Abstract
We present high-resolution (0.14 arcsec × 0.12 arcsec or 31 × 25 pc2) Atacama Large Millimeter/sub-millimeter Array 12CO(J = 2–1) observations of the spiral galaxy NGC 5064. Our study identifies 478 molecular clouds, of which 387 are resolved both spatially and spectrally. These clouds exhibit similarities to those of the Milky Way in terms of their sizes, molecular gas masses, velocity dispersions, velocity gradients, and Larson relations. However, the NGC 5064 clouds stand out with slightly higher gas mass surface densities, lower virial parameters (〉αvir〈 = 0.48 ± 0.03 assuming a standard conversion factor XCO = 2 × 1020 cm−2 (K km s−1)−1; αvir = 1 for a lower conversion factor of XCO = 0.96 ± 0.02 × 1020 cm−2 (K km s−1)−1), and an unusually high fraction of retrograde rotation (fretro ≈ 67 per cent). Retrograde clouds are 18 per cent larger, 58 per cent more massive, 15 per cent more turbulent and have 17 per cent larger gas mass surface densities than prograde clouds. The velocity gradients in the clouds seem to arise from turbulence rather than clouds’ intrinsic rotation or large-scale galaxy rotation. Cloud-cloud collisions provide the most plausible explanation for the elevated retrograde fraction, though further investigation is needed to confirm this scenario. Projection effects due to the galaxy’s high inclination (i = 70.8°) may further enhance the apparent retrograde fraction. Confirmation using less inclined systems is essential to determine whether the observed dominance of retrograde rotation reflects a genuine physical phenomenon or is significantly shaped by projection effects.
WISDOM Project - XXIV. Giant molecular clouds of the spiral galaxy NGC 5064: high fraction of retrograde rotation
Monthly Notices of the Royal Astronomical Society, 541, 4, 3081-3100
Liu, Lijie; Shu, Fanglin; Bureau, Martin; Onishi, Kyoko; Davis, Timothy A.; Liang, Fu-Heng; Choi, Woorak; Williams, Thomas G.; Lu, Anan; Iguchi, Satoru
(ADS) / (arXiv)