LOFAR low-band antenna observations of the 3C295 and Bootes fields: source counts and ultra-steep spectrum sources

R. J. van Weeren; W. L. Williams; C. Tasse; H. J. A. Rottgering; D. A. Rafferty; S. van der Tol; G. Heald; G. J. White; A. Shulevski; P. Best; H. T. Intema; S. Bhatnagar; W. Reich; M. Steinmetz; S. van Velzen; T. A. Ensslin; I. Prandoni; F. de Gasperin; M. Jamrozy; G. Brunetti; M. J. Jarvis; J. P. Mckean; M. W. Wise; C. Ferrari; J. Harwood; J. B. R. Oonk; M. Hoeft; M. Kunert-Bajraszewska; C. Horellou; O. Wucknitz; A. Bonafede; N. R. Mohan; A. M. M. Scaife; H. -R. Klockner; I. M. van Bemmel; A. Merloni; K. T. Chyzy; D. Engels; H. Falcke; M. Pandey-Pommier; A. Alexov; J. Anderson; I. M. Avruch; R. Beck; M. E. Bell; M. J. Bentum; G. Bernardi; F. Breitling; J. Broderick; W. N. Brouw; M. Bruggen; H. R. Butcher; B. Ciardi; E. de Geus; M. de Vos; A. Deller; S. Duscha; J. Eisloffel; R. A. Fallows; W. Frieswijk; M. A. Garrett; Jean-Mathias Grießmeier; A. W. Gunst; J. P. Hamaker; T. E. Hassall; J. Horandel; A. van der Horst; M. Iacobelli; N. J. Jackson; E. Juette; V. I. Kondratiev; M. Kuniyoshi; P. Maat; G. Mann; D. Mckay-Bukowski; M. Mevius; R. Morganti; H. Munk; A. R. Offringa; E. Orru; H. Paas; V. N. Pandey; G. Pietka; R. Pizzo; A. G. Polatidis; A. Renting; A. Rowlinson; D. Schwarz; M. Serylak; J. Sluman; O. Smirnov; B. W. Stappers; A. Stewart; J. Swinbank; Michel Tagger; Y. Tang; S. Thoudam; C. Toribio; R. Vermeulen; C. Vocks; P. Zarka

doi:10.1088/0004-637X/793/2/82

Journal articles

LOFAR low-band antenna observations of the 3C295 and Bootes fields: source counts and ultra-steep spectrum sources

R. J. van Weeren ^{1, 2} W. L. Williams ³ C. Tasse ^{4, 5, 6} H. J. A. Rottgering ³ D. A. Rafferty ⁷ S. van der Tol G. Heald ¹ G. J. White ⁸ A. Shulevski P. Best ⁹ H. T. Intema S. Bhatnagar ¹⁰ W. Reich ¹¹ M. Steinmetz S. van Velzen T. A. Ensslin I. Prandoni F. de Gasperin M. Jamrozy G. Brunetti M. J. Jarvis ¹² J. P. Mckean ¹ M. W. Wise ^{1, 13} C. Ferrari ¹⁴ J. Harwood J. B. R. Oonk ¹ M. Hoeft ¹⁵ M. Kunert-Bajraszewska C. Horellou O. Wucknitz ¹⁶ A. Bonafede ¹⁷ N. R. Mohan A. M. M. Scaife ¹⁸ H. -R. Klockner I. M. van Bemmel A. Merloni K. T. Chyzy D. Engels H. Falcke ^{19, 11, 1} M. Pandey-Pommier ²⁰ A. Alexov ¹ J. Anderson ²¹ I. M. Avruch ²² R. Beck ²³ M. E. Bell ²⁴ M. J. Bentum ¹ G. Bernardi F. Breitling ²⁵ J. Broderick ²⁴ W. N. Brouw ²⁶ M. Bruggen ¹⁷ H. R. Butcher ¹ B. Ciardi ²⁷ E. de Geus ²⁸ M. de Vos A. Deller S. Duscha J. Eisloffel ¹⁵ R. A. Fallows ²⁹ W. Frieswijk M. A. Garrett ^{3, 1} Jean-Mathias Grießmeier ^{30, 31} A. W. Gunst ¹ J. P. Hamaker T. E. Hassall ³² J. Horandel A. van der Horst M. Iacobelli ^{33, 34} N. J. Jackson E. Juette ³⁵ V. I. Kondratiev ¹ M. Kuniyoshi ¹¹ P. Maat ¹ G. Mann ²¹ D. Mckay-Bukowski ³⁶ M. Mevius ¹ R. Morganti ^{26, 1} H. Munk ¹ A. R. Offringa E. Orru ³⁷ H. Paas ¹ V. N. Pandey G. Pietka ³⁸ R. Pizzo ¹ A. G. Polatidis ¹ A. Renting A. Rowlinson D. Schwarz ³⁹ M. Serylak ³¹ J. Sluman ¹ O. Smirnov ⁵ B. W. Stappers ³² A. Stewart ⁴⁰ J. Swinbank ¹³ Michel Tagger ³¹ Y. Tang S. Thoudam ¹⁹ C. Toribio R. Vermeulen C. Vocks P. Zarka ⁴¹

