Determination of Galaxy Rotation Curves from the HALOGAS and LITTLE THINGS Surveys Using 2D and 3D Techniques Azumah Yasmin (a*), Hesti Wulandari (ab)
a) Astronomy Research Group, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Bandung, Indonesia
*azumahyasmin[at]gmail.com
b) Bosscha Observatory, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Lembang, Indonesia
Abstract
The derivation of galactic rotation curves plays a fundamental role in the study of galactic dynamics, particularly in understanding the mass distribution of various structural components and providing compelling evidence for the presence of dark matter, which dominates at galactic scales. However, obtaining accurate and reliable rotation curves remains challenging due to factors such as determination of inclination angles, beam smearing effects and the presence of non-circular motions caused by unique galactic features, such as bar. The advancement of observational technologies has further supported the development of various methods for rotation curve extraction, each with differing assumptions and computational strategies. In this paper, rotation curves are derived using both two-dimensional (2D) and three-dimensional (3D) methods, with the aim of identifying the most robust method across different galaxy types and observational conditions. The analysis employs the tilted-ring model and harmonic decomposition using the software packages 3DBarolo (applying both the 3DBarolo and 2DBarolo methods) and DiskFit (applying the 2DiskFit method with disk and disk\(+\)bar models). A total of 15 spiral galaxies from the HALOGAS survey and 13 dwarf galaxies from the LITTLE THINGS survey were analyzed, selected to have intermediate inclination angles in the range of \(45^{\circ}<i<75^{\circ}\). Evaluation was carried out through visual inspection of the rotation curves and comparison of galactic parameters such as inclination and position angle (PA). The quality of the derived rotation curves varied, with some exhibiting significant fluctuations. In several cases, the different methods produced consistent results with one another and with the reference data. However, the 3DBarolo method generally yielded smoother and more stable rotation curves, despite its inability to model specific non-axisymmetric features, such as bars. The 2DBarolo method frequently resulted in highly fluctuating curves, while the 2DiskFit disk model showed moderate stability, outperforming 2DBarolo in most cases. Fluctuations were also observed in curves derived using the bar model- however, this model has the added advantage of indicating the possible presence of bar structures in galaxies, although further investigation is required for confirmation. Based on the findings of this study, 3DBarolo is recommended as a more reliable and robust tool for the derivation of galactic rotation curves without bar, and 2DiskFit bar model is recommended for galaxy with bar.
