Active galaxies

The Metsähovi research team studies the radio emission of quasars and other active galactic nuclei using the 14-metre dish in Metsähovi. Observations can be made 24 hours a day, every day of the year, and they are used to model the radio variability of quasars.

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.

image caption: Total flux density variability of the quasar 3C279 at 37 GHz since 1980.

The Metsähovi team uses also other ground-based and spaceborne instruments and collaborates with other international research teams to better understand the structure and physics of quasars.

The main research topics of our AGN team are:

• Radio variability: long term behaviour, statistics, radio variability models.
• Multifrequency studies: multifrequency variability models, radio to gamma-ray connection in blazars.
• Source populations, source samples, unified models.
• 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.
• Narrow-line Seyfert 1 (NLS1) galaxies: multifrequency observations, statistical studies, large-scale environments, evolutionary scenarios.
• Ultra-high resolution imaging of the black hole powered jets close to their formation site using state-of-the-art very long baseline interferometry techniques, including space-VLBI and mm-VLBI. Studying the launching, acceleration and collimation of jets. 
• Statistical studies of parsec-scale jets of AGN within the MOJAVE programme - a long-term VLBA monitoring survey
• 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.

 Observations

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.

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 (typically one full week) 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.

We also use other instruments operating across the electromagnetic spectrum in order to study the multifrequency behaviour of AGNs.