Abstract

The supermassive black holes (SMBHs) that reside at the centers of massive galaxies are observed as active galactic nuclei (AGN) when they are rapidly consuming matter from a surrounding accretion disk, which releases large amounts of electromagnetic radiation. Closely surrounding this engine are the dense gas clouds of the broad line region (BLR), which are photoionized by the continuum radiation emitted by the accretion disk. As these clouds are deep within the potential well of the SMBH, the gas emission lines (the broad emission lines; BELs) are Doppler-broadened by several 1,000 km/s. Measuring the size and velocity dispersion of the BLR provides a way to infer the mass of the SMBH. However, the distances to most active galactic nuclei (AGN) make spatially resolving the BLR very challenging, and much of its structure and dynamics are uncertain. The variable continuum emission of an AGN produces corresponding responses in the broad lines that are modulated by light travel-time delays. The response is described by the transfer function, which contains information on the physical properties, structure, and kinematics of the BLR. The reverberation mapping technique, a time-series analysis of the driving light continuum curve and time-delayed response of the BELs, can recover some of this information. We have developed a new forward-modeling tool, the Broad Emission Line MApping Code (BELMAC), to simulate the velocity-resolved reverberation response of the BLR to an observed input light curve, given the bolometric luminosity and spectral energy distribution of the AGN. It is the first reverberation mapping code to incorporate photoionization models to enable modeling of multi-BEL. We present numerical approximations to the transfer function by simulating the velocity-resolved responses to a single continuum pulse for sets of models representing a spherical BLR with a radiatively driven outflow and a disk-like BLR with Keplerian rotation, as well as biconical winds. We explore how the structure, velocity field, and other BLR properties affect the transfer function. We calculate the response-weighted time delay, which is considered to be a proxy for the luminosity-weighted radius of the BLR. We find in certain BLR environments, the line response is inversely correlated to changes in the continuum. In such cases, the response-weighted delay can overestimate the luminosity-weighted radius by a factor of 2 or more. We used BELMAC to model the broad H𝛽 response of Markarian 142 and found a delay of 12 days, which is consistent with previous results. We also infer an SMBH mass of 5 x 10⁷ M⊙, which is about an order of magnitude greater than in previous studies. BELMAC has a fast and flexible design that allows other geometries and velocity fields to be easily added as modules. Therefore, BELMAC is a unique tool for interpreting the wealth of BLR reverberation and spectroscopy data that will come from near-future, large-scale time-domain surveys.

Publication Date

6-2024

Document Type

Dissertation

Student Type

Graduate

Degree Name

Astrophysical Sciences and Technology (Ph.D.)

Department, Program, or Center

Physics and Astronomy, School of

College

College of Science

Advisor

Andrew Robinson

Advisor/Committee Member

Triana Almeyda

Advisor/Committee Member

Sarah Gallagher

Campus

RIT – Main Campus

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