Apertif 1.4 GHz continuum observations of the Boötes field and their combined view with LOFAR
Journal article, 2023
We present a new image of a 26.5 square degrees region in the Boötes constellation obtained at 1.4 GHz using the Aperture Tile in Focus (Apertif) system on the Westerbork Synthesis Radio Telescope. We use a newly developed processing pipeline that includes direction-dependent self-calibration, which provides a significant improvement in the quality of the images compared to those released as part of the Apertif first data release. For the Boötes region, we mosaicked 187 Apertif images and extracted a source catalog. The mosaic image has an angular resolution of 27 × 11.5″ and a median background noise of 40 μJy beam-1. The catalog has 8994 sources and is complete down to the 0.3 mJy level. We combined the Apertif image with LOFAR images of the Boötes field at 54 and 150 MHz to study the spectral properties of the sources. We find a spectral flattening toward sources with a low flux density. Using the spectral index limits from Apertif nondetections, we derive that up to 9% of the sources have ultrasteep spectra with a slope below -1.2. A steepening of the spectral index with increasing redshift is also seen in the data, which shows a different dependence for the low-and high-frequency spectral index. The explanation probably is that a population of sources has concave radio spectra with a turnover frequency of about the LOFAR band. Additionally, we discuss cases of individual extended sources with an interesting resolved spectral structure. With the improved pipeline, we aim to continue to process data from the Apertif wide-area surveys and release the improved 1.4-GHz images of several well-known fields.
Surveys
Catalogs
Radio continuum: general
Author
A. M. Kutkin
Netherlands Institute for Radio Astronomy (ASTRON)
T. Oosterloo
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
R. Morganti
Netherlands Institute for Radio Astronomy (ASTRON)
University of Groningen
A. R. Offringa
Netherlands Institute for Radio Astronomy (ASTRON)
University of Groningen
E. A.K. Adams
University of Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
B. Adebahr
Ruhr-Universität Bochum
H. Dénes
Yachay Tech
Netherlands Institute for Radio Astronomy (ASTRON)
Kelley Hess
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Institute of Astrophysics of Andalusia (IAA)
Netherlands Institute for Radio Astronomy (ASTRON)
J. M. van der Hulst
University of Groningen
W.J.G. de Blok
University of Groningen
University of Cape Town
Netherlands Institute for Radio Astronomy (ASTRON)
A. Bozkurt
Netherlands Institute for Radio Astronomy (ASTRON)
W. van Cappellen
Netherlands Institute for Radio Astronomy (ASTRON)
A.W. Gunst
Netherlands Institute for Radio Astronomy (ASTRON)
H. Holties
Netherlands Institute for Radio Astronomy (ASTRON)
J. van Leeuwen
Netherlands Institute for Radio Astronomy (ASTRON)
G. M. Loose
Netherlands Institute for Radio Astronomy (ASTRON)
L. C. Oostrum
Anton Pannekoek Institute for Astronomy
Netherlands Institute for Radio Astronomy (ASTRON)
Netherlands eScience Center
D. Vohl
Netherlands Institute for Radio Astronomy (ASTRON)
S. J. Wijnholds
Netherlands Institute for Radio Astronomy (ASTRON)
J. Ziemke
University of Oslo
Netherlands Institute for Radio Astronomy (ASTRON)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 676 A37Subject Categories
Remote Sensing
Astronomy, Astrophysics and Cosmology
Software Engineering
DOI
10.1051/0004-6361/202346618