The Book of Dust: Reverberation Mapping of the Circumnuclear Dusty Region of Active Galactic Nuclei

Abstract

The circumnuclear dust region which surrounds the central engine of Active Galactic Nuclei (AGN) provides the angle-dependent obscuration necessary under the unification scheme.
Sublimating dust grains set the inner edge of this region (at temperature T ∼ 1500K) and thermally absorb and re-emit incident light from the accretion disc. This leads to a delayed response of the dusty light curve after the accretion disc light curve. The lag time, τ , is expected to have a simple Stefan-Boltzmann relationship with the luminosity of the AGN, i.e. τ ∝ √ L. This gives the dust time lags the potential to be used as cosmological probes.
In this thesis I present new time lags from three AGN: NGC3783, ESO323-G77 and H0557-385, which were observed with the ANDICAM instrument on the SMARTS 1.3m telescope and then reverberation mapped to recover their dust time lags.
These time lags are placed on a lag-luminosity plot with previously reverberation mapped AGN to determine the intrinsic scatter and the power-law index, β. β is determined to be 0.404^+0.057_-0.049 which is lower than the expected 0.5 from the Stefan-Boltzmann Relationship. The intrinsic scatter is 0.0114^+0.0085 _−0.0054 which is very low and is necessary to use AGN as cosmological probes.
Previously dust reverberation mapped AGN from Koshida et al. (2014) and Minezaki et al. (2019) were self consistently re-analyzed to find whether the lower-than-expected value of β was due to differences in analysis methods.
The values of β determined from the new lag luminosity plots remain lower than 0.5 in a 95% confidence interval. The intrinsic scatter for these plots is still very low, indicating that the dust time lags can be used as a proxy for the luminosity of the AGN. This means that the ongoing ESO Public Survey VEILS can move forward with creating a Hubble Diagram using dust time lags.

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ORCID for Elizabeth Boulderstone: orcid.org/0000-0002-2442-9966

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