The nature of radio-intermediate quasars: What is radio-loud and what is radio-quiet?

被引:116
作者
Falcke, H [1 ]
Sherwood, W [1 ]
Patnaik, AR [1 ]
机构
[1] MAX PLANCK INST RADIOASTRON,D-53121 BONN,GERMANY
关键词
galaxies; active; jets; nuclei; quasars; general; radio continuum;
D O I
10.1086/177956
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We have performed quasi-simultaneous radio flux density measurements at 2.7 and 10 GHz for all Palomar-Green (PG) quasars with radio flux densities between 4 and 200 mJy. We find that a large fraction of these sources are variable, flat-spectrum quasars. This brings to 40% the total fraction of flat-spectrum quasars with a radio-to-optical flux ratio R > 10 in the PG quasar sample. We also find that the median R-parameter of these flat-spectrum quasars is lower than those of steep-spectrum radio-loud quasars. This contradicts the predictions of the unified scheme and the idea that all flat-spectrum, core-dominated quasars are relativistically boosted lobe-dominated quasars. We show that this discrepancy is due to a population of flat-spectrum radio-intermediate quasars with 25 < R < 250 that can be explained neither as relativistically boosted radio-loud quasars nor as normal radio-weak quasars. We point out that a natural explanation for the flat-spectrum radio-intermediate quasars is relativistic boosting in radio-weak quasars. If the flat-spectrum radio-intermediate quasars are considered the boosted counterparts to usual radio-weak: quasars, their fraction among radio-weak quasars is roughly 10%, similar to the fraction of boosted radio-loud quasars. This would point toward average Lorentz factors of y(jet) = 2-4 for radio-loud and radio-weak quasars. The presence of the flat-spectrum radio-intermediate quasars changes the definition of ''radio-loud'' and can bias some conclusions drawn from optically selected quasar samples, where R similar or equal to 1-10 is used as the dividing line for both flat- and steep-spectrum quasars. Instead, one should use separate R-parameters for the dividing line in steep-spectrum (R similar or equal to 25) and flat-spectrum (R similar to 250) quasars.
引用
收藏
页码:106 / 114
页数:9
相关论文
共 27 条
[11]  
FALCKE H, 1994, THESIS RFW U BONN
[12]   3-EPOCH VLBI OBSERVATIONS OF THE NUCLEUS IN THE LOBE-DOMINATED QUASAR-3C-334 [J].
HOUGH, DH ;
READHEAD, ACS ;
WOOD, DA ;
FELDMEIER, JJ .
ASTROPHYSICAL JOURNAL, 1992, 393 (01) :81-86
[13]   VLA OBSERVATIONS OF OBJECTS IN THE PALOMAR BRIGHT QUASAR SURVEY [J].
KELLERMANN, KI ;
SRAMEK, R ;
SCHMIDT, M ;
SHAFFER, DB ;
GREEN, R .
ASTRONOMICAL JOURNAL, 1989, 98 (04) :1195-1207
[14]   THE RADIO STRUCTURE OF RADIO-LOUD AND RADIO-QUIET QUASARS IN THE PALOMAR BRIGHT QUASAR SURVEY [J].
KELLERMANN, KI ;
SRAMEK, RA ;
SCHMIDT, M ;
GREEN, RF ;
SHAFFER, DB .
ASTRONOMICAL JOURNAL, 1994, 108 (04) :1163-1177
[15]  
MACHALSKI J, 1993, ASTRON ASTROPHYS, V267, P363
[16]   THE RADIO AND OPTICAL-PROPERTIES OF THE Z-LESS-THAN-0.5 BQS QUASARS [J].
MILLER, P ;
RAWLINGS, S ;
SAUNDERS, R .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1993, 263 (02) :425-460
[17]  
NEUMANN M, 1994, ASTRON ASTROPHYS SUP, V106, P303
[18]  
OTT M, 1994, ASTRON ASTROPHYS, V284, P331
[19]   INTERFEROMETER PHASE CALIBRATION SOURCES .1. THE REGION 35-DEGREES LESS-THAN-OR-EQUAL-TO DELTA LESS-THAN-OR-EQUAL-TO 75-DEGREES [J].
PATNAIK, AR ;
BROWNE, IWA ;
WILKINSON, PN ;
WROBEL, JM .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1992, 254 (04) :655-676
[20]   QUASAR EVOLUTION DERIVED FROM THE PALOMAR BRIGHT QUASAR SURVEY AND OTHER COMPLETE QUASAR SURVEYS [J].
SCHMIDT, M ;
GREEN, RF .
ASTROPHYSICAL JOURNAL, 1983, 269 (02) :352-&