6,849 research outputs found
Keck Observations of the Hidden Quasar IRAS P09104+4109
We present imaging and spectro- polarimetric observations of the
ultraluminous infrared galaxy IRAS P09104+4109 using the Keck 10-m Telescope.
We detect the clear presence of broad Hb, Hg, and MgII 2800 emission lines in
the polarized flux spectra of the nucleus and of an extranuclear emission
region ~ 4" away, confirming the presence of a hidden central quasar. The
polarization of the broad Mg II emission line is high (~ 29%), consistent with
the remarkably high polarization (~ 30%-40%) observed in the extended continuum
emission. The narrow emission lines are polarized in a stratified fashion, with
the high ionization lines being polarized 0.7%-1.7% and [O II] essentially
unpolarized. The line polarizations are positively correlated with critical
density, ionization potential, and velocity width of the emission lines. This
indicates that the NLR may be partially shadowed by the putative torus, with
the higher ionization lines originating closer to the nucleus. One notable
characteristic of the extranuclear knot is that all species of Fe are markedly
absent in its spectrum, while they appear prominently in the nucleus. Our
favored interpretation is that there is a large amount of dust in the
extranuclear regions, allowing gaseous refractory metals to deposit. The
extended emission regions are most likely material shredded from nearby cluster
members and not gas condensed from the cooling flow or expelled from the
obscured quasar. Our data provide strong evidence for matter-bounded clouds in
addition to ionization-bounded clouds in the NLR. Ionization by pure velocity
shocks can be ruled out. Shocks with photoionizing precursors may be present,
but are probably not a dominant contributor to the energy input.Comment: 32 pages, including 9 figs and 2 tables, to be published in the
Astronomical Journa
A vestige low metallicity gas shell surrounding the radio galaxy 0943-242 at z=2.92
Observations are presented showing the doublet CIV 1550 absorption lines
superimposed on the CIV emission in the radio galaxy 0943-242. Within the
errors, the redshift of the absorption system that has a column density of
N_CIV = 10^{14.5 +- 0.1} cm-2 coincides with that of the deep Ly-alpha
absorption trough observed by Rottgering et al. (1995). The gas seen in
absorption has a resolved spatial extent of at least 13 kpc (the size of the
extended emission line region). We first model the absorption and emission gas
as co-spatial components with the same metallicity and degree of excitation.
Using the information provided by the emission and absorption line ratios of
CIV and Ly-alpha, we find that the observed quantities are incompatible with
photoionization or collisional ionization of cloudlets with uniform properties.
We therefore reject the possibility that the absorption and emission phases are
co-spatial and favour the explanation that the absorption gas has low
metallicity and is located further away from the host galaxy (than the emission
line gas). The estimated low metallicity for the absorption gas in 0943-242 (Z
\~ 1% solar) and its proposed location -outer halo outside the radio cocoon-
suggest that its existence preceeds the observed AGN phase and is a vestige of
the initial starburst at the onset of formation of the parent galaxy.Comment: 11 pages,5 figures, A&A accepte
CO line emission in the halo of a radio galaxy at z=2.6
We report the detection of luminous CO(3-2) line emission in the halo of the
z=2.6 radio galaxy (HzRG) TXS0828+193, which has no detected counterpart at
optical to mid-infrared wavelengths implying a stellar mass < few x10^9 M_sun
and relatively low star-formation rates. With the IRAM PdBI we find two CO
emission line components at the same position at ~80 kpc distance from the HzRG
along the axis of the radio jet, with different blueshifts of few 100 km s^-1
relative to the HzRG and a total luminosity of ~2x10^10 K km s^-1 pc^2 detected
at 8 sigma significance. HzRGs have significant galaxy overdensities and
extended halos of metal-enriched gas often with embedded clouds or filaments of
denser material, and likely trace very massive dark-matter halos. The CO
emission may be associated with a gas-rich, low-mass satellite galaxy with
little on-going star formation, in contrast to all previous CO detections of
galaxies at similar redshifts. Alternatively, the CO may be related to a gas
cloud or filament and perhaps jet-induced gas cooling in the outer halo,
somewhat in analogy with extended CO emission found in low-redshift galaxy
clusters.Comment: MNRAS Letters, accepte
Quasar Evolution and the Baldwin Effect in the Large Bright Quasar Survey
From a large homogeneous sample of optical/UV emission line measurements for
993 quasars from the Large Bright Quasar Survey (LBQS), we study correlations
between emission line equivalent width and both restframe ultraviolet
luminosity (i.e., the Baldwin Effect) and redshift. Our semi-automated spectral
fitting accounts for absorption lines, fits blended iron emission, and provides
upper limits to weak emission lines. Use of a single large, well-defined sample
and consistent emission line measurements allows us to sensitively detect many
correlations, most of which have been previously noted. A new finding is a
significant Baldwin Effect in UV iron emission. Further analysis reveals that
the primary correlation of iron emission strength is probably with redshift,
implying an evolutionary rather than a luminosity effect. We show that for most
emission lines with a significant Baldwin Effect, and for some without,
evolution dominates over luminosity effects. This may reflect evolution in
abundances, in cloud covering factors, or overall cloud conditions such as
density and ionization. We find that in our sample, a putative correlation
between Baldwin Effect slope and the ionization potential is not significant.
