not resolved and one can show that standard estimator is always biased low

MM & Worseck 2013Wednesday, November 27, 13

This can be done better for COS by forward modeling

the resolved HI field

Caveat 1: This will be biased by thermal broadening. Mocks from cosmological simulations show that this bias is small.Caveat 2: Continuum uncertainty in the HI is still a problem as a 𝝉HI =0.02 maps to 𝝉HeII = 0.5 for η=100

estimated HeII Transmission = exph�⌘

4⌧HI

i


We produced mocks that replicate the statistical properties of the data. Also

mocks are fit HI data with same automated continuum fitting algorithm.

Noiseless mocks w/ input 𝜂 = 100

We tuned continuum fitting algorithm to be unbiased on mocks.Wednesday, November 27, 13

Our 𝜂 measurement: Noiseless mocks w/ 𝜂 = 100

⌘ ⌘ nHeII

nHI= 4

⌧HeII

⌧HI⇡ .4

�HI

�HeII

MM & Worseck 2013Wednesday, November 27, 13

Other Implications

• Quasar lifetimes: > 10 Myr

• Quasars dominate z~2.5 HI ionizing background

HE2347+4342 HS1700+6416

Quasars identified in Worseck et al ‘07 and Shull and Syphers ‘13

where ✏4Ry

✏1Ry= 4�↵eff


Now to the question you’re all asking:How does the EUV impact galaxy formation? (and by extension the formation of the Crab pulsar and hot Jupiters)

Hypotheses for what sets minimum size of galaxies:

• internal feedback processes (e.g., supernova)

• set by reionization/photoionizing background

1. given by the Jeans’ (filtering) mass of photoionized gas at zcoll (e.g. Gnedin ’00; does not work very well; e.g Hoeft et al ’06)

2. given by when Tgaseq < Thalo; Okamoto & Theuns ’08


Physics of dwarf galaxy formation

Text

Noh & MM (almost finished)



Shell that collapses at z=6,reionization at z=10

Text




Text




• We find that these curves are essentially reproduced following particles in simulations except with two differences

1. MJeans => MJeans/4

2. gas first often goes through filaments and so collapse on average occurs quicker than the spherical collapse trajectories I just showed you

3. Dependence on the EUV is weak!!

Noh & McQuinn (almost finished)Wednesday, November 27, 13

the sad story of the cosmic EUV

Early on the EUV showed much promise, even mustering just enough photons to ionize the Universe and perhaps having some interesting dynamics.

Later on (z~2.5), indications were that it might be up to something interesting, but alas no...

And it was only downhill from there. After z~2.5, the quasars turned off, the galaxies emitted less, and the cosmic EUV shut off.....never to do something interesting (like reionization) again.

(and galaxy formation was only weakly affected by the cosmic EUV.)

The EndWednesday, November 27, 13

What is expected level of η fluctuations?

The statistics of all of these cases seem consistent w/ the observation.

HE2347


Trajectories in sims


Jeans’ mass in simulations


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