WALLABY Pilot Survey: Characterizing Low-rotation Kinematically Modeled Galaxies

Many of the tensions in cosmological models of the Universe lie in the low-mass, low-velocity regime. Probing this regime requires a statistically significant sample of galaxies with well-measured kinematics and robustly measured uncertainties. The Widefield ASKAP L -band Legacy All-sky Blind surveY (WALLABY), as a wide-area, untargeted H i survey, is well positioned to construct this sample. As a first step toward this goal, we develop a framework for testing kinematic modeling codes in the low-resolution, low signal-to-noise ratio, low rotation velocity regime. We find that the WALLABY Kinematic Analysis Proto-Pipeline is remarkably successful at modeling these galaxies when compared to other algorithms, but, even in idealized tests, there is a significant fraction of false positives found below inclinations of ≈40°. We further examine the 11 detections with rotation velocities below 50 km s −1 in the WALLABY pilot data releases. We find that those galaxies with inclinations above 40° lie within 1 σ –2 σ of structural scaling relations that require reliable rotation velocity measurements, such as the baryonic Tully–Fisher relation. Moreover, the subset that has consistent kinematic and photometric inclinations tends to lie nearer to the relations than those that have inconsistent inclination measures. This work both demonstrates the challenges faced in low-velocity kinematic modeling and provides a framework for testing modeling codes as well as constructing a large sample of well-measured low-rotation models from untargeted surveys.