skip to main content

Title: TLDR: time lag/delay reconstructor
ABSTRACT We present the time lag/delay reconstructor (TLDR), an algorithm for reconstructing velocity delay maps in the maximum a posteriori framework for reverberation mapping. Reverberation mapping is a tomographical method for studying the kinematics and geometry of the broad-line region of active galactic nuclei at high spatial resolution. Leveraging modern image reconstruction techniques, including total variation and compressed sensing, TLDR applies multiple regularization schemes to reconstruct velocity delay maps using the alternating direction method of multipliers. Along with the detailed description of the TLDR algorithm we present test reconstructions from TLDR applied to synthetic reverberation mapping spectra as well as a preliminary reconstruction of the Hβ feature of Arp 151 from the 2008 Lick Active Galactic Nuclei Monitoring Project.
; ;
Award ID(s):
Publication Date:
Journal Name:
Monthly Notices of the Royal Astronomical Society
Page Range or eLocation-ID:
2903 to 2912
Sponsoring Org:
National Science Foundation
More Like this
  1. The size and structure of the dusty circumnuclear torus in active galactic nuclei (AGNs) can be investigated by analyzing the temporal response of the torus's infrared (IR) dust emission to variations in the AGN ultraviolet/optical luminosity. This method, reverberation mapping, is applicable over a wide redshift range, but the IR response is sensitive to several poorly constrained variables relating to the dust distribution and its illumination, complicating the interpretation of measured reverberation lags. We have used an enhanced version of our torus reverberation mapping code (TORMAC) to conduct a comprehensive exploration of the torus response functions at selected wavelengths, for the standard interstellar medium grain composition. The shapes of the response functions vary widely over the parameter range covered by our models, with the largest variations occurring at shorter wavelengths (≤4.5 μm). The reverberation lag, quantified as the response-weighted delay (RWD), is most affected by the radial depth of the torus, the steepness of the radial cloud distribution, the degree of anisotropy of the AGN radiation field, and the volume filling factor. Nevertheless, we find that the RWD provides a reasonably robust estimate, to within a factor of ~3, of the luminosity-weighted torus radius, confirming the basic assumption underlying reverberationmore »mapping. However, overall, the models predict radii at 2.2 μm that are typically a factor of ~2 larger than those derived from K-band reverberation mapping. This is likely an indication that the innermost region of the torus is populated by clouds dominated by large graphite grains.« less
  2. Abstract

    High-accuracy black hole (BH) masses require excellent spatial resolution that is only achievable for galaxies within ∼100 Mpc using present-day technology. At larger distances, BH masses are often estimated with single-epoch scaling relations for active galactic nuclei. This method requires only luminosity and the velocity dispersion of the broad-line region (BLR) to calculate a virial product, and an additional virial factor,f, to determine the BH mass. The accuracy of these single-epoch masses, however, is unknown, and there are few empirical constraints on the variance offbetween objects. We attempt to calibrate single-epoch BH masses using spectropolarimetric measurements of nine megamaser galaxies from which we measure the velocity distribution of the BLR. We do not find strong evidence for a correlation between the virial products used for single-epoch masses and dynamical mass, either for the megamaser sample alone or when it is combined with dynamical masses from reverberation mapping modeling. Furthermore, we find evidence that the virial parameterfvaries between objects, but we do not find strong evidence for a correlation with other observable parameters such as luminosity or broad-line width. Although we cannot definitively rule out the existence of any correlation between dynamical mass and virial product, we find tension betweenmore »the allowedf-values for masers and those widely used in the literature. We conclude that the single-epoch method requires further investigation if it is to be used successfully to infer BH masses.

    « less
  3. We present new near-infrared VLTI/GRAVITY interferometric spectra that spatially resolve the broad Br γ emission line in the nucleus of the active galaxy IRAS 09149−6206. We use these data to measure the size of the broad line region (BLR) and estimate the mass of the central black hole. Using an improved phase calibration method that reduces the differential phase uncertainty to 0.05° per baseline across the spectrum, we detect a differential phase signal that reaches a maximum of ∼0.5° between the line and continuum. This represents an offset of ∼120  μ as (0.14 pc) between the BLR and the centroid of the hot dust distribution traced by the 2.3 μ m continuum. The offset is well within the dust sublimation region, which matches the measured ∼0.6 mas (0.7 pc) diameter of the continuum. A clear velocity gradient, almost perpendicular to the offset, is traced by the reconstructed photocentres of the spectral channels of the Br γ line. We infer the radius of the BLR to be ∼65  μ as (0.075 pc), which is consistent with the radius–luminosity relation of nearby active galactic nuclei derived based on the time lag of the H β line from reverberation mapping campaigns. Our dynamicalmore »modelling indicates the black hole mass is ∼1 × 10 8   M ⊙ , which is a little below, but consistent with, the standard M BH – σ * relation.« less

    We present the accretion disc-size estimates for a sample of 19 active galactic nuclei (AGNs) using the optical g-, r-, and i-band light curves obtained from the Zwicky Transient Facility survey. All the AGNs have reliable supermassive black hole (SMBH) mass estimates based on previous reverberation mapping measurements. The multiband light curves are cross-correlated, and the reverberation lag is estimated using the Interpolated Cross-Correlation Function method and the Bayesian method using the javelin code. As expected from the disc-reprocessing arguments, the g − r band lags are shorter than the g − i band lags for this sample. The interband lags for all, but five sources, are larger than the sizes predicted from the standard Shakura Sunyaev (SS) analytical model. We fit the light curves directly using a thin disc model implemented through the javelin code to get the accretion disc sizes. The disc sizes obtained using this model are on an average 3.9 times larger than the prediction based on the SS disc model. We find a weak correlation between the disc sizes and the known physical parameters, namely the luminosity and the SMBH mass. In the near future, a large sample of AGNs covering broader ranges of luminositymore »and SMBH mass from large photometric surveys would be helpful in a better understanding of the structure and physics of the accretion disc.

    « less
  5. Abstract

    In recent years, continuum-reverberation mapping involving high-cadence UV/optical monitoring campaigns of nearby active galactic nuclei has been used to infer the size of their accretion disks. One of the main results from these campaigns has been that in many cases the accretion disks appear too large, by a factor of 2–3, compared to standard models. Part of this may be due to diffuse continuum emission from the broad-line region (BLR), which is indicated by excess lags around the Balmer jump. Standard cross-correlation lag-analysis techniques are usually used to just recover the peak or centroid lag and cannot easily distinguish between reprocessing from the disk and BLR. However, frequency-resolved lag analysis, where the lag is determined at each Fourier frequency, has the potential to separate out reprocessing on different size scales. Here we present simulations to demonstrate the potential of this method and then apply a maximum-likelihood approach to determine frequency-resolved lags in NGC 5548. We find that the lags in NGC 5548 generally decrease smoothly with increasing frequency, and are not easily described by accretion-disk reprocessing alone. The standard cross-correlation lags are consistent with lags at frequencies lower than 0.1 day−1, indicating they are dominated from reprocessing at sizemore »scales greater than ∼10 light days. A combination of a more distant reprocessor, consistent with the BLR, along with a standard-sized accretion disk is more consistent with the observed lags than a larger disk alone.

    « less