Quasars at the Cosmic Dawn

Yuexing LiPenn State University

Main Collaborators: Lars Hernquist (Harvard) Volker Springel (Heidelberg) Tiziana DiMatteo (CMU),

Liang Gao (NAOC)

The Most Distant Quasars Discovered

Fan+06

Presence of SMBHs to power these quasars, MBH~109 M ⊙ at z>6

Presence of large stellar component in host galaxies, Mstar > 1011 M⊙

Presence of copious molecular gas Mgas~1010

M⊙ and dust Mdust~108 M⊙ in the quasar

hosts

Questions & MythsI: Can such massive objects form so early in the

LCDM cosmology?– myth: there is a “cut-off” at z~5 (Efstathiou & Rees 88)– myth: some 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)

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

Multi-scale Cosmological Sims(GADGET2 Springel 05)

+ART2

(Li et al 08)

(All-wavelength Radiative Transfer with Adaptive Refinement Tree)

Formation, evolution & multi-band properties of galaxies & quasars

CARTCosmological All-wavelength Radiative Transfer

• Multi-scale simulations– cosmological simulation in 3 Gpc3

– Identify dark matter 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

• Each galaxy progenitor contains a 100 M ⊙ BH seed– Left behind by PopIII stars

– Grows at Eddington rate until it enters merger tree (104-5 M⊙)

• Self-regulated BH growth model– Bondi accretion under Eddington limit– Feedback by BHs in thermal energy coupled to gas

Formation of z~6 Quasars from Hierarchical Mergers

Age of Universe (Gyr)

Redshift z

• <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

Li et al 07

Co-evolution of SMBHs and Host

Evolution of SEDs

obs (m)Li et al 08

post-QSO

starburst-like

quasar-like

Origin of Thermal Emission

• 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⊙)

L FIR

(L ⊙

)

LB (L⊙)

L FIR

(L ⊙

)

• SPH cosmological simulations with BHs• They form in massive halos in overdense

regions• They are highly clustered• May provide patchy ionization of HI

Z>6 Galaxies & Quasars in a Cosmological Volume

starsY

(h-1

Mpc

)

X (h-1 Mpc)

BH

Log

Ifra

c

X (h-1 Mpc)

quasar

galaxy

Predictions for Future Surveys

JWST

Can z>6 SMBHs form from ~100 M⊙ BH seeds?

• BHs from PopIII stars at z~20-30 may have ~100 M⊙

• This would require BHs accrete at near Eddington rate for much of its early life

• Previous studies suggest that radiative feedback strongly suppresses BH accretion rate– Johnson & Bromm 07, Alvarez+08: AR <1% Eddington

– Milosavljevic+08,09: AR ~30% Eddington

• However, we should note that– Not every BH seed grows into a SMBH

– Small box in simulations may prevent gas replenish

– Self-gravity may boost accretion

Accretion onto ~100 M⊙ BH Seeds

• 1-D spherical accretion, including gas self-gravity– Modified VH1 code (Blondin & Lufkin 93)– Logarithmic grid, 10-4 -1 pc

• Feedback processes– Photoionization heating– Radiation pressure

• Thomson scattering• photoionization

Self-gravity Aided Accretion

Self-gravity Aided Accretion

Summary

• The first SMBHs can form from ~100 M⊙ BH seeds in high overdensity peak with abundant gas supply, because self-gravity overcomes radiative feedback and boots accretion rate

• Luminous z~6 quasars can form in the LCDM cosmology via hierarchical mergers of gas-rich proto-galaxies

• 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

• 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

Predictions & Observational Tests