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Quasars at all cosmic epochs

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Front. Astron. Space Sci. | doi: 10.3389/fspas.2018.00005

On the selection of high-z quasars using LOFAR observations

  • 1Leiden University, Netherlands

We present a method to identify candidate quasars which combines optical/infrared color selection with radio detections from the Low Frequency ARray (LOFAR) at 150MHz. We apply this {method} in a region of 9 square degrees located in the Bo\"{o}tes field, with a wealth of multi-wavelength data. Our LOFAR imaging in the central region reaches a rms noise of $\sim50\mu$Jy with a resolution of $5''$. This is so deep that we also routinely, `radio-quiet' quasars. We use quasar spectroscopy from the literature to calculate the completeness and efficiency of our selection method. We conduct our analysis in two redshift intervals, $1-1.0$ sources can be detected in the WSRT-Bo\"{o}tes map, we find that the spectral index distribution of the 21 quasars in the resulting sample is steeper than the general LOFAR-WSRT spectral index distribution with a median of $\alpha=-0.80\pm0.06$. As the upcoming LOFAR wide area surveys are much deeper than the traditional 1.4GHz surveys like NVSS and FIRST, this indicates that LOFAR in combination with optical and infrared will be an excellent fishing ground to obtain large samples of quasars.

Keywords: quasars, active galactic nuclei, surveys, Radio, extragalactic astronomy, Photometry, spectroscopy

Received: 31 Jul 2017; Accepted: 31 Jan 2018.

Edited by:

Paola Marziani, Osservatorio Astronomico di Padova (INAF), Italy

Reviewed by:

Daniela Bettoni, Osservatorio Astronomico di Padova (INAF), Italy
Andjelka B. Kovacevic, Department of Astronomy,Faculty of Mathematics, University of Belgrade, Serbia
Paola Marziani, Osservatorio Astronomico di Padova (INAF), Italy  

Copyright: © 2018 Retana-Montenegro and Rottgering. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Mr. Edwin Retana-Montenegro, Leiden University, Leiden, Netherlands,