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Enormous disc of cool gas surrounding the nearby powerful radio galaxy NGC 612 (PKS 0131-36)

By B. H. C. Emonts, R. Morganti, T. A. Oosterloo, J. Holt, C. N. Tadhunter, J. M. Van Der Hulst, R. Ojha and E. M. Sadler


We present the detection of an enormous disc of cool neutral hydrogen (H I) gas surrounding the S0 galaxy NGC 612, which hosts one of the nearest powerful radio sources (PKS 0131-36). Using the Australia Telescope Compact Array, we detect MHI = 1.8 × 10 9 M ⊙ of H I emission-line gas that is distributed in a 140 kpc wide disc-like structure along the optical disc and dust-lane of NGC 612. The bulk of the gas in the disc appears to be settled in regular rotation with a total velocity range of 850 km s −1, although asymmetries in this disc indicate that perturbations are being exerted on part of the gas, possibly by a number of nearby companions. The H I disc in NGC 612 suggests that the total mass enclosed by the system is Menc ≈ 2.9 ×10 12 sin −2 i M⊙, implying that this early-type galaxy contains a massive dark matter halo. We also discuss an earlier study by Holt et al. that revealed the presence of a prominent young stellar population at various locations throughout the disc of NGC 612, indicating that this is a rare example of an extended radio source that is hosted by a galaxy with a large-scale star-forming disc. In addition, we ma

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