Metsähovi Radio Observatory
The largest research program in Metsähovi is the study of
quasars and other Active Galactic Nuclei (AGNs).
We work in very close collaboration with the
Tuorla Observatory AGN group, having several joint
research projects, student exchange, etc.
Main research topics
- Radio variability: long term behaviour, statistics,
source populations, radio variability models.
- Multifrequency studies: radio to gamma-ray connection
in blazars, radio vs. optical behaviour,
multifrequency variability models.
- AGN contribution to the extragalactic foreground:
pre-launch work for the Planck surveyor satellite to study
extragalactic point sources.
- Inverted-spectrum sources: compact steep-spectrum (CSS) sources,
Gigahertz-peaked spectrum (GPS) sources, high-frequency peakers,
variable flat-spectrum sources; long term studies, multifrequency
studies, evolutionary models.
- BL Lacertae Objects: Multifrequency variability, radio behaviour,
spectral energy distributions, intermediate BLOs, ultra-high
energy peaked BLOs.
- Source populations, source samples, unified models.
We use the 14 metre radio telescope in Metsähovi
to study the long-term variability of a set of sources at
22 and 37 GHz (13 and 8 mm), and observe very large source
samples at 37 GHz in order to study the high-frequency
radio behaviour of various source populations.
The observations are radio continuum observations and the
goal is to obtain the total flux density of the source.
At 22 and 37 GHz we use a dual-horn dual beam-switching
method which eliminates the effects of the background
One integration typically takes ca. 30 minutes,
and our detection limit (for S/N > 4) under normal conditions is
on the order of 0.3 Jy.
The Metsähovi radio telescope is operated 24 hrs / day,
365 days / year, and a vast majority of the observing
time is dedicated for the AGN project. Only rain and snow,
or very humid clouds, stop the observations. Nowadays
most of the AGN observations are carried out in a
semi-automatic mode where human supervision is not
constantly needed. We always have one of
the team members assigned as an observer for a given
observing shift (usually 3-7 days) and human intervention
is still required semi-regularly throughout the shift,
but this can partly be done via remote access e.g.
from the observer's home.
use other instruments operating across the electromagnetic
spectrum in order to study the multifrequency behaviour
of AGNs. We have extensive experience from using
Swedish-ESO Submillimetre Telescope (SEST)
to observe Southern and equatorial sources at (sub)millimetre
wavelengthts. Our team got an incredible 2614 hours of observing
time during its 15 years of operation in 1988-2003.
In addition to the extensive experience from Metsähovi and SEST
our team members have personal experience from using the
Nordic Optical Telescope (NOT)
James Clerk Maxwell
Additionally, we have been co-investigators in a large number
of projects using other instruments across the electromagnetic
spectrum, e.g. VLBA, VLA, CMVA, HALCA,
INTEGRAL, XMM-Newton, etc. We also participate in many
international multifrequency campaigns organised by
ENIGMA network or the
Whole Earth Blazar Telescope (WEBT).
The Metsähovi AGN team members are often seen lecturers at
amateur astronomy clubs, schools etc. as well as at
"studia generalia" type lectures.
For the Finnish-speaking audience we have a web page introducing
quasars and radio observations:
Additional information in Finnish can be found in the lecture material
of the TKK course "Radio astronomy", lectured every two years
by the Metsähovi research staff
(usually by Tornikoski & Lähteenmäki):