Constraining the timescale of activity in Mrk 1018

Abstract

We present analysis of an extended emission line region projected 3.77 kpc from the nucleus of the canonical changing-look AGN Mrk~1018, found in MUSE integral-field observations from the Close AGN Reference Survey. Emission-line ratios show that the region exhibits AGN ionisation but has a very low velocity dispersion, $77\pm 1$ kms${}^{-1}$, ruling out an ionised outflow. The lower limit on the light travel time is $12,300\pm 2,300$ yr, implying that the nucleus has therefore been active for at least this long. This is much longer than the duration of either observed changing-look transition, which occurred over several years. This implies that Mrk 1018's multi-year variations are occurring within a longer term active phase.

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