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 Hα emission line 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 Hα 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 × 10 −2 M /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 Hα emission line is dominated by the contrail of the infalling 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.

The Size, Structure, and Ionization of the Broad-Line Region in NGC 3227

“…Specific results for NGC 3227 are summarized in Table 5, following the procedure described most recently in Devereux (2011b). An important result is that the observed mass inflow rate, ∼10 −2 M yr −1 , is commensurate with that required to power the central UV-X-ray source in NGC 3227, assuming radiatively inefficient accretion as parameterized by Merloni et al (2003).…”

“…Consequently, knowing the relationship between velocity and radius allows the broad emission line profiles to be modeled revealing the shape and size of the BLR. This technique has led to large BLR size discrepancies for the LLAGNs M81, NGC 3998, and NGC 4203 (Devereux & Shearer 2007;Devereux 2011aDevereux , 2011b. Specifically, the dimensions of the BLR deduced from emission line profile fitting are much larger than expected based on the reverberation size-UVluminosity correlation of Kaspi et al (2005).…”

“…The forbidden line model produced using the G750M spectrum is also subtracted from the lower resolution G750L spectrum, motivated by the observation that the flux in the two [S ii] lines did not change between 1999 and 2000, with the result that the broad Hα emission line flux in the G750L spectrum is ∼11% smaller than measured in the G750M spectrum (see Table 2), presumably a consequence of the aforementioned decrease in the underlying continuum. Figures 3 and 4 illustrate the consequence of subtracting the forbidden [O iii] emission lines from the Hβ and Hγ lines following the procedure described in Devereux (2011b). Emission line fluxes are reported in Table 3 Figure 5) diagnostic diagram.…”

“…The relativistic accretion disk model, presented by Chen & Halpern (1989), has been described most recently by Devereux (2011b). Past experience with this model has revealed that a single peak broad line profile requires a large ratio of outer radius to inner radius, sufficient inclination to produce a symmetrical profile shape, and adequate velocity dispersion to merge the two peaks, a feature of disk models, into a single peak.…”

THE BROAD LINE REGION IN NGC 4051: AN INFLOW ILLUMINATED BY A 105K ACCRETION DISK

“…The number of ionizing photons produced by the central AGN in NGC 4051 can be estimated using the prescription in Devereux (2011) where the 912Å flux is extrapolated from the 1450Å flux using a UV spectral index α = 2 (where f ν ∝ ν −α ) reported 2 in Kaspi et al (2004). An analysis, by Vasudevan & Fabian (2009), of contemporaneous UV and X-ray measurements obtained in the year 2001 reveal that the X-rays and consequently the UV-Xray spectral index, α ox , varies widely on a monthly timescale with values ranging between 1.17 and 1.51.…”