Mass Outflow of the X-ray Emission Line Gas in NGC 4151

Abstract

We have analysed Chandra/High Energy Transmission Gratings spectra of the X-ray emission line gas in the Seyfert galaxy NGC 4151. The zeroth order spectral images show extended H- and He-like O and Ne, up to a distance \(r \sim\) 200 pc from the nucleus. Using the 1st order spectra, we measure an average line velocity \(\sim -230\) km s\(^{-1}\), suggesting significant outflow of X-ray gas. We generated Cloudy photoionisation models to fit the 1st order spectra. We required three emission-line components, with column density, log\(N_{H}\), and ionisation parameter, log\(U\), of 22.5/1.0, 22.5/0.19, and 23.0/-0.50, respectively. To estimate the total mass of ionised gas and the mass outflow rates, we applied the model parameters to fit the zeroth order emission-line profiles of Ne~IX and Ne~X. We determined the total mass of \(\approx 5.4 \times\) 10\(^{5}\) M_sun. Assuming the same kinematic profile as that for the [O~III] gas, the peak X-ray mass outflow rate was \(\approx 1.8\) M_sun yr\(^{-1}\), at \(r \sim 150\) pc. The total mass and mass outflow rates are similar to those determined using [O~III], implying that the X-ray gas is a major outflow component. However, unlike the optical outflows, the X-ray outflow rate does not drop off at \(r >\) 100 pc, which suggests that it may have a greater impact on the host galaxy.