432 research outputs found
A Spectropolarimetric Atlas of Seyfert 1 Galaxies
We present optical spectropolarimetry of the nuclei of 36 Seyfert 1 galaxies,
obtained with the William Herschel and the Anglo-Australian Telescopes from
1996 to 1999. In 20 of these, the optical emission from the active nucleus is
intrinsically polarized. We have measured a significant level of polarization
in a further 7 objects but these may be heavily contaminated by Galactic
interstellar polarization. The intrinsically polarized Seyfert 1s exhibit a
variety of characteristics, with the average polarization ranging from < 0.5 to
5 per cent and many showing variations in both the degree and position angle of
polarization across the broad H alpha emission line. We identify a small group
of Seyfert 1s that exhibit polarization properties similar to those of Seyfert
2 galaxies in which polarized broad-lines have been discovered. These objects
represent direct observational evidence that a Seyfert 2-like far-field polar
scattering region is also present in Seyfert 1s. Several other objects have
features that can be explained in terms of equatorial scattering of line
emission from a rotating disk. We propose that much of the diversity in the
polarization properties of Seyfert galaxies can be understood in terms of a
model involving both equatorial and polar scattering, the relative importance
of the two geometries as sources of polarized light being determined
principally by the inclination of the system axis to the line-of-sight.Comment: Accepted for publication in MNRAS (28 pages, 25 figures
Streaming Motions Towards the Supermassive Black Hole in NGC 1097
We have used GMOS-IFU and high resolution HST-ACS observations to map, in
unprecedented detail, the gas velocity field and structure within the 0.7 kpc
circumnuclear ring of the SBb LINER/Seyfert 1 galaxy NGC 1097. We find clear
evidence of radial streaming motions associated with spiral structures leading
to the unresolved (<3.5 parsecs) nucleus, which we interpret as part of the
fueling chain by which gas is transported to the nuclear starburst and
supermassive black hole.Comment: 4 pages, 3 figures using emulateapj. Accepted for publication in
Astrophysical Journal Letters. Download high-resolution version from
http://www.astro.uu.se/~kambiz/DOC/paper-N1097.pd
Occupational asthma: a review.
Occupational asthma is the most common form of occupational lung disease in the developed world at the present time. In this review, the epidemiology, pathogenesis/mechanisms, clinical presentations, management, and prevention of occupational asthma are discussed. The population attributable risk of asthma due to occupational exposures is considerable. Current understanding of the mechanisms by which many agents cause occupational asthma is limited, especially for low-molecular-weight sensitizers and irritants. The diagnosis of occupational asthma is generally established on the basis of a suggestive history of a temporal association between exposure and the onset of symptoms and objective evidence that these symptoms are related to airflow limitation. Early diagnosis, elimination of exposure to the responsible agent, and early use of inhaled steroids may play important roles in the prevention of long-term persistence of asthma. Persistent occupational asthma is often associated with substantial disability and consequent impacts on income and quality of life. Prevention of new cases is the best approach to reducing the burden of asthma attributable to occupational exposures. Future research needs are identified
Integral Field Spectroscopy of 23 Spiral Bulges
We have obtained Integral Field Spectroscopy for 23 spiral bulges using
INTEGRAL on the William Herschel Telescope and SPIRAL on the Anglo-Australian
Telescope. This is the first 2D survey directed solely at the bulges of spiral
galaxies. Eleven galaxies of the sample do not have previous measurements of
the stellar velocity dispersion (sigma*). These data are designed to complement
our Space Telescope Imaging Spectrograph program for estimating black hole
masses in the range 10^6-10^8M_sun using gas kinematics from nucleated disks.
These observations will serve to derive the stellar dynamical bulge properties
using the traditional Mgb and CaII triplets. We use both Cross Correlation and
Maximum Penalized Likelihood to determine projected sigma* in these systems and
present radial velocity fields, major axis rotation curves, curves of growth
and sigma* fields. Using the Cross Correlation to extract the low order 2D
stellar dynamics we generally see coherent radial rotation and irregular
velocity dispersion fields suggesting that sigma* is a non-trivial parameter to
estimate.Comment: 11 pages, 30 figures, accepted for publication in ApJ
Hubble Space Telescope Observations of NGC 6240: a Case Study of an Ultra-Luminous Infrared Galaxy with Obscured Activity
We present results from an HST study of the morphology and kinematics of NGC
6240. This merging galaxy with a double nucleus is one of the nearest and
best-studied ultraluminous infrared galaxies. HST resolves both nuclei into
seperate components. The distance between the northern and southern
optical/near-infrared components is greater than that observed in radio and
X-ray studies, arguing that even in K-band we may not be seeing all the way
through the dust to the true nuclei. The ionized gas does not display rotation
around either of the nuclei, or equilibrium motion in general. There is a
strong velocity gradient between the nuclei, similar to what is seen in CO
data. There is no such gradient in our stellar kinematics. The velocity
dispersion of the gas is larger than expected for a cold disk. We also map and
model the emission-line velocity field at an off-nuclear position where a steep
velocity gradient was previously detected in ground-based data. Overall, the
data indicate that line-of-sight projection effects, dust absorption,
non-equilibrium merger dynamics, and the possible influence of a wind may be
playing an important role in the observed kinematics. Chandra observations of
