Polarization in the ELAIS-N1 LOFAR deep field
Licentiate thesis, 2023
The advantage of low radio-frequency observations over higher-frequency ones is the better precision on the inferred RM values. On the other hand, at low radio-frequency observations are more affected by depolarization, which affect the detection rate. Indeed, the population of faint polarized extragalac- tic sources at low radio frequencies is still mostly unknown.
In this context, the LOw Frequency ARray (LOFAR) plays an important role because of sensitivity, angular resolution and precision on the inferred RM values that can be achieved through low-frequency broad-band polarimetry, allowing us to study the polarized radio emission at frequencies around 150 MHz.
In our work, we developed a new method to combine polarimetric obser- vations with slightly different frequency configurations, and we applied this method to the European Large Area ISO Survey-North 1 (ELAIS-N1) deep field, one of the deepest of the LOFAR Two-Meter Sky Survey (LoTSS) Deep Fields so far, at 114.9–177.4 MHz. We imaged an area of 25 deg2 at 6-arcsec of resolution in which, through stacking of 19 8-hour-long epochs, detected 1.28 sources per square degrees, the highest number density of polarized sources ever found at low radio frequencies. We compared our results with other RM catalogs and we quantified the depolarization properties of sources detected also at 1.4 GHz. We also modeled the source counts in polarization from the source counts in total flux density.
This work dealt with technical and theoretical challenges inherent to the observation and interpretation of polarimetric data and represents a step in solving complex issues that modern radio astronomy is facing due the large amounts of data generated by new-generation radio-interferometers.
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
LOFAR for Space Weather
European Commission (EC) (EC/H2020/777442), 2017-12-01 -- 2021-05-31.
Astronomy, Astrophysics and Cosmology
C3SE (Chalmers Centre for Computational Science and Engineering)
Onsala Space Observatory
SAL EC, Hörsalsvägen 11, EDIT-huset
Opponent: Rosita Paladino, adjunct professor at the Department of Physics and Astronomy of the University of Bologna, Italy