Hidden Accretion onto Supermassive Black Holes

Revealed

X-ray AGN Workshop / Apr 2014

Johannes Buchner

MPE :: High-Energy :: AGN

in collaboration with A. Georgakakis, K. Nandra, Li-Ting Hsu, Sotiria Fotopoulou, Marie-Luise Menzel, C. Rangel, M. Brightman, A. Merloni and M. Salvato

Overview

  1. Active Galactic Nuclei (AGN) in X-ray
  2. Obscuration effects
  3. Research question
  4. Approach & Data
  5. Visualisations
  6. Models for the obscurer

X-ray effects

Emittors, Detectors, Telescope location

X-ray spectrum of AGN

  • Powerlaw - Luminosity $L$
  • Absorption - Column density $N_H$
  • Squeezing - Redshift $z$
  • Soft scattering component
  • Compton scattering - Covering $R$ Buchner+2014

Research Question

  • Relationship accretion - obscuration ($L_X$ - $N_H$)
  • Cosmic evolution, Co-evolution with galaxies?

$\Rightarrow$ Investigate distribution of population
in luminosity, redshift and $N_H$

  • What fraction are obscured $N_H>{10}^{22} \text{cm}^{-2}$?
  • What fraction are Compton-thick $N_H>{10}^{24} \text{cm}^{-2}$?
  • Does the obscurer "react" to the luminosity?

Survey fields

Data

Side-note: X-ray spectra


  • $\phi = k / t$ ?
  • $k \sim \text{Poisson}(\phi \cdot t \cdot \text{bias})$
  • $\rightarrow$ find all $\phi$ that could produce $k$ counts
  • $\rightarrow$ Find all $L_X$, $z$, $N_H$ which could produce $k$ (spectrum)

Data

$z=0.5-3$, $L_X={10}^{42-46} \text{erg/s}$
What is the distribution of the population?

Luminosity function

  • $\phi = k / V$ ?
  • $k \sim \text{Poisson}(\phi \cdot t \cdot \text{bias})$
  • $\rightarrow$ find all $\phi$ that could produce $k$ detected objects
    • Bias against faint, obscured, high-z
    • Can use smoothness between bins
    • Uncertainty which bin

Model


  • "Fit a 3d histogram"
  • Smooth density function
  • "Debiased"

Total luminosity function

Density evolution

$\int \phi dL$

Obscured: ${{76}^{+4}_{-5}\%}$, Compton-thick: ${36}^{+8}_{-8}\%$

Luminosity density

$$\int L \times \phi dL$$

Accretion happens mostly in obscured AGN (75%)

Accretion relics

  1. $L_{bol} = \epsilon \cdot \dot{M}$ (Thermal equilibrium of accretion disk)
  2. $\epsilon = 0.1$ (non-rotating BH: 0.06, rotating BH: 0.4)
  3. $L_{bol} = 40 \times L_X$ (Elvis+99, first order)

$$\Rightarrow \dot{M}(L) = 40 \times L_X / \epsilon$$ The luminosity output of the AGN population indicates how much mass is being trapped into black holes (Soltan argument)

Accretion relics

Obscuration - Luminosity

Models

Evolutionary model

More realistic picture of AGN

Conclusions

  • Sample of 2000 AGN analysed for X-ray properties $L$, $z$, $N_H$
  • luminosity function determined $\phi(L, z, N_H)$
  • fraction $N_H>10^{22} \text{cm}^{-2}$: 75% (45°)
  • fraction $N_H>10^{24} \text{cm}^{-2}$: 35% (20°)
  • The accretion in obscured AGN can explain local black hole mass density
  • Obscured fraction is luminosity dependent
    • Relationship evolves
    • why? $\rightarrow$ need more research
      • parametric model