Publication Date:
2014-04-19
Description:
We have identified ionized outflows in the narrow-line region of all but one Sloan Digital Sky Survey type 2 quasars (QSO2) at z 0.1 (20/21, detection rate 95 per cent), implying that this is a ubiquitous phenomenon in this object class also at the lowest z . The outflowing gas has high densities ( n e 1000 cm –3 ) and covers a region the size of a few kpc. This implies ionized outflow masses M outf ~ (0.3–2.4) 10 6 M and mass outflow rates M〈 few M yr –1 . The triggering mechanism of the outflows is related to the nuclear activity. The QSO2 can be classified into two groups according to the behaviour and properties of the outflowing gas. QSO2 in Group 1 (5/20 objects) show the most extreme turbulence; they have on average higher radio luminosities and higher excess of radio emission. QSO2 in Group 2 (15/20 objects) show less extreme turbulence; they have lower radio luminosities and, on average, lower or no radio excess. We propose that two competing outflow mechanisms are at work: radio jets and accretion disc winds. Radio jet induced outflows are dominant in Group 1, while disc winds dominate in Group 2. We find that the radio jet mode is capable of producing more extreme outflows. To test this interpretation, we predict that (1) high resolution radio imaging will reveal the presence of jets in Group 1 QSO2; (2) the morphology of their extended ionized nebulae must be more highly collimated and kinematically perturbed.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
