809 research outputs found
The nature of close companions of the BL Lac Objects 1ES 0502+675 and 1ES 1440+122
We report on deep radio images and optical spectroscopy of two BL Lac objects
that have very close compact companions. The two targets, 1ES 0502+675 and 1ES
1440+122, were selected from the HST imaging survey of 110 BL Lacs as
candidates for possible gravitational lensing. The new observations clearly
demonstrate that the companion objects are not secondary images of the active
nuclei but, in spite of the relatively low chance projection probability,
foreground Galactic stars. Gravitational lensing appears to be unimportant to
the BL Lac phenomenon. We discuss the radio properties of the BL Lac objects in
the context of standard beaming models, and show they are as expected for
beamed FRI radio galaxies.Comment: 13 pages, 5 figures, ApJ in pres
X-ray-emitting Atmospheres of B2 Radio Galaxies
We report ROSAT PSPC spatial and spectral analysis of the eight B2 radio
galaxies NGC 315, NGC 326, 4C 35.03, B2 0326+39, NGC 2484, B2 1040+31, B2
1855+37, and 3C 449, expected to be representative of the class of low-power
radio galaxies. Multiple X-ray components are present in each, and the gas
components have a wide range of linear sizes and follow an extrapolation of the
cluster X-ray luminosity/temperature correlation, implying that there is no
relationship between the presence of a radio galaxy and the gas fraction of the
environment. No large-scale cooling flows are found. There is no correlation of
radio-galaxy size with the scale or density of the X-ray atmosphere. This
suggests that it is processes on scales less than those of the overall gaseous
environments which are the major influence on radio-source dynamics. The
intergalactic medium is usually sufficient to confine the outer parts of the
radio structures, in some cases even to within 5 kpc of the core. In the case
of NGC 315, an extrapolation suggests that the pressure of the atmosphere may
match the minimum pressure in the radio source over a factor of about 40 in
linear size (a factor of about 1600 in pressure).Comment: 34 pages, including 10 figures, using aasms4.sty To appear in the Ap
Obscuration and Origin of Nuclear X-ray emission in FR I Radio Galaxies
We present X-ray observations of the nuclear region of 25 Fanaroff-Riley I
radio galaxies from the 3CRR and B2 catalogs, using data from the Chandra and
XMM archives. We find the presence of a X-ray Central Compact Core (CCCX) in
13/25 sources, in 3/25 sources the detection of a CCCX