807 research outputs found
Polarization of Broad Absorption Line QSOs I. A Spectropolarimetric Atlas
We present a spectropolarimetric survey of 36 broad absorption line
quasi-stellar objects (BAL QSOs). The continuum, absorption trough, and
emission line polarization of BAL QSOs yield clues about their structure. We
confirm that BAL QSOs are in general more highly polarized than non-BAL QSOs,
consistent with a more equatorial viewing direction for the former than the
latter. We have identified two new highly-polarized QSOs in our sample
(1232+1325 and 1333+2840). The polarization rises weakly to the blue in most
objects, perhaps due to scattering and absorption by dust particles. We find
that a polarization increase in the BAL troughs is a general property of
polarized BAL QSOs, indicating an excess of scattered light relative to direct
light, and consistent with the unification of BAL QSOs and non-BAL QSOs. We
have also discovered evidence of resonantly scattered photons in the red wing
of the C IV broad emission lines of a few objects. In most cases, the broad
emission lines have lower polarization and a different position angle than the
continuum. The polarization characteristics of low-ionization BAL QSOs are
similar to those of high-ionization BAL QSOs, suggesting a similar BAL wind
geometry.Comment: 39 pages, 6 figures (20 .gif files), accepted for publication in The
Astrophysical Journal Supplement
Structure of the X-ray Emission from the Jet of 3C 273
We present images from five observations of the quasar 3C 273 with the
Chandra X-ray Observatory. The jet has at least four distinct features which
are not resolved in previous observations. The first knot in the jet (A1) is
very bright in X-rays. Its X-ray spectrum is well fitted with a power law with
alpha = 0.60 +/- 0.05. Combining this measurement with lower frequency data
shows that a pure synchrotron model can fit the spectrum of this knot from
1.647 GHz to 5 keV (over nine decades in energy) with alpha = 0.76 +/- 0.02,
similar to the X-ray spectral slope. Thus, we place a lower limit on the total
power radiated by this knot of 1.5e43 erg/s; substantially more power may be
emitted in the hard X-ray and gamma-ray bands.
Knot A2 is also detected and is somewhat blended with knot B1. Synchrotron
emission may also explain the X-ray emission but a spectral bend is required
near the optical band. For knots A1 and B1, the X-ray flux dominates the
emitted energy. For the remaining optical knots (C through H), localized X-ray
enhancements that might correspond to the optical features are not clearly
resolved. The position angle of the jet ridge line follows the optical shape
with distinct, aperiodic excursions of +/-1 deg from a median value of
-138.0deg. Finally, we find X-ray emission from the ``inner jet'' between 5 and
10" from the core.Comment: 10 pages, 5 figures; accepted for publication in the Astrophysical
Journal Letters. For the color image, see fig1.ps or
http://space.mit.edu/~hermanm/papers/3c273/fig1.jp
Scattered Nuclear Continuum and Broad H-alpha in Cygnus A
We have discovered scattered broad Balmer emission lines in the spectrum of
Cygnus A, using the Keck II telescope. Broad H-alpha appears in polarized flux
from components on either side of the nucleus, and to a lesser extent in the
nucleus. The full-width at half-maximum of broad H-alpha is 26,000 km/s,
comparable to the widest emission lines seen in broad-line radio galaxies.
Scattered AGN light provides a significant contribution to the total flux at
3800 Angstroms (rest) of the western component, where the polarization rises to
16%. The spatially integrated flux of Cygnus A at 5500 Angstroms can be
decomposed into an elliptical galaxy fraction (Fg=0.70), a highly polarized
blue component (FC1=0.15), a less polarized red component (FC=0.09), and a
contribution from the nebular continuum (0.06). Imaging polarimetry shows a
double fan of polarization vectors with circular symmetry which corresponds to
the ionization cone seen in HST images. Our results are consistent with
scattering of light from a hidden quasar of modest luminosity by an extended,
dusty narrow-line region.Comment: 13 pages, 4 figures, Latex, to appear in ApJ Letter
PAH Emission from Ultraluminous Infrared Galaxies
We explore the relationships between the Polycyclic Aromatic Hydrocarbon
(PAH) feature strengths, mid-infrared continuum luminosities, far-infrared
spectral slopes, optical spectroscopic classifications, and silicate optical
depths within a sample of 107 ULIRGs observed with the Infrared Spectrograph on
the Spitzer Space Telescope. The detected 6.2 micron PAH equivalent widths
(EQWs) in the sample span more than two orders of magnitude (0.006-0.8 micron),
and ULIRGs with HII-like optical spectra or steep far-infrared spectral slopes
(S_{25} / S_{60} < 0.2) typically have 6.2 micron PAH EQWs that are half that
of lower-luminosity starbursts. A significant fraction (~40-60%) of HII-like,
LINER-like, and cold ULIRGs have very weak PAH EQWs. Many of these ULIRGs also
have large (tau_{9.7} > 2.3) silicate optical depths. The far-infrared spectral
slope is strongly correlated with PAH EQW, but not with silicate optical depth.
