Optical archival spectra of blazar candidates of uncertain type in the 3rd Fermi Large Area Telescope Catalog

Abstract

Despite the fact that blazars constitute the rarest class among active galactic nuclei (AGNs) they are the largest known population of associated γ-ray sources. Many of the γ-ray objects listed in the Fermi-Large Area Telescope Third Source catalog (3FGL) are classified as blazar candidates of uncertain type (BCUs), either because they show multifrequency behavior similar to blazars but lacking optical spectra in the literature, or because the quality of such spectra is too low to confirm their nature. Here we select, out of 585 BCUs in the 3FGL, 42 BCUs which we identify as probable blazars by their WISE infrared colors and which also have optical spectra that are available in the Sloan Digital Sky Survey (SDSS) and/or Six-Degree Field Galaxy Survey Database (6dFGS). We confirm the blazar nature of all of the sources. We furthermore conclude that 28 of them are BL Lacs, 8 are radio-loud quasars with flat radio spectrum and 6 are BL Lac whose emission is dominated by their host galaxy

Fermi Large Area Telescope Fourth Source Catalog

“…In addition, to assess the real nature and classify all newly associated sources, it has been crucial to perform additional spectroscopic optical observations, which, for extragalactic objects, were also able to provide estimates of their cosmological distances (see, e.g., Shaw et al 2013aShaw et al , 2013bPaggi et al 2014;Landoni et al 2015aLandoni et al , 2015bMassaro et al 2015aMassaro et al , 2015bRicci et al 2015;Álvarez Crespo et al 2016aÁlvarez Crespo et al , 2016cChiaro et al 2016;Paiano et al 2017aPaiano et al , 2017cPaiano et al , 2017dPeña-Herazo et al 2017;Landoni et al 2018;Marchesi et al 2018;Marchesini et al 2019). These campaigns are continuously updated including searches in the optical databases of the major surveys (see, e.g., Cowperthwaite et al 2013;Massaro et al 2014Maselli et al 2015;Álvarez Crespo et al 2016b;de Menezes et al 2019).…”

The gamma-ray blazar quest: new optical spectra, state of art and future perspectives

“…• The BCU NVSS J132210+084231 associated with 3FGL J1322.3+0839 was observed inÁlvarez Crespo et al (2016a) andÁlvarez Crespo et al (2016c) in a different state, since it appeared as a BZB first and a BZQ at z =0.32549 later. The optical spectrum of 3FGL J0158.6+0102 is reported Massaro et al (2014) as well as in the current paper.…”

“…• Only for the AGU: TXS 1801+253 associated in the 2FGL with 2FGL J1803.6+2523c, we were not able to find a WISE counterpart, due to a confusion with a nearby star (seeÁlvarez- Crespo et al 2016c, for more details).…”

Optical spectroscopic observations of gamma-ray blazar candidates. IX. Optical archival spectra and further observations from SOAR and OAGH

“…We remark that to mitigate the impact on telescopes schedules we tend to observe small samples of BCUs and UGS candidate counterparts during each observing run. Our observations are also combined with an extensive search in optical databases as the SDSS (Alam et al 2015) and/or the Six-Degree Field Galaxy Survey (Jones et al 2009) (see e.g., Massaro et al 2014;Massaro et al 2015a;Álvarez-Crespo et al 2016c;Massaro et al2016).…”