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

Abstract

Understanding how gas flows into galactic centres, fuels the 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. We use the MUSE-AO optical spectra of the inner 7".5x 7".5 of the nearby Seyfert 1 galaxy NGC 4593 to characterise its ionised gas kinematics. We fit single-Gaussian components to the [O iii]$\lambda$ 5007 and [N ii]$\lambda$ 6583 emission lines, and double-Gaussian components to H$\alpha$ and H$\beta$ 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]$\lambda$ 5007 line. Based on the stellar kinematic maps, we confirm the presence of a rotating disc. For the ionised gas, we find high-velocity dispersion values of up to $\mathrm{200-250\,km\,s^{-1}}$ 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 4arcsec (680pc) diameter of the galaxy. At larger radii, the emission line ratios correspond to values in the composite region of the BPT diagram. The broad-component of [O iii]$\lambda$ 5007 shows blue-shifted velocities on the east side of the central 2arcsec (340pc), 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 ${\dot{M}}\geq {0.048 \,M_\odot\,{{\rm yr}^{-1}} }$ and ${\dot{E}_{\text{kin}}} \geq 4.09 \times 10^{39} \, \text{erg} \, \text{s}^{-1}$. 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.