Uniform measurements of other large quasar samples will extend the luminosity
and redshift range of such spectral studies and provide even stronger tests of
spectral evolution.Comment: 16 pages, Latex, emulateapj style, including 3 tables and 6 figures.
Accepted April 02, 2001 for publication in ApJ Main Journal. See also
http://hea-www.harvard.edu/~pgreen/Papers.htm
A rapid community based health evaluation of pregnant women in low socioeconomic settlements of Karachi
A rapid nutritional and health evaluation of a random sample of 163 pregnant women was conducted in low socioeconomic settlements of Karachi, with the objective of determining the morbidity and nutritional status of pregnant women. These data are expected to be used in an ongoing community-based antenatal care programme. Twenty-nine percent of women reported fever, 14 percent diarrhoea and 33 percent respiratory infections in the previous week. Mean weight was 54.8 (+/- 10.6) kg, mean height was 151.6 (+/- 6.0) cm and mean midarm circumference was 25.6 (+/- 3.2) cm. The mean uterine height at gestational ages 8 months and over was 32.1 (+/- 10.2) cm which is below the 10th percentile. These results suggest a chronic, mildly malnourished population with a high rate of infections. Specifically, we suggest that maternal height and uterine height be used to assess women at high risk for low birthweight
Computing the Casimir energy using the point-matching method
We use a point-matching approach to numerically compute the Casimir
interaction energy for a two perfect-conductor waveguide of arbitrary section.
We present the method and describe the procedure used to obtain the numerical
results. At first, our technique is tested for geometries with known solutions,
such as concentric and eccentric cylinders. Then, we apply the point-matching
technique to compute the Casimir interaction energy for new geometries such as
concentric corrugated cylinders and cylinders inside conductors with focal
lines.Comment: 11 pages, 18 figure
Field Induced Multiple Reentrant Quantum Phase Transitions in Randomly Dimerized Antiferromagnetic S=1/2 Heisenberg Chains
The multiple reentrant quantum phase transitions in the
antiferromagnetic Heisenberg chains with random bond alternation in the
magnetic field are investigated by the density matrix renormalization group
method combined with the interchain mean field approximation. It is assumed
that the odd-th bond is antiferromagnetic with strength and even-th bond
can take the values {\JS} and {\JW} ({\JS} > J > {\JW} > 0) randomly
with probability and , respectively. The pure version ( and
) of this model has a spin gap but exhibits a field induced
antiferromagnetism in the presence of interchain coupling if Zeeman energy due
to the magnetic field exceeds the spin gap. For , the
antiferromagnetism is induced by randomness at small field region where the
ground state is disordered due to the spin gap in the pure case. At the same
time, this model exhibits randomness induced plateaus at several values of
magnetization. The antiferromagnetism is destroyed on the plateaus. As a
consequence, we find a series of reentrant quantum phase transitions between
the transverse antiferromagnetic phases and disordered plateau phases with the
increase of the magnetic field for moderate strength of interchain coupling.
Above the main plateaus, the magnetization curve consists of a series of small
plateaus and the jumps between them, It is also found that the
antiferromagnetism is induced by infinitesimal interchain coupling at the jumps
between the small plateaus. We conclude that this antiferromagnetism is
supported by the mixing of low lying excited states by the staggered interchain
mean field even though the spin correlation function is short ranged in the
ground state of each chain.Comment: 5 pages, 8 figure
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