The optical polarizations of high- and intermediate-redshift radio galaxies

Tadhunter, C. N.; Scarrott, S. M.; Draper, P. W.; Rolph, C. D.

doi:10.1093/mnras/256.1.53p

Cited by 74 publications

(71 citation statements)

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“…shown that the rest-frame UV/optical/IR emission coming from the off-nuclear locations is substantially polarized perpendicular to the radio axis, as expected in the obscuring torus scenario (56)(57)(58). The prototypical NLRG, Cygnus A, has now been clearly shown to harbor a QSR nucleus, both from the detection of (scattered) BLR in the rest-frame UV (59) and from the expected polarization behavior of the optical emission in the lobes on both sides of the dust lane (56).…”

Section: The Origin Of the Aspect Dependencesupporting

confidence: 62%

“…The prototypical NLRG, Cygnus A, has now been clearly shown to harbor a QSR nucleus, both from the detection of (scattered) BLR in the rest-frame UV (59) and from the expected polarization behavior of the optical emission in the lobes on both sides of the dust lane (56). Further, in some nearby NLRGs, it was found that while the optical emission is polarized perpendicular to the radio axis in the off-nuclear regions, the polarization becomes parallel to the radio axis near the nucleus (60); such a nuclear polarization can be readily understood in terms of multiple scattering through a torus whose axis is roughly aligned with the radio source.…”

Section: The Origin Of the Aspect Dependencementioning

confidence: 99%

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The case for unification.

Gopal-Krishna

1995

Proc. Natl. Acad. Sci. U.S.A.

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I investigate the issue of whether the various subclasses of radio-loud galaxies are intrinsically the same but have been classified differently mainly due to their being viewed from different directions. Evidence for the two key elements of this popular version of the "unified scheme (US)," relativistic jets and nuclear tori, is updated. The case for the torus opening angle increasing with the radio luminosity of the active galactic nucleus (AGN) is freshly argued. Radio-loud AGN are particularly suited for testing the US, since their structures and polarization properties on different scales, as well as their overall radio sizes, provide useful statistical indicators of the relative orientations of their various subclasses. I summarize recent attempts to bring under a single conceptual framework the USs developed for radio-moderate [Fanaroff-Riley type I (FRI)] and radio-powerful (FRII) AGN. Bytocusing on FRII radio sources, I critically examine the recent claims of conflict with the US, based on the statistics of radio-size measurements for large, presumably orientation-independent, samples with essentially complete optical identifications. Possible ways of reconciling these results, and also the ones based on very-long-baseline radio interferometry polarimetric observations, with the US are pointed out. By incorporating a highly plausible temporal evolution of radio source properties into the US, I outline a scenario that allows the median linear size of quasars to approach, or even exceed, that of radio galaxies, as samples with decreasing radio luminosity are observed. Thus, even though a number of issues remain to be fully resolved, the scope of unified models continues to expand.

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Section: The Origin Of the Aspect Dependencesupporting

confidence: 62%

Section: The Origin Of the Aspect Dependencementioning

confidence: 99%

The case for unification.

Gopal-Krishna

1995

Proc. Natl. Acad. Sci. U.S.A.

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“…Scattered light of the QSO owing to large amounts of dust within the host could significantly contribute to the apparent host light in rest-frame blue and UV bands (e.g. Tadhunter et al 1992;Zakamska et al 2006). We therefore looked at the GALEX UV images of the Medium Imaging Survey for HE 2158−0107.…”

Section: An Sed-based Stellar Mass Estimatementioning

confidence: 99%

The low-metallicity QSO HE 2158 − 0107: a massive galaxy growing by accretion of nearly pristine gas from its environment?

Wisotzki

Jahnke

Sánchez

2011

A&A

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The metallicities of active galactic nuclei (AGN) are usually well above solar in their narrow-line regions, often reaching up to several times solar in their broad-line regions independent of redshift. Low-metallicity AGN are rare objects that have so far always been associated with low-mass galaxies hosting low-mass black holes (M BH 10 6 M ). We present integral field spectroscopy data of the low-redshift (z = 0.212) quasi-stellar object (QSO) HE 2158−0107 for which we find strong evidence of sub-solar NLR metallicities associated with a massive black hole (M BH ∼ 3 × 10 8 M ). The QSO is surrounded by a large extended emission-line region reaching out to 30 kpc from the QSO in a tail-like geometry. We present optical and near-infrared images and investigate the properties of the host galaxy. The host of HE 2158−0107 is most likely a very compact bulge-dominated galaxy with a size of r e ∼ 1.4 kpc. The multi-colour spectral energy distribution (SED) of the host is quite blue, indicative of a significant young age stellar population formed within the last 1 Gyr. A 3σ upper limit of L bulge,H < 4.5 × 10 10 L ,H for the H-band luminosity and a corresponding stellar mass upper limit of M bulge < 3.4 × 10 10 M show that the host is offset from the local black hole-bulge relations. This is independently supported by the kinematics of the gas. Although the stellar mass of the host galaxy is lower than expected, it cannot explain the exceptionally low metallicity of the gas. We suggest that the extended emission-line region and the galaxy growth are caused by the infall of nearly pristine gas from the environment of the QSO host. Minor mergers of low-metallicity dwarf galaxies or the theoretically predicted smooth accretion of cold (∼ 10 4 K) gas are both potential drivers behind that process. Because the metallicity of the gas in the QSO narrow-line region is much lower than expected, we suspect that the external gas has already reached the galaxy centre and may even contribute to the current feeding of the black hole. HE 2158−0107 appears to represent a particular phase of substantial black hole and galaxy growth that can be observationally linked with the accretion of external material from its environment.

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“…These form a representative sample of the different morphologies present in this redshift band: 3C 22 and 3C 41 are bright and appear pointlike; 3C 114 and 3C 356 display complex knotted morphologies with large scale alignments between the K-band structure and the radio axis; 3C 54, 3C 65 and 3C 441 are faint sources with some indication of K-band structure. Of these three faint sources, 3C 54 displays an alignment between the K-band morphology and the radio axis (Dunlop & Peacock 1993), 3C 65 shows no preferred direction in its H-band structure (Rigler & Lilly 1994), and 3C 441 has a broad-band optical polarization which is roughly perpendicular to its radio structure (Tadhunter et al 1992). Table 1 lists the sources observed with their redshifts and the rest-frame wavelength of the observed light.…”

Section: Our Samplementioning

confidence: 99%

K-band polarimetry of seven high-redshift radio galaxies

Leyshon

Eales

1998

Monthly Notices of the Royal Astronomical Society

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We present the results of K-band imaging polarimetry of seven 3CR radio galaxies with 0.7 < z < 1.2. We find strong evidence for polarization in three sources: 3C 22, 3C 41 and 3C 114. Of these, 3C 41 shows strong evidence of having a quasar core whose infrared light is scattered by dust. We also find some evidence for polarization in 3C 54 and in 3C 356. The two pointlike sources (3C 22 and 3C 41) and the barely-elongated 3C 54 appear to have of order ten per cent of their K-band flux contributed by scattered light from the active nucleus. We conclude that scattered nuclear light can form a significant component of the near-infrared light emitted by high-redshift radio galaxies, and discuss models in which the scattering particles are electrons and dust-grains.

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The optical polarizations of high- and intermediate-redshift radio galaxies

Cited by 74 publications

References 0 publications

The case for unification.

The case for unification.

The low-metallicity QSO HE 2158 − 0107: a massive galaxy growing by accretion of nearly pristine gas from its environment?

K-band polarimetry of seven high-redshift radio galaxies

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