skip to main content

SciTech ConnectSciTech Connect

Title: LOFAR low-band antenna observations of the 3C 295 and Boötes fields: source counts and ultra-steep spectrum sources

We present Low Frequency Array (LOFAR) Low Band observations of the Boötes and 3C 295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam{sup –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 17-52 deg{sup 2}. From the observations, we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and Very Large Array 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 toward 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 (α < –1.1) radio sources that could be associated with massive high-redshift radio galaxies,more » we compute spectral indices between 62 MHz, 153 MHz, and 1.4 GHz for sources in the Boötes field. We cross-correlate these radio sources with optical and infrared catalogs 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 ≲ z ≲ 2.5 range.« less
Authors:
 [1] ; ; ; ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ; ;  [8] ;  [9] ;  [10] ;  [11] ;  [12] ; ;  [13] ;  [14] ;  [15] more »; « less
  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  2. Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands)
  3. Department of Physics and Electronics, Rhodes University, P.O. Box 94, Grahamstown 6140 (South Africa)
  4. Netherlands Institute for Radio Astronomy (ASTRON), P.O. Box 2, NL-7990 AA Dwingeloo (Netherlands)
  5. Department of Physics and Astronomy, The Open University, Buckinghamshire MK7 6AA (United Kingdom)
  6. Kapteyn Astronomical Institute, P.O. Box 800, NL-9700 AV Groningen (Netherlands)
  7. Institute for Astronomy, University of Edinburgh, Royal Observatory of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)
  8. National Radio Astronomy Observatory, Socorro, NM 87801 (United States)
  9. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)
  10. Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany)
  11. Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University Nijmegen, P.O. Box 9010, NL-6500 GL Nijmegen (Netherlands)
  12. Max Planck Institute for Astrophysics, Karl-Schwarzschildstrasse 1, D-85748 Garching (Germany)
  13. INAF—Istituto di Radioastronomia, Via Gobetti 101, I-40129 Bologna (Italy)
  14. Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, D-21029 Hamburg (Germany)
  15. Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków (Poland)
Publication Date:
OSTI Identifier:
22370593
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 793; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CATALOGS; ENERGY SPECTRA; EUCLIDEAN SPACE; EV RANGE; GHZ RANGE; IMAGES; MHZ RANGE; RADIO GALAXIES; RED SHIFT; SCALING