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15 March 2006 The End of the Dark Ages 1
Old Massive Galaxies
in the Early Universe
tell better Stories
about Reionization
Nino Panagia (STScI, INAF, SN Ltd)
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15 March 2006 The End of the Dark Ages 2
Mostly based on work done
in collaboration with: (in inverse alphabetical order)
Tommy Wiklind
Massimo Stiavelli
Bahram Mobasher
Mike Fall
Et Al.
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15 March 2006 The End of the Dark Ages 3
We know that the Universe is not quite ionized
at redshift z=6.28
Becker et al. (2001)
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15 March 2006 The End of the Dark Ages 4
Becker et al (2001):The full story
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The Principles of Reionization (RI)
• Reionization requires sources of Lyman continuum photons
• Reionization depends primarily on the UV output of the RI sources integrated over time
• Reionization is a function of the UV photon escape fraction, f, from the RI sources and the clumpiness of the IGM
<Q> = <MHI> × f –1 × B(z1,z2,C) Ly-c photons HI mass =
HI×Volumeescapefraction
photons neededper ionization
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The effect of the IGM clumping on Reionization
[Stiavelli, Fall & Panagia 2004a]
Clumping factor C = <n2H>/<nH>2
Eff
ecti
ve n
umbe
r of
pho
tons
to io
nize
an
atom
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15 March 2006 The End of the Dark Ages 7
Recognizing the Reionization Agents
• (Young Bright) Galaxies at z>6.5 are doing it
• (Evolved Massive) Galaxies at z<6.5 have done it
• Together they define the process of Reionization
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32 30 28 26 24 32 30 28 26 24 mAB(rest=1400Å)
Reionization constraints from HUDF observationsStiavelli, Fall & Panagia (2004b)
T=100,000K (Z=0) T=50,000K (Z=Z/100)
The blue line refers to UDF objects selected by i-z>2, the red one to i-z>1.3.
The galaxies that may be ionizing NOW…
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z=2.5-3.4
HUDF-JD2, a Balmer Break Galaxy prototypeA galaxy that did it in the past?
[Mobasher et al. 2005]
z = 6.5M = 61011 M
Observed [m] 0.5 1 2 5 10
Rest-frame [m] 0.1 0.2 0.4 0.8
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Properties of HUDF-JD2[Mobasher et al 2005, Panagia et al 2005]
Massive M/M = 6 × 1011
Bright L/L = 1012
Evolved Age > 350-650 Myr zform > 9
Ionizing Q ~ 4 × 1072 Ly-c photons
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15 March 2006 The End of the Dark Ages 11
HUDF-JD2:An Old Galaxy
that did a LOT
eff: Ratio of the time averaged Lyman continuum
photon flux to the present UV flux
Age
Model includingchemical evolution
[Panagia et al 2005]
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HUDF-JD2
dereddenedcompanions
Enough to re-ionizeits region of Universe?
By itself only if high escape fractionand low clumping
Easily if invisible companions with a reasonable LF are present
Panagia et al. 2005
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HUDF-JD2: A summary
• Massive, luminous, protypical Balmer-break galaxy
• It has had an important impact (>20%) on the reionization of the IGM starting a z~15
• With the “help” of fainter companions distributed according to an =1.6 Schechter LF it may account for the whole effect
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15 March 2006 The End of the Dark Ages 14
Is HUDF-JD2 unique?
• Tommy Wiklind answered this question: “not quite”
• Actually, combining deep HST and Spitzer multi-band photometry one finds about one bright BBG per 10 square-arcmin field
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Re-Ionization Balance - I
• UV output from BBGs in the Chandra Deep Field South Qtot = 4.2 × 1073 f Lyman-continuum photons
• H-atoms in a volume in the redshift interval 7-15
NH = 1.2 × 1073 atoms
• If the detected BBGs are the only UV sources in the field
B/f = 3.5
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15 March 2006 The End of the Dark Ages 17
The effect of the IGM clumping on Reionization
[Stiavelli, Fall & Panagia 2004a]
Clumping factor C = <n2H>/<nH>2
Eff
ecti
ve n
umbe
r of
pho
tons
to io
nize
an
atom
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Re-Ionization Balance - II• With a clumping C > 10 B > 2 f > 0.6 unlikely!?
• The IMF may be top-heavy too easy!!!
• Additional, fainter, undetected galaxies contribute to the reionization possible
• In this case, with C>10 and f<0.2, the fainter companions should provide an additional ~200% of ionizing radiation.
• This corresponds to a Schechter luminosity function steeper than =1.3 quite reasonable
• Detecting and studying the fainter companions is not easy with current telescopes but it will feasible with JWST.
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Conclusions
Big
Ban
g
H II
z ~
6-1
0
“Dark Ages”
TIGM ~ 4z K
z ~
10
3 z ~
∞ re
com
bin
ati
on
t z
H I
TIGM ~ 104 K
normal galaxy
S1Here Now
primordial galaxy
Hubble Deep Field
Hubble Ultra Deep Field
end of reionization
JWSTHST
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Conclusions
• Balmer-Break Galaxies (BBG) are important for the reionization of the IGM starting at z~15 or higher
• With the help of fainter companions they have the potential of ionizing the IGM entirely
• JWST is needed to detect and study the population of “reionizers”
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15 March 2006 The End of the Dark Ages 21
THE END