Classical radio source propagating into outer H i disc in NGC 3801

Authors

  • B. H. C. Emonts,

    Corresponding author
    1. CSIRO Astronomy and Space Science, Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia
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  • C. Burnett,

    1. CSIRO Astronomy and Space Science, Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia
    2. School of Physics, University of Melbourne, Parkville, VIC 3010, Australia
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  • R. Morganti,

    Corresponding author
    1. Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, the Netherlands
    2. Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, the Netherlands
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  • C. Struve

    1. Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, the Netherlands
    2. Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, the Netherlands
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E-mail: bjorn.emonts@csiro.au

ATNF Summer Student 2009–10.

ABSTRACT

We present observations of a large-scale disc of neutral hydrogen (H i) in the nearby Fanaroff–Riley type I (FR I) radio galaxy NGC 3801 with the Westerbork Synthesis Radio Telescope. The H i disc (34 kpc in diameter and with inline image) is aligned with the radio jet axis. This makes NGC 3801 an ideal system for investigating the evolution of a small radio source through its host galaxy’s cold interstellar medium (ISM). The large-scale H i disc is perpendicular to a known inner CO disc and dust lane. We argue that the formation history of the large-scale H i disc is in agreement with earlier speculation that NGC 3801 was involved in a past gas-rich galaxy–galaxy merger (although other formation histories are discussed). The fact that NGC 3801 is located in an environment of several H i-rich companions, and shows indications of ongoing interaction with the nearby companion NGC 3802, strengthens this possibility. The large amounts of ambient cold ISM, combined with X-ray results by Croston, Kraft & Hardcastle on the presence of overpressured radio jets and evidence for an obscuring torus, are properties that are generally not, or no longer, associated with more evolved FR I radio sources. We do show, however, that the H i properties of NGC 3801 are comparable to those of a significant fraction of nearby low-power compact radio sources, suggesting that studies of NGC 3801 may reveal important insight into a more general phase in the evolution of at least a significant fraction of nearby radio galaxies.

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