Symposia & Conferences

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A comparison of black hole mass scaling relations and galactic morphologies of spiral galaxies
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Jeewantha, K.; Hewageegana, P. S.; Abdeen, S.
We investigated the relationships between black hole mass scaling relations and the galactic morphologies of spiral galaxies using density wave theory. Drawing on spiral arm pitch angle measurements, the theory predicts a correlation between these angles and the wavelengths observed in galaxy images. The study involved 20 grand-design spiral galaxies belonging to the NGC catalogue with clearly visible spiral arms, including both inner and outer arms. We deprojected the original images to face-on orientation using the IRAF package and parametric data from the NED and HyperLeda databases. Pitch angles were measured visually using the Python-OL script, and a pitch angle range was evaluated using six wavebands: 3.6 µm, 8.0 µm, B-band, Hα, HI, and CO. Pitch angles were then individually determined for each spiral arm using a MATLAB-based script SPIRALITY. When comparing with existing literature values this study revealed discrepancies in spiral arm pitch angle measurements across several galaxies. These discrepancies were mainly due to variations in the inclination angles of these galaxies. As the theory predicted, we noticed the wavelength dependence of the pitch angle. The pitch angle measurements in wavebands 3.6 µm and 8.0 µm, B and 8.0 µm, and Hα and 8.0 µm showed a 1:1 correlation. Central supermassive black hole (SMBH) masses and dark matter halo (DMH) masses were determined using standard scaling equations for 3.6 µm waveband pitch angles. We used average spiral arm pitch angles to calculate masses for both the inner and outer arms separately. We discovered that the average pitch angle of inner arms determines the black hole mass of a galaxy with both inner and outer arms, as per existing literature. The study found an SMBH mass-pitch angle relation, log (𝑀𝐵𝐻 𝑀⨀ ) = (6.69 ± 0.64) - (0.001 ± 0.030)(|𝜙|) and proposed four other SMBH mass-pitch angle relations for Inner, Inner-Outer, SAB, and Pseudobulges. The SMBH mass calculations presented in this work are in good agreement with available direct measurements. This spiral arm pitch angle based SBHM mass estimation model is suitable for determining the black hole masses of galaxies with an inclination angle between 7° - 22°. The DMH mass-pitch angle relation was found to be, log (𝑀𝐷𝑀 𝑀⨀ ) = (-0.02 ± 0.02)(|𝜙|) + (12.17 ± 0.33) for the sample. We proposed an SMBH mass - DMH mass relation, log (𝑀𝐵𝐻 𝑀⨀ ) = (4.07 ± 0.03)log (𝑀𝐷𝑀 𝑀⨀ ) - (41.69 ± 0.40) for the sample, and another two relations for galaxies with inner arms and those with both inner and outer arms. We examined the variations of SMBH and DMH masses in host galaxies, identifying three morphological subcategories: SA, SAB, and SB morphologies; (s) and (rs) morphologies; and ab, b, bc, c, and cd morphologies. A normalised form of black hole mass and dark matter halo mass, KD, was defined and plotted against these morphologies. Results showed that the KD in barred morphology decreases from unbarred to barred, the spiral feature decreases from complete spiral (s) to mixed spiral (rs), and the Hubble subtype decreases from 'b' to 'c'. The highest KD of morphological subtypes SA, (s), and 'b' are identified for each morphological subcategory separately.
A theoretical study of identifying co-rotation radii and galactic resonances of spiral galaxies
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Jeewanthi, K.G.V.; Hewageegana, P.S.; Abdeen, S.
This study delved into the dynamic behaviours of spiral galaxies, employing a robust approach to analyse co-rotation radii and galactic resonances within the framework of Density Wave Theory. It aimed to develop new methods for identifying resonance locations and co-rotation radii, conduct comparative analyses across ten diverse spiral galaxies, predominantly grand-design spiral galaxies with different pattern speeds, and validate these methods against existing techniques. The first method used rotation curve analysis to identify Inner Lindblad Resonances, 4:1 resonances, co-rotation radii, and Outer Lindblad Resonances, utilising two pattern speeds from literature for comparative purposes. The first pattern speeds yielded co-rotation radii closer to literature values for galaxies NGC 1566, NGC 4254, NGC 4303, NGC 4321, and NGC 5247. Conversely, for NGC 5194 and NGC 5248, the second pattern speeds yielded better alignment. However, NGC 1365 and NGC 5236 showed deviations from literature values for both pattern speeds, while NGC 4535 posed challenges in determining its corotation radius. A comparative analysis of co-rotation radii against mean literature values indicated successful alignment despite significant uncertainties for NGC 1365, NGC 4254, and NGC 4303. The second approach used 3D surface intensity plots to identify resonance regions, focusing on low star formation areas, enhancing understanding of dynamic structures. It compared co-rotation radii with literature values, highlighting probable regions and addressing uncertainties, particularly in NGC 1365, NGC 5236, and NGC 5247. Methodological precision was crucial, given the nuances revealed by these plots. Comparing Method I and II, Method I aligned better with literature values for NGC 4254, NGC 4303, NGC 4321, NGC 5194, NGC 5247, and NGC 5248, while Method II showed closer alignment for NGC 1566 and NGC 4535. NGC 1365 and NGC 5236 exhibited discrepancies in co-rotation radii values across both methods compared to the literature. The third methodology employed theoretical calculations to align empirical observations with theoretical predictions, enhancing the understanding of galactic resonant dynamics. NGC 4535 was excluded due to data limitations. The systematic approach derived theoretical resonance locations for co-rotation radii, outlining an analytical roadmap. Comparative analysis between empirical and theoretical resonance values revealed close alignment for most galaxies, enriching insights into resonant phenomena within galactic systems. The fourth method involved measuring spiral arm pitch angle measurements across multiple wavelengths (3.6 μm, 8.0 μm, B-band, Hα). A custom Python code facilitated the overlaying of spiral arm patterns from different wavebands onto FITS images, enabling detailed comparative analyses. The identification of crossing points, coupled with consideration of pitch angle uncertainties, offered a sophisticated approach to delineating resonance locations on the galactic disk. Challenges in measuring and comparing pitch angles highlighted the complexities of detecting outer arms and resolving discrepancies across imaging wavelengths. In conclusion, each method employed in this study has its unique strengths and challenges while no single method was universally superior, as galaxies showed varying compatibility with each approach. These findings enhance the understanding of galactic morphology and evolution, including implications for galactic habitable zones.