Optical characterization of WISE selected blazar candidates

Author(s):Show less -

de Menezes, Raniere ; Pena-Herazo, Harold A. ; Marchesini, Ezequiel J. ; D'Abrusco, Raffaele ; Masetti, Nicola ; Nemmen, Rodrigo ; Massaro, Francesco ; Ricci, Federica ; Landoni, Marco ; Paggi, Alessandro ; Smith, Howard A.

• Document type: Journal article
• Source: ASTRONOMY & ASTROPHYSICS; v. 630, p. 10-pg., 2019-09-23.

Abstract

Context. Over the last decade more than five thousand gamma-ray sources have been detected by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. Given the positional uncertainty of the telescope, nearly 30% of these sources remain without an obvious counterpart at lower energies. This has motivated the release of new catalogs of gamma-ray counterpart candidates and several follow up campaigns in the last decade. Aims. Recently, two new catalogs of blazar candidates were released. These are the improved and expanded version of the WISE Blazar-Like Radio-Loud Sources (WIBRaLS2) catalog and the Kernel Density Estimation selected candidate BL Lacs (KDE-BLLACS) catalog, both selecting blazar-like sources based on their infrared colors from the Wide-field Infrared Survey Explorer (WISE). In this work we characterize these two catalogs, clarifying the true nature of their sources based on their optical spectra from SDSS data release 15, thus testing their efficiency in selecting true blazars. Methods. We first selected all WIBRaLS2 and KDEBLLACS sources with available optical spectra in the footprint of Sloan Digital Sky Survey data release 15. We then analyzed these spectra to verify the nature of each selected candidate and to measure the fraction of the catalogs composed by spectroscopically confirmed blazars. Finally, we evaluated the impact of selection effects, especially those related to optical colors of WIBRaLS2/KDEBLLACS sources and their optical magnitude distributions. Results. We found that at least similar to 30% of each catalog is made up of confirmed blazars, with quasars being the major contaminants in the case of WIBRaLS2 (approximate to 58%) and normal galaxies in the case of KDEBLLACS (approximate to 38.2%). The spectral analysis also allowed us to identify the nature of 11 blazar candidates of uncertain type (BCUs) from the Fermi-LAT fourth Point Source Catalog (4FGL) and to find 25 new BL Lac objects. (AU)

• FAPESP's process: 18/24801-6 - Multislit spectroscopy of unidentified gamma-ray sources
• Grantee: Raniere Maciel de Menezes
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 17/01461-2 - The extreme universe: black holes and the Fermi telescope
• Grantee: Rodrigo Nemmen da Silva
• Support Opportunities: Research Grants - Young Investigators Grants
• FAPESP's process: 16/25484-9 - Optical observations of blazar candidates and unknown gamma-ray sources
• Grantee: Raniere Maciel de Menezes
• Support Opportunities: Scholarships in Brazil - Doctorate