Galaxies counts

VERY DEEP K-BAND IMAGING FOR GALAXY COUNTING ... 

Key words sky survey - infrared star counts - infrared galaxy counts... 

The IRAS galaxies provided some of the earliest evidence from redshift surveys, and from source counts as a function of observed flux, that the spiral galaxy population has undergone evolution (ORS see Fig. 12.2). This result is analogous to similar evidence from source counts of radio galaxies and quasars, as well as quasar redshifts, and a correlation that has been observed between radio and infrared luminosity suggests that the evolution could be similar in both cases. Typical simple models for such evolution include luminosity evolution according to... 

In 1917 Harlow Shapley mapped the extent of the galaxy by counting globular clusters rather than stars. Globular clusters are collections of roughly 100,000 stars. They can be seen from the distant reaches of the Milky Way. Just as Copernicus before him concluded that Earth is not the center of the solar system, Shapley proved that the solar system was not at the center of the galaxy. Since Shapley s time, astronomers have refined his technique and discovered new ways to deduce the size, structure, and contents of the Milky Way. 

Counts of luminous supergiants in nearby galaxies under the assumption that their number is proportional to the SFR. 

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. 

This is a difficult question to answer, but we can provide a very rough estimate. In our galaxy alone, there are roughly 10" to 10 stars. Then consider that there are roughly 10" to 10 2 galaxies in total, and, if we assume the other galaxies are similar to ours, this would put the total number of stars in existence somewhere between 10 to 10 stars. Clearly there are too many to count ... 

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. 

At first glance, establishing the lipid composition of the brain could be compared to counting the stars in a galaxy. This metaphor is not particularly stimulating, but it is not totally incorrect... 

Arrays have made it possible to derive luminosity functions not only for the stellar populations in the bulge (DePoy et al. 1993) and nucleus (Rieke 1993) of the Milky Way but also in other galaxies. These studies count on most of the IR advantages listed earlier with adaptive optics likely to yidd significant improvements in the future since field crowding is frequently a limiting factor in the accuracies achievable. 

Abstract. 1 present K band photometry of the objects in the spectroscopic redshift survey of [CoUess et al., 1990]. The absolute K magnitudes of the objects are consistent with the no-evolution or pure luminosity evolution models. The excess f t blue galaxies seen in the B band number counts at intermediate magnitudes are a result of a low normalization, and do not dominate the population until B 25. Extreme merging or excess dwarf models are not needed. 

Much attention has been paid recently to an apparent excess of faint blue galaxies observed in photometric surveys. When the models of the B band number counts are normalized at B=16, the data show an excess over the luminosity evolution models of a factor of 2 at B=22. ([Tyson, 1988], [Lilly et al., 1991]) However, the K band number counts do not show this same excess, ([Gardner et al., 1993]). The shape of the number-redshifr distribution of surveys conducted at 20 < B < 22.5 by [Broadhurst et al., 1988] and [CoUess et al., 1990] are fitted by the no-evolution model. The median redshifts of the data from these surveys, and deeper data of [Cowie et al., 1991] and [AUington-Smith et al., 1992] show no evolution as faint as B=24. Proposed explanations for the high B band number counts include massive amounts of merging at intermediate redshifts (z 0.4) ([Broadhurst et al., 1992]) and an excess population of dwarf galaxies which appears at these redshifts, but has dissipated or faded by the present epoch. ([Cowie et al., 1991])... 

For galaxy samples selected in the near IR the situation is rather different. The counts show little excess over that expected for no evolution until K>20 (Gardner et al. 1993). Since L in the K band is a function of galaxy type. 

Abstract. We have obtained deep K-band images of 2 sq. aranin of sky to count galaxies down to a limiting magnitude of 21.5. At the foint end the counts are marginally fairer than those determined by the Hawaii Deep Surrey, but the two results are consistent within the error bars. We also present results from a larger area surrey to K=20. 

Fig. 5. The sui ce density of galaxies in the (1 = 135 , 6 = —25 ) field (histogram) compared with surface densities of field galaxies from Broadhurst et dl. 1992 (shaded line). The large excess of galaxies at K < 11 nutg. appears to be caused by the large number of galaxies concentrated at z 0.017. A model of field counts plus siqierdnster members (solid line) is described in the text.

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