The Impact of Bar-induced Noncircular Motions on the Measurement of Galactic Rotation Curves
We study the impact of bar-induced noncircular motions on the derivation of galactic rotation curves (RCs) using hydrodynamic simulations and observational data from the PHANGS-ALMA survey. We confirm that noncircular motions induced by a bar can significantly bias RCs derived from the conventional...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/adabe0 |
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| Summary: | We study the impact of bar-induced noncircular motions on the derivation of galactic rotation curves (RCs) using hydrodynamic simulations and observational data from the PHANGS-ALMA survey. We confirm that noncircular motions induced by a bar can significantly bias RCs derived from the conventional tilted-ring method, consistent with previous findings. The shape of the derived RC depends on the difference in position angle (Δ ϕ ) between the major axes of the bar and the disk in the face-on plane. For $\left|{\rm{\Delta }}\phi \right|\lesssim 40^\circ $ , noncircular motions produce a bar-induced “dip” feature (rise–drop–rise pattern) in the derived RC, which shows higher velocities near the nuclear ring and lower velocities in the bar region compared to the true RC (RC _true ). We demonstrate convincingly that such dip features are very common in the PHANGS-ALMA sample of barred galaxies. Hydrodynamical simulations reveal that the “dip” feature is caused by the perpendicular orientation of the gas flows in the nuclear ring and the bar; at low $\left|{\rm{\Delta }}\phi \right|$ streamlines in the nuclear ring tend to enhance V _los , while those in the bar tend to suppress V _los . We use a simple “misaligned ellipses” model to qualitatively explain the general trend of RCs from the tilted-ring method (RC _tilted ) and the discrepancy between RC _tilted and RC _true . Furthermore, we propose a straightforward method to implement a first-order correction to the RC derived from the tilted-ring method. Our study is the first to systematically discuss the bar-induced “dip” feature in the RCs of barred galaxies by combining both simulations and observations. |
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| ISSN: | 1538-4357 |