Clues of the restarting active galactic nucleus activity of Mrk 1498 from GTC/MEGARA integral field spectroscopy data

¹ IAA-CSIC – IAA – Instituto de Astrofísica de Andalucía (CSIC), Apdo. 3004, 18008 Granada, Spain
² Millennium Institute of Astrophysics, Nuncio Monseñor Sótero Sanz 100, Providencia, Santiago, Chile
³ Instituto de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Chile
⁴ INAF – Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, 00133 Roma, Italy
⁵ Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, Bologna, Italy

Received: 20 March 2024
Accepted: 23 August 2024

Abstract

Context. Some giant radio galaxies selected at X-rays with active galactic nuclei (AGN) show signs of a restarted nuclear activity (old lobes plus a nuclear young radio source probed by giga-hertz peaked spectra). The study of these sources gives us insights into the AGN activity history. More specifically, the kinematics and properties of the outflows can be used as a tool to describe the activity of the source.

Aims. One object in this peculiar class is Mrk 1498, a giant low-frequency double radio source that shows extended emission in [O III]. This emission is likely related to the history of the nuclear activity of the galaxy. We investigate whether this bubble-like emission might trace an outflow from either present or past AGN activity.

Methods. Using a medium-resolution spectroscopy (R ∼ 10 000) available with MEGARA/GTC, we derived kinematics and fluxes of the ionised gas from modelling the [O III] and Hβ features. We identified three kinematic components and mapped their kinematics and flux.

Results. All the components show an overall blue to red velocity pattern, with similar peak-to-peak velocities but a different velocity dispersion. At a galactocentric distance of ∼2.3 kpc, we found a blob with a velocity up to 100 km s⁻¹, and a high velocity dispersion (∼170 km s⁻¹) that is spatially coincident with the direction of the radio jet. The observed [O III]/Hβ line ratio indicates possible ionisation from AGN or shocks nearly everywhere. The clumpy structure visibile in HST images at kiloparsec scales show the lowest values of log[O III]/Hβ (< 1), which is likely not related to the photoionisation by the AGN.

Conclusions. Taking optical and radio activity into account, we propose a scenario of two different ionised gas features over the radio AGN lifecycle of Mrk 1498. The radio emission suggests at least two main radio activity episodes: an old episode at megaparsec scales (formed during a time span of ∼100 Myr), and a new episode from the core (> 2000 yr ago). At optical wavelengths, we observe clumps and a blob that are likely associated with fossil outflow. The latter is likely powered by past episodes of the flickering AGN activity that may have occurred between the two main radio phases.