Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983apjs...53...17d&link_type=abstract
Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 53, Sept. 1983, p. 17-39. Research supported by the Centre Nation
Astronomy and Astrophysics
Astrophysics
43
Barred Galaxies, Fabry-Perot Interferometers, Galactic Evolution, H Alpha Line, Hydrogen Clouds, Velocity Distribution, Astronomical Catalogs, Emission Spectra, Galactic Structure, Gas Dynamics, Mass To Light Ratios, Nebulae
Scientific paper
The velocity field in the weakly barred spiral NGC 5236=M83, type SAB(s)c, MOT(B) = - 20.00, at a distance δ = 3.7 Mpc in the Centaurus group, is derived from 2770 velocities measured on 16 Hα Fabry-Perot interferograms taken with the Galaxymeter attached to the 205 cm reflector of McDonald Observatory. A contour map of Ha emission intensity and a catalog of 60 bright H II regions derived from the photometry of Talbot, Jensen, and Dufour are also presented.
Isovelocity maps at 12", 15", and 21" resolution are used to analyze the velocity field within 3'.6 = 3.8 kpc from the center. With an assumed inclination i = 24° (from the axis ratio), the position angle of the line of nodes is θ0 = 43°, in approximate agreement with available photometry. There is little or no indication of a warping of the disk within 3.8 kpc from the center. The systemic velocity is VS = 509±2 km s-1. The mean maximum rotational velocity VM = 205 km s-1s probably reached near RM ≍ 5' =5.4 kpc.
The masses estimated by fitting the observed mean rotation curve to various conventional axisymmetric mass distribution models-neglecting velocity dispersion-are in the range 5.8 ≤ sunT ≤ 14.6 × 1010 solar units. A more satisfactory fit in better agreement with the photometry is obtained with a two-component generalized Toomre model with a "hot" bulge. The best-fit model has a total mass sunT = (1.00±0.05) × 1011 solar masses of which 4% is in the spheroid. The calculated velocity dispersion at the center σr = 78 ± 10: km s-1 in fair agreement with the value (103) predicted by a revised version of the Faber-Jackson (L ∝ σ4) relation for the absolute magnitude (-17.50) of the bulge. The mass-luminosity ratio, corrected for galactic and internal extinction, is f0(B) ≍ 7; it is 2.7 for the bulge component and ∼7 for the disk component.
A map of the ()- C velocity residuals discloses systematic departures attributable to streaming motions of the gas around the bar and perturbations associated with the spiral arms. A nonaxisymmetric model including a bar and logarithmic spiral arms with oval streamlines along the equipotentials around the bar reduces these residuals and gives also a good representation of the velocity field in NGC 253. A comparison of the two galaxies, both of type SAB(s)c, demonstrates the close similarity of all their physical, kinematical, and dynamical properties.
Davoust Emmanuael
de Vaucouleurs Gerard
Pence William D.
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