NEAR-INFRARED AND OPTICAL MORPHOLOGY OF THE DUSTY GALAXY NGC-972

Near-infrared (NIR) and optical surface photometric analyses of the du sty galaxy NGC 972 are presented. The photometric profiles in the BVRJ HK bands can be fitted with a combination of Gaussian and exponential profiles, corresponding to a starburst nucleus and a stellar disk, res pectively. The exponential scale length in the B band is 2.8 times lar ger than in the K band, which implies a central B-band optical depth a s high as 11. A bulge is absent even in the NIR bands, and hence the g alaxy must be of a morphological type later than the usually adopted S b type. Relatively low rotational velocity and high gas content also f avor a later type, probably Sd, for the galaxy. Only one arm can be tr aced in the distribution of old stars; the second arm, however, can be traced in the distribution of dust and H II regions. Data suggest a s hort NIR bar, which ends inside the nuclear ring. The slowly rising na ture of the rotation curve rules out a resonance origin of the nuclear ring. The ring is most likely not in the plane of the galaxy, given i ts circular appearance, in spite of the moderately high inclination of the galaxy. The off-planar nature of the star-forming ring, the unusu ally high fraction (30%) of the total mass in molecular form, the pres ence of a nuclear starburst, and the asymmetry of spiral arms are prob ably the result of a merger with a gas-rich companion galaxy.