Gas flows in the central region of the Seyfert galaxy NGC 4593 with MUSE

¹ Department of Physics, Technical University of Kenya, Nairobi, Kenya
² Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38206 Tenerife, Spain
⁴ Instituto de Física Fundamental, CSIC, Calle Serrano 123, 28006 Madrid, Spain
⁵ Department of Mathematical Sciences, University of South Africa, Cnr Christian de Wet Rd and Pioneer Avenue, Florida Park, 1709 Roodepoort, South Africa

Received: 22 March 2024
Accepted: 6 August 2024

Abstract

Context. Understanding how gas flows into galactic centres, fuels the active galactic nucleus (AGN), and is in turn expelled back through feedback processes is of great importance to appreciate the role AGN play in the growth and evolution of galaxies.

Aims. We use Multi Unit Spectroscopic Explorer-adaptive optics (MUSE-AO) optical spectra of the inner 7″​.5 × 7″​.5 (1.3 kpc × 1.3 kpc) of the nearby Seyfert 1 galaxy NGC 4593 to characterise its ionised gas kinematics.

Methods. We fitted single-Gaussian components to the [O III] λ5007 and [N II] λ6583 emission lines, and double-Gaussian components to Hα and Hβ to determine the main ionisation mechanism of the gas. To determine the kinematics of the ionised gas, we fit double-Gaussian components to the [O III] λ5007 line.

Results. The high angular resolution MUSE data (∼0″​​​​. 12 = 20 pc) capture structures of the circumnuclear region including the innermost spiral that feeds the nucleus. Based on the stellar kinematic maps, we confirm the presence of a rotating disc, whilst for the ionised gas, we find high-velocity dispersion values of up to 200 − 250 km s⁻¹ that show that part of the gas is highly perturbed. The dominant ionisation mechanism of the gas is AGN photoionisation, which reaches the highest values within the innermost 4″ (680 pc) diameter of the galaxy. At larger radii, the emission line ratios correspond to values in the composite region of the Baldwin, Phillips and Terlevich (BPT) diagram.

Conclusions. The broad-component of [O III] λ5007 shows blue-shifted velocities on the east side of the central 2″ (340 pc), which spatially coincide with a region of high velocity-dispersion. This confirms the presence of outflowing gas. We estimate a mass outflow rate and kinetic power of Ṁ ≥ 0.048 M_⊙ yr⁻¹ and Ė_kin ≥ 4.09 × 10³⁹ erg s⁻¹. The derived mass outflow rate is consistent with that expected from empirical relations between mass outflow rate and AGN luminosity for a low-luminosity AGN such as NGC 4593. High angular resolution integral field observations can enable multi-component analysis of the innermost regions of galaxies, allowing a detailed view of ionised gas flows.