The Apertif science verification campaign: Characteristics of polarised radio sources
Journal article, 2022
Context. The characteristics of the polarised radio sky are a key ingredient in constraining evolutionary models of magnetic fields in the Universe and their role in feedback processes. The origin of the polarised emission and the characteristics of the intergalactic medium on the line of sight can be investigated using large samples of polarised sources. Ancillary infrared (IR) and optical data can be used to study the nature of the emitting objects. Aims. We analyse five early science datasets from the APERture Tile in Focus (Apertif) phased array feed system to verify the polarisation capabilities of Apertif in view of future larger data releases. We aim to characterise the source population of the polarised sky in the L-Band using polarised source information in combination with IR and optical data.
Methods. We use automatic routines to generate full field-of-view Q- and U-cubes and perform rotation measure (RM)-Synthesis, source finding, and cross-matching with published radio, optical, and IR data to generate polarised source catalogues. All sources were inspected individually by eye for verification of their IR and optical counterparts. Spectral energy distribution (SED)-fitting routines were used to determine photometric redshifts, star-formation rates, and galaxy masses. IR colour information was used to classify sources as active galactic nuclei (AGN) or star-forming-dominated and early- or late-type.
Results. We surveyed an area of 56 deg2 and detected 1357 polarised source components in 1170 sources. The fraction of polarised sources is 10.57% with a median fractional polarisation of 4.70 ± 0.14%. We confirmed the reliability of the Apertif measurements by comparing them with polarised cross-identified NVSS sources. Average RMs of the individual fields lie within the error of the best Milky Way foreground measurements. All of our polarised sources were found to be dominated by AGN activity in the radio regime with most of them being radio-loud (79%) and of the Fanaroff-Riley (FR)II class (87%). The host galaxies of our polarised source sample are dominated by intermediate disc and star-forming disc galaxies. The contribution of star formation to the radio emission is on the order of a few percent for 10% of the polarised sources while for 90% it is completely dominated by the AGN. We do not see any change in fractional polarisation for different star-formation rates of the AGN host galaxies.
Conclusions. The Apertif system is suitable for large-area high-sensitivity polarised sky surveys. The data products of the polarisation analysis pipeline can be used to investigate the Milky Way magnetic field on projected scales of several arcminutes as well as the origin of the polarised emission in AGN and the properties of their host galaxies.
Methods. We use automatic routines to generate full field-of-view Q- and U-cubes and perform rotation measure (RM)-Synthesis, source finding, and cross-matching with published radio, optical, and IR data to generate polarised source catalogues. All sources were inspected individually by eye for verification of their IR and optical counterparts. Spectral energy distribution (SED)-fitting routines were used to determine photometric redshifts, star-formation rates, and galaxy masses. IR colour information was used to classify sources as active galactic nuclei (AGN) or star-forming-dominated and early- or late-type.
Results. We surveyed an area of 56 deg2 and detected 1357 polarised source components in 1170 sources. The fraction of polarised sources is 10.57% with a median fractional polarisation of 4.70 ± 0.14%. We confirmed the reliability of the Apertif measurements by comparing them with polarised cross-identified NVSS sources. Average RMs of the individual fields lie within the error of the best Milky Way foreground measurements. All of our polarised sources were found to be dominated by AGN activity in the radio regime with most of them being radio-loud (79%) and of the Fanaroff-Riley (FR)II class (87%). The host galaxies of our polarised source sample are dominated by intermediate disc and star-forming disc galaxies. The contribution of star formation to the radio emission is on the order of a few percent for 10% of the polarised sources while for 90% it is completely dominated by the AGN. We do not see any change in fractional polarisation for different star-formation rates of the AGN host galaxies.
Conclusions. The Apertif system is suitable for large-area high-sensitivity polarised sky surveys. The data products of the polarisation analysis pipeline can be used to investigate the Milky Way magnetic field on projected scales of several arcminutes as well as the origin of the polarised emission in AGN and the properties of their host galaxies.
Surveys
Galaxies: magnetic fields
Methods: data analysis
Polarization
Galaxies: active
Author
B. Adebahr
Ruhr-Universität Bochum
A. Berger
Ruhr-Universität Bochum
E. A.K. Adams
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
K. M. Hess
Netherlands Institute for Radio Astronomy (ASTRON)
University of Groningen
Institute of Astrophysics of Andalusia (IAA)
W.J.G. de Blok
University of Groningen
University of Cape Town
Netherlands Institute for Radio Astronomy (ASTRON)
H. Dénes
Netherlands Institute for Radio Astronomy (ASTRON)
V. A. Moss
Netherlands Institute for Radio Astronomy (ASTRON)
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
The University of Sydney
R. Schulz
Netherlands Institute for Radio Astronomy (ASTRON)
J. M. van der Hulst
Netherlands Institute for Radio Astronomy (ASTRON)
L. Connor
Netherlands Institute for Radio Astronomy (ASTRON)
California Institute of Technology (Caltech)
Sieds Damstra
Netherlands Institute for Radio Astronomy (ASTRON)
B. Hut
Netherlands Institute for Radio Astronomy (ASTRON)
Marianna Ivashina
Chalmers, Electrical Engineering, Communication, Antennas and Optical Networks
G. M. Loose
Netherlands Institute for Radio Astronomy (ASTRON)
Y. Maan
Netherlands Institute for Radio Astronomy (ASTRON)
National Centre for Radio Astrophysics India
Mika
Netherlands Institute for Radio Astronomy (ASTRON)
H. Mulder
Netherlands Institute for Radio Astronomy (ASTRON)
M. J. Norden
Netherlands Institute for Radio Astronomy (ASTRON)
L. C. Oostrum
Netherlands Institute for Radio Astronomy (ASTRON)
Netherlands eScience Center
Anton Pannekoek Institute for Astronomy
E. Orrú
Netherlands Institute for Radio Astronomy (ASTRON)
Mark Ruiter
Netherlands Institute for Radio Astronomy (ASTRON)
R. Smits
Netherlands Institute for Radio Astronomy (ASTRON)
W. van Cappellen
Netherlands Institute for Radio Astronomy (ASTRON)
J. van Leeuwen
Anton Pannekoek Institute for Astronomy
Netherlands Institute for Radio Astronomy (ASTRON)
N. Vermaas
Netherlands Institute for Radio Astronomy (ASTRON)
D. Vohl
University of Amsterdam
Netherlands Institute for Radio Astronomy (ASTRON)
J. Ziemke
Netherlands Institute for Radio Astronomy (ASTRON)
University of Oslo
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 663 A103Subject Categories
Accelerator Physics and Instrumentation
Astronomy, Astrophysics and Cosmology
Environmental Sciences
DOI
10.1051/0004-6361/202243201