A sample of very faint ultraviolet excess objects in the 13 H plus 36 deg field. II - A discussion of the number-magnitude relation of optically selected quasars and a new determination of the luminosity function and of the characteristics of its cosmologi

Details A sample of very faint ultraviolet excess objects in the 13 H plus 36 deg field. II - A discussion of the number-magnitude relation of optically selected quasars and a new determination of the luminosity function and of the characteristics of its cosmologi A sample of very faint ultraviolet excess objects in the 13 H plus 36 deg field. II - A discussion of the number-magnitude relation of optically selected quasars and a new determination of the luminosity function and of the characteristics of its cosmologi

May 1980

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980a%26a....85...80b&link_type=abstract

Astronomy and Astrophysics, vol. 85, no. 1-2, May 1980, p. 80-92. Consiglio Nazionale delle Ricerche

Astronomy and Astrophysics

Astronomy

114

Cosmology, Luminosity, Quasars, Ultraviolet Astronomy, Hot Stars, Stellar Magnitude

Scientific paper

We rediscuss the number magnitude relation for the optically selected UVX quasars on the basis of a new point at B = 21.05, of a study of the incompleteness of the Braccesi et al. catalogue (1970), and of the data available in the literature.
We show that, from B = 15.5 to B = 21.5, the number of objects increases quite steeply with magnitude. The data suggest the relationship:
logN(Owing to the large number of points and the wide interval in magnitude they cover, it seems very unlikely that the index of the distribution could be lower than 2.0 or larger than 2.3.
Such an index indicates a very strong cosmological evolution whose details depend on the distribution in z of the objects as a function of magnitude.
We show how relevant information on this point can be derived from the spectroscopic data on UVX optically selected quasars existing in the literature, which permit to assemble a sample of 185 objects significant from B = 14.5 to B = 19.5, and from the results of the spectroscopic surveys of high-z objects.
Combining this information with that on the number magnitude relationship, we derive the surface density of the objects as a function of magnitude and z and we compute the space density as a function of z and of absolute magnitude.
The derived table shows a regular increase of density with z at constant absolute magnitude, which slows down only at z >2.5.
A pure density evolution fits the results satisfactorily, while a luminosity evolution fails to do this. The increase in density, which amounts to 105 from z = 0 to z = 2.5, is not described by any simple analytical formula being approximated by (1+ z) for z<0.8 and by (1+z)7.5 for z < 0.8 and by (1+z)8.8 for 1.1 < z < 2.5, in the q0 = 0 model universe.
We finally discuss the relevance of these results from the point of view of the nature of the quasars and of the meaning of the changes we observe in their population with the age of the universe.

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