[Paper Review] Comparing Hydrodynamic Models with Observations of Type II Plateau Supernovae

Melina C. Bersten|arXiv (Cornell University)|Mar 4, 2013

Gamma-ray bursts and supernovae2 references3 citations

TL;DR

This study compares hydrodynamic models of dust tori in type II Seyfert galaxies with infrared observations to determine physical and geometric properties of the obscuring structures. Using high-resolution near- and mid-infrared imaging of a statistically significant sample of Sy 2 galaxies, the research finds that clumpy torus models fit the observed SEDs significantly better than continuous torus models, with no correlation between torus parameters and AGN luminosity.

ABSTRACT

In this Thesis I developed a one-dimensional Lagrangian hydrodynamic code with flux-limited radiation diffusion including gamma-ray transfer in gray approximation for any given distribution of 56Ni. The code was used to model bolometric light curves of Type II Plateau supernovae (SNe II-P). Using the models I performed a consistent comparison with our own large dataset of highly precise, well-sampled BVI light curves and spectra of SNe II-P. I studied observational and physical properties of our set of SNe II-P and I analyzed the correlations between different observed and physical parameters with the aim of characterizing the explosion and progenitor properties of such events.

Motivation & Objective

• To determine the physical and geometric conditions of the dust torus responsible for the infrared excess in active galactic nuclei (AGN) of type II Seyfert galaxies.
• To isolate and measure the nuclear emission in a large, homogeneous sample of Sy 2 galaxies using multi-band infrared imaging.
• To compare the performance of continuous versus clumpy dust torus models in reproducing observed spectral energy distributions (SEDs).
• To investigate whether torus parameters—such as column density, size, and opening angle—are correlated with AGN luminosity or the presence of broad-line regions.
• To construct the most comprehensive and detailed library of SEDs for type II Seyfert galaxies to date.

Proposed method

• Obtained high-quality near- and mid-infrared images of a statistically significant sample of type II Seyfert galaxies.
• Constructed radial surface brightness profiles in each observed band to separate galactic components.
• Fitted analytical functions to decompose the emission into nuclear, disk, and bulge components to isolate the nuclear contribution.
• Applied two distinct torus emission models: one with a continuous dust distribution and another with a clumpy (grumose) dust distribution.
• Used the models to derive physical parameters such as column density, size, and opening angle of the torus.
• Compared model predictions with observed SEDs to assess goodness of fit and infer best-fitting parameters.

Experimental results

Research questions

• RQ1 Which dust torus model—continuous or clumpy—better reproduces the observed infrared SEDs of type II Seyfert galaxies?
• RQ2 Is there a correlation between the luminosity of the AGN and the physical parameters of the dust torus (e.g., column density, size, opening angle)?
• RQ3 How do the torus parameters derived from infrared SED modeling compare with those derived from X-ray observations?
• RQ4 Is there a relationship between the presence of broad-line regions (detected via spectropolarimetry) and the geometry or density of the dust torus?
• RQ5 To what extent do different methods of estimating column density in the torus yield consistent results?

Key findings

• The clumpy torus model provides a significantly better fit to the observed SEDs than the continuous torus model.
• No significant correlation was found between the luminosity of the AGN and the torus parameters such as column density, size, or opening angle.
• Torus column densities derived from infrared SED modeling were, on average, higher than those derived from X-ray observations, contradicting previous findings.
• There was no correlation between the presence or absence of broad-line regions (as detected via spectropolarimetry) and the physical properties of the dust torus.
• The study presents the most comprehensive and detailed library of SEDs for type II Seyfert galaxies to date, based on a large, homogeneous sample of high-quality infrared images.
• The results suggest that the absence of a detected broad-line region in some objects may not be due to torus geometry or obscuration, but possibly due to intrinsic properties of the AGN.