Extended X-ray emission in the Hi cavity of NGC 4151: Galaxy-scale active galactic nucleus feedback?

We present the Chandra discovery of soft diffuse X-ray emission in NGC 4151 (L0.5–2 keV ∼ 1039 erg s−1), extend- ing∼2 kpc from the active nucleus and filling in the cavity of the H i material. The best fit to the X-ray spectrum requires either a kT∼ 0.25 keV thermal plasma or a photoionized component. In the thermal scenario, hot gas heated by the nuclear outflow would be confined by the thermal pressure of the H i gas and the dynamic pressure of inflowing neutral material in the galactic disk. In the case of photoionization, the nucleus must have experienced an Eddington limit outburst. For both scenarios, the active galactic nucleus (AGN)–host interaction in NGC 4151 must have occurred relatively recently (some 104 yr ago). This very short timescale to the last episode of high activity phase may imply such outbursts occupy 1% of AGN lifetime.