Radio Polarisation Studies of Galaxies at Z &gt; 2

Athreya, R.; Kapahi, V. K.; McCarthy, P. J.; Breugel, Wil van

doi:10.1007/978-94-009-0295-4_63

Cited by 48 publications

(72 citation statements)

References 4 publications

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“…There appears to be an RM gradient across the eastern jet (Fig. 3 of Athreya et al 1998), oriented in the CCW direction. Unfortunately, we do not have access to these data and were not able to quantatively analyze the significance of this gradient.…”

Section: Tentative Gradients From An Initial Inspection Of Rm Maps Inmentioning

confidence: 98%

“…3.1 and 3.2 were initially identified via an initial inspection of published Faraday RM maps of extragalactic radio sources on kiloparsec scales, carried out for 85 objects (Athreya et al 1998;Best et al 1998Best et al , 1999Feretti et al 1999;Venturi & Taylor 1999;Taylor et al 2001;Eilek & Owen 2002;Goodlet et al 2004;Govoni et al 2006Govoni et al , 2010Laing et al 2006Laing et al , 2008Kharb et al 2008;Guidetti et al 2008Guidetti et al , 2010Feain et al 2009;Kronberg 2009;Bonafede et al 2010;Kronberg et al 2011;Algaba et al 2013). In all cases, the authors of these studies took care to ensure that the RM images were constructed using only data with sufficiently high signal-to-noise ratios, and that the resulting λ 2 fits for the RM values were sufficiently good.…”

Section: Tentative Gradients From An Initial Inspection Of Rm Maps Inmentioning

confidence: 99%

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Dominance of outflowing electric currents on decaparsec to kiloparsec scales in extragalactic jets

Christodoulou

Gabuzda

Knuettel

et al. 2016

A&A

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Context. Helical magnetic fields embedded in the jets of active galactic nuclei (AGNs) are required by the broad range of theoretical models that advocate for electromagnetic launching of the jets. In most models, the direction of the magnetic field is random, but if the axial field is generated by a Cosmic Battery generated by current in the direction of rotation in the accretion disk, there is a correlation between the directions of the spin of the AGN accretion disk and of the axial field, which leads to a specific direction for the axial electric current, azimuthal magnetic field, and the resulting observed transverse Faraday-rotation (FR) gradient across the jet, due to the systematic change in the line-of-sight magnetic field. Aims. We consider new observational evidence for the presence of a nested helical magnetic-field structure such as would be brought about by the operation of the Cosmic Battery, and make predictions about the expected behavior of transverse FR gradients observed on decaparsec and kiloparsec scales. Methods. We have jointly considered 27 detections of transverse FR gradients on parsec scales, four reports of reversals in the directions of observed transverse FR gradients observed on parsec-decaparsec scales, and five detections of transverse FR gradients on decaparsec-kiloparsec scales, one reported here for the first time. We also consider seven tentative additional examples of transverse FR gradients on kiloparsec scales, based on an initial visual inspection of published Very Large Array FR maps of 85 extragalactic radio sources, for three of which we have carried out quantitative analyses in order to quantitatively estimate the significances of the gradients. Results. The data considered indicate a predominance of transverse FR gradients in the clockwise direction on the sky (i.e., net axial current flowing inward in the jet) on parsec scales and in the counter-clockwise direction on the sky (i.e., net axial current flowing outward) on scales greater than about 10 pc, consistent with the expectations for the Cosmic Battery. The predominance of counter-clockwise FR gradients on larger scales has been established at the 3σ confidence level. Conclusions. The collected results provide evidence for a reversal in the direction of the net azimuthal magnetic field determining the ordered component of the observed FR images, with distance from the jet base. This can be understood if the dominant azimuthal field on parsec scales corresponds to an axial electric current flowing inward along the jet, whereas the (weaker) dominant azimuthal field on kiloparsec scales corresponds to a outward-flowing current in the outer sheath of the jet and/or an extended disk wind. This is precisely the current/magnetic field structure that should be generated by the Cosmic Battery.

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Section: Tentative Gradients From An Initial Inspection Of Rm Maps Inmentioning

confidence: 98%

Section: Tentative Gradients From An Initial Inspection Of Rm Maps Inmentioning

confidence: 99%

Dominance of outflowing electric currents on decaparsec to kiloparsec scales in extragalactic jets

Christodoulou

Gabuzda

Knuettel

et al. 2016

A&A

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“…Extended gas disks within the radio galaxy Best (2000) pointed out that radio galaxies with very extended radio sources are particularly good candidates for being cluster central galaxies because the pressure from the Mpc-scale intracluster medium boosts the luminosity of the radio source even for comparably extended jets (see also Athreya et al 1998;Klamer et al 2006). Many authors have previously suggested that the progenitors of brightest cluster galaxies are likely to be found among HzRGs (e.g., Pentericci et al 2001;Miley et al 2006;Hatch et al 2009), andWylezalek et al (2013) find from IRAC imaging that TXS 2353-003 is even associated with the most strongly pronounced overdensity within their sample.…”

