1. Galaxies and Quasars in the Epoch of Reionization
Yuexing Li
Keck Fellow
Harvard-CfA

2. Main Collaborators
Thoeretical: Lars Hernquist (CfA), Volker Springel (MPA), Tiziana Di Matteo (CMU), Tom Abel (Stanford)
Observational: Giovanni Fazio (CfA), Xiaohui Fan (Arizona)

3. Courtesy: George Djorgovski
Cosmic Hisotry
recombination
Cosmic Dark Ages: no light
no star, no quasar; IGM: HI
First light: the first galaxies
and quasars in the universe
Epoch of reionization: radiation from the first objects lit up and ionize IGM : HI  HII
 reionization completed,
the universe is transparent and
the dark ages ended
today
Courtesy: George Djorgovski

4. Exciting Era for High-z Objects
Courtesy: Edo Berger
HST
Chandra
Spitzer
SDSS
Subaru
SWIFT
GLAST
MAMBO ….
Fan+01,03,04,06
Schneider+03,05,07
Willott+07 ….
Giavalisco+04
Bouwens+06, 07
Thompson+05, 06
Iye+06, Yan+06 ….
Brandt+02
Shemmer+06
Bertoldi+03, Carilli+04
Beelen+06, Jiang+06
Maiolino+04,
Wang+07 …
Schady+08
Fynbo+08 …
Presence of large stellar component in galaxies, Mstar > M⊙ at z>6
Presence of SMBH in quasars, MBH~109 M⊙
Presence of copious dust Mdust~108 M⊙ in these objects

5. Questions & Myths
I: Can such massive objects form so early in the LCDM cosmology?
myth: there is a “cut-off” at z~5 (Efstathiou & Rees 88)
myth: exotic mechanisms required, e.g., super-Eddington accretion (Volonteri & Rees 05, 06); supermassive BH seeds (Bromm & Loeb 03, Haiman 04, Dijstra+08)
II: How do they grow and evolve?
myth: z~6 quasars have “undersized” host galaxies (Walter+2003)
myth: SMBH – host correlations don’t hold at high z
III: What are their contributions to IR emission and reionization?
myth: all FIR comes from star heating (Bertoldi+2003, Carilli+2004)
myth: quasars don’t contribute to reionization (e.g., Gnedin+04)

6. Modeling Galaxies & QSOs
Physics to account for close link between galaxy formation and BH growth
SMBH - host correlations (e.g, Magorrian+98, Gebhardt+00, Ferrarese+00, Tremaine+02…)
Similarity between cosmic SFH & quasar evolution (e.g., Madau+95, Shaver+96)
Hydrodynamic simulations to follow evolution of quasar activity and host galaxy
Large-scale structure formation
Galactic-scale gasdynamics, SF, BH growth
Feedback from both stars and BHs
Radiative transfer calculations to track interaction between photons and ISM /IGM
Radiation from stars & BHs
Scattering, extinction of ISM & reemission by dust
Evolution of SEDs, colors, luminosities, AGN contamination

7. CART Cosmological All-wavelength Radiative Transfer
GADGET2 (Springel 05) + ART2 (Li et al 08A) (All-wavelength Radiative Transfer with Adaptive Refinement Tree)
Formation, evolution & multi-band properties
of galaxies & quasars

8. I: Quasar Formation - MIM
Zoom: HR-region ~60 h-1Mpc, 4003
X (h-1 Mpc)
Y (h-1 Mpc)
Zoom-in sims
Multi-scale simulations with GADGET2 (Springel 05)
N-body cosmological simulation in 3 Gpc3
Identify halos of interest at z=0
Zoom in & re-simulate the halo region with higher res.
Merging history extracted
Re-simulate the merger tree hydrodynamically
Self-regulated BH growth model (DiMatteo et al. 05)
Bondi accretion under Eddington limit
Feedback by BHs in thermal energy coupled to gas

