236 research outputs found
Models relating the radio emission and ionised gas in Seyfert nuclei
Possible models are discussed in which the radio emitting components in Seyfert II nuclei can compress and accelerate the ambient nuclear medium to produce the characteristics of the narrow line region. A first order model, which considers only the expansion of the radio components, is briefly described. However, in many Seyfert nuclei it appears that the linear motion of the radio components is also important. This can result in shock heating of the ambient medium, and if the cooling time is long enough, can lead to a displacement between the radio component and the associated emission lines. This effect may be present in NGC 1068 and NGC 5929 and by considering ram pressure balance and the cooling length it is possible to estimate lobe velocities and ambient densities
HST and Spitzer point source detection and optical extinction in powerful narrow-line radio galaxies
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 1.025m, to 80 per cent at 2.05m, and to 100 per cent at 8.0m.
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 9.7m
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.Comment: 18 pages, 7 figures, 8 tables, accepted for publication in MNRA
Kinematics of ionized gas associated with the radio nucleus and lobes in the active galaxy IRAS 04210+0400
We have used high resolution longslit spectroscopy to investigate the ionized
gas in the active galaxy IRAS 04210+0400 and its association with the radio
structure.
We suggest that two of the ionized components are associated with the central
double radio source and observe that the relative positions of these components
vary for different emission lines. Both results are consistent with the radio
components representing the working surfaces of a pair of jets emerging from
the centre of the galaxy. In this scenario, the optical emission in the centre
arises behind the bowshocks produced by the jets in the interstellar medium.
The emission lines are detected and show a dramatic (~ 900 km/s) spread in
velocity at the position of the radio lobe hotspots. We suggest a model which
explains this phenomenon as the result of a jet head emerging through the
boundary between the interstellar and intergalactic medium. A similar scenario
has previously been suggested as a model to explain wide angle tail radio
sources (WAT's). Based on this model, we simulate the longslit spectra of these
regions and compare the results with the observations.Comment: Latex format, 12 pages, 6 figures included, to appear in MNRAS. Also
available as Postscript with figures at
http://axp2.ast.man.ac.uk:8000/Preprints.htm
HST FOC spectroscopy of the NLR of NGC 4151. I. Gas kinematics
We present the results from a detailed kinematic analysis of both
ground-based, and Hubble Space Telescope/Faint Object Camera long-slit
spectroscopy at sub-arcsec spatial resolution, of the narrow-line region of NGC
4151. In agreement with previous work, the extended emission gas (R > 4") is
found to be in normal rotation in the galactic plane, a behaviour that we were
able to trace even across the nuclear region, where the gas is strongly
disturbed by the interaction with the radio jet, and connects smoothly with the
large scale rotation defined by the neutral gas emission. The HST data, at
0.029" spatial resolution, allow us for the first time to truly isolate the
kinematic behaviour of the individual clouds in the inner narrow-line region.
We find that, underlying the perturbations introduced by the radio ejecta, the
general velocity field can still be well represented by planar rotation down to
a radius of ~ 0.5" (30 pc), distance at which the rotation curve has its
turnover.
The most striking result that emerges from our analysis is that the galaxy
potential derived fitting the rotation curve changes from a "dark halo" at the
ENLR distances to dominated by the central mass concentration in the NLR, with
an almost Keplerian fall-off in the 1"< R < 4" interval. The observed velocity
of the gas at 0.5" implies a mass of M ~ 10E9 M(sol) within the inner 60 pc.
