Optical Spectra of Candidate International Celestial Reference Frame (ICRF) Flat-spectrum Radio Sources. III.

Titov, Oleg; Pursimo, T.; Johnston, Helen M.; Stanford, Laura M.; Hunstead, R. W.; Jauncey, D. L.; Zenere, Katrina A.

doi:10.3847/1538-3881/aa61fd

Cited by 6 publications

(4 citation statements)

References 24 publications

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“…Previous spectra obtained by SOAR, with a moderate S/N (Landoni et al 2015), and by EFOSC, with a low S/N (Titov et al 2017), are featureless. We performed two separate observations with SALT/RSS at distance of two days with a total exposure time of 4660 s. The total averaged spectrum with a S/N of 113 is presented in Fig.…”

Section: Sumss J014347-58455mentioning

confidence: 79%

Optical spectroscopy of blazars for the Cherenkov Telescope Array – III

D’Ammando,

Goldoni,

Max-Moerbeck

et al. 2024

A&A

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Blazars, which include BL Lacs and flat-spectrum radio quasars (FSRQs), represent the brightest persistent extragalactic sources in the high-energy (HE; 10 MeV -- 100 GeV) and very-high-energy (VHE; $E$ $>$ 100 GeV) gamma -ray sky. Due to their almost featureless optical/UV spectra, it is challenging to measure the redshifts of BL Lacs. As a result, about 50<!PCT!> of gamma -ray BL Lacs lack a firm measurement of this property, which is fundamental for population studies, indirect estimates of the extragalactic background light (EBL), and fundamental physics probes (e.g. searches for Lorentz-invariance violation or axion-like particles). This paper is the third in a series of papers aimed at determining the redshift of a sample of blazars selected as prime targets for future observations with the next generation, ground-based VHE gamma -ray astronomy observatory, Cherenkov Telescope Array Observatory (CTAO). The accurate determination of the redshift of these objects is an important aid in source selection and planning of future CTAO observations. Promising targets were selected following a sample selection obtained with Monte Carlo simulations of CTAO observations. The selected targets were expected to be detectable with CTAO in observations of 30 hours or less. We performed deep spectroscopic observations of 41 of these blazars using the Keck II, Lick, SALT, GTC, and ESO/VLT telescopes. We carefully searched for spectral lines in the spectra and whenever features of the host galaxy were detected, we attempted to model the properties of the host galaxy. The magnitudes of the targets at the time of the observations were also compared to their long-term light curves. Spectra from 24 objects display spectral features or a high signal-to-noise ratio (S/N). From these, 12 spectroscopic redshifts were determined, ranging from 0.2223 to 0.7018. Furthermore, 1 tentative redshift (0.6622) and 2 redshift lower limits at $z$ > 0.6185 and $z$ > 0.6347 were obtained. The other 9 BL Lacs showed featureless spectra, despite the high S/N (geq 100) observations. Our comparisons with long-term optical light curves tentatively suggest that redshift measurements are more straightforward during an optical low state of the active galactic nucleus (AGN). Overall, we have determined 37 redshifts and 6 spectroscopic lower limits as part of our programme thus far.

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Section: Sumss J014347-58455mentioning

confidence: 79%

Optical spectroscopy of blazars for the Cherenkov Telescope Array – III

D’Ammando,

Goldoni,

Max-Moerbeck

et al. 2024

A&A

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“…Therefore, a conservative estimate of the redshift formal errors at z ∼ 3 is about σ z = 0.005 (e.g., Titov et al 2013Titov et al , 2017.…”

Section: The Sample and Observationsmentioning

confidence: 99%

Astrometric Apparent Motion of High-redshift Radio Sources

Titov

Frey

Melnikov

et al. 2023

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Radio-loud quasars at high redshift (z ≥ 4) are rare objects in the universe and rarely observed with Very Long Baseline Interferometry (VLBI). But some of them have flux density sufficiently high for monitoring of their apparent position. The instability of the astrometric positions could be linked to the astrophysical process in the jetted active galactic nuclei in the early universe. Regular observations of the high-redshift quasars are used for estimating their apparent proper motion over several years. We have undertaken regular VLBI observations of several high-redshift quasars at 2.3 GHz (S band) and 8.4 GHz (X band) with a network of five radio telescopes: 40 m Yebes (Spain), 25 m Sheshan (China), and three 32 m telescopes of the Quasar VLBI Network (Russia)—Svetloe, Zelenchukskaya, and Badary. Additional facilities joined this network occasionally. The sources have also been observed in three sessions with the European VLBI Network in 2018–2019 and one Long Baseline Array experiment in 2018. In addition, several experiments conducted with the Very Long Baseline Array in 2017–2018 were used to improve the time sampling and the statistics. Based on these 37 astrometric VLBI experiments between 2017 and 2021, we estimated the apparent proper motions of four quasars: 0901+697, 1428+422, 1508+572, and 2101+600.

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“…While there have been systematic programs to concatenate catalog photometry and redshifts of nearly all ICRF objects (e.g., Malkin 2018), relatively few ICRF objects have been spectroscopically characterized (e.g., Titov et al 2017), and efforts have mainly focused on the determination of redshift (e.g., Titov & Malkin 2009). Optical spectra contain an abundant amount of information regarding the physical processes powering AGNs and quasars.…”

Section: Introductionmentioning

confidence: 99%

The US Naval Observatory VLBI Spectroscopic Catalog

Sexton¹,

Secrest²,

Johnson³

et al. 2022

ApJS

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Despite their importance for astrometry and navigation, the active galactic nuclei (AGNs) that comprise the International Celestial Reference Frame (ICRF) are relatively poorly understood, with key information such as their spectroscopic redshifts, AGN spectral type, and emission-/absorption-line properties generally missing from the literature. Using an updated, publicly available, state-of-the-art spectroscopic fitting code optimized for the spectra of AGNs from low to high redshift, we present a catalog of emission-line and spectral continuum parameters for 1014 unique ICRF3 objects with single-fiber spectra from the Sloan Digital Sky Survey DR16. We additionally present black hole virial mass scaling relationships that use Hα-, Hβ-, Mg ii-, and C iv-based line widths, all consistent with each other, which can be used in studies of radio-loud objects across a wide range of redshifts, and we use these scaling relationships to provide derived properties such as black hole masses and bolometric luminosities for the catalog. We briefly comment on these properties for the ICRF objects, as well as their overall spectroscopic characteristics.

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Optical Spectra of Candidate International Celestial Reference Frame (ICRF) Flat-spectrum Radio Sources. III.

Cited by 6 publications

References 24 publications

Optical spectroscopy of blazars for the Cherenkov Telescope Array – III

Optical spectroscopy of blazars for the Cherenkov Telescope Array – III

Astrometric Apparent Motion of High-redshift Radio Sources

The US Naval Observatory VLBI Spectroscopic Catalog

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