On the origin of the anomalous gas, non-declining rotation curve and disc asymmetries in NGC253

Abstract

We present a multi-wavelength (from far ultraviolet to HI emission) study of star formation feedback on the kinematics of the interstellar medium in the Sculptor Galaxy, NGC253. Its three well-known features (a disrupted stellar disc, a previously reported delining rotation curve, and anomalous HI gas) are studied in a common context of disc asymmetries. About 170 h of on-source ATCA observations are collected and reduced into two versions of \HI\ data cubes of different angular resolution (30'' / 2') and HI column density sensitivity (7.4 $\times$ $10^{19}$cm${}^{-2}$ / 4$\times$ $10^{18}$cm${}^{-2}$). We separate the anomalous gas from the disc using a custom-made line profile fitting toolkit called FMG. Two star formation tracers (H$\alpha$, FUV emission) are carefully processed and studied. We find that at $R>7.5\mathrm{kpc}$ the star formation activity is strongly lopsided (SFR${}_{NE}$ >SFR${}_{SW}$), and investigate several other properties (H$\alpha$/FUV, dust temperature, stellar age, and disc stability parameters). We also find that the declining nature of the rotation curve perceived by previous studies is not intrinsic but a combined effect of kinematical asymmetries at $R=7.5$--$16\mathrm{kpc}$. This is likely the consequence of star formation triggered outflow. The mass distribution and the timescale of the anomalous gas also imply that it originates from gas outflow, which is perhaps caused by galaxy-galaxy interaction considering the crowded environment of NGC253.

22 pages, 23 figures, accepted for publication in MNRAS

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