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 A37

Subject Categories

Remote Sensing

Astronomy, Astrophysics and Cosmology

Software Engineering

DOI

10.1051/0004-6361/202346618

More information

Latest update

8/31/2023