Modelling the bar in the centre of the starburst galaxy M82 |
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| Authors: | K A Wills M Das A Pedlar T W B Muxlow T G Robinson |
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| Institution: | Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH;University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire SK11 9DL;Raman Research Institute, Sadashivanagar, Bangalore 560 080, India |
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| Abstract: | We present VLA A-array 21-cm atomic hydrogen (H i ) absorption observed against the central region of the starburst galaxy M82 with an angular resolution of ～1.3 arcsec (?20 pc). These observations, together with MERLIN H i absorption measurements, are compared with the molecular (CO) and ionized (Ne ii ]) gas distributions and are used to constrain the dynamics and structure of the ionized, neutral and molecular gas in this starburst.
A position–velocity diagram of the H i distribution reveals an unusual 'hole' feature which, when previously observed in CO, has been interpreted as an expanding superbubble contained within a ring of gas in solid body rotation. However, we interpret this feature as a signature of a nearly edge-on barred galaxy. In addition, we note that the CO, H i and Ne ii ] position–velocity diagrams reveal two main velocity gradients, and we interpret these as gas moving on x1- and x2-orbits within a bar potential. We find the best fit to the data to be produced using a bar potential with a flat rotation curve velocity v b=140 km s?1 and a total length of 1 kpc, a non-axisymmetry parameter q =0.9, an angular velocity of the bar Ωb=217 km s?1 arcsec?1, a core radius R c=25 pc, an inclination angle i =80° and a projected angle between the bar and the major axis of the galaxy φ '=4°. We also discuss the orientation of the disc and bar in M82. |
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| Keywords: | galaxies: individual: M82 galaxies: kinematics and dynamics galaxies: starburst |
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