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Date and Time of the Query: 2019-06-27 T00:48:10 PDT
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For refcode 1993A&A...272...63M:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1993A&A...272...63M Distribution and motions of H I in the ringed galaxy NGC 4736 P.S. Mulder and W. van Driel Kapteyn Astronomical Institute, Kapteyn Laboratorium, Postbus 800, NL- 9700 AV Groningen, The Netherlands Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, NL-l098 SJ Amsterdam, The Netherlands Kapteyn Astronomical Institute, Laboratory for Space Research, Postbus 800, NL-9700 AV Groningen, The Netherlands Received June 25, accepted December 20,1992 Abstract. The ringed Sab-type galaxy NGC 4736 was mapped in the 21 cm HI line at Westerbork with a resolution of 13" X 20"({alpha} x {delta} and a velocity resolution of 33 km s^-1^. Detailed maps of H I distribution and motions were constructed for the entire galaxy, including the outer ring (R ~ 6'). The loci of H{alpha}, H I line and 21 cm continuum radiation from the inner ring (R ~ 50") are found to be generally coincident. Only towards the S and SE the H I line radiation comes from regions some 8" to 17" farther away from the nucleus than the H{alpha} and the 21 cm continuum. The velocity field can be modelled well assuming circular rotation of the gas in a plane with a constant inclination of 40^deg^, but with a position angle of the Kinematical major axis varying with radius by 20^deg^. The rotation velocity falls, in this model, from ca. 175 km s^-1^ at a radius of 50" to ca. 125 km s^-1^ at 500". The H I Kinematics show evidence for the presence of a slight warp or an oval distortion. In a future paper this will be modelled in detail. The outer ring is found to be a smooth continuation of the H I disc in its Kinematics. A total HI mass of (9.9 +/- 0.3)10^8^ M_sun_ is found. Assuming a distance of 6.6 Mpc, this implies a M_H I_/L_B_^0^ ratio of 0.04 in solar units. A total mass of 5.1 10^10^ M_sun_ is found from the rotation curve. This implies a global M/L ratio of 2.0 in solar (blue) units, which is exceptionally low. Since the galaxy has a normal total blue luminosity its total mass, including a possible dark halo, must be lower than normal for this type of object. Key words: galaxies: NGC 4736 - galaxies: kinematics and dynamics of- galaxies: radio - galaxies: spiral - galaxies: structure of
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