An optical view of BL Lacertae objects

Falomo, R.; Pian, E.; Treves, A.

doi:10.1007/s00159-014-0073-z

Cited by 139 publications

(123 citation statements)

References 275 publications

(329 reference statements)

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“…Assuming the observed targets have giant elliptical host galaxies of similar luminosity distribution of the population of BLLs for which the host galaxy has been resolved it is plausible to assume that they are hosted by massive early type galaxies (see e.g. Falomo et al (2014) and references therein). Since the luminosity distribution of these host galaxies is relatively narrow (see e.g.…”

Section: Discussionmentioning

confidence: 99%

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On the Redshift of TeV BL Lac Objects

Paiano

Landoni

Falomo

et al. 2017

ApJ

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We report results of a spectroscopic campaign carried out at the 10 m Gran Telescopio Canarias for a sample of 22 BL Lac objects detected (or candidates) at TeV energies, aimed to determine or constrain their redshift. This is of fundamental importance for the interpretation of their emission models, for population studies and also mandatory to study the interaction of high energy photons with the extragalactic background light using TeV sources. High signal-to-noise optical spectra in the range 4250 -10000Å were obtained to search for faint emission and/or absorption lines from both the host galaxy or the nucleus. We determine a new redshift for PKS 1424+240 (z = 0.604) and a tentative one for 1ES 0033+595 (z = 0.467). We are able to set new spectroscopic redshift lower limits for other three sources on the basis of Mg II and Ca II intervening absorption features: BZB J1243+3627 (z > 0.483), BZB J1540+8155 (z > 0.672), and BZB 0J2323+4210 (z > 0.267). We confirm previous redshift estimates for four blazars: S3 0218+357 (z = 0.944), 1ES 1215+303 (z = 0.129), W Comae (z = 0.102), and MS 1221.8+2452 (z = 0.218). For the remaining targets, in seven cases (S2 0109+22, 3C 66A, VER J0521+211, S4 0954+65, BZB J1120+4214, S3 1227+25, BZB J2323+4210), we do not validate the proposed redshift. Finally for all sources of still unknown redshift, we set a lower limit based on the minimum equivalent width of absorption features expected from the host galaxy.

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Section: Discussionmentioning

confidence: 99%

“…From the optical point of view, blazars showing very weak lines or a completely featureless spectra are named BL Lac objects (BLLs) (see e.g. the review of Falomo et al 2014).…”

Section: Introductionmentioning

confidence: 99%

On the Redshift of TeV BL Lac Objects

Paiano

Landoni

Falomo

et al. 2017

ApJ

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“…They have high luminosity, large amplitude and rapid variability, high and variable polarization, radio core dominance, and apparent super-luminal speeds (Urry & Padovani 1995;Massaro et al 2016). Generally, Blazars are divided into subcategories of BL Lacs objects (BL Lacs), characterized by almost completely lacking of emission lines or only showing weak emission lines (EW 5Å), and highly polarized quasars or flat spectral radio quasars (FSRQs), showing broad strong emission lines (Falomo et al 2014;Massaro et al 2014). The broadband spectral energy distributions (SEDs) of blazars are double peaked.…”

Section: Introductionmentioning

confidence: 99%

The physical properties ofFermiTeV BL Lac objects’ jets

Ding¹,

Zhang²,

Xiong³

et al. 2016

Mon. Not. R. Astron. Soc.

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We investigate the physical properties of Fermi TeV BL Lac objects jets by modeling the quasi-simultaneous spectral energy distribution of 29 Fermi TeV BL Lacs in the frame of a one-zone leptonic synchrotron self-Compton model. Our main results are the following: (i) There is a negative correlation between B and δ in our sample, which suggests that B and δ are dependent on each other mainly in Thomson regime. (ii) There are negative correlations between ν sy and r, the ν IC and r, which is a signature of the energy-dependence statistical acceleration or the stochastic acceleration. There is a significant correlation between r and s, which suggests that the curvature of the electron energy distribution is attributed to the energydependence statistical acceleration mechanism. (iii) By assuming one proton per relativistic electron, we estimate the jet power and radiative power. A size relation P e ∼ P p > P r P B is found in our sample. The P e > P B suggests that the jets are particle dominated, and the P e ∼ P p means that the mean energy of relativistic electrons approaches m p /m e . There are not significant correlations between P jet and black hole mass in high or low state with a subsample of 18 sources, which suggests that the jet power weakly depends on the black hole mass. (iv) There is a correlation between the changes in the flux density at 1 TeV and the changes in the γ peak , which suggests the change/evolution of electron energy distribution may be mainly responsible for the flux variation.

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“…They are one of the most powerful astrophysical sources and are characterized by rapid, strong, and irregular flux variability (e.g., Falomo et al 2014). There are two populations of blazars, flat-spectrum radio quasars (FSRQ), and BL Lacertae (BL-Lac) objects.…”

Section: Introductionmentioning

confidence: 99%

The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies atz= 0.343

Muriel

Donzelli

Rovero

et al. 2015

A&A

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Context. The BL-Lac blazar PKS 0447-439 is one of the brightest HE gamma-ray sources that were first detected by Fermi-LAT. It was also detected by H.E.S.S. at VHE gamma-rays, which allowed constraining the redshift of PKS 0447-439 by considering the attenuation caused by gamma-ray interactions with ambient photons in the extragalactic background light (EBL). This constraint agreed with color-magnitude and spectroscopic redshift constraints (0.179 < z < 0.56). Recently, however, a much higher redshift was proposed for this blazar (z > 1.2). This value was debated because if true, it would imply either that the relevant absorption processes of gamma-rays are not well understood or that the EBL is dramatically different from what is believed today. This high redshift was not confirmed by three independent new spectroscopic observations at high signal-to-noise ratios. The scenario is clear evidence of the difficulties in estimating the redshift of BL-Lac objects, whose optical spectra are typically featureless. Neither of the estimated redshifts for PKS 0447-439 are confirmed as yet. Aims. Given that BL-Lac are typically hosted by elliptical galaxies, which in turn are associated with groups, we aim to find the host group of galaxies of PKS 0447-439. The ultimate goal is to estimate a redshift for this blazar. Methods. Spectra of twenty-one objects in the field of view of PKS 0447-439 were obtained with the Gemini Multi-Object Spectrograph. Based on the redshifts and coordinates of these galaxies, we searched for groups of galaxies. Using a deep catalog of groups, we studied the probability of finding by chance a group of galaxies in the line of sight of PKS 0447-439. Results. We identified a group of galaxies that was not previously cataloged at z = 0.343 with seven members, a virial radius of 0.42 Mpc, and a velocity dispersion of 622 km s −1 . We found that the probability of the host galaxy of PKS 0447-439 to be a member of the new group is > ∼ 97%. Therefore, we propose to adopt z = 0.343 ± 0.002 as the most likely redshift for PKS 0447-439.

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An optical view of BL Lacertae objects

Cited by 139 publications

References 275 publications

On the Redshift of TeV BL Lac Objects

On the Redshift of TeV BL Lac Objects

The physical properties ofFermiTeV BL Lac objects’ jets

The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies atz= 0.343

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