Arp 102B: An ADAF and a Torus?

Abstract

Arp 102B is a nearby radio galaxy which displays the presence of double-peaked Balmer emission lines. Sub-arcsec Keck mid-infrared imaging and Spitzer spectroscopy reveal a spatially compact mid-infrared source which displays tentative evidence for variability. The F_v ∝ ν^(−1.2) spectral energy distribution is suggestive of an advection-dominated accretion flow. The absence of dust features over the 5−40 μm range make it unlikely that thermal dust emission dominates the mid-infrared luminosity. We also detect the presence of molecular hydrogen in emission which is asymmetrically redshifted by ~500-1000 km/s from the systemic velocity of the galaxy. Since the forbidden, low-ionization lines in this galaxy are at the systemic velocity, we suggest that the molecular hydrogen emission arises from a rotating molecular gas structure surrounding the nuclear black hole at a distance of ~1 pc.