Feeding and feedback in the inner kiloparsec of the active galaxy NGC 2110

Abstract

We present two-dimensional gaseous kinematics of the inner 1.1 × 1.6 kpc² of the Seyfert 2 galaxy NGC 2110, from optical spectra (5600–7000 Å) obtained with the GeminiMulti Object Spectrograph integral field spectrograph on the Gemini South telescope at a spatial resolution of ≈100 pc. Gas emission is observed over the whole field of view, with complex – and frequently double – emission-line profiles. We have identified four components in the emitting gas, according to their velocity dispersion (σ), which we refer to as: (1) warm gas disc (σ = 100–220 km s-ˡ); (2) cold gas disc (σ = 60–90 km s-ˡ); (3) nuclear component (σ = 220–600 km s-ˡ) and (4) northern cloud (σ = 60–80 km s-ˡ). Both the cold and warm disc components are dominated by rotation and have similar gas densities, but the cold gas disc has lower velocity dispersions and reaches higher rotation velocities.We attribute thewarm gas disc to a thick gas layer which encompasses the cold disc as observed in some edge-on spiral galaxies. After subtraction of a rotation model from the cold disc velocity field, we observe excess blueshifts of ≈50 km s-ˡ in the far side of the galaxy (NE) as well as similar excess redshifts in the near side (SW). These residuals can be interpreted as due to nuclear inflow in the cold gas, with an estimated ionized gas mass inflow rate of φ ≈ 2.2 ×10-²Mʘyr-ˡ. We have also subtracted a rotating model from the warm disc velocity field and found excess blueshifts of ≈100 km s-ˡ to the SW of the nucleus and excess redshifts of ≈40 km s-ˡ to the NE, which we attribute to gas disturbed by an interaction with a nuclear spherical outflow. This nuclear outflow is the origin of the nuclear component observed within the inner 300 pc and it has a mass outflow rate of 0.9Mʘyr-ˡ. In a region between 1 and 4 arcsec north of the nucleus, which shows strong X-ray and [O III] λ5007Å emission, we find a new low σ component of ionized gas which we attribute to a high latitude cloud photoionized by the nuclear source. The identification of the four distinct kinematic components has clarified the nature of the apparent asymmetry in the rotation curve of the galaxy pointed out in previous studies: it results from the dominance of different components to the south and north of the nucleus. We conclude that a comprehensive two-dimensional coverage of the kinematics and geometry of the nuclear gas around the active galactic nucleus is necessary to reveal the different processes at play, such as its feeding – via the cold inflowing gas – and the feedback, via the warm gas outflows.