Young clusters and associations

6.5.1 Associations and superassociations Star formation can take place on a variety of scales. The largest star forming complexes in the Large Cloud have been dubbed constellations by McKibben Fig. 6.6. Color-magnitude diagrams of six LMC globular clusters obtained with the Hubble Space Telescope. Adapted from Olsen et al. (1998). Note that these clusters all have significant numbers of stars to the blue of the RR Lyrae gap. Fig. 6.6. Color-magnitude diagrams of six LMC globular clusters...

Kinematics ofM31 clusters

The first study of the kinematics of the M31 globular cluster system was by van den Bergh (1969), who obtained radial velocities for 42 globular clusters associated with the Andromeda galaxy. He found that metal-poor globular clusters in M31 had a significantly higher velocity dispersion (a 138 km s-1) relative to circular motion than did metal-rich clusters (a 58 km s-1). Using the projected mass method of Bahcall & Tremaine (1981), van den Bergh (1981a) obtained M (9 2) x 1010 M0 from the...

The Galactic halo

Toomre (1977) wrote that It seems almost inconceivable that there wasn't a great deal of merging of sizable bits and pieces (including quite a few lesser galaxies) early in the career of every major galaxy, no matter what it now looks like. Prima facie evidence for such mergers is provided by the Sagittarius dwarf (Ibata et al. 1994), which is presently being disrupted by, and is merging with, the Milky Way system. The debris from previous merger events may still be detectable as moving groups...

The spheroidal galaxy NGC 205

The luminosity of NGC 205 is similar to that of M32. However, it has a much more extended structure. Furthermore M32 rotates, but NGC 205 does not (Bender, Paquet & Nieto 1991). A good photograph of NGC 205 is shown in the Hubble Atlas of Galaxies (Sandage 1961). Images taken in the ultraviolet (Baade 1951) show it to contain a small number of young blue stars. Deep exposures (see Figure 12.1) reveal some extended patches of dust absorption. Moreover, inspection of the image of NGC 205 on...

The Phoenix dwarf galaxy

This object was discovered on an ESO blue plate by Schuster & West (1976), who opined that it might be an extremely distant globular cluster. Subsequently, Canterna & Flower (1977) obtained images of the Phoenix system with the 4-m Blanco telescope at Cerro Tololo, which demonstrated that Phoenix was, in fact, a low-luminosity galaxy. From a color-magnitude diagram in B and V, Canterna & Flower were able to show that the Phoenix dwarf contained young blue stars, in addition to a...

Associations and spiral structure

The Triangulum galaxy is a late-type spiral of DDO type Sc II-III. This classification indicates that this object has rather open, and not very well-developed, spiral structure. NGC 2403 see panel 36 of the Hubble Atlas of Galaxies (Sandage 1961) in the nearby M81 group is a close morphological match to the Triangulum galaxy. Inspection of Figure 5.1 shows that M33 has two main spiral arms, both of which have a rather patchy and discontinuous structure. A number of stellar interarm features are...

The nucleus of the galaxy

The compact radio source Sgr A* is located at a 17h 45m 39 9, 5 29 00' 28 (J2000). Backer & Sramek (1982) find that its proper motion is consistent with the hypothesis that this source is at rest in the Galactic nucleus (i.e., the observed proper motion may be interpreted as being entirely due to reflected solar motion). Available evidence on the distance to the Galactic nucleus has been reviewed by Reid (1993), who concludes that Ro 8.5 0.5 kpc. From the HIPPARCOS proper motions of...

Central bulge and halo of M33

The existence of a tiny nuclear bulge within the central part of the disk of M33 remains controversial. Such a bulge was first reported by Patterson (1940), but it is not clearly seen in the UBV photometry of de Vaucouleurs (1959a). However, Boulesteix et al. (1979) do find such a bulge with a luminosity 1 of that of the M33 exponential disk. They claim that this small nuclear bulge exhibits an r1 4 law profile with an effective radius re 2.'75. Possible evidence for such a nuclear bulge is...

The nucleus of M33

The Triangulum galaxy consists of four principal components (1) an exponential disk, (2) a halo that contains RR Lyrae variables and clusters, which, on the basis of their colors and kinematics, are globulars, (3) a semi-stellar nucleus, and (4) possibly a small nuclear bulge. An image of the nucleus of M33, obtained in subarcsecond seeing with the Canada-France-Hawaii telescope, has been published by Kormendy & McClure (1993). A color image of the M33 nucleus obtained with the Hubble Space...

The Wolf LundmarkMelotte system DDO 221

The Wolf-Lundmark-Melotte (WLM) system was discovered by Wolf (1923) and independently by Lundmark and by Melotte (1926). Melotte comments that the appearance of the WLM system is similar to that of NGC 6822. This conclusion is confirmed by the fact that both WLM (van den Bergh 1966a) and NGC 6822 are classified as being of DDO type Ir IV-V. A nice photograph of the WLM system is shown in de Vaucouleurs & Freeman (1972, p. 222). The most detailed photometry of this object is by Ables &...

Preface

In April of 1968 I gave a series of lectures on the structure, evolution, and stellar content of nearby galaxies at the University of California in Berkeley. An outline of these talks was printed as a slender volume entitled The Galaxies of the Local Group van den Bergh 1968a . Since the publication of this booklet the number of known members of the Local Group has doubled. Furthermore both the quantity, and the quality, of the data that are available on the previously known Local Group members...