In this part, we discuss the properties of the Galaxy center, and finish with a selection of multiwavelength all-sky images of the Galaxy.
The Galaxy is an Sbc/SBbc spiral galaxy and in the atlas it is classified in the normal (N) category of our sample, yet additional categories interacting (I), and active? (A?) (see Table 1, page 18) are also assigned. The Galaxy (along with the LMC and SMC) is classified I due to the existence of the H I Magellanic Stream (Wannier and Wrixon 1972; Murai and Fujimoto 1986) as shown in Figure 1.22. An A? classification is also given because the optical spectrum integrated over the central parsec of the Galaxy resembles a Seyfert galaxy (Mezger et al. 1996). This is consistent with results that suggest the presence of a several million M⊙ black hole in the nucleus.
Quiet monster – Sagittarius A*
Our Galaxy's nucleus, some 8.5 kpc distant in the constellation of Sagittarius, has long been a target for multiwavelength observations. Because of the large amounts of obscuring dust towards the nucleus and in the disk of the Galaxy, infrared observations have proved invaluable in showing the content and structure of this region. Figure 3.1 shows a 48° by 33° IRAS IR image of the central region of the Galaxy. The disk of the Galaxy is the bright band running diagonally across the image.
The bright central region contains the nucleus. The concentrated blobs of yellow are giant clouds of interstellar gas and dust heated by recently formed stars and nearby massive, hot stars.