Infrared photometric scanning of galaxies.
2015-11-19T09:18:03Z (GMT) by
Surface photometric observations at near infrared wavelengths (J, H and K wavebands) of the galaxies M31, M82 and NGC 972 are described and the results discussed in the light of other, recent literature. The techniques used in surface photometry of extended objects at near infrared wavelengths are described and, as an introduction, a detailed review of near infrared, extragalactic astronomy is given. R.A. and Dec. scans through the centre of M31 show the two micron surface brightness distribution in the nuclear bulge follows the de Vaucouleurs law and that the V-K gradient within the central +/- 5 arcmins is small, ? (V-K)r=5' < 0.1. Comparisons are made with other published data. Photometric scans through the active, central region of M82 reveal that the two micron emission from the galaxy is concentrated within a very high surface brightness "core" source measuring approximately 25" x 8" (375 x 120 pc). The core is surrounded by a disk measuring 90" by 35" (1350 pc x 525 pc) which though of lower surface brightness is still much brighter than the corresponding region in other normal disk systems. Contour maps of the two regions are presented. The asymmetry in the brightness distribution along the major axis is attributed to obscuration by the major dust lane, from which it is inferred that the extinction produced by the lane is, Av ~ 16. The two micron core is approximately coincident and co-extensive with the diffuse radio emission and the visible "hot-spot" region, and is probably associated with a burst of star formation near the centre of the galaxy. Two micron scanning observations of NGC 972 yield a low resolution contour map of the whole galaxy which is similar in some respects to published blue-waveband maps. In particular, the similarity in the gross distribution of B and K light along the major axis suggests the unusual structure seen at shorter wavelengths cannot be due to dust obscuration as was previously assumed. An exciting possibility arising from this work is that the secondary feature in the southeast of the system may be a small, previously unsuspected, interacting galaxy, which might account for the IO-type appearance of NGC 972. The two micron luminosity of the central region of the galaxy is unusually high for its low mass and young mean spectral type, and is comparable with that of M82. J, H and K slit aperture scans yielded J-H and H-K colour indices which suggest the presence of an extended source of free-free emission near the centre of the galaxy. These are the first reported observations of NGC 972 at infrared wavelengths.