An H-alpha nuclear spiral structure in the E0 active galaxy Arp102B
  We report the discovery of a two-armed mini-spiral structure within the inner
kiloparsec of the E0 LINER/Seyfert 1 galaxy Arp102B. The arms are observed in
H-alpha emission and located East and West of the nucleus, extending up to
about 1 kpc from it. We use narrow-band imaging from the Hubble Space Telescope
Advanced Camera for Surveys, in combination with archival VLA radio images at
3.6 and 6 cm to investigate the origin of the nuclear spiral. From the H-alpha
luminosity of the spiral, we obtain an ionized gas mass of the order of one
million solar masses. One possibility is that the nuclear spiral represents a
gas inflow triggered by a recent accretion event which has replenished the
accretion disk, giving rise to the double-peaked emission-line profiles
characteristic of Arp102B. However, the radio images show a one-sided curved
jet which correlates with the eastern spiral arm observed in the H-alpha image.
A published milliarcsecond radio image also shows one-sided structure at
position angle about 40 degrees, approximately aligned with the inner part of
the eastern spiral arm. The absence of a radio counter-part to the western
spiral arm is tentatively interpreted as indicating that the jet is
relativistic, with an estimated speed of 0.45c. Estimates of the jet kinetic
energy and the ionizing luminosity of the active nucleus indicate that both are
capable of ionizing the gas along the spiral arms. We conclude that, although
the gas in the nuclear region may have originated in an accretion event, the
mini-spiral is most likely the result of a jet-cloud interaction rather than an
inflowing stream.
