Vulcano Workshop - 24 May 2010 Vulcano Workshop - 24 May 2010 Evolution and Reionization of the Universe The Impact of the Hubble Space Telescope Nino Panagia (STScI/INAF-CT/Supernova Ltd)
Main Phases of the BIG BANG Universe Evolution 14.5 14.5 24 May 2010 HST and the Early Evolution of the 2 Universe
A concise history of the Universe Dark Ages Primordial stars Reionization 24 May 2010 HST and the Early Evolution of the 3 Universe
We know that the Universe is not quite ionized at redshift z~6.3 Becker et al. (2001) 24 May 2010 HST and the Early Evolution of the 4 Universe
Becker et al (2001): The full story 24 May 2010 HST and the Early Evolution of the 5 Universe
Why do we care? • Reionization is the last global phase transition in the Universe • Reionization drastically changes the environment for galaxy formation and evolution • In a hierarchical clustering scenario, the galaxies responsible for reionization may be the seeds of the most massive galaxies in the local Universe. 24 May 2010 HST and the Early Evolution of the 6 Universe
Basic processes (e.g., Barkana & Loeb, Phys. Reports , 2001) • Ionizing UV radiation origin: either fusion (pop III and II stars) or gravitational energy (QSO, AGN, BH) • If fusion, each hydrogen atom releases 7 MeV but requires 13.6 eV to be ionized a mass fraction 0.2 × 10 -5 undergoing fusion is sufficient to re-ionize all hydrogen (in practice the required mass in stars is 10-100 times larger) • Different lines of sight may look very different (e.g. QSOs at 6.28 and 6.43). 24 May 2010 7
Population III stars (Z=0) Even “normal” mass stars with zero- metallicity would be much hotter than their solar analogues. Tumlinson & Shull (2000) 24 May 2010 HST and the Early Evolution of the 8 Universe
Let’s estimate the luminosity of reionization sources from first principles Recombination lines HII region escape, ∝ ( 1-f ) Dense HI Some Lyman α escapes, ∝ Velocity width × (1-f) Escaping UV radiation Dense HI A fraction f ≤ 1 of UV Some photons ionize Dense HI radiation escapes and can dense hydrogen clouds ionize the Universe that recombine → C ≥ 1 24 May 2010 HST and the Early Evolution of the 9 Universe
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> = <M HI > × f –1 × B(z 1 ,z 2 ,C) escape required Ly-c photons HI mass = photons needed fraction ρ HI ×Volume per ionization 24 May 2010 HST and the Early Evolution of the 10 Universe
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 24 May 2010 HST and the Early Evolution of the 11 Universe
Reionization constraints for identical sources Stia iavelli, lli, Pop III - Z=0 Pop II - Z<Z /100 Fall ll & Panagia ia (2004a) 24 May 2010 HST and the Early Evolution of the 12 Universe
The effect of the IGM clumping on Effective number of photons to ionize an atom Reionization [Stiavelli, Fall & Panagia 2004a] Clumping factor C = <n 2 H >/<n H > 2 24 May 2010 HST and the Early Evolution of the 13 Universe
Can we detect the Sources of Reionization NOW? It is not easy… but it can be done! 24 May 2010 HST and the Early Evolution of the 14 Universe
Let’s interrogate the sky: The H ubble U ltra- D eep F ield 24 May 2010 HST and the Early Evolution of the 15 Universe
The Renaissance after the Dark Ages Hubble Ultra Deep Field “Dark Hubble Ages” e n Deep d o f Field r primordial e i o Big Bang n galaxy Here i z a S1 t i recombination Now o n normal galaxy H I ∞ H II 0 1 - ~ 6 z ~ 10 3 z ~ z T IGM ~ 4 z K T IGM ~ 10 4 K t z 24 May 2010 HST and the Early Evolution of the 16 Universe
Location of the HUDF 24 May 2010 HST and the Early Evolution of the 17 Universe
Ultra Deep Field • Deep enough to study “typical” z=6 galaxies <10 -34 W m -2 s -1 Hz -1 • • ~0.1 photon/s (Stiavelli, Fall, Panagia, 2004a) 1 8
HUDF- z>5.5 objects • The great SB sensitivity of HUDF allows us to begin seeing substructure in z>5 objects. GOODS selected z=5.8 QSO at z=5.5 spectroscopically galaxy. In HUDF it has confirmed by GRAPES using S/N=100 . ACS/GRISM 24 May 2010 HST and the Early Evolution of the 19 Universe
The large number of z>6 objects opens up the possibility of learning something about the reionization of the Universe. What do we learn?
