|Annu. Rev. Astron. Astrophys. 1999. 37: 445-486
Copyright © 1999 by Annual Reviews. All rights reserved
7.3. M82 and NGC 1275 as Prototypes of Starburst Galaxies and Other Violent Events
We conclude this review with a glimpse at a few of the most bizarre objects found over the years with the 200-inch and other large telescopes. The types of galaxies in this category are now commonplace as prototypes of violent processes, but were not so at their discovery.
The subject, which is also a part of the discipline of high energy astrophysics, was reviewed early by Burbidge, Burbidge, & Sandage (1963), where photographs of some of the unusual galaxies are shown and analyses of the physics given.
Most of the types now recognized (Seyfert galaxies such as NGC 1068 and NGC 4151), the new amorphous galaxy type characterized by M82, possible colliding or even merging galaxies as in NGC 1275, jets as in M87, and starburst galaxies, probably with M82 again as a prototype) were shown.
One of the more spectacular examples is the enormous outflow of material from the "starburst" galaxy M82, shown in a composite photograph in Figure 3. The photographs making up this composite were made with the 200-inch using special filters. The energetics in the M82 system have proved to be important in understanding the general class of starburst galaxies, which have been found to be ubiquitous.
Figure 3. Composite photograph of M82 made by photographically subtracting a continuum image in broad-band yellow wavelengths, from a narrow-band H alpha photograph showing the H alpha emission strung along the minor axis. (Photograph from Lynds & Sandage 1963. Also in the Carnegie Atlas of Galaxies, Panel 333.)
We finally comment on either a new type of violent event or a radical type of starburst galaxy where "violent star formation" is taking place. The type examples are NGC 625, NGC 1569, NGC 1705, and M82 in which copious star formation is clearly taking place and in which one or more very bright compact (essentially unresolved) embedded objects exist. A new morphological galaxy class for the type was invented (Sandage and Brucato 1979), called "amorphous." The class is illustrated in the Carnegie Atlas of Galaxies (panels 333-340) where descriptions of the many examples of the bright embedded objects are given.
The importance of these bright objects became apparent when high dispersion spectra were taken by Arp with the 200-inch of the two luminous knots in NGC 1569. The spectra show narrow absorption lines of hydrogen and a definite Balmer discontinuity, characteristic of supergiant stars of type A0. However, the luminosities of the knots are MB = -14, showing that the objects are very young superluminous star clusters (Arp and Sandage 1985). They are probably proto-globular clusters, just formed and with their main sequences intact all the way to high luminosities. The phenomenon is ubiquitous in the amorphous types, as described in the Carnegie Atlas (Sandage & Bedke 1994).
The high-energy properties of the violent star formation in NCG 1705 and the formation of its supercluster at absolute magnitude near -14 in NGC 1705 is discussed by Mauer et al (1988, 1992). The two young globular clusters in NGC 1569 were known already in 1952 by Baade and by Hubble from their early 200-inch plates, but the ubiquitous character of the phenomenon has only recently become known, based on the Carnegie/Las Campanas morphological survey of Shapley-Ames galaxies that led to the Carnegie Atlas of Galaxies.