Gas inflows towards the nucleus of the active galaxy NGC 7213

Abstract

We present two-dimensional stellar and gaseous kinematics of the inner 0.8 × 1.1 kpc² of the LINER/Seyfert 1 galaxy NGC 7213, from optical spectra obtained with the Gemini Multi- Object Spectrograph integral field spectrograph on the Gemini South telescope at a spatial resolution of ≈ 60 pc. The stellar kinematics shows an average velocity dispersion of 177 km s-ˡ, circular rotation with a projected velocity amplitude of 50 km s-ˡ and a kinematic major axis at a position angle of ≈−4º (west of north). From the average velocity dispersion we estimate a black hole mass of MBH = 8 +16 −6 ×107Mʘ. The gas kinematics is dominated by non-circular motions, mainly along two spiral arms extending from the nucleus out to ≈4 arcsec (280 pc) to the NW and SE, that are cospatial with a nuclear dusty spiral seen in a structure map of the nuclear region of the galaxy. The projected gas velocities along the spiral arms show blueshifts in the far side and redshifts in the near side, with values of up to 200 km s-ˡ. This kinematics can be interpreted as gas inflows towards the nucleus along the spiral arms if the gas is in the plane of the galaxy. We estimate the mass inflow rate using two different methods. The first is based of the observed velocities and geometry of the flow, and gives a mass inflow rate in the ionized gas of ≈7 × 10-²Mʘyr-ˡ. In the second method, we calculate the net ionized gas mass flow rate through concentric circles of decreasing radii around the nucleus resulting in mass inflow rates ranging from ≈0.4M yr-ˡ at 300 pc down to ≈0.2M yr-ˡ at 100 pc from the nucleus. These rates are larger than necessary to power the active nucleus.