264 research outputs found
High redshift radio galaxies
There is considerable evidence that powerful radio quasars and radio galaxies
are orientation-dependent manifestations of the same parent population: massive
spheroids containing correspondingly massive black holes. Following the
recognition of this unification, research is directed to the task of
elucidating the structure and composition of the active nuclei and their hosts
to understand the formation and evolution of what we expect to become the most
massive of galaxies. In contrast to the quasars, where the nucleus can outshine
the galaxy at optical/near infrared wavelengths by a large factor, the radio
galaxies contain a 'built-in coronograph' that obscures our direct view to the
nucleus. These objects present our best opportunity to study the host galaxy in
detail. Of particular interest are those sources with redshifts greater than
about 2 that represent an epoch when nuclear activity was much more common that
it is now and when we believe these objects were in the process of assembly. In
combination with high resolution imaging from space (HST), optical
spectropolarimetry with Keck II allows us to clearly separate the scattered
nuclear radiation from the stellar and gaseous emission from the host galaxy.
The rest-frame ultraviolet emission line spectra suggest that rapid chemical
evolution is occurring at this epoch. Near infrared spectroscopy with the VLT
is giving us access to both the lines and continuum in the rest-frame optical
spectrum, allowing investigations of the evolved stellar population and
extending the composition analysis with measurements of the familiar
forbidden-line spectrum.Comment: 7 pages including 2 figures. Paper no. 4005-10 in the proceedings of
the SPIE International Symposium on 'Astronomical Telescopes and
Instrumentation' held in Munich, Germany from 27-31 March 200
Polarized Broad H-alpha Emission from the LINER Nucleus of NGC 1052
Optical spectropolarimetry of the nucleus of the LINER NGC 1052, obtained at
the Keck Observatory, reveals a rise in polarization in the wings of the
H-alpha line profile. The polarization vector of H-alpha is offset by 67
degrees from the parsec-scale radio axis and by 83 degrees from the
kiloparsec-scale radio axis, roughly in accord with expectations for scattering
within the opening cone of an obscuring torus. The broad component of H-alpha
has FWHM ~ 2100 km/s in total flux and FWHM ~ 5000 km/s in polarized light.
Scattering by electrons is the mechanism most likely responsible for this
broadening, and we find T_e ~ 10^5 K for the scattering medium, similar to
values observed in Seyfert 2 nuclei. This is the first detection of a polarized
broad emission line in a LINER, demonstrating that unified models of active
galactic nuclei are applicable to at least some LINERs.Comment: 6 pages, 2 figures, prepared using the emulateapj style file,
accepted for publication in The Astrophysical Journal Letter
HST Observations and Photoionization Modeling of the LINER Galaxy NGC 1052
We present a study of available Hubble Space Telescope (HST) spectroscopic
and imaging observations of the low ionization nuclear emission line region
(LINER) galaxy NGC 1052. The WFPC2 imagery clearly differentiates extended
nebular Halpha emission from that of the compact core. Faint Object
Spectrograph (FOS) observations provide a full set of optical and UV data
(1200-6800 Angstroms).
These spectral data sample the innermost region (0."86 x 0."86 ~ 82pc x 82pc)
and exclude the extended Halpha emission seen in the WFPC2 image. The derived
emission line fluxes allow a detailed analysis of the physical conditions
within the nucleus. The measured flux ratio for Halpha/Hbeta,
F{Halpha}/F{Hbeta}=4.53, indicates substantial intrinsic reddening,
E(B-V)=0.42, for the nuclear nebular emission. This is the first finding of a
large extinction of the nuclear emission line fluxes in NGC 1052. If the
central ionizing continuum is assumed to be attenuated by a comparable amount,
then the emission line fluxes can be reproduced well by a simple
photoionization model using a central power law continuum source with a
spectral index of alpha = -1.2 as deduced from the observed flux distribution.
A multi-density, dusty gas gives the best fit to the observed emission line
spectrum. Our calculations show that the small contribution from a highly
ionized gas observed in NGC 1052 can also be reproduced solely by
photoionization modeling. The high gas covering factor determined from our
model is consistent with the assumption that our line of sight to the central
engine is obscured.Comment: 23 pages, 7 Postscript figures, 1 jpeg figure ; uses aaspp4.sty, 11pt
to appear in The Astrophysical Journa
Jet-gas interactions in z~2.5 radio galaxies: evolution of the ultraviolet line and continuum emission with radio morphology
We present an investigation into the nature of the jet-gas interactions in a
sample of 10 radio galaxies at 2.3<z<2.9 using deep spectroscopy of the UV line
and continuum emission obtained at Keck II and the Very Large Telescope.
Kinematically perturbed gas, which we have shown to be within the radio
structure in previous publications, is always blueshifted with respect to the
kinematically quiescent gas, is usually spatially extended, and is usually
detected on both sides of the nucleus. In the three objects from this sample
for which we are able to measure line ratios for both the perturbed and
quiescent gases, we suggest that the former has a lower ionization state than
the latter.
We propose that the perturbed gas is part of a jet-induced outflow, with dust
obscuring the outflowing gas that lies on the far side of the object. The
spatial extent of the blueshifted perturbed gas, typically ~35 kpc, implies
that the dust is spatially extended at least on similar spatial scales.
We also find interesting interrelationships between UV line, UV continuum and
radio continuum properties of this sample.Comment: Accepted for publication in MNRA
Radio jet interactions in the radio galaxy PKS 2152-699
We present radio observations of the radio galaxy PKS 2152-699 obtained with
the Australia Telescope Compact Array (ATCA). The much higher resolution and
s/n of the new radio maps reveals the presence of a bright radio component
about 10 arcsec NE of the nucleus. This lies close to the highly ionized cloud
previously studied in the optical and here shown in a broadband red snapshot
image with the HST PC2. It suggests that PKS 2152-699 may be a jet/cloud
interaction similar to 3C277.3. This could cause the change in the position
angle (of ~20 deg) of the radio emission from the inner to the outer regions.
On the large scale, the source has Fanaroff & Riley type II morphology although
the presence of the two hot-spots in the centres of the lobes is unusual. The
northern lobe shows a particularly relaxed structure while the southern one has
an edge-brightened, arc-like structure.Comment: 7 pages, 5 encapsulated figures, 1 JPEG figure, accepted for MNRA
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