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

TL;DR

This study uses Hubble Space Telescope spectroscopy to observe time-variable broad H-alpha emission in NGC 4203, suggesting a red supergiant contrail and inflow dynamics, revealing complex interactions near the galaxy's central black hole.

Contribution

It presents evidence for a stellar contrail causing double-peaked emission lines and models the gas distribution as a ring, offering new insights into the galaxy's nuclear activity.

Findings

Double-peaked H-alpha emission increased by a factor of 2.2 from 1999 to 2010.

The gas distribution is best modeled as a ring, likely a stellar contrail.

Inflow rate exceeds the accretion requirement for observed X-ray luminosity.

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.