The presence of a turnover in the rotation curve indicates that this central
mass concentration is extended. The first measured velocity point (outside the
region saturated by the nucleus) would imply an enclosed mass of ~ 5E7 M(sol)
within R ~ 0.15" (10 pc) which represents an upper limit to any nuclear point
mass.Comment: 30 pages (aaspp4.sty), 14 figures. Fig. 1, 2 and 4 available by
anonymous FTP at 143.54.2.51 (cd /pub/winge) as GIF files; or upon request to
[email protected]. Accepted for publication in the Astrophysical Journal
(part 1
Polarimetry and the High-Energy Emission Mechanisms in Quasar Jets
The emission mechanisms in extragalactic jets include synchrotron and various
inverse-Compton processes. At low (radio through infrared) energies, it is
widely agreed that synchrotron emission dominates in both low-power (FR I) and
high-power (FR II and quasar) jets, because of the power-law nature of the
spectra observed and high polarizations. However, at higher energies, the
emission mechanism for high-power jets at kpc scales is hotly debated. Two
mechanisms have been proposed: either inverse-Compton of cosmic microwave
background photons or synchrotron emission from a second, high-energy
population of electrons. Here we discuss optical polarimetry as a method for
diagnosing the mechanism for the high-energy emission in quasar jets, as well
as revealing the jet's three-dimensional energetic and magnetic field
structure. We then discuss high-energy emission mechanisms for powerful jets in
the light of the HST polarimetry of PKS 1136-135.Comment: 4 pages, 1 figure. To appear in proceedings of "The Monster's Fiery
Breath: Feedback in galaxies, groups, and clusters" meeting, June 1-5, 2009
held in Madison, WI, US
Pressure Dependence of the Elastic Moduli in Aluminum Rich Al-Li Compounds
I have carried out numerical first principles calculations of the pressure
dependence of the elastic moduli for several ordered structures in the
Aluminum-Lithium system, specifically FCC Al, FCC and BCC Li, L1_2 Al_3Li, and
an ordered FCC Al_7Li supercell. The calculations were performed using the full
potential linear augmented plane wave method (LAPW) to calculate the total
energy as a function of strain, after which the data was fit to a polynomial
function of the strain to determine the modulus. A procedure for estimating the
errors in this process is also given. The predicted equilibrium lattice
parameters are slightly smaller than found experimentally, consistent with
other LDA calculations. The computed elastic moduli are within approximately
10% of the experimentally measured moduli, provided the calculations are
carried out at the experimental lattice constant. The LDA equilibrium shear
modulus C11-C12 increases from 59.3 GPa in Al, to 76.0 GPa in Al_7Li, to 106.2
GPa in Al_3Li. The modulus C_44 increases from 38.4 GPa in Al to 46.1 GPa in
Al_7Li, then falls to 40.7 GPa in Al_3Li. All of the calculated elastic moduli
increase with pressure with the exception of BCC Li, which becomes elastically
unstable at about 2 GPa, where C_11-C_12 vanishes.Comment: 17 pages (REVTEX) + 7 postscript figure
The NICMOS Snapshot Survey of nearby Galaxies
We present ``snapshot'' observations with the NearInfrared Camera and
MultiObject Spectrometer (NICMOS) on board the Hubble Space Telescope (HST) of
94 nearby galaxies from the Revised Shapley Ames Catalog. Images with 0.2 as
resolution were obtained in two filters, a broad-band continuum filter (F160W,
roughly equivalent to the H-band) and a narrow band filter centered on the
Paschen alpha line (F187N or F190N, depending on the galaxy redshift) with the
51x51 as field of view of the NICMOS camera 3. A first-order continuum
subtraction is performed, and the resulting line maps and integrated Paschen
alpha line fluxes are presented. A statistical analysis indicates that the
average Paschen alpha surface brightness {\bf in the central regions} is
highest in early-type (Sa-Sb) spirals.Comment: Original contained error in flux calibration. Table 1 now has correct
Paschen Alpha fluxes. 14 pages LaTeX with JPEG and PS figures. Also available
at http://icarus.stsci.edu/~boeker/publications.htm
Chandra Observations of 3C Radio Sources with z<0.3: Nuclei, Diffuse Emission, Jets and Hotspots
We report on our Chandra Cycle 9 program to observe half of the 60
(unobserved by Chandra) 3C radio sources at z<0.3 for 8 ksec each. Here we give
the basic data: the X-ray intensity of the nuclei and any features associated
with radio structures such as hot spots and knots in jets. We have measured
fluxes in soft, medium and hard bands and are thus able to isolate sources with
significant intrinsic column density. For the stronger nuclei, we have applied
the standard spectral analysis which provides the best fit values of X-ray
spectral index and column density. We find evidence for intrinsic absorption
exceeding a column density of 10^{22} cm^{-2} for one third of our sources.Comment: 12 pages, 37 figures (the complete version of the paper with all
figures is available on line, see appendix for details), ApJ accepte
Challenges in the Analysis of Historic Concrete:Understanding the Limitations of Techniques, the Variability of the Material and the Importance of Representative Samples
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