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
Planck data will help studying which models best describe active galactic
nuclei (AGNs). For example, the appearance of an AGN depends on the angle
that we look at it. Are we looking along its powerful radio jet, or towards the
centre of the galaxy? Sometimes there is a dusty torus between us and the
centre so we can't see it. All this is why, when we are looking at an active
galaxy from different angles, we see a variety of properties and events which
lead to the division of active galaxies into several classes. There may be a
way of unifying all the different classes of AGNs -by studying their viewing
angles, brightness, structure, and spectra. We can also use the information
we get of the bright knots -or shocks- moving along the powerful radio jets
for developing and testing shock models.
Figure: C.M. Urry & P. Padovani |
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BL Lac objects
BL 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 AGNs
So 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.
Variability
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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
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With the shorter timescale data, especially the data taken at an interval
of a few hours, we can study intraday variability (IDV). It is usually
believed to be generated by interstellar scintillation. However, the
high frequency observations provided by Planck can help to distinguish
whether IDV is indeed produced in this manner, or if it is actually
generated within the sources themselves (which would require rewriting
the whole synchrotron model of AGNs!).
Follow-up satellite and ground based observations
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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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Follow-up observations at radio and optical frequencies are of course possible
from the ground. Our group in Metsähovi and Tuorla will use our own
facilities for this purpose. Very high-energy gamma-rays can be observed
from the ground as well (VERITAS, HESS, and Magic -instruments).
The brightest active galaxies have been monitored in Metsähovi already
for many years, so we know quite well how they behave. However, Planck will
observe a wealth of much less known objects. We are also interested in
studying unexpectedly bright or otherwise peculiar sources. The best way
to do this is to observe them at a lot of different frequencies and
techniques as soon after the original Planck measurement as possible.
For this purpose we are developing, in cooperation with the Planck LFI
Data Processing Centre (DPC), a Quick Detection System
software package. It will alert scientists quickly, in a week or two from
the initial Planck detection, to unexpectedly bright sources.
A dedicated Work Group (WG 6.1) was set up for the QDS development, coordinated
by our Metsähovi and Tuorla team researchers. Juha Aatrokoski from
Metsähovi is responsible for the design and coding of the system.
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