1 ASTRON - Netherlands Institute for Radio Astronomy

2 CfA - Harvard-Smithsonian Center for Astrophysics

3 Leiden Observatory [Leiden]

4 SKA South Africa

5 Rhodes University

6 GEPI - Galaxies, Etoiles, Physique, Instrumentation

7 Department of Astronomy and Astrophysics [PennState]

8 SLAC - Stanford Linear Accelerator Center

9 University of Edinburgh

10 CSA - Department of Computer Science and Automation [Bangalore]

11 MPIFR - Max-Planck-Institut für Radioastronomie

12 Charles Darwin University

13 AI PANNEKOEK - Astronomical Institute Anton Pannekoek

14 LRGP - Laboratoire Réactions et Génie des Procédés

15 TLS - Thüringer Landessternwarte Tautenburg

16 AlfA - Argelander-Institut für Astronomie

17 Jacobs University [Bremen]

18 School of Physics and Astronomy [Southampton]

19 Radboud university [Nijmegen]

20 CRAL - Centre de Recherche Astrophysique de Lyon

21 AIP - Leibniz-Institut für Astrophysik Potsdam

22 SRON - SRON Netherlands Institute for Space Research

23 LCPM - Laboratoire de Chimie Physique Moléculaire

24 University of Southampton

25 AIP - Leibniz-Institut für Astrophysik Potsdam

26 Kapteyn Astronomical Institute [Groningen]

27 Max Planck Institute for Astrophysics

28 Medstar Research Institute

29 Institute of Mathematical and Physical Sciences

30 USN - Unité Scientifique de la Station de Nançay

31 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace

32 Jodrell Bank Centre for Astrophysics

33 Sapienza University of Rome - Dipartimento di Matematica "Guido Castelnuovo" [Roma I]

34 CMLS - Centre de Mathématiques Laurent Schwartz

35 Ruhr-Universität Bochum [Bochum]

36 University of Oulu

37 IMAPP - Applied Stochastics

38 Oxford Astrophysics

39 Interactions Son Musique Mouvement

STMS - Sciences et Technologies de la Musique et du Son

40 LASP - Laboratory for Atmospheric and Space Physics [Boulder]

41 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique

Abstract : We present LOFAR Low Band observations of the Bootes and 3C295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam$^{-1}$, making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17 to 52 deg$^{2}$. From the observations we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and VLA 74 MHz differential source counts, scaling with a spectral index of $-0.7$. We find that a spectral index scaling of $-0.5$ is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens towards lower frequencies. We also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum ($\alpha < -1.1$) radio sources, that could be associated with massive high redshift radio galaxies, we compute spectral indices between 62 MHz, 153 MHz and 1.4 GHz for sources in the Bo\"otes field. We cross-correlate these radio sources with optical and infrared catalogues and fit the spectral energy distribution to obtain photometric redshifts. We find that most of these ultra-steep spectrum sources are located in the $ 0.7 \lesssim z \lesssim 2.5$ range.

Document type :

Journal articles

Domain :

Sciences of the Universe [physics]

Sciences of the Universe [physics] / Astrophysics [astro-ph]

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