High Resolution Neutral Hydrogen Observations of the Barred Spiral Galaxy NGC 1365
We have observed the barred spiral galaxy NGC 1365 with the VLA in the BnA, CnB, and DnC configurations. We have refined the flux determination for partially cleaned images of very non-Gaussian VLA multiconfiguration naturally weighted beams as described in the Appendix. NGC 1365 is found to contain 15.2 x 1O^9^M_sun_ of HI. The velocity field is strongly affected by the bar in the inner parts, but it is relatively undisturbed in the outer parts. The H I morphology is similar to that in the optical, but the HI is more uniformly distributed and there is no trace of the bar. NGC 1365 is found to have four well developed arms and two rudimentary ones. The inclination of the inner disk is determined to be 40^deg^, substantially different from that obtained by optical means (55^deg^). There is a central H I hole which is filled with molecular gas. We find that NGC 1365 has the most strongly dropping rotation curve known to us, falling to 63% of its peak value. It starts to drop already at 2/3 of R_25_. In the outer 40% it is well modeled by a Keplerian. We deduce a total mass for NGC 1365 of 3.9 x 10^11^ M_sun_, resulting in a M/L_B_ of 4.8. Strongly noncircular motions (radial velocity residuals up to 100 km s^-1^) are seen in the bar region. The influence of the bar drops rapidly outside of it and the orbits become rather circular. The ratio between H I diameter and R_25_ is unusually small and NGC 1365 lacks a extended H I halo. A similar behavior is displayed by NGC 1300, data for which we have reduced anew, and we discuss whether this could be common among strongly barred galaxies. NGC 1365 has a warp which starts already at 2/3 of R_25_. The classical resonances may be identified with kinematical and morphological features of the spiral arms. The good agreement with gas dynamical models give strong support to this identification. We find a common corotation radius of arms and bar at 1.4 times the bar major axis. This corresponds to a pattern velocity of 21 +/- I km s^-`^ kpc^-1^. The -4/1 resonance is the most clearly seen feature. The corotation radius corresponds to the maximum deviation from circular motion in the arms. The bright parts of the arms end at the OLR. The spiral arms of NGC 1365 have a very circular symmetry when viewed face on, and are substantially more tightly wound than they appear in the sky plane. NGC 1365 shows a straight front on the W side, which may be a sign of interaction with the intergalactic medium. The H I is elongated in the direction of the Fornax cluster center.
The Astronomical Journal
- Pub Date:
- November 1995
- GALAXIES: INDIVIDUAL: NGC 1365;
- GALAXIES: SPIRAL;
- KINEMATICS AND DYNAMICS