H_I kinematics of the Large Magellanic Cloud revisited: Evidence of possible infall and outflow

Abstract

Aim: The neutral atomic Hydrogen (H_I) kinematics of the Large Magellanic Cloud (LMC) is revisited in light of two new proper motion estimates. Methods: We analysed the intensity weighted H_I velocity maps of the Australia Telescope Compact Array (ATCA)/Parkes and the Parkes Galactic all sky survey (GASS) data sets. We corrected the line-of-sight velocity field for the systemic, transverse, precession, and nutation motions of the disk using two recent proper motion estimates, and estimated the kinematic parameters of the H_I disk. Result: The value of position angle (PA) of kinematic major axis estimated using ATCA/Parkes data (126° ± 23°) is found to be similar to the recent estimate of the PA using stellar tracers. The effect of precession and nutation in the estimation of PA is found to be significant. The modelled H_I disk is found to be disturbed within 1°.0 radius and beyond 2°.9 radius. Using ATCA/Parkes data, most of the H_I gas in the LMC (∼87.9% of the data points) is found to be located in the disk. We detected 12.1% of the data points as kinematic outliers. A significant part of type 1 as well as slow type 2 H_I gas is identified with Arm E. We identified the well-known Arm S, Arm W, Arm B and a new stream, Outer Arm, as part of fast type 2 outlier component. The GASS data analysis brings out the velocity details of the Magellanic Bridge (MB) and its connection to the LMC disk. We find that the Arm B and the Outer Arm are connected to the MB. We detect high velocity gas in the western disk of the LMC and the south-west and southern parts of the MB. Conclusion: We proposed two models (in-plane and out-of-plane) to explain the outlier gas. We suggest that the Arm B could be an infall feature, originating from the inner MB. The Arm E could be an outflow feature. We suggest possible outflows from the western LMC disk and south and south-western MB, which could be due to ram pressure. The velocity pattern observed in the MB suggests that it is being sheared. We suggest that the various outliers identified in this study may be caused by a combination of tidal effects and hydrodynamical effect due to the motion of the LMC in the Milky Way halo.