Reverberation mapping

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Reverberation mapping is an astrophysical technique used to measure structures in the Broad Emission-Line Region (BLR) around a supermassive black hole in the center of an active galaxy and to estimate the mass of the hole. It is viewed primarily as a method of mass estimation, meaning mass is measured directly from the motion that causes gravity in the nearby gas.

The mass of the black hole is determined using the following formula:

In this formula is

  • Δ V the Root mean square ( RMS velocity ) of the gas movement in the BLR in the vicinity of the black hole as measured by the Doppler spread ( Doppler broadening ) of the gaseous emission lines.
  • R BLR is the radius of the broad-line region.
  • G is the gravitational constant .
  • f is a poorly known form factor that depends on the shape of the BLR.

The biggest problem with using this formula is measuring the R BLR . A standard technique for measuring is based on the fact that the emission line flux densities change greatly in response to changes in the continuum; h., the light from the accretion disk near the black hole ("reverberation") ( One standard technique is based on the fact that the emission-line fluxes vary strongly in response to changes in the continuum, ie, the light from the accretion disk near the black hole ("reverberation") ). It should also be noted that the changes in the emission lines take place with a delay to the change in the continuum. Assuming that the delay is due to the time of flight, the size of the BLR can be measured.

Only a small handful of AGNs (less than 40) were accurately mapped this way. An alternative approach is to use an empirical correlation between R BLR and the continuum luminosity.

Another uncertainty is the value of f . In principle, the response of the BLR to variations in the continuum could be used to map the three-dimensional structure of the BLR. In practice, the amount and quality of data required to perform such a deconvolution is prohibitive. Until around 2004, f ab initio was defined on the basis of simple structural models of the BLR. Recently the value of f has been determined in such a way that the M – sigma relation for active galaxies is as compatible as possible with the M – sigma relation for calm galaxies. When f is determined in this way, reverberation mapping becomes a "secondary" rather than a "primary" mass estimation technique.

See also

Web link

Individual evidence

  1. ↑ a b c David Merritt: Dynamics and Evolution of Galactic Nuclei . Ed .: Princeton University Press. Princeton 2013, ISBN 978-1-4008-4612-2 (English, openlibrary.org [accessed December 28, 2016]).
  2. ^ BM Peterson, K. Horne: Reverberation Mapping of Active Galactic Nuclei . July 26, 2004, doi : 10.1002 / asna.200310207 , arxiv : astro-ph / 0407538 .