9. Formation of a z~6 QSO from Hierarchical Mergers
7.7x1012 M⊙
Merger tree with 7 major mergers z~14-7
Idealized galaxy using MMW model with properties (Mvir, Rvir, Cvir) scaled with z (Mo+98)
BH seeds from remnants of PopIII stars (Abel+02, Bromm & Larson04, Yoshida+06, 08), M=200 M⊙ at z=30
BH binary merge when separation below resolution:
At high-z, the potential well is deeper because galaxies are more compact
BH binary merge rapidly in gaseous environment (Escala+04,05)
Gravitational recoil may eject BH if Vkick > Vesc, Vkick ~100 – 475 km/s (e.g., Gonzalez+07, Campanelli+07)
Maximum Vkick < 200 km/s in gas-rich galaxy mergers (Bogdanovic+07)
Our halos have Vesc > 300 km/s
Maximum Vkick < 200 km/s in gas-rich galaxy mergers, because torques from accreting gas suffice to align the orbit and spins of both BHs with large-scale gas flow (Bogdanovic+07)

11. Co-evolution of SMBHs and Host
Age of Universe (Gyr)
Co-evolution of SMBHs and Host
<SFR> ~ 103 M⊙/yr, at z>8, drops to ~100 M⊙/yr at z~6.5  heavy metal enrichment at z>10
Indiv. BH grows via gas accretion, total system grows collectively
System evolves from starburst  quasar
Merger remnant MBH ~ 2*109 M⊙ , M* ~ 1012 M⊙  Magorrian relation
Redshift z
Li et al 07

12. II: Multi-band Properties - ART2
X (kpc)
Y (kpc)
II: Multi-band Properties - ART2
rest (m)
Opacity  (cm2/g)
3-D Monte Carlo RT code ART2 treats radiative equilibrium  calculate dust emission self-consistently (Bjorkman & Wood 01)
Adaptive grid (Jonsson06)  cover large dynamical range, capture inhomogeneous density distribution
Multi-phase ISM model (McKee & Ostriker 77) + GMC scaling relations (Larson 1981)
Supernova-origin dust model  dust in young, high-z objects (e.g., Maiolino+04, Todini & Ferrara 01)

13. Evolution of SEDs quasar-like starburst-like post-QSO obs (m)
Li et al 08A
quasar-like
starburst-like
post-QSO

14. Origin of Thermal Emission
LFIR
SFR
Li et al 08
Redshift z
LIR (Lsun)
F25um/F60um
Li et al 08
Quasar system evolves from cold --> warm
In peak quasar phase, radiation /heating is dominated by AGN
Starbusts and quasars have different IR-optical-Xray correlations
Lx (L⊙)
LFIR (L⊙)
LB (L⊙)
Li et al 08B, in prep

15. III. Galaxies & Quasars in Cosmological Volume
stars
Y (h-1 Mpc)
X (h-1 Mpc) BH
Log Ifrac
quasar
galaxy
Li et al. 08C, in prep
Li et al 09, in prep
SPH cosmological simulations with BHs
They form in massive halos in overdense regions
They are highly clustered
May provide patchy ionization of HI
SMBH -- host correlations hold

16. Summary
CART is a powerful approach to study the formation, evolution, and multi-band properties of galaxies and quasars.
Luminous z~6 quasars can form in the LCDM cosmology  hierarchical mergers of gas-rich proto-galaxies, with BH accretion under Eddington limit.
Galaxy progenitors of these quasars are strong starbursts, providing important contribution to metal enrichment & dust production.
Early galaxies and quasars form in highly overdense region, highly clustered  patchy reionization

17. Predictions & Observational Tests
Birth place: massive halos in overdense region
Clustering, cross correlations of galaxies and quasars
Lensing
Triggering mechanism: hierarchical merger
Morphology, pairs, CO maps
MBH --  relation
Merger rate
Evolutionary path: Starburst --> quasar
Star formation history, evolved stellar components, mass functions
Metal enrichment, molecular gas, dust
Thermal emission: stars --> AGN
SFR indicators
IR - optical relations
End product: SMBH -- host correlations
MBH -- Mhost relation