Near-infrared images of the prototype LINER / Seyfert 1 galaxy NGC 1097 observed with the Very Large Telescope ( VLT ) using adaptive optics disclose with unprecedented detail a complex central network of filamentary structure spiralling down to the center of the galaxy .
The structure , consisting of several spiral arms , some almost completing a revolution about the center , is most prominent within the radius of about 300 pc .
Gas and dust may be channelled to the center of NGC 1097 along this central spiral .
Some filaments can be traced further out , where they seem to connect with the nuclear star-forming ring at 0.7 kpc radius .
Straight principal shocks running along the primary large-scale bar of NGC 1097 , seen in the optical images as prominent dust lanes , curve into this ring , but radio polarization vectors cross the nuclear ring under a rather large angle .
Here we attempt to explain this morphology in terms of three-dimensional gas flow in a barred galaxy .
In our scenario , parts of the principal shock , which propagate in the off-plane gas , can cross the nuclear star-forming ring , and excite waves inward from it .
If the dispersion relation of the excited waves allows for their propagation , they will naturally take the shape of the observed central spiral .
The nuclear region of NGC 1097 remains unresolved at sub-arcsec scales in the near-IR , with an upper size limit of < 10 pc FWHM .
Thus , any putative central dusty torus or gaseosus disk envisaged by the AGN unified schemes has to be smaller than 10 pc in diameter at near-IR wavelengths .
The extinction in the region between the nuclear star-forming ring and the nucleus increases very moderately , reaching A _ { v } \sim 1 at the immediate surrounding of the nucleus .
Thus , if the nuclear filaments are tracing cold dust , they contribute to a very low extinction in the line of sight and are likely to be distributed in a rather thin disk .