VIEWS: 9 PAGES: 29 POSTED ON: 12/24/2011
The Obscured Growth Phase of Black Holes in Distant Massive Galaxies David M Alexander (Durham) What I’m not Going to Talk About: Robust Identification of z~2-2.5 Compton-thick Quasars Optical AGN IR AGN Compton-thick quasars (LX>1044 erg/s) at z~2 are as numerous as unobscured quasars: extending Daddi et al. (2007) to confirming individual C-thick AGNs What I will Talk About: Black-hole-Galaxy Growth in z~2 Starbursts and Quasars “Weighing the Black Holes of z~2 Submillimeter Galaxies and Exploring their Evolutionary Status” D.M. Alexander et al. AJ, submitted “Is there an Evolutionary Link between Quasars and Submillimeter Galaxies?” K. Coppin et al. in prep. Today’s most massive galaxies hint of a violent past Heavens et al. (2004) Formation must have been M87 distant, rapid, and luminous Also need to grow a massive black hole Probe black-hole growth with AGN activity All massive galaxies appear to host a massive black hole => all galaxies have undergone luminous AGN activity in the past Black Hole-Stellar Growth Cannot “age” a black Action: AGN activity MBH = 0.15 % Mbulge hole, as you can age stars but the tightness of the black-hole- spheroid mass relationship suggests they may have grown concordantly Challenging tests for Tremaine et al. (2002) structure-formation models Action: Star formation Submillimeter/Millimeter: efficient selection of the most bolometrically luminous far-IR galaxies in Universe 850 micron SCUBA image (Blain & Longair 1996) Lots of them! Before SCUBA2, submm will miss hot Coppin et al. (2006) ultraluminous sources Submillimeter/Millimeter: efficient selection of the most bolometrically luminous far-IR galaxies in Universe 850 micron SCUBA image (Blain & Longair 1996) Hughes et al. (1998) Lots of them! Before SCUBA2, submm will miss hot Smail et al. (2002) ultraluminous sources Galactic Properties… Chapman et al. (2003, 2005) Strongly clustered Distant: typically Swinbank et al. (2004) z~2-3 Massive (Ha) Blain et al. (2004) Neri et al. (2003) Gas rich (CO) Progenitors of todays massive galaxies? All massive galaxies possibly went through a “SCUBA phase” ~3x108 yr activity cycle (based on gas consumption) and then passive evolution Faber-Jackson Est. halo velocity dispersion Swinbank et al. (2006) Space density consistent with >3L* galaxies (duty cycle corrected) AGN properties? Has been challenging… An optically bright AGN (Ivison et al. 2002) Pope et al. (2008) (Ivison et al. 1998) A mid-IR bright AGN A radio-bright AGN Alexander et al. (2005) Alexander et al. (2005) Most moderately luminous Most are heavily obscured A few mid-IR/optical/radio bright AGN but most of the AGN are X-ray faint: heavily obscured and only moderately luminous Bolometric Luminosity typically Dominated by Star Formation Alexander et al. (2005) AGN contribution ~10% at FIR and <30% at mid-IR Pope et al. (2008) SMGs are distant (z~2), massive (~1011 solar masses), and gas rich (~30% gas mass fraction) galaxies… potentially all massive galaxies were SMGs at some time in the past AGN activity is often present but intense star formation appears to dominate the energetics (i.e., similar to ULIRGs) 17/20 SMGs with redshifts Are X-ray detected: ~28-50% 2Ms Chandra AGNs (bias corrected) (CDF-N/GOODS-N) field However a large fraction of SMGs host AGNs (~28-50% of SMGs with f850>4mJy) …indicating long (almost continuous) black-hole growth during intense star-formation episodes Rapid black-hole growth phase, initiated by major mergers? BH mass Accretion S.Form Chapman et al. (2003) Fuel Supply Eddington-limited growth Archibald et al. (2002) Di Matteo et al. (2005) Eddington-limited growth during peak star formation? Black-hole-host galaxy relationship in SMGs? Stellar masses estimated using Spitzer IRAC (+optical+near-IR) Borys et al. (2005) If assumed Eddington-limited accretion then the black-hole growth substantially lags the stellar growth (by a factor ~50!) However: (1) are Eddington-limited black-hole masses appropriate? want to be able to “weigh” the black holes (2) has the intrinsic AGN luminosity been underestimated (extinction corrections)? (3) are the host-galaxy masses accurate? Weighing the Black Holes in SMGs D.M. Alexander, AJ, submitted Not all SMGs are heavily obscured, some have broad Ha or Hb in the near-IR (Swinbank et al. 2004; Takata et al. 2006) Swinbank et al. (2004) Chapman et al. (2005) Can “weigh” their black holes using the virial black-hole mass estimator: MBH=G-1 RBLR V2BLR (e.g., Kaspi et al. 2000) Eddington Ratios and Black-Hole Masses Careful use of the virial black-hole mass estimator for the broad Ha and Hb emission line (Greene & Ho 2005) Spread of properties (MBH and dM/dt): For broad-line objects, median MBH~(1-3)x108 Msolar and fEdd~0.2-0.5 (depending on BLR geometry) – two types of broad-line SMGs: high luminosity and low luminosity Are the Intrinsic AGN Luminosities Underestimated? Absorption corrections consistent with other studies and AGN properties consistent with ULIRGs (potential local analogs) Agreement between AGN mid-IR component and intrinsic X-ray luminosity: mid-IR appears to be isotropic indicator of AGN luminosity Host-Galaxy Masses? Borys et al. (2005) Greve et al. (2005) Stellar masses: some contaminated CO dynamical masses: by an AGN in near-IR avg ~1011 solar masses within (revised average ~2x1011 solar ~2 kpc radius (i.e., bulge scale) masses with these removed) Physical properties of SMGs used here: • Edd rate, h>0.1 and h~0.2 (BL SMGs/obscured ULIRGs) • This implies MBH~(0.6-1)x108 solars for typical SMGs • M*,dyn(CO)~1011 solars for r~2kpc (within bulge; Greve et al. 2005) • M*,stellar~2x1011 solars (Borys et al. 2005 with near-IR excess objects removed): whole gal but ultimate system mass? SMGs Lie Suggestively Below Local Relationship Consistent with Chakrabarti et al. (2007,2008) simulations of SMGs; see talk tomorrow And statistically below the apparent z~2 relationship Conclusion: black-holes in typical SCUBA galaxies appear to be comparatively small [~(0.6-1)x108 Msolar, for ~0.1-0.2*Edd] The black-hole growth appears to lag that of the host galaxy in massive star-forming galaxies, in apparent contradiction with that found for z~2 quasars/radio galaxies Appears to necessitate the need for an AGN dominated phase that predominantly grows the black hole Major-Merger Induced Growth of Massive Galaxies? The Dave Sanders et al. evolutionary picture SCUBA galaxies Normal QSOs Obscured QSOs/IR lum QSOs Page et al. (2004) Normal quasars: not undergoing extreme star formation Page et al. (2004) Submm quasars Alexander et al. (2005) Black Holes getting bigger Testing the Evolutionary Link between Quasars and Submm Galaxies K. Coppin et al. in prep. IRAM CO observations Selected submm detected quasars in same redshift range as submm galaxies: some are rare monsters and some are more typical systems Comparison between Quasars and SMGs Average gas masses and implied CO dynamical masses similar between SMGs and quasars (if quasars are assumed to be more face on: i~20 degrees) Black-hole Host galaxy properties Avg Quasars Avg SMGs Quasars Are submm Quasars at a different evolutionary stage to SMGs? Low dyn masses consistent with other CO studies of Quasars (e.g., Walter+ 04) but does the CO trace the bulge in these systems? Conclusions • Compton-thick quasars (ID’d from optical-mid-IR spectra and X-rays) at z~2-2.5 are as numerous as unobscured quasars • SMGs host concordant black hole-stellar growth: all massive galaxies were potentially SMGs at some time during the past • The black holes of SMGs are comparatively small (typically MBH=(0.6-1)x108 Msolar for 0.1-0.2*Edd) • Given their host-galaxy masses (>1011 Msolar), the black hole growth appears to lag the stellar growth, contrary to that found in z~2 quasars • Are submm-detected quasars more evolved than SMGs? • the CO detected quasars have similar gas and dynamical masses as the SMGs but have black holes ~30x larger: not clear if the CO traces the bulge in these systems?
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