Section: Partial Agn Illumination Of Ambient Halo Cloudsmentioning

confidence: 99%

Defying jet-gas alignment in two radio galaxies atz~ 2 with extended light profiles: Similarities to brightest cluster galaxies

Collet

Nesvadba

Breuck

et al. 2015

A&A

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We report the detection of extended warm ionized gas in two powerful high-redshift radio galaxies, NVSS J210626-314003 at z = 2.10 and TXS 2353-003 at z = 1.49, that does not appear to be associated with the radio jets. This is contrary to what would be expected from the alignment effect, a characteristic feature of distant, powerful radio galaxies at z ≥ 0.6. The gas also has smaller velocity gradients and line widths than most other high-z radio galaxies with similar data. Both galaxies are part of a systematic study of 50 high-redshift radio galaxies with SINFONI, and are the only two that are characterized by the presence of high surface-brightness gas not associated with the jet axis and by the absence of such gas aligned with the jet. Both galaxies are spatially resolved with ISAAC broadband imaging covering the rest-frame R band, and have extended wings that cannot be attributed to line contamination. We argue that the gas and stellar properties of these galaxies are more akin to gas-rich brightest cluster galaxies in cool-core clusters than the general population of high-redshift radio galaxies at z > ∼ 2. In support of this interpretation, one of our sources, TXS 2353-003, for which we have Hα narrowband imaging, is associated with an overdensity of candidate Hα emitters by a factor of ∼8 relative to the field at z = 1.5. We discuss possible scenarios of the evolutionary state of these galaxies and the nature of their emission line gas within the context of cyclical AGN feedback.

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“…Detection of ordered magnetic fields at scale of hundreds to thousand pc in high redshift objects of z > 2 (Udomprasert et al 1997;Athreya et al 1998) poses a stiff challenge to the dynamo mechanism for generating magnetic fields, primarily due to the very short time available for amplification of the initial seed field.…”

Section: Radio Galaxies and Quasarsmentioning

confidence: 99%

“…However, magnetic fields in high redshift (z ∼ 2.0 -3.0) objects with Lyman-α damped systems have been found to be as strong as in nearby galaxies and in some clusters of galaxies (e.g., Kronberg et al 1990Kronberg et al , 1992Athreya et al 1998). This poses some challenge to galactic dynamo, since, at that time, galaxies should have rotated only a few times.…”

Section: The Origin Of Magnetic Fieldsmentioning

confidence: 99%

Milestones in the Observations of Cosmic Magnetic Fields

Han

Wielebinski

2002

Chin. J. Astron. Astrophys.

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Magnetic fields are observed everywhere in the universe. In this review, we concentrate on the observational aspects of the magnetic fields of Galactic and extragalactic objects. Readers can follow the milestones in the observations of cosmic magnetic fields obtained from the most important tracers of magnetic fields, namely, the star-light polarization, the Zeeman effect, the rotation measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio polarization observations, as well as the newly implemented sub-mm and mm polarization capabilities. The magnetic field of the Galaxy was first discovered in 1949 by optical polarization observations. The local magnetic fields within one or two kpc have been well delineated by starlight polarization data. The polarization observations of diffuse Galactic radio background emission in 1962 confirmed unequivocally the existence of a Galactic magnetic field. The bulk of the present information about the magnetic fields in the Galaxy comes from analysis of rotation measures of extragalactic radio sources and pulsars, which can be used to construct the 3-D magnetic field structure in the Galactic halo and Galactic disk. Radio synchrotron spurs in the Galactic center show a poloidal field, and the polarization mapping of dust emission and Zeeman observation in the central molecular zone reveal a toroidal magnetic field parallel to the Galactic plane. For nearby galaxies, both optical polarization and multifrequency radio polarization data clearly show the large-scale magnetic field following the spiral arms or dust lanes. For more distant objects, radio polarization is the only approach available to show the magnetic fields in the jets or lobes of radio galaxies or quasars. Clusters of galaxies also contain widely distributed magnetic fields, which are reflected by radio halos or the RM distribution of background objects. The intergalactic space could have been magnetized by outflows or galactic superwinds even in the early universe. The Zeeman effect and polarization of sub-mm and mm emission can be used for the study of magnetic fields in some Galactic molecular clouds but it is observed only at high intensity. Both approaches together can clearly show the role that magnetic fields play in star formation and cloud structure, which in principle would be analogous to galaxy formation from protogalactic clouds. The origin of the cosmic magnetic fields is an active field of research. A primordial magnetic field has not been as yet directly detected, but its ⋆

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Radio Polarisation Studies of Galaxies at Z > 2

Cited by 48 publications

References 4 publications

Dominance of outflowing electric currents on decaparsec to kiloparsec scales in extragalactic jets

Dominance of outflowing electric currents on decaparsec to kiloparsec scales in extragalactic jets

Defying jet-gas alignment in two radio galaxies atz~ 2 with extended light profiles: Similarities to brightest cluster galaxies

Milestones in the Observations of Cosmic Magnetic Fields

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