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Micro-Turbulence in Emission and Absorption in AGN. Steve Kraemer (Catholic Univ. of America). Via collaborations with: Mike Crenshaw (GSU), Mark Bottorff (Southwestern), Jane Turner (UMBC), Lance Miller (Oxford). Is Micro-Turbulence Present?.

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Micro-Turbulence in Emission and Absorption in AGN

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micro turbulence in emission and absorption in agn

Micro-Turbulence in Emission and Absorption in AGN

Steve Kraemer (Catholic Univ. of America)

Via collaborations with:

Mike Crenshaw (GSU), Mark Bottorff (Southwestern), Jane Turner (UMBC), Lance Miller (Oxford)

is micro turbulence present
Is Micro-Turbulence Present?
  • Emission lines in AGN are broad. In Seyferts galaxies, FWHM for optical UV Broad Lines < 10,000 km/sec; NLR lines < 1000 km/sec
  • In general, widths decrease with distance from the central source
  • In all cases, FWHM >> thermal (~ few km/sec). Possibilities:
  • Superposition of knots with range in velocities.
  • Micro-Turbulence
Superposition likely. Central knots seen in [OIII] with very large dispersions.
  • BLR emission lines are very smooth (e.g. Dietrich et al. 1999). If thermal, need huge number within light-days of central potential
  • Bottorff &Ferland (2000) – BLR clouds internally turbulent. vturb >> vthermal
  • Note: turbulence present in ISM. Larson (1981) – power-law correlation btw molecular cloud sizes and line widths (see Elmegreen & Scalo 2004) –

Why not in AGN?

Causes of turbulence in ISM:
  • Stars – via winds and Supernovae
  • Galactic rotation
  • Gaseous self-gravity/cloud collapse
  • Kelvin-Helmholtz and other fluid instabilities

Fluid Mechanics:

convective acceleration: time independent acceleration of fluid w.r.t space

non-linear advection operator → distortion of velocity field

Bottorff & Ferland (2002) – included dissipative heating w/micro –turbulence for BLR. With heating rate Q:

Q = ηνρ (vturb 3 /D) ergs cm-3 s-1

(vturb equivalent to b or 1/1.665 FWHM)

  • We applied same formalism for NLR emission-line gas:

NV 1240, affected by photo-excitation + heating, [NeV] 3426 bossted by heating.


High resolution X-ray spectra of AGN show myriad of soft X-ray emission lines arising in NLR

Ratios of resonance to forbidden lines in He-like triplets can indicate temperature and density. High r/f ratios: collisionally excited gas (Ogle et al. 2000); Photo-excitation (Sako et al. 2000; Kinkhabwala et al. 2002)/


Narrowness of Radiative Recombination Continua suggests low Temps (Photo-ionization) → photo-excitation.

But photo-excitation depends strongly on vturb

Sim of OVII triplet, courtesy of R. Porter.

Cloudy models, (logU=0), showing dependence of r/f ratio on vturb and column density.


Is turbulence present in intrinsic absorbers?

Most readily answered using high-res UV spectra of Type 1 Seyferts.

STIS spectra of NGC 5548, showing multiple kinematic components in HI, NV, and CIV. Note the difference in the profiles.


STIS spectra of NGC 3783 (Gabel et al. 2003), showing variations in absorption over three epochs, separated by 13 and 9 months. Radial velocity changes or profile changes (superposition of components)?


Comparison of FWHM and total H column densities (derived from photo-ionization models) for absorbers in NGC 3516, NGC 4051, NGC 4151, NGC 5548, and Mrk 509 (Crenshaw, in prep). Note even smallest large column density absorbers have super-thermal widths.

Slope of Nh to FWHM is ~ 1.5. For Kolmogorov cascade, slope is unity. Note: slope is flatter for the lower envelope. Combination of turbulence and superposition?


If minimum widths due to turbulence, what would we see?

Two cases, logU=-1.5, logNh=20.5

FWHM = 1000 km/s at face; no decay. Profile difference dominated by differences in ionic columns and oscillator strengths.

FWHM = 1000 km/s at face; exponential decay. Local value of vturb has strong effect.

Conclusions? Perhaps“open questions” is better term:
  • Are emission lines enhanced by turbulence?
  • Are smooth line profiles due to turbulence?
  • How is the turbulence generated?
  • Does turbulence damp out? If so , how and over what scale lengths (see Mark Bottorff)
  • Is there associated dissipative heating?
  • How does this affect cloud lifetimes, acceleration, etc.