Mass outflow of the X-ray emission line gas in NGC 4151

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 ∼ 200 pc from the nucleus. Using the first-order spectra, we measure an average line velocity ∼-230 km s^-1, suggesting significant outflow of X-ray gas. We generated CLOUDY photoionization models to fit the first-order spectra; the fit required three distinct emission line components. To estimate the total mass of ionized 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 ≈5.4 × 10⁵ M_⊙. Assuming the same kinematic profile as that for the [O III] gas, derived from our analysis of Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra, the peak X-ray mass outflow rate was ≈1.8 M_⊙ yr^-1, at r ∼ 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.