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

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} H. J. A. Rottgering ³ D. A. Rafferty ⁶ S. van der Tol G. Heald ¹ G. J. White ⁷ A. Shulevski P. Best ⁸ H. T. Intema S. Bhatnagar ⁹ W. Reich ¹⁰ M. Steinmetz S. van Velzen T. A. Ensslin I. Prandoni F. de Gasperin M. Jamrozy G. Brunetti M. J. Jarvis ¹¹ J. P. Mckean ¹ M. W. Wise ^{1, 12} C. Ferrari ¹³ J. Harwood J. B. R. Oonk ¹ M. Hoeft ¹⁴ M. Kunert-Bajraszewska C. Horellou O. Wucknitz ¹⁵ A. Bonafede ¹⁶ N. R. Mohan A. M. M. Scaife ¹⁷ H. -R. Klockner I. M. van Bemmel A. Merloni K. T. Chyzy D. Engels H. Falcke ^{18, 10, 1} M. Pandey-Pommier ¹⁹ A. Alexov ¹ J. Anderson ²⁰ I. M. Avruch ²¹ R. Beck ²² M. E. Bell ²³ M. J. Bentum ¹ G. Bernardi ²⁴ F. Breitling ²⁵ J. Broderick ²³ W. N. Brouw ²⁶ M. Bruggen ¹⁶ H. R. Butcher ¹ B. Ciardi ²⁷ E. de Geus ²⁸ M. de Vos A. Deller S. Duscha J. Eisloffel ¹⁴ 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 ¹⁰ P. Maat ¹ G. Mann ²⁰ D. Mckay-Bukowski ³⁶ M. Mevius ¹ R. Morganti ^{26, 37} H. Munk ¹ A. R. Offringa E. Orru ³⁸ H. Paas ¹ V. N. Pandey G. Pietka ³⁹ R. Pizzo ¹ A. G. Polatidis ¹ A. Renting A. Rowlinson D. Schwarz ⁴⁰ M. Serylak ^{31, 30} J. Sluman ¹ O. Smirnov ⁵ B. W. Stappers ³² A. Stewart ⁴¹ J. Swinbank ¹² Michel Tagger ³¹ Y. Tang S. Thoudam ¹⁸ C. Toribio R. Vermeulen C. Vocks P. Zarka ⁴²

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 Department of Astronomy and Astrophysics [PennState]

7 SLAC - Stanford Linear Accelerator Center

8 University of Edinburgh

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

10 MPIFR - Max-Planck-Institut für Radioastronomie

11 Charles Darwin University

12 AI PANNEKOEK - Astronomical Institute Anton Pannekoek

13 LRGP - Laboratoire Réactions et Génie des Procédés

14 TLS - Thüringer Landessternwarte Tautenburg

15 AlfA - Argelander-Institut für Astronomie

16 Jacobs University [Bremen]

17 School of Physics and Astronomy [Southampton]

18 Radboud university [Nijmegen]

19 CRAL - Centre de Recherche Astrophysique de Lyon

20 AIP - Leibniz-Institut für Astrophysik Potsdam

21 SRON - SRON Netherlands Institute for Space Research

22 LCPM - Laboratoire de Chimie Physique Moléculaire

23 University of Southampton

24 LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies

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 ASTRON - Netherlands Institute for Radio Astronomy

38 IMAPP - Applied Stochastics

39 Oxford Astrophysics

40 Interactions Son Musique Mouvement

STMS - Sciences et Technologies de la Musique et du Son

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

42 OP - Observatoire de Paris - Site de Paris

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]

Complete list of metadatas

https://hal-insu.archives-ouvertes.fr/insu-01284922
Contributor : Nathalie Rouchon <>
Submitted on : Tuesday, March 8, 2016 - 11:51:45 AM
Last modification on : Thursday, August 22, 2019 - 12:04:03 PM

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

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

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