Nuclear spirals as feeding channels to the Supermassive Black Hole: the case of the galaxy NGC 6951

TL;DR

This study discovers gas streaming along nuclear spirals in galaxy NGC 6951, providing evidence that such structures channel matter inward to feed the supermassive black hole, with implications for understanding galactic nucleus fueling mechanisms.

Contribution

It presents the first detailed kinematic analysis of nuclear spirals as feeding channels in NGC 6951, demonstrating their role in gas inflow towards the black hole.

Findings

Gas streaming motions are observed along nuclear spirals.

Estimated gas inflow rate matches the accretion needs of the nucleus.

Similar phenomena are observed in NGC 1097, supporting a common feeding mechanism.

Abstract

We report the discovery of gas streaming motions along nuclear spiral arms towards the LINER nucleus of the galaxy NGC 6951. The observations, obtained using the GMOS integral field spectrograph on the Gemini North telescope, yielded maps of the flux distributions and gas kinematics in the Halpha, [NII]6584 and [SII]6717,31 emission lines of the inner 7x5 arcsec^2 of the galaxy. This region includes a circumnuclear star-forming ring with radius 500pc, a nuclear spiral inside the ring and the LINER nucleus. The kinematics of the ionized gas is dominated by rotation, but subtraction of a kinematic model of a rotating exponential disk reveals deviations from circular rotation within the nuclear ring which can be attributed to (1) streaming motions along the nuclear spiral arms and (2) a bipolar outflow which seems to be associated to a nuclear jet. On the basis of the observed streaming velocities and geometry of the spiral arms we estimate a mass inflow rate of ionized gas of 3x10^(-4) Msun/yr, which is of the order of the accretion rate necessary to power the LINER nucleus of NGC 6951. Similar streaming motions towards the nucleus of another galaxy with LINER nucleus -- NGC 1097 -- have been reported by our group in a previous paper. Taken together, these results support a scenario in which nuclear spirals are channels through which matter is transferred from galactic scales to the nuclear region to feed the supermassive black hole.