HST and Spitzer point source detection and optical extinction in powerful narrow-line radio galaxies

Abstract

We present the analysis of infrared HST and Spitzer data for a sample of 13 FRII radio galaxies at 0.03<z<0.11 that are classified as narrow-line radio galaxies (NLRG). In the context of the unified schemes for active galactic nuclei (AGN), our direct view of the AGN in NLRG is impeded by a parsec-scale dusty torus structure. Our high resolution infrared observations provide new information about the degree of extinction induced by the torus, and the incidence of obscured AGN in NLRG. We find that the point-like nucleus detection rate increases from 25 per cent at 1.025$\mu$m, to 80 per cent at 2.05$\mu$m, and to 100 per cent at 8.0$\mu$m. 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$\mu$m 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.

18 pages, 7 figures, 8 tables, accepted for publication in MNRAS

References in corpus (31)

• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• Detailed Structural Decomposition of Galaxy Images
• The Mid-Infrared Spectrum of Star-Forming Galaxies: Global Properties of PAH Emission
• The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 microns Using GLIMPSE Data
• Dust Emission from Active Galactic Nuclei
• An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. II. Spectroscopic classes and accretion modes in radio-loud AGN
• Three-dimensional radiative transfer models of clumpy tori in Seyfert galaxies
• The active nuclei of z<1.0 3CRR radio sources
• The X-ray nuclei of intermediate-redshift radio sources
• The Detection of Silicate Emission from Quasars at 10 and 18 Microns
• Testing the Unification Model for AGN in the Infrared: are the obscuring tori of Type 1 and 2 Seyferts different?
• Chandra and XMM-Newton Observations of a Sample of Low-Redshift FRI and FRII Radio-Galaxy Nuclei
• 9.7 um Silicate Features in AGNs: New Insights into Unification Models
• An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. I. Presentation of the data
• Are luminous radio-loud active galactic nuclei triggered by galaxy interactions?
• Observed properties of FRII quasars and radio galaxies at z < 1.0
• Spitzer mid-IR spectroscopy of powerful 2Jy and 3CRR radio galaxies. I. Evidence against a strong starburst-AGN connection in radio-loud AGN
• Understanding the nature of FRII optical nuclei: a new diagnostic plane for radio galaxies
• A Chandra X-ray Study of Cygnus A - II. The Nucleus
• Complete Multiwavelength Characterization of Faint Chandra X-ray Sources Seen in the Spitzer Wide-Area IR Extragalactic (SWIRE) Survey
• Hubble Space Telescope Near-Infrared Snapshot Survey of 3CR radio source counterparts at low redshift
• The Spitzer view of FR-I radio galaxies: on the origin of the nuclear mid-infrared continuum
• A Radio Through X-ray Study of the Jet/Companion-Galaxy Interaction in 3C 321
• The 1.6 micron near infrared nuclei of 3C radio galaxies: Jets, thermal emission or scattered light?
• The origin of the infrared emission in radio galaxies I: new mid- to far-infrared and radio observations of the 2Jy sample
• Dust tori in radio galaxies
• High-Resolution Mid-Infrared Morphology of Cygnus A
• The Mid-Infrared Spectral Energy Distribution, Surface Brightness and Color Profiles in Elliptical Galaxies
• XMM-Newton Observations of the Nuclei of the Radio Galaxies 3C 305, DA 240, and 4C 73.08
• Probing the nuclear obscuration in radio-galaxies with near infrared imaging
• The Nature of the Near-IR Core Source in 3C 433

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