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  • 1
    Electronic Resource
    Electronic Resource
    A blue, polarized continuum source near radio galaxy PKS2152–69 (1988)
    [s.l.] : Nature Publishing Group
    Nature 334 (1988), S. 591-593 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The radio galaxy PKS2152-69 is characterized by z = 0.028, P5GHz = 5 x 1025 WHz-1 with H0 = 50kms-1 Mpc-1. The continuum fluxes were measured on images taken with the CCD camera at the 2.2-m ESO/Max-Planck-Gesellschaft telescope on La Silla, Chile, through medium-broad band filters avoiding the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/334591a0
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Detached nuclear-like activity in the radio galaxy PKS 2152–69 (1987)
    [s.l.] : Nature Publishing Group
    Nature 325 (1987), S. 504-507 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The presence of regions of ionized gas at distances ranging from a few to a hundred or so kiloparsecs (extended emission line regions-EELRs) from the nuclei of a significant fraction of radio galaxies and quasars is now well established and the current status of the observational studies has been ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/325504a0
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  • 3
    Electronic Resource
    Electronic Resource
    Polarized light in high-redshift radio galaxies (1989)
    [s.l.] : Nature Publishing Group
    Nature 341 (1989), S. 307-309 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Ultraviolet excesses are an ubiquitous feature of high-redshift radio galaxies1'2. Attempts to understand this excess have centred on star formation models, although it has been difficult to explain the ultraviolet-optical and optical-infrared colours simultaneously in the framework of galaxy ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/341307a0
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  • 4
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    On the nature of the red, 2MASS-selected AGN in the local Universe I: an optical spectroscopic study (2013)
    Oxford University Press
    Details
    Publication Date: 2013-06-09
    Description: We present optical spectra for a representative sample of 27 nearby ( z  〈 0.2) Two Micron All Sky Survey (2MASS)-selected active galactic nuclei (AGN) with red near-infrared colours ( J  – K S 2.0). The spectra were taken with the ISIS spectrograph on the William Herschel Telescope with the aim of determining the nature of the red 2MASS AGN, in particular whether they are young quasars obscured by their natal cocoons of gas and dust. We compare our findings with those obtained for comparison samples of PG quasars and unobscured type 1 AGN. The spectra show a remarkable variety, including moderately reddened type 1 objects (45 per cent), type 1 objects that appear similar to traditional ultraviolet (UV)-/optical-selected AGN (11 per cent), narrow-line type 1 Seyfert AGN (15 per cent), type 2 AGN (22 per cent) and H ii /composite objects (7 per cent). The high Balmer decrements that we measure in many of the type 1 objects are consistent with their red J  – K S colours being due to moderate levels of dust extinction (0.2 〈 E ( B  – V ) 〈 1.2). However, we measure only modest velocity shifts and widths for the broader [O iii ]5007 emission-line components that are similar to those measured in the comparison samples. This suggests that the outflows in the red 2MASS objects are not unusual compared with those of optical-/UV-selected AGN of similar luminosity. In addition, the Eddington ratios for the 2MASS sample are relatively modest. Overall, based on their optical spectra, we find no clear evidence that the population of red, 2MASS-selected AGN at low redshifts represents young quasars. Most plausibly, these objects are normal type 1 AGN that are moderately obscured by material in the outer layers of the circumnuclear tori or in the discs of the host galaxies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Upholding the unified model for active galactic nuclei: VLT/FORS2 spectropolarimetry of Seyfert 2 galaxies (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-06
    Description: The origin of the unification model for active galactic nuclei (AGN) was the detection of broad hydrogen recombination lines in the optical polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden broad-line region (HBLR) of nearby Sy2s started, but polarized broad lines have only been detected in ~30–40 per cent of the nearby Sy2s observed to date. Here we present new VLT/FORS2 optical spectropolarimetry of a sample of 15 Sy2s, including Compton-thin and Compton-thick sources. The sample includes six galaxies without previously published spectropolarimetry, some of them normally treated as non-hidden BLR (NHBLR) objects in the literature, four classified as NHBLR, and five as HBLR based on previous data. We report ≥4 detections of a HBLR in 11 of these galaxies (73 per cent of the sample) and a tentative detection in NGC 5793, which is Compton-thick according to the analysis of X-ray data performed here. Our results confirm that at least some NHBLRs are misclassified, bringing previous publications reporting differences between HBLR and NHBLR objects into question. We detect broad Hα and Hβ components in polarized light for 10 targets, and just broad Hα for NGC 5793 and NGC 6300, with line widths ranging between 2100 and 9600 km s –1 . High bolometric luminosities and low column densities are associated with higher polarization degrees, but not necessarily with the detection of the scattered broad components.