view Abstract Citations (17) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detailed Study of the Barred Spiral Galaxy NGC 4027. II. Internal Kinematics Pence, W. D. ; Taylor, K. ; Freeman, K. C. ; de Vaucouleurs, G. ; Atherton, P. Abstract The two-dimensional velocity field of the asymmetric barred spiral galaxy NGC 4027 has been mapped with the TAURUS Fabry-Perot interferometer mounted on the Anglo-Australian telescope. The Hα emission line was measured at more than 6000 positions over the galaxy disk to derive maps showing the distributions of central velocity, line width, and line intensity. The intensity map shows that the Hα emission is mainly concentrated in a giant ring 1.7 kpc in diameter which includes the bar and the southern spiral arm. By contrast, the H I emission seems to come mainly from the northern half of the galaxy, suggesting that the H I in the southern half has been depleted by recent star formation. The velocity dispersion of the H II gas is 30 km s^-1^ throughout the galaxy, including the bar, arms, and interarm regions. A simple axisymmetric kinematic model is able to fit the observed velocity field very well; the RMS velocity residual between the observed and modeled velocities is only 13.9 km s^-1^, which is not much more than the estimated observation error per point of +/-10 km s^-1^. The most surprising result is that the center of symmetry of the velocity field coincides to high precision with the center of the bar even though the bar is displaced by 5" from the center of the outer optical isophotes. This was unexpected because previous lower precision observations, and the theoretical models based on them, suggested that the bar should be significantly displaced from the center of mass of the galaxy. The derived circular rotation curve has a peak rotational velocity of 160 km s^-1^, assuming the disk has an inclination of i = 40^deg^. The best fitting two-component exponential disk mass model has a total mass of 1.1 x 10^10^ M_sun_ and a mass to blue luminosity ratio of M/L_B_ = 2.7 at the adopted distance of 10 Mpc. The H I mass fraction is M_HI_/M = 0.086 which is typical for late-type spiral galaxies. There are small systematic departures from circular motion near the bar center and along the minor axis of NGC 4027. An area about 3" = 150 pc in diameter near the center of the bar has a blueshift of 30 km s^-1^. The noncircular velocities seen along the minor axis qualitatively agree with the expected streaming motions of the gas around the bar gravitational potential. The apparent effects are rather small in NGC 4027, however, because the long axis of the bar is nearly perpendicular to the line of nodes. Publication: The Astrophysical Journal Pub Date: March 1988 DOI: 10.1086/166117 Bibcode: 1988ApJ...326..564P Keywords: Barred Galaxies; Galactic Structure; Stellar Motions; Frequency Shift; Gas Dynamics; H Alpha Line; Interstellar Gas; Velocity Distribution; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4027; GALAXIES: INTERNAL MOTIONS; GALAXIES: STRUCTURE; RADIO SOURCES: 21 CM RADIATION full text sources ADS | data products SIMBAD (2) NED (2) Related Materials (1) Part 1: 1985ApJ...298..560P