We present the first high-resolution X-ray spectrum of the Seyfert 1.5 galaxy NGC 4151. Observations with the Chandra High-Energy Transmission Grating Spectrometer reveal a spectrum dominated by narrow emission lines from a spatially resolved (1.6 kpc), highly ionized nebula. The X-ray narrow-line region is composite, consisting of both photoionized and collisionally ionized components. The X-ray emission lines have similar velocities, widths, and spatial extent to the optical emission lines, showing that they arise in the same region. The clouds in the narrow-line region must contain a large range of ionization states in order to explain both the optical and X-ray photoionized emission. Chandra data give the first direct evidence of X-ray line emission from a hot plasma ( T ~ 10 7 K) that may provide pressure confinement for the cooler ( T = 3 × 10 4 K) photoionized clouds.
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Ogle et al. (2000) studied this question.