Open AccessFaint radio‐loud quasars: clues to their evolution
Author(s) -
Cirasuolo M.,
Magliocchetti M.,
Celotti A.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.08729.x
Subject(s) - quasar , physics , astrophysics , ovv quasar , astronomy , luminosity , population , redshift , sky , luminosity function , galaxy , demography , sociology
The quasar sample selected by cross‐correlating the Faint Images of the Radio Sky at Twenty cm (FIRST) survey and the 2‐degree Field Quasar Redshift Survey (2QZ) allows us to explore, for the first time, the faint end of the radio and optical luminosity functions up to z ≃ 2.2 . We find indications (∼3σ) of a negative evolution for these faint sources at z ≳ 1.8 , both in radio and optical bands. This corresponds to a decrement in the space density of faint quasars of approximately a factor 2 at z = 2.2 and confirms the presence of a differential evolution for the population of radio‐active quasars. The faint end of both luminosity functions flattens and the comparison with the (optical) number density of the whole quasar population supports a dependence of the fraction of radio‐detected quasars on the optical luminosity. A progressive decrease in the fraction of quasars in the whole radio source population can be consistently accounted for within the receding torus scenario. The population of low‐luminosity quasars, which the FIRST–2dF detects, appears to depart from the classical scheme for radio‐loud quasars.