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29 March 2024
 
  » arxiv » astro-ph/0303333

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Decline of the space density of quasars between z=2 and z=4
M. Vigotti ; R. Carballo ; C.R. Benn ; G. de Zotti ; R. Fanti ; J.I. Gonzalez Serrano ; K.-H. Mack ; J. Holt ;
Date 14 Mar 2003
Journal Astrophys.J. 591 (2003) 43-52
Subject astro-ph
Affiliation2,3), C.R. Benn , G. de Zotti , R. Fanti (6,1), J.I. Gonzalez Serrano , K.-H. Mack (1,7,8), J. Holt ( Istituto di Radioastronomia del CNR, Bologna, Italy; Dpto. de Matematica Aplicada y C. Computacion, Santander, Spain; Instituto di Fisica de Canta
AbstractWe define a new complete sample of 13 optically-luminous radio quasars M_AB(1450 Angstrom) < -26.9 mag and log P_1.4 GHz(W/Hz) > 25.7 with redshift 3.8 < z < 4.5, obtained by cross-correlating the FIRST radio survey and the APM catalogue of POSS-I. We measure the space density to be 1.0 +/- 0.3 /Gpc^3, a factor 1.9 +/- 0.7 smaller than the space density of similar quasars at z=2. Using a new measurement of the radio-loud fraction of quasars we find that at z=4 the total space density of quasars with M_AB(1450 Angstrom) < -26.9 is 7.4 +/- 2.6/Gpc^3. This is a factor 1.8 +/- 0.8 less than the space density at z=2, found by the 2dF quasar survey. This (z=2)/(z=4) ratio, consistent with that of the radio-loud quasars, is significantly different from the ratio of about 10 found for samples including lower-luminosity quasars. This suggests that the decline of the space density beyond z=2 is slower for optically-luminous quasars than for less-luminous ones.
Source arXiv, astro-ph/0303333
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