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Active galaxies

The backbone of Metsähovi's observations are the long-term lightcurves of radio-bright active galaxies at high radio frequencies. Our 37 GHz light curves span four decades for many sources. Quasars and other active galactic nuclei (AGN) produce vast amounts of energy in a very small volume, and therefore are much brighter than the galaxy that hosts them. They harbour supermassive black holes in their nucleus, with masses as high as a billion Solar masses. Quasars can emit radiation across the whole electromagnetic spectrum, from radio to gamma-rays.

Radio lightcurve of quasar 3C279 observed at Metsähovi Radio Observatory.

AGN research

The main research topics of Metsähovi's AGN research teams are:

  • Radio variability

    • long term behaviour
    • statistics
    • radio variability models
  • Multifrequency studies
    • multifrequency variability models
    • radio to gamma-ray connection in blazars

Within the "AGN zoo", the sources of particular interest to us are

  • Inverted-spectrum sources

    • compact steep-spectrum (CSS) sources
    • gigahertz-peaked spectrum (GPS) sources
    • high-frequency peakers
    • variable flat-spectrum sources
  • BL Lacertae Objects
    • multifrequency variability
    • radio behaviour
    • spectral energy distributions
    • intermediate BLOs
    • ultra-high-energy peaked BLOs.
  • Narrow-line Seyfert 1 (NLS1) galaxies
    • multifrequency observations
    • statistical studies
    • large-scale environments
    • evolutionary scenarios.

In addition to single-dish observations and multifrequency analysis, we also utilise radio interferometry for various purposes:

  • Ultra-high resolution VLBI

    • imaging of the black hole powered jets close to their formation site
    • state-of-the-art very long baseline interferometry techniques
    • space-VLBI and mm-VLBI
    • studying the launching, acceleration and collimation of jets
  • Long-term monitoring surveys
    • Statistical studies of parsec-scale jets of AGN within the MOJAVE programme
  • Polarization and magnetic fields in AGN
    • connection between 15 GHz radio and optical polarization in blazars
    • VLBA observations of large-scale magnetic fields in parsec-scale jets

Continuum observations at 22 and 37 GHz

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 very efficiently. 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. For details of the observing system, see Teräsranta et al. (1992).

The 14-metre radio telescope is operated "24/7/365", and the vast majority of the observing time is dedicated for the AGN project. Outside VLBI sessions, only rain and snow, or very humid clouds, stop the observations.

The AGN observations are carried out by researchers and students working at Metsähovi, with observing shifts lasting typically one full week. During this time the observer operates the radio telescope, determining the sources to be observed based on priority campaigns, weather conditions and other factors. This can often be done remotely, and in case of optimal conditions the telescope can be set to follow through a short observing programme for example throughout the night.

 

Enquiries

For data requests etc., please contact [email protected] .