1. Introduction
• Recently, two types of bulges have been recognized with different
formation mechanisms: classical and pseudo-bulges.
• Classical bulges are thought to form via hierarchical merging of
smaller bulges, while pseudo-bulges arise though action of spiral
density waves within the disk.
• Current paradigms suggest that all galaxies contain massive black
holes whose mass scales with the bulge: Mbh = 0.002 Mbulge (Fig. 1).
• Pseudo-bulges do not follow this relation with the central black hole.
• Mechanisms which build galactic bulges may be related to
those which grow black holes.
What is a Seyfert Galaxy?
• Seyfert galaxies are a type of Active Galactic Nucleus (AGN).
• Gravitational energy is released as heat, shockwaves,
radiation, plasma jets, etc., as matter falls into black hole.
• Seyferts are classified based on the strength of the central
source.
• Strong unresolved nucleus in Seyfert 1.
• Weaker nucleus in Seyfert 2.
NGC 4151 & NGC 1068: BULGE OR PSEUDO-BULGE?
Department of Physics and Astronomy, College of Arts and Sciences
Glenn Wilson, Courtney Mueller, Joseph Mullen, Nur Shafiqa Fitri Kamsani, Charles Nelson (Mentor)
Methods
• GALFIT is a 2D fitting algorithm utilizing parametric analysis.
• GALFIT fits models to galaxy images. Subtracting the model
from the original image obtains a residual image. The
residual image can reveal fine bulge structure and show
where a model fails.
• Improved models can be made by convolving the image
with a PSF and/or including a bad pixel mask, both of which
provide GALFIT with a truer image of the galaxy to be fitted.
Future Work
• Improve the GALFIT model fit of NGC 4151.
• Extend the study to all galaxies in the data set to reveal
details of each galaxy’s morphology.
• Investigate the role of the bulge in the development of
Seyfert nuclei.
References and Acknowledgements
Nelson, Charles H. "The Relationship Between Black Hole Mass and VelocityDispersion in Seyfert 1
Ga." The Astrophysical Journal 615.2 (2004): 652-61. ApJ.
Peng, Chien Y., and Luis C. Ho. "DetailedDecomposition of Galaxy Images. II. Beyond Axisymmetric
Models." The Astrophysical Journal 139.6 (2010): 2097-129. Print.
Figure 3: GALFIT used to produce model images. Row 1: Bulge and disk with various
amounts of rotation. Row 2: Same galaxies with a different power law. Row 3: The
galaxies inclined to the line of sight.
NGC 1068 (Fig. 2)
Galaxy Morphology: Sa
Redshift: 0.003793
Apparent Magnitude: 9.61
Figure 1: The Mbh - σ relation for Seyfert galaxies (green dots) and normal galaxies
(red +). The parameter σ scales with bulge mass in this figure. (Nelson et. al 2001)
Objectives
• NGC 4151 and NGC 1068 are the prototypical Seyfert 1 and Seyfert 2
galaxies; however, their bulge structures are different.
• Attempt to systematically differentiate between bulges and pseudo
bulges in Seyfert galaxies using GALFIT.
NGC 1068 Model Residual
Results
• Used GALFIT on NGC 1068/4151 to reveal galaxy morphology.
• Investigated the role of different model parameters in the
GALFIT fitting. (Fig. 3)
• A tight fitting model to NGC1068 was produced using a bulge,
two disks, and a sky component. (Fig. 2)
• The fitted model’s Sersic parameter led us to conclude
NGC1068 contains a pseudo bulge.
NGC 4151 (left)
Galaxy Morphology: Sab
Redshift: 0.003319
Apparent Magnitude: 11.5
Figure 2: GALFIT algorithm implementation. The first image is the input image taken, the second is the GALFIT model of the bulge and disk, and the final image is the residual.