J/A+A/683/A222 Optical spectroscopy of blazars for CTA. III (D'Ammando+, 2024)
Optical spectroscopy of blazars for the Cherenkov Telescope Array. III.
D'Ammando F., Goldoni P., Max-Moerbeck W., Becerra Gonzalez J., Kasai E.,
Williams D.A., Alvarez-Crespo N., Backes M., Barres de Almeida U.,
Boisson C., Cotter G., Fallah Ramazani V., Hervet O., Lindfors E.,
Mukhi-Nilo D., Pita S., Splettstoesser M., van Soelen B.
<Astron. Astrophys. 683, A222 (2024)>
=2024A&A...683A.222D 2024A&A...683A.222D (SIMBAD/NED BibCode)
ADC_Keywords: BL Lac objects ; Spectroscopy
Keywords: galaxies: active - BL Lacertae objects: general -
galaxies: distances and redshifts - gamma rays: galaxies
Abstract:
Blazars, which include BL Lacs and flat-spectrum radio quasars
(FSRQs), represent the brightest persistent extragalactic sources in
the high-energy (HE; 10MeV-100GeV) and very-high-energy (VHE;
E>100GeV) 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% 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 (>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.
Description:
Flux-calibrated spectra of the 24 sources observed with Keck II, SALT,
GTC, and ESO/VLT. The flux is in units of erg/cm2/s/Å. Very noisy
regions, often at the beginning or the end of the spectra, have been
sometimes cut from the spectra.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
sources.dat 77 24 List of studied sources
sp/* . 25 Individual spectra
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Byte-by-byte Description of file: sources.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 10 F4.1 s RAs Right ascension (J2000)
12 A1 --- DE- Declination sign (J2000)
13- 14 I2 deg DEd Declination (J2000)
16- 17 I2 arcmin DEm Declination (J2000)
19- 20 I2 arcsec DEs Declination (J2000)
22- 45 A24 --- Name Name
47- 56 A10 --- Inst Instrument
59- 77 A19 --- FileName Name of the spectrum file in subdirectory sp
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
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6- 13 F8.2 0.1nm lambda Wavelength
15- 26 E12.6 cW/m2/nm Flux Flux density (in erg/cm2/s/Å)
28- 39 E12.6 cW/m2/nm e_Flux []? Flux density error (in erg/cm2/s/Å)
40 A1 --- neFlux [I] I for Inf
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Acknowledgements:
Filippo D'Ammando, dammando(at)ira.inaf.it
References:
Goldoni et al., Paper I 2021A&A...650A.106G 2021A&A...650A.106G
Kasai et al., Paper II 2023MNRAS.518.2675K 2023MNRAS.518.2675K
(End) Patricia Vannier [CDS] 26-Jan-2024