Formation of z~6 Quasarsfrom Hierarchical GalaxyMergersYuexing Li et alPresentation by: William GrayDefinitions and Jargon¥ QUASAR stands for QUASI-stellAR radio source¥ Extremely bright and active nucleus of a younggalaxy¥ Z~6 = about 800 million years after Big Bang.¥ SED - Spectral Energy Distribution¥ FIR Galaxy - Far InfraRed Galaxy¥ BH / SMBH - Black Hole/ Super Massive BlackHoleProperties of Z~6 Quasar¥ Low space density (~10^-9 MPC^-3)¥ High luminosities (M1450• < -26 )¥ Gunn-Peterson absorption troughs intheir spectra (places them at the end ofthe epoch of reionization)¥ Lack of evolution in their SEDcompared to low redshift QuasarsSDS J1148+5251¥ Most distant quasar know. Discoveredby the Sloan Digital Sky Survey.¥ Z = 6.42. M1450• = -27.8¥ Lbol = 1014 Lsun¥ SMBH = (1-5)*10^9 Msun¥ Near Solar metallicity in Quasar hostVery rare Quasar¥ Low abundance of such quasars.¥ Hosted by massive halos (>1013Msun) in raredensity peaks¥ !CDM cosmology suggests that small objectsform first and merge - Òhierarchical assemblyÓ¥ Originates in highly overdense regions in theinitial dark matter density distribution.¥ Quasar and host form from many gas-richmergers.Cosmological ParametersWilkinson microwave Anistropy ProbeWMAP1 - ("m = 0.3, "b = 0.04, "! = 0.7, h = 0.7, ns = 1,#8 = 0.9)WMAP3 - ("m = 0.236, "b = 0.042, "! = 0.759, h =0.732, ns = 0.95, #8 = 0.74)For the purpose of this paper, the simulations usedWMAP1 values because WMAP3 predicts lower halomasses and longer formation time. Although they docompare results using WMAP3.Little Methodology¥ 1: Perform a coarse dark matter sim ofvolume of 1 h-3 Gpc3 to find candidatehalo for quasar.¥ 2. Largest halo is candidate forformation of quasar at z= 6.5¥ 3. ÒZoom-inÓ on candidate region andsimulation is rerun with higherresolutionMerger Trees¥ Traces mergers throughout redshift¥ The most massive progenitors at eachredshift are traced by tags to identify earlierprogenitors¥ Groups that contribute >10% of the halo massat each time step are progenitors¥ This will give the history of our suspectquasarHalo Mass functions from cosmological simulations.Coarse Run.Halo Mass functions from cosmological simulations.Zoom in Run.Merging history of the largest halo.Modeling Mergers major factors¥Major mergers = mass ratio of the merging galaxiesare near unity.¥Only the major mergers play the most importantrole in the formation and evolution of massivegalaxies¥Gas in a rotationally supported disk loses angularmomentum through gravitational torques excited bytidal forces in a merger, driving the growth of SMBH.This is most effective in a major mergers.Table of MergersBlack Hole seeds¥Need to grow a BH up to 109 Msun in less than 800million years.¥1. Pair instability PopIII - BH ~102 Msun¥2. Hot, dense clumps of gas collapse to form ~106 Msun¥3. ~20 Msun BHs from direct collapse of self-gravitatinggas due to global instabilities.¥In simulation - it is necessary for galaxy progenitors tohave massive BH seeds (~105 Msun)Escaping BHs ?¥ When galaxies merge, the BHÕs may mergeor be ejected by gravitational recoil.¥ Depends on: Vesc=ý2|$[r]|) .Hierarchical Assembly of the Quasar¥ Progenitors are very compact and gas rich.¥ Strong gravitational interactions between themerging galaxies lead to tidal tails, strongshocks and efficient gas inflow that triggerslarge-scale starbursts.¥ Highly concentrated gas fuels rapid accretiononto the SMBH¥ Z ~14-9, merging systems are small (tens ofkiloparsecs). By Z~ 9-7, scale and strengthare much greater.Part 2¥ At Z ~6.5, progenitors galaxies coalesceSMBH accretion and feedback to a climax.¥ This feedback introduces a powerful wind thatclears the material around the quasar.¥ The largest SMBH appears as a opticallybright quasar. After this, the quasar feedbackquenches star formation and quasar activitydies down.Star formation¥ As progenitors undergo stronginteractions, stars form rapidly.¥ Total SFR : 100 to > 104 Msun/year¥ By Z < 7, SFR decreases gradually dueto depletion of gas supply and strongfeedback¥ By Z ~ 6.5 SFR: ~ 100 Msun / year(order of mag lower than J1148+5251)Metallicities¥ Rapid star formationproduces an abundantmass of heavyelements.¥ Dips and jumps aredue to new materialmergers.¥ Metals are widespreaddue to outflows.Some regions aresupersolarmetallicity.Due to infallingmaterial triggeringsmall scale starformation.Growth of SMBH¥ Total BH accretion rate grows steadilyduring assembly.¥ Eddington ratio: Lbol/Ledd (3.3 10^4 (M/Msun) *Lsun)¥ Although each BH may not accrete atEddingtion rate, so growth of quasar isa collective contribution of each BH.Escaping BHs?¥ Emission of gravitational waves carriesaway linear momentum, could causeBH to recoil.¥ If recoil velocity is greater than escapevelocity, BH escape.¥ But, simulation shows that recoil/kickvelocity is much smaller than escapevelocitiesEvolution of total BH and stellar mass.Quasar Luminosities¥ Lbol=%rMc2, %r=0.1¥ If BHs are spinning, L isincreased by a factor of4.¥ Host appears as anultraluminous infraredgalaxy (ULIRG) Lbol>1012LsunQuasar lifetimesFeedback from Starburst Driven wind¥ Samesimulation run,but at lowerresolution andwind model.¥ Effect of windon quasarevolution isminorNumber of such Quasars¥ Depends oncosmologicalconstants used.¥ WMAP1 ~ 36¥ WMAP3 ~handful¥ WMAP3 willproduce fewerluminous quasarsEra of Reionization¥ WMAP3 results - universe was 50%ionized at Z ~9.3Summary¥ Find target halo by performing a N-bodysimulation in large volume.¥ Largest halo reaches M ~ 5.4x1012 h-1 Gpc3through 7 major mergers between Z ~14.4and Z~6.5¥ Quasar host galaxy build rapidly through gasrich mergers.¥ SFR up to 104 Msun /year¥ Reaching stellar mass of 1012Msun at Z~6.5¥ BH accretion reaches 20 Msun/year and M =2*109 Msun¥ At peak, this is consistent with J1148-5251Questions????Comments????Rude