De Vaucouleurs Atlas Type: (R)SB(rl)0+
Telescope: KPNO 0.9-m+WIYN 3.5-m
North left , East down
Field Dimensions: 8.9 x 6.7 arcminutes
RC3 Type: (R)SB(rs)0+
RSA Type: RSB02
Surface Brightness Range Displayed: 17.5-26.0 mag per square arcsec
Absolute Blue Magnitude: -20.4
De Vaucouleurs Atlas Description:
NGC 3945 is similar to NGC 2859 in having a dominant outer ring . The ring is not as bright as that in NGC 2859 , but it is still very well-defined. Faint knots, presumably blue associations, line the outer edge of the ring in the northeast and southwest quadrants. The ring is not conspicuous in the B-V color index map. The inner regions include a well-defined ansae -type bar and an inner ring made of thin, tightly-wrapped spiral arms. The center of the galaxy includes a round core surrounded by a highly elongated oval. Since the shape and position angle of the oval matches that of the outer disk, Erwin and Sparke (1999) argued it could instead be a bright inner disk region. The disk nature of this feature was also demonstrated kinematically by Kormendy (1982), who measured a value of Vmax/sigma, the ratio of maximum rotation velocity to mean velocity dispersion, almost twice as high for the inner oval as expected for an isotropic, oblate galaxy flattened solely by rotation (Binney 1978). This would be expected only for a disk-shaped structure.
Inside the bright inner oval, Erwin and Sparke (1999) also detected a small secondary bar that is only weakly evident in the Atlas image. The high inclination makes a near-side dust lane visible on the north end of the bar.