Journal Article

Detection of a Sub-Keplerian Water Maser Disk at the Active Galactic Nucleus of the Galaxy IC 1481

Koichi Mamyoda, Naomasa Nakai, Aya Yamauchi, Philip Diamond and Jean-Marc HurÉ

in Publications of the Astronomical Society of Japan

Volume 61, issue 5, pages 1143-1151
Published in print October 2009 | ISSN: 0004-6264
Published online October 2009 | e-ISSN: 2053-051X | DOI:
Detection of a Sub-Keplerian Water Maser Disk at the Active Galactic Nucleus of the Galaxy IC 1481

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  • Galaxies
  • Astrometry and Celestial Mechanics


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We present a study of H[math]O maser emission from the LINER, IC 1481, based on single-dish and highly sensitive VLBI observations. The Nobeyama 45-m telescope detected new maser features near the systemic velocity and blue-shifted by 124–205 km s[math]. In addition, the known features red-shifted by [math]97–155 km s[math] were monitored. VLBI observations with the High Sensitivity Array (HSA) revealed that the maser features are distributed along a line, with a velocity gradient, strongly suggesting a nearly edge-on molecular gas disk. The radius and thickness of the disk are [math] [math] 2.8–14.0 pc and 2[math] [math] 1.5–4.2 pc, respectively, which are the largest among the maser disks detected in active galactic nuclei. The disk is rotating at [math] [math] 124–168 km s[math], having a large velocity dispersion of [math] [math] 31 km s[math]. The rotation curve of the disk is sub-Keplerian ([math] [math] [math]), indicating a massive disk. The disk mass is estimated to be (4.3[math]0.3) [math] 10[math] and the mass of a putative central black hole is [math]10[math]. The massive disk is gravitationally unstable. A radio continuum source was also detected to be offset from the maser disk by 1.6 pc.

Keywords: galaxies: active; galaxies: individual (IC 1481); galaxies: nuclei; masers

Journal Article.  5079 words.  Illustrated.

Subjects: Galaxies ; Astrometry and Celestial Mechanics

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