(obscured) supermassive black holes

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The Space Density of CT AGN and the XRB. (Obscured) Supermassive Black Holes. Ezequiel Treister (IfA) Meg Urry, Shanil Virani, Priya Natarajan (Yale). Credit: ESO/NASA, the AVO project and Paolo Padovani. Supermassive Black Holes. Many obscured by gas and dust. How do we know that? - PowerPoint PPT Presentation


  • (Obscured) Supermassive Black HolesEzequiel Treister (IfA)Meg Urry, Shanil Virani, Priya Natarajan (Yale)Credit: ESO/NASA, the AVO project and Paolo PadovaniThe Space Density of CT AGN and the XRB

  • Supermassive Black Holes Credit: ESO/NASA, the AVO project and Paolo PadovaniMany obscured by gas and dust How do we know that?

    Local AGN Unification

    Explain Extragalactic X-ray Background

  • Compton Thick AGN Defined as obscured sources with NH>1024 cm-2. Very hard to find (even in X-rays). Observed locally and needed to explain the X-ray background. Number density highly uncertain. High energy (E>10 keV) observations are required to find them.


  • ISDCSwift SourcesTueller et al. 2007

  • Significance Image, 20-50 keVDeep INTEGRAL Survey (3 Msec)

  • Log N-Log STreister et al. in prep.

  • Log N-Log STreister et al. in prep.

  • Fraction of CT AGNTreister et al. in prep.X-ray background does not constrain density of CT AGN

  • CT AGN and the XRBTreister et al. in prep.

  • X-Ray Background SynthesisTreister et al. in prep.

  • Contribution of CT AGN to the XRBTreister et al. in prep.

  • CT AGN at High RedshiftTreister et al. in prep.

  • How Many CT AGN?At low redshift (z
  • CT AGN Space Density (Lx>1045)Treister et al. in prep.Polletta+06

  • Treister et al. in prep.Polletta+06CT AGN Space Density (Lx>1045)

  • Treister et al. in prep.Tozzi+06Alexander+08CT AGN Space Density (Lx>1044)

  • Treister et al. in prep.Tozzi+06Alexander+08CT AGN Space Density (Lx>1044)

  • Treister et al. in prep.Tozzi+06Fiore+08Risaliti+99INTEGRALCT AGN Space Density (Lx>1043)

  • Treister et al. in prep.INTEGRALTozzi+06Fiore+08Risaliti+99CT AGN Space Density (Lx>1043)

  • Treister et al. in prep.Daddi+07CT AGN Space Density (Lx>1042)

  • Treister et al. in prep.Daddi+07CT AGN Space Density (Lx>1042)

  • SMBHs Spatial DensityNatarajan & Treister, 2008

  • UMBHs Spatial DensityNatarajan & Treister, 2008

  • UMBHs Spatial DensityNatarajan & Treister, 2008Self-Regulation

    Momentum-driven winds (Murray et al. 2004).Radiation pressure (Haehnelt et al. 98)Energy Driven Superwind (King 05)

  • SummaryThe number of CT AGN in the local Universe can be constrained, thanks to Swift and INTEGRAL.Number of CT AGN still roughly consistent with XRB, but can be increased by ~4x.Strong decrease in the number of UMBHs -> Self regulation process. (???)

  • Observed X-ray BackgroundFrontera et al. (2006)

  • AGN in X-raysIncreasing NH Photoelectric absorptionaffect mostly low energy emission making the observed spectrum look harder.

  • How to find high-z CT AGN NOW?X-rays?Trace rest-frame higher energies at higher redshifts Less affected by obscurationTozzi et al. claimed to have found 14 CT AGN (reflection dominated) candidates in the CDFS.Polletta et al. (2006) report 5 CT QSOs (transmission dominated) in the SWIRE survey.

  • Extremely Red X-ray Objects (ERXOs)ERXOs are new class of X-ray emitters about which little is known7 found in CDFS (Koekemoer et al, 2004)Defined by very red colors: R-K > 7 (Vega)Given X-ray detection and very red optical-IR spectrum, either:very high redshift AGN z > 6very obscured AGN with old or dusty host galaxies at z~2-3Probably a heterogeneous population?

  • ERXOs Examples in the ECDF-SUrry et al. in prep.

  • ECDF-S K band vs Hard X-ray FluxUrry et al. in prep.* ERXOs

  • Confirming the ERXOs NatureNo GALEX or GEMS counterpartsNIR spectroscopy crucial to determine the intrinsic nature no ERXO has a measured spectroscopic redshift4 ERXOs in ECDFS are bright enough to perform NIR spectroscopy. Targeted with VLT/SINFONI IFU. Three sources observed.