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    CO(1-0) survey of high-z radio galaxies: alignment of molecular halo gas with distant radio sources (2014)
    Oxford University Press
    Details
    Publication Date: 2014-02-20
    Description: We present a CO(1–0) survey for cold molecular gas in a representative sample of 13 high- z radio galaxies (HzRGs) at 1.4 〈 z 〈 2.8, using the Australia Telescope Compact Array. We detect CO(1–0) emission associated with five sources: MRC 0114-211, MRC 0152-209, MRC 0156-252, MRC 1138-262 and MRC 2048-272. The CO(1–0) luminosities are in the range $L^{\prime }_{\rm CO} \sim (5\hbox{--}9) \times 10^{10}$ K km s –1 pc 2 . For MRC 0152-209 and MRC 1138-262, part of the CO(1–0) emission coincides with the radio galaxy, while part is spread on scales of tens of kpc and likely associated with galaxy mergers. The molecular gas mass derived for these two systems is M H2  ~ 6 10 10 M ( M H2 / $L^{\prime }_{\rm CO}$  = 0.8). For the remaining three CO-detected sources, the CO(1–0) emission is located in the halo (~50-kpc) environment. These three HzRGs are among the fainter far-IR emitters in our sample, suggesting that similar reservoirs of cold molecular halo gas may have been missed in earlier studies due to pre-selection of IR-bright sources. In all three cases, the CO(1–0) is aligned along the radio axis and found beyond the brightest radio hotspot, in a region devoid of 4.5 μm emission in Spitzer imaging. The CO(1–0) profiles are broad, with velocity widths of ~1000–3600 km s –1 . We discuss several possible scenarios to explain these halo reservoirs of CO(1–0). Following these results, we complement our CO(1–0) study with detections of extended CO from the literature and find at marginal statistical significance (95 per cent level) that CO in HzRGs is preferentially aligned towards the radio jet axis. For the eight sources in which we do not detect CO(1–0), we set realistic upper limits of $L^{\prime }_{\rm CO} \sim 3\hbox{--}4 \times 10^{10}$ K km s –1 pc 2 . Our survey reveals a CO(1–0) detection rate of 38 per cent, allowing us to compare the CO(1–0) content of HzRGs with that of other types of high- z galaxies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Near-infrared Hubble Space Telescope polarimetry of a complete sample of narrow-line radio galaxies (2014)
    Oxford University Press
    Details
    Publication Date: 2014-08-20
    Description: We present an analysis of 2.05 μm Hubble Space Telescope polarimetric data for a sample of 13 nearby Fanaroff–Riley type II (FRII) 3CR radio sources (0.03 〈  z  〈 0.11) that are classified as narrow-line radio galaxies (NLRG) at optical wavelengths. We find that the compact cores of the NLRG in our sample are intrinsically highly polarized in the near-infrared (near-IR) (6 〈 P 2.05 μm 〈 60 per cent), with the electric vector (E-vector) perpendicular to the radio axis in 54 per cent of the sources. The levels of extinction required to produce near-IR polarization by the dichroic extinction mechanism are consistent with the measured values recently reported in Ramírez et al., provided that this mechanism has its maximum efficiency. This consistency suggests that the nuclear polarization could be due to dichroic extinction. In this case, toroidal magnetic fields that are highly coherent would be required in the circumnuclear tori to align the elongated dust grains responsible for the dichroic extinction. However, it is not entirely possible to rule out other polarization mechanisms (e.g. scattering, synchrotron emission) with our observations at only one near-IR wavelength. Therefore, further polarimetry observations at mid-IR and radio wavelengths will be required to test whether all the near-IR polarization is due to dichroic extinction.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    No evidence for large-scale outflows in the extended ionized halo of ULIRG Mrk273 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-05
