Time Variable Broad Line Emission in NGC 4203: Evidence for Stellar Contrails

Abstract

Dual epoch spectroscopy of the lenticular galaxy, NGC 4203, obtained with the Hubble Space Telescope (HST) has revealed that the double-peaked component of the broad H{\alpha} emission line profile is time variable, increasing by a factor of 2.2 in brightness between 1999 and 2010. Modeling the gas distribution responsible for the double-peaked profiles indicates that a ring is a more appropriate description than a disk and most likely represents the contrail of a red supergiant star that is being tidally disrupted at a distance of ~ 1500 AU from the central black hole. There is also a bright core of broad H{\alpha} line emission that is not time variable and identified with a large scale inflow from an outer radius ~1 pc. If the gas number density is > 10^6 cm^{-3}, as suggested by the absence of similarly broad [O I] and [O III] emission lines, then the steady state inflow rate is ~ 2 x 10^{-2} M{_{\sun}}/yr which exceeds the inflow requirement to explain the X-ray luminosity in terms of radiatively inefficient accretion by a factor of ~6. The central AGN is unable to sustain ionization of the broad line region, the discrepancy is particularly acute in 2010 when the broad H{\alpha} emission line is dominated by the contrail of the in-falling supergiant star. However, ram pressure shock ionization produced by the interaction of the in-falling supergiant with the ambient interstellar medium may help alleviate the ionizing deficit by generating a mechanical source of ionization supplementing the photoionization provided by the AGN.