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 \sim 10 ^ { 7 } K ) which may provide pressure confinement for the cooler ( T = 3 \times 10 ^ { 4 } K ) photoionized clouds .