Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-07-31
Astronomy and Astrophysics
Astrophysics
4 pages, conference proceedings for "The Central Kiloparsec, Active Galactic Nuclei and Their Hosts" to appear in Volume 79 of
Scientific paper
Previous surveys for HI 21-cm absorption in z > 0.1 radio galaxies and quasars yield a 40% detection rate, which is attributed to unified schemes of active galactic nuclei (AGN). In this paradigm absorption is only witnessed in (close to) type-2 objects, where the central obscuration is viewed (nearly) edge-on and thus absorbs the rest frame 1420 MHz emission along our sight-line. However, we find this mix of detections and non-detections to only apply at low redshift (z < 1): From a sensitive survey of eight z > 3 radio sources we find no 21-cm absorption, indicating a low abundance of cold neutral gas in (the sight-lines searched in) these objects. Analysing the spectral energy distributions of these sources, we find that our high redshift selection introduces a bias where our sample consists exclusively of quasars with ultra-violet luminosities in excess of 10e23 W/Hz. This may suggest that we have selected a class of particularly UV bright type-1 objects. Whatever the cause, it must also be invoked to explain the non-detections in an equal number of z < 0.7 sources, where we find, for the first time, the same exclusive non-detections at > 10e23 W/Hz. These objects also turn out to be quasars and, from these exclusive high UV luminosity--21-cm non-detections, it is apparent that orientation effects alone cannot account for the mix of 21-cm detections and non-detections at any redshift.
Curran Stephen J.
Webb John K.
Whiting Matthew T.
No associations
LandOfFree
Where is the Cold Neutral Gas in the Hosts of High Redshift AGN? does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Where is the Cold Neutral Gas in the Hosts of High Redshift AGN?, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Where is the Cold Neutral Gas in the Hosts of High Redshift AGN? will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-363083