Faint galaxies

Figure 3.9. Left (1) Bright end of the Coma GLF we clearly see the bump at bright magnitudes and the whole just after. This is interpreted as the accretion or the merging of moderatly faint galaxies in order to form brighter galaxies (Lobo et al. 1997). (2) Right solid line Coma inner core GLF, short dashed line Global Coma GLF we clearly see the cut-off with magnitude in the Coma cluster inner core.

We can draw a very simplified picture of a z 0 cluster in the optical (e.g. Sarazin 1986). If a cluster is virialized, on the one hand bright and/or red cluster galaxies (mainly early types) will have small velocity dispersions and will be central objects with circular orbits. On the other hand, faint and/or blue cluster galaxies (mainly late types) will be external objects with radial orbits in the cluster. This is verified for nearby clusters (e.g. ENACS survey Adami et al. 1998a)(Fig. 6). 

White dwarfs Small, hot, white, dim stars, about the size of Earth. Smaller stars (like our Sun) eventually become faint white dwarfs off the Main Sequence. Nuclear fusion no longer occurs, but the stars possess sufficient heat to be visible using telescopes. These hot, shrinking stars have depleted their nuclear fuels and slowly evolve into cold, dark, black dwarfs. The companion of Sirius is a white dwarf. White dwarfs are not visible to the naked eye but are believed to be common, accounting for 10 percent of all stars in the Galaxy. 

Red dwarfs Small, cool, very faint, Main Sequence star. Surface temperature is less than 4,000 K. Some speculate that these are the most common type of star in the Galaxy. The nearest red dwarf is Proxima Centauri. Red dwarfs are not visible to the naked eye and are about 0.08 to 0.43 solar masses. 

When students ask astronomer William Keel of The University of Alabama in Tuscaloosa how many stars exist in our Milky Way Galaxy, his standard answer is about as many as the number of hamburgers sold by McDonald s. It is difficult to be precise because distance and dust absorption dim incoming light. Measurements of the relative numbers of stars with different absolute brightness suggests that for every Sun-like star there are about 200 faint red M-class dwarfs. (As you ll learn, the class of a star is determined by its surface tem-... 

Those numbers, in turn, apart from being given for H = 100 km/sec/Mpc, were very much like those of Table 1. The references indicated in the table are a very small subset of recent ones, not always the most comprehensive, but they provide a representative view of details of the determinations and the major potential sources of errors. Divergent views exist, and recent papers in the ApXX series (15) each include a few data sets for which a matter density close to the closure value (9.5 X 10 30 g-cm 3) is a good a fit as, or better than, the consensus value of 27% of this. Some special mention must be made of Jan H. Oort, whose early papers (21, 22) drew attention to dark matter in our own and other galaxies, which he took to be very faint stars and/or gas at temperatures not then observable, and who continued to consider related issues, including black holes at galactic centers, for another half century. 

M/Lb increases by a factor of 3 from faint to bright ellipticals implying a tilt of the fundamental plane of ellipticals (Bender et al. 1992). The fundamental plane is the particular plane occupied by these galaxies in the space defined by the stellar velocity dispersion, the effective radius and the surface brigthness. 

Dickinson, Persson 1994), the DLA counts would naturally be dominated by the far more numerous galaxies at the steep (a = —1.6) faint end of the luminosity function. 

Because the temperature decreases from the center towards the shell, the light emitted from the center may be absorbed in outer layers. Thus the protostar may be invisible, but as it gradually heats up it begins to emit light. There are many such faint objects in our galaxy. 

Faint Object Camera A narrow field of view camera able to utilize the full resolution capabilities of the LST. Provided with a photon counting detector, it would be able to reach the faintest possible stars and galaxies. 

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