hard X-rays have shown that both of the nuclei contain an Active Galactic
Nucleus (AGN). The HST data show no clear sign of the two AGNs: neither
continuum nor narrow-band imaging shows evidence for unresolved components in
the nuclei, and there are no increased emission line widths or rapid rotation
near the nuclei. This underscores the importance of X-ray data for identifying
AGNs in highly dust-enshrouded environments.Comment: LaTeX, 32 pages, 9 figures, 2 tables, accepted for publication in The
Astronomical Journal (Jan 2004). Paper with high-resolution (non-compressed)
color figures in gzipped postscript format available at
http://www.stsci.edu/~marel/psgzdir/ngc6240v11.ps.g
STIS Echelle Observations of the Seyfert Galaxy NGC 4151: Physical Conditions in the Ultraviolet Absorbers
We have examined the physical conditions in intrinsic UV-absorbing gas in the
Seyfert galaxy NGC 4151, using echelle spectra obtained with the Space
Telescope Imaging Spectrograph (STIS). We confirm the presence of the kinematic
components detected in earlier GHRS observations as well as a new broad
absorption feature at a radial velocity of -1680 km/s. The UV continuum of NGC
4151 decreased by a factor of 4 over the previous two years, and we argue the
changes in the column density of the low ionization absorption lines associated
with the broad component at -490 km/s reflect the decrease in the ionizing
flux. Most of the strong absorption lines (e.g., N V, C IV, Si IV) from this
component are saturated, but show substantial residual flux in their cores,
indicating that the absorber does not fully cover the source of emission. Our
interpretation is that the unocculted light is due to scattering by free
electrons from an extended region, which reflects continuum, emission lines,
and absorption lines. We have been able to constrain the densities for the
kinematic components based on absorption lines from metastable states of C III
and Fe II, and/or the ratios of ground and fine structure lines of O I,C II,
and Si II. We have generated a set of photoionization models which match the
ionic column densities for each component during the present low flux state and
those seen in previous high flux states with the GHRS and STIS, confirming that
the absorbers are photoionized and respond to the changes in the continuum
flux. We have been able to map the relative radial positions of the absorbers,
and find that the gas decreases in density with distance. None of the UV
absorbers is of sufficiently large column density or high enough ionization
state to account for the X-ray absorption.Comment: 46 pages (Latex), 14 figures (postscript), plus a landscape table
(Latex), to appear in the Astrophysical Journa
The highly polarized open cluster Trumpler 27
We have carried out multicolor linear polarimetry (UBVRI) of the brightest
stars in the area of the open cluster Trumpler 27. Our data show a high level
of polarization in the stellar light with a considerable dispersion, from to . The polarization vectors of the cluster members appear to be
aligned. Foreground polarization was estimated from the data of some non-member
objects, for which two different components were resolved: the first one
associated with a dust cloud close to the Sun producing
and degrees, and a second component, the main source of
polarization for the cluster members, originated in another dust cloud, which
polarizes the light in the direction of degrees. From a detailed
analysis, we found that the two components have associated values for the first one, and for the other. Due the
difference in the orientation of both polarization vectors, almost 90 degrees
(180 degrees at the Stokes representation), the first cloud (
degrees) depolarize the light strongly polarized by the second one ( degrees).Comment: 12 Pages, 6 Figures, 2 tables (9 Pages), accepted for publication in
A
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
Unveiling the Active Nucleus of Centaurus A
We report new HST WFPC2 and NICMOS observations of the center of the nearest
radio galaxy Centaurus A (NGC 5128) and discuss their implications for our
understanding of the active nucleus and jet. We detect the active nucleus in
the near-IR (K and H) and, for the first time, in the optical (I and V),
deriving the spectral energy distribution of the nucleus from the radio to
X-rays. The optical and part of the near-IR emission can be explained by the
extrapolation of the X-ray power law reddened by A_V~14mag, a value consistent
with other independent estimates.
The 20pc-scale nuclear disk discovered by Schreier et al. (1998) is detected
in the [FeII] 1.64mic line and presents a morphology similar to that observed
in Pa alpha with a [FeII]/Pa alpha ratio typical of low ionization Seyfert
galaxies and LINERs. NICMOS 3 Pa alpha observations in a 50"x50" circumnuclear
region suggest enhanced star formation (~0.3Msun/yr) at the edges of the
putative bar seen with ISO, perhaps due to shocks driven into the gas.
The light profile, reconstructed from V, H and K observations, shows that
Centaurus A has a core profile with a resolved break at ~4" and suggests a
black--hole mass of ~10^9 Msun. A linear blue structure aligned with the
radio/X-ray jet may indicate a channel of relatively low reddening in which
dust has been swept away by the jet.Comment: 19 pages, 13 figures, Astrophysical Journal, in press. High quality
figures available at http://www.arcetri.astro.it/~marconi/colpic.htm
An optical-IR jet in 3C133
We report the discovery of a new optical-IR synchrotron jet in the radio
galaxy 3C133 from our HST/NICMOS snapshot survey. The jet and eastern hotspot
are well resolved, and visible at both optical and IR wavelengths. The IR jet
follows the morphology of the inner part of the radio jet, with three distinct
knots identified with features in the radio. The radio-IR SED's of the knots
are examined, along with those of two more distant hotspots at the eastern
extreme of the radio feature. The detected emission appears to be synchrotron,
with peaks in the NIR for all except one case, which exhibits a power-law
spectrum throughout.Comment: ApJ accepted. 14 pages, 6 figure
- …