HIGH-z detections in the HUDF • Bouwens et al. (2004), from ACS+NICMOS imaging, find 4 candidate galaxies at redshifts 7-8 that “could play an important role in re-ionization at these redshifts” • Yan and Windorst (2004b), from ACS+NICMOS imaging, find one candidate at possible redshift 6.5-7. • Mobasher et al (2005), from combined HST, VLT- ISAAC, and Spitzer ST imaging up to 8.5 µ m , identify a galaxy at z ≈ 7 (HUDF-JD2) that could have re-ionized its region of Universe 24 May 2010 HST and the Early Evolution of the 21 Universe
HUDF-JD2: A Distant Galaxy in the HUDF 24 May 2010 HST and the Early Evolution of the 22 Universe
Combined Visible+Infrared HUDF-JD2 24 May 2010 HST and the Early Evolution of the 23 Universe
The Balmer break is a prominent feature for stellar populations age t > 100 Myrs z = 7 no extinction t = 50 Myr t = 100 Myr t = 300 Myr t = 500 Myr t = 600 Myr t = 800 Myr 24 May 2010 HST and the Early Evolution of the 24 Universe
HUDF-JD2, a Balmer Break Galaxy prototype A galaxy that did it in the past? [Mobasher et al. 2005] Rest-frame [ µ m] 0.1 0.2 0.4 0.8 z = 6.5 M = 6 × 10 11 M z=2.5-3.4 0.5 1 2 5 10 Observed λ [ µ m] 24 May 2010 HST and the Early Evolution of the 25 Universe
24 May 2010 HST and the Early Evolution of the 26 Universe
Properties of HUDF-JD2 [Mobasher et al 2005, Panagia et al 2005] Massive M/M = 6 × 10 11 Bright L/L = 10 12 Evolved Age > 350-650 Myr z form > 9 Ionizing Q ~ 4 × 10 72 Ly-c photons 24 May 2010 HST and the Early Evolution of the 27 Universe
HUDF-JD2 Enough to re-ionize its region of Universe? By itself only if companions high escape fraction dereddened and low clumping Easily if undetectable companions with a reasonable LF are present Panagia et al. 2005 24 May 2010 HST and the Early Evolution of the 28 Universe
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 α =1.6 Schechter LF it may account for the whole effect 24 May 2010 HST and the Early Evolution of the 29 Universe
Is HUDF-JD2 unique? • Inspecting the GOODS Deep-Field South, Wiklind et al. (2006) answer this question: “not quite” • Actually, combining deep HST and Spitzer multi-band photometry they detect about one bright BBG at z>5 every 9 square-arcmin field 24 May 2010 HST and the Early Evolution of the 30 Universe
From Observations to Physical Parameters • Fitting the SED: – Photometric redshift – Age & formation redshift – Total Luminosity – Average Metallicity • M/L ratio (from models) – Present mass in stars 24 May 2010 HST and the Early Evolution of the 31 Universe
An example of BBG candidate 24 May 2010 HST and the Early Evolution of the 32 Universe
BBGs in the GOODS Deep-Field South Insert table from Wikind et al 24 May 2010 HST and the Early Evolution of the 33 Universe
Ionizing Properties of BBGs in the GOODS Deep-Field South [Wiklind et al 2006, Panagia et al 2010] 18 BBGs in 160 arcmin 2 <logL/L > = 11.9 <logM 0 /M > = 11.6 <logQ> = 72.5 24 May 2010 HST and the Early Evolution of the 34 Universe
Re-Ionization Balance - I • UV output from BBGs in the Chandra Deep Field South Q obs = 5.1 × 10 73 f Lyman-continuum photons • Correcting for incompleteness (50%) Q tot = 10.3 × 10 73 f Lyman-continuum photons 24 May 2010 HST and the Early Evolution of the 35 Universe
Lyman Continuum Photon Production History BBG ionization is most efficient in the interval z~7-15 24 May 2010 HST and the Early Evolution of the 36 Universe
Re-Ionization Balance - I • UV output from BBGs in the Chandra Deep Field South Q obs = 5.1 × 10 73 f Lyman-continuum photons • Correcting for incompleteness (50%) Q tot = 10.3 × 10 73 f Lyman-continuum photons • H-atoms in a volume in the redshift interval 7-15 N H = 0.9 × 10 73 atoms 24 May 2010 HST and the Early Evolution of the 37 Universe
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