  • Sinfoni SpectroscopyUrry et al. in prep.Lx= 4.1x1044 erg/s = 1.20.4Lx= 2.6x1043 erg/s = 1.50.4Lx= 1.2x1043 erg/s = 1.31.0

  • How to find high-z CT AGN NOW?Mid-IR?

  • NuSTAR

    We know that there should be many obscured SMBHs, why?Locally the obscured/unobscured ratio is ~3:1. In fact, 2 of the 3 nearest AGN are Compton Thick. More importantly, this is the case at all redshifts because of the X-ray background*There is a population that was completely missed in soft energies surveys.Those are the most obscured sources. So obscured that are not detectedeven in X-rays. Those are the CT AGN.

    Even though we dont know the exact density of these sources, they arerequired in large numbers by XRB synthesis models and are observed locally.*Right now we are starting to construct a better view of the local (z LargeDiscrepancy of factors of ~2-3.Why? XRB does not constrain number of CT AGN.**However, now we can constrain the density of CT AGN directly from theINTEGRAL observations, finding that the most likely solution has aCT AGN fraction ~4x lower than previously expected.We can see that adding ~4 times more CT AGN doesnt change the XRBsignificantly.*The situation is even worse at high-z. This is because ~50% of the XRB comesFrom AGN with z2 only change total contribution ofCT AGN by ~10%.*How to count CT at moderate redshifts, z~0.5-1?Not now, but with new planned missions like EXIST and NuSTAR it will be possible inless than 10 years.*So, how many CT AGN there are?We need high energy observations at intermediate redshifts. We will have to wait for EXIST, NuSTAR and Simbol-X.*- Very luminous sources: 5 CT candidate AGN (transmission dominated) in the Chandra/SWIRE field*Density higher than expected from XRB models*At Lx=10^44, Tozzi et al. found ~7 CT AGN candidates. Alexander et al. used mid-IR Excess to find a sample of ~6 CT AGN candidates confirmed by IRS spectroscopy.*Risaliti and INTEGRAL measurements in the local Universe. Tozzi et al in the CDFSAnd Fiore et al from mid-IR excess. Corrections to Tozzi et al. comes from fraction ofCT AGN expected to be missed based on flat NH distribution.*Obvious mismatch in the local Universe, but works well at high-z.*Daddi et al. number still under heavy discussion. From excess of mid-IR SFR comparedto UV SFR.*However matches expectations from XRB models.*In general good match between observed space density of SMBHs.Efficiencies of ~10%, consistent with common assumptions.However, only works well up to 10^9*At higher masses, extrapolation of LF just doesnt work.

    Tell us something about BH growth Harder to keep increasingBH mass after ~10^9

    *Tried playing with Efficiency or Eddington ratio, as a function of massOr redshift Nothing really worked!

    Only way to fix it: change luminosity function.

    Self regulation processes?

    **We know now that the X-ray background is just collective emission from previously unresolved sources,90% of them AGN.The X-ray background spectrum is very steep, with a peak at ~30 keV.This is good indication that obscured AGN should outnumber the unobscured ones.*The reason is that obscuration makes the X-ray spectrum appear harder. In these units, an unobscured AGNis roughly flat, while as we add more and more obscuration (parameterized as a neutral hydrogen column density)the observed spectrum appears harder and harder, thus closer to the observed X-ray background.Can we start now?

    K correction help us! We can start looking now in Chandra and XMM data.Examples from Tozzi et al. and Polletta et al.*How do the CT AGN at high-z look like? Probably like ERXOs.i.e., no optical counterpart, but strong near and mid-IR sourcesSo we started studying ERXOS.*This is how they look line: no BVR detection to mag~27K detection and strong in Spitzer IRAC bands*In a K-band versus hard X-ray they are separated from the rest of the population.They are in a location dominated by hard spectrum sources.*Only way to confirm their real nature -> near-IR spectroscopy*We got SINFONI spectra for these three sources.

    In all cases we detect continuum and at least two emission linesLx~43-44.Not possible to measure NH (only 50 counts maximum), but they have very hard spectra!*Another way to find CT AGN: mid-IR excess sources

    Somewhat more indirect than X-rays, but seems to workConfirmed by X-ray stacking. *EXIST will be a all-sky mission covering from 5-600 keV. Like ROSAT but at higher energies. Many (~1000) AGN includingCT ones up to z~0.5.*NuSTAR is a complementary approach.

    Pointed observations, covering relatively small areas (maximum ~1 sq. degree)But ~20x deeper than NuSTAR. Good for sources up to z~2.*