Redshifted Cool Gas in the Disturbed HI Disk of the Starburst Dwarf NGC 4214

Abstract

We report redshifted cool gas toward the central star-forming region of the nearby starburst dwarf galaxy NGC 4214. HST/COS spectra show low-ionization absorbers redshifted relative to the systemic velocity, most clearly in SII ($Δv=19.8\pm2.6\ {\rm km\,s^{-1}}$) and supported by MgII ($Δv=30.3\pm3.0\ {\rm km\,s^{-1}}$), while PII remains tentative ($Δv=7.5\pm3.4\ {\rm km\,s^{-1}}$). The Keck/HIRES spectra also reveal a redshifted CaII absorption component ($Δv=25.6\pm1.5\ {\rm km\,s^{-1}}$). Because the absorption is detected against the central UV or optical continuum, the gas must lie in the foreground of the star-forming region and is moving away from the observer and toward the background UV source in projection. A VLA--THINGS HI spectrum extracted at the COS position within one VLA beam also shows a redshifted neutral component at $v_{\rm hel}=329.2\pm0.9\ {\rm km\ s^{-1}}$, offset by $38.2\pm1.3\ {\rm km\ s^{-1}}$ from systemic and by $27.6\pm1.0\ {\rm km\ s^{-1}}$ from the dominant local HI component. The FAST HI mapping further reveals an extended, kinematically disturbed neutral disk, with residual structures relative to a warped-disk model. Together, the redshifted UV absorption, the redshifted HI component, and the disturbed large-scale HI velocity field show that the central anomalous cool gas is observed in a galaxy with a disturbed extended neutral disk. This geometry suggests that the redshifted cool gas may trace inflow or recycled fallback toward the central region, although warped-disk or non-circular disk motions cannot be fully excluded.