The astrophysics of quasars and BL Lac objects
| Our research team is responsible for the preliminary work before
launch and for the exploitation of the satellite data.
Planck satellite will scan the whole sky twice at high radio frequencies. Several types of active galaxies will be found in these maps, giving us lots of new information at many new radio frequencies. It is possible that we will find new types of active galaxies, too!
Planck will help us study, among others, the following topics:
Physical models of active galactic nuclei
BL Lac objectsBL Lac objects (BLOs) are active galaxies with no emission lines in their spectra (or the lines are very weak). There are different types of BLOs, depending on the frequency they are brightest at (radio or X-ray domain). Currently we are not sure whether this is due to different viewing angles or if the sources are intrinsically different. A class of BLOs intermediate to the two main classes has been recently discovered. With the extensive data from the Planck satellite we can study all these classes of BL Lac objects, and try to find out how and why they are different.
Fainter flat-spectrum AGNsSo far all full-sky surveys have been performed at low frequencies -at 8.4 GHz or lower. This is because it is usually presumed, by looking at their spectra which are flat at lower frequencies but get much steeper at higher frequencies, that quasars are very faint at higher frequencies. Our group has recently discovered that some sources are unexpectedly bright at high radio frequencies. This is possibly due to a different (flatter) shape of their spectra or to the variability of their brightness over time. The Planck satellite survey will provide us with a catalog of fainter sources like this, and we can study their spectra, as well as the potential differences between the bright and the faint flat-spectrum radio sources.
| Planck will produce observations at a variety of timescales,
from a few hours (position of the receiver horns, changes in the
satellite's orbit) to six months (whole sky scanned twice in one
year). These variability data can be used in several ways. With the
longer timescale data we can study the structure of the radio jets
of quasars, the variability of individual shocks in the jets, and
possibly the variability of the core.
Click figure to see a larger version
|Several other satellites, at other frequencies, will be operational about the same time as Planck. This will enable us to observe the interesting sources found by Planck at several frequencies. This is very important, since all these observations tell us about the sources different, but equally important facts! The satellites include, for example, GLAST, Integral, and AGILE at gamma-ray frequencies, XMM and Chandra at the X-ray domain, and IRIS/ASTRO-F and Herschel at infrared frequencies.|
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