In addition, the PAH EQW decreases with increasing rest-frame 24 micron
luminosity. We argue that this trend results primarily from dilution of the PAH
EQW by continuum emission from dust heated by a compact central source,
probably an AGN. High luminosity, high-redshift sources studied with Spitzer
appear to have a much larger range in PAH EQW than seen in local ULIRGs, which
is consistent with extremely luminous starburst systems being absent at low
redshift, but present at early epochs.Comment: 15 pages, 9 Figures; Accepted for publication in Ap
Strong molecular hydrogen emission and kinematics of the multiphase gas in radio galaxies with fast jet-driven outflows
Observations of ionized and neutral gas outflows in radio-galaxies (RGs)
suggest that AGN radio jet feedback has a galaxy-scale impact on the host ISM,
but it is still unclear how the molecular gas is affected. We present deep
Spitzer IRS spectroscopy of 8 RGs that show fast HI outflows. All of these
HI-outflow RGs have bright H2 mid-IR lines that cannot be accounted for by UV
or X-ray heating. This suggests that the radio jet, which drives the HI
outflow, is also responsible for the shock-excitation of the warm H2 gas. In
addition, the warm H2 gas does not share the kinematics of the ionized/neutral
gas. The mid-IR ionized gas lines are systematically broader than the H2 lines,
which are resolved by the IRS (with FWHM up to 900km/s) in 60% of the detected
H2 lines. In 5 sources, the NeII line, and to a lesser extent the NeIII and NeV
lines, exhibit blue-shifted wings (up to -900km/s with respect to the systemic
velocity) that match the kinematics of the outflowing HI or ionized gas. The H2
lines do not show broad wings, except tentative detections in 3 sources. This
shows that, contrary to the HI gas, the H2 gas is inefficiently coupled to the
AGN jet-driven outflow of ionized gas. While the dissipation of a small
fraction (<10%) of the jet kinetic power can explain the dynamical heating of
the molecular gas, our data show that the bulk of the warm molecular gas is not
expelled from these galaxies.Comment: 26 pages, 15 figures, Accepted for ublication in Ap
Covering one eye in fixation-disparity measurement causes slight movement of fellow eye
In the subjective measurement of fixation disparity (FD), the subject fuses contours presented in the peripheral macular areas of both eyes (fusion lock). The position of the eyes relative to each other is monitored by means of two haploscopically seen vertical lines presented in the central macular area, one above and one below a binocularly seen horizontal line. The subject is instructed to shift one of the vertical lines horizontally until the two are aligned, while fixating their intersection with the horizontal line. It has recently been questioned whether the foveolae really are pointed towards the perceived intersection. In this study, we monitored the position of one eye while intermittently covering the fellow eye, while the subject maintained fixation of the intersection of the remaining vertical line and the horizontal line. We found slight differences in position of the measured eye, depending on whether the other eye was covered or not, i.e. depending on the presence or absence of fusion in the macular periphery. These differences were more pronounced in the non-dominant eye
Effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on associated soil bacterial communities: a field-based experiment
Loss of plant biodiversity can result in reduced abundance and diversity of associated species with implications for ecosystem functioning. In ecosystems low in plant species diversity, such as Neotropical mangrove forests, it is thought that genetic diversity within the dominant plant species could play an important role in shaping associated communities. Here, we used a manipulative field experiment to study the effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on the composition and richness of associated soil bacterial communities. Using terminal restriction fragment length polymorphism (TâRFLP) community fingerprinting, we found that bacterial community composition differed among R. mangle maternal genotypes but not with genetic diversity. Bacterial taxa richness, total soil nitrogen, and total soil carbon were not significantly affected by maternal genotypic identity or genetic diversity of R. mangle. Our findings show that genotype selection in reforestation projects could influence soil bacterial community composition. Further research is needed to determine what impact these bacterial community differences might have on ecosystem processes, such as carbon and nitrogen cycling
Spatially Resolved Chandra HETG Spectroscopy of the NLR Ionization Cone in NGC 1068
We present initial results from a new 440âks Chandra HETG GTO observation of the canonical Seyfert 2 galaxy NGC 1068. The proximity of NGC 1068, together with Chandraâs superb spatial and spectral resolution, allow an unprecedented view of its nucleus and circumnuclear NLR. We perform the first spatially resolved highâresolution Xâray spectroscopy of the âionization coneâ in any AGN, and use the sensitive line diagnostics offered by the HETG to measure the ionization state, density, and temperature at discrete points along the ionized NLR. We argue that the NLR takes the form of outflowing photoionized gas, rather than gas that has been collisionally ionized by the smallâscale radio jet in NGC 1068. We investigate evidence for any velocity gradients in the outflow, and describe our next steps in modeling the spatially resolved spectra as a function of distance from the nucleus
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