    Description: We present deep new Gran Telescopio Canarias (GTC) narrow-band images and William Herschel Telescope (WHT) long-slit spectroscopy of the merging system Mrk273 that show a spectacular extended halo of warm ionized gas out to a radius of ~45 kpc from the system nucleus. Outside of the immediate nuclear regions ( r 〉 6 kpc), there is no evidence for kinematic disturbance in the ionized gas: in the extended regions covered by our spectroscopic slits the emission lines are relatively narrow (full width at half-maximum, FWHM 350 km s –1 ) and velocity shifts small (| V | 250 km s –1 ). This is despite the presence of powerful near-nuclear outflows (FWHM 〉 1000 km s –1 ; | V | 〉 400 km s –1 ; r 〈 6 kpc). Diagnostic ratio plots are fully consistent with Seyfert 2 photoionization to the NE of the nuclear region, however to the SW the plots are more consistent with low-velocity radiative shock models. The kinematics of the ionized gas, combined with the fact that the main structures are aligned with low-surface-brightness tidal continuum features, are consistent with the idea that the ionized halo represents tidal debris left over from a possible triple-merger event, rather than a reservoir of outflowing gas.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    The importance of warm, AGN-driven outflows in the nuclear regions of nearby ULIRGs (2013)
    Oxford University Press
    Details
    Publication Date: 2013-05-21
    Description: We present an optical spectroscopic study of a 90 per cent complete sample of nearby ULIRGs ( z  〈 0.175) with optical Seyfert nuclei, with the aim of investigating the nature of the near-nuclear ( r 3.5 kpc) warm gas outflows. A high proportion (94 per cent) of our sample show disturbed emission line kinematics in the form of broad (FWHM 〉 500 km s –1 ) and/or strongly blueshifted ( V  〈 –150 km s –1 ) emission line components. This proportion is significantly higher than found in a comparison sample of nearby ultraluminous infrared galaxies (ULIRGs) that lack optical Seyfert nuclei (19 per cent). We also find evidence that the emission line kinematics of the Sy-ULIRGs are more highly disturbed than those of samples of non-ULIRG Seyferts and Palomar–Green quasars in the sense that, on average, their [O iii ] 5007, 4959 emission lines are broader and more asymmetric. The Sy-ULIRG sample encompasses a wide diversity of emission line profiles. In most individual objects, we are able to fit the profiles of all the emission lines of different ionization with a kinematic model derived from the strong [O iii ] 4959, 5007 lines, using between two and five Gaussian components. From these fits, we derive diagnostic line ratios that are used to investigate the ionization mechanisms for the different kinematic components. We show that, in general, the line ratios are consistent with gas of supersolar abundance photoionized by a combination of AGN and starburst activity, with an increasing contribution from the AGN with increasing FWHM of the individual kinematic components, and the AGN contribution dominating for the broadest components. However, shock ionization cannot be ruled out in some cases. Our derived upper limits on the mass outflows rates and kinetic powers of the emission line outflows show that they can be as energetically significant as the neutral and molecular outflows in ULIRGs – consistent with the requirements of the hydrodynamic simulations that include AGN feedback. However, the uncertainties are large, and more accurate estimates of the radii, densities and reddening of the outflows are required to put these results on a firmer footing.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Hubble Space Telescope and Spitzer point-source detection and optical extinction in powerful narrow-line radio galaxies (2014)
    Oxford University Press
    Details
    Publication Date: 2014-03-09
    Description: We present an analysis of infrared Hubble Space Telescope ( HST ) and Spitzer data for a sample of 13 Fanaroff–Riley II (FRII) radio galaxies at 0.03 〈  z  〈 0.11 that are classified as narrow-line radio galaxies (NLRGs). In the context of unified schemes for active galactic nuclei (AGNs), our direct view of AGNs in NLRGs is impeded by a parsec-scale dusty torus structure. Our high-resolution infrared observations provide new information about the degree of extinction resulting from the torus, and about the incidence of obscured AGNs in NLRGs. We find that the point-like nucleus detection rate increases from 25 per cent at 1.025 μm, to 80 per cent at 2.05 μm, and to 100 per cent at 8.0 μm. This supports the idea that most NLRG host an obscured AGN in their centre. We estimate the extinction from the obscuring structures using X-ray, near-IR and mid-IR data. We find that the optical extinction derived from the 9.7 μm silicate absorption feature is consistently lower than the extinction derived using other techniques. This discrepancy challenges the assumption that all the mid-infrared emission of NLRG is extinguished by a simple screen of dust at larger radii. This disagreement can be explained in terms of either weakening of the silicate absorption feature by (i) thermal mid-IR emission from the narrow-line region, (ii) non-thermal emission from the base of the radio jets, or (iii) by direct warm dust emission that leaks through a clumpy torus without suffering major attenuation.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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