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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 | Affiliation: | 2,3), 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 | Abstract: | We 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 | Services: | Forum | Review | PDF | Favorites |
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