Artículos de revistas
Hubble Space Telescope and Spitzer point-source detection and optical extinction in powerful narrow-line radio galaxies
Fecha
2014Registro en:
Monthly Notices of the Royal Astronomical Society, Oxford, v. 439, p. 1270-1285, 2014
0035-8711
10.1093/mnras/stt2444
Autor
Alonso, Edgar Andre Ramirez
Tadhunter, C. N.
Dicken, D.
Rose, M.
Axon, D.
Sparks, W.
Packham, C.
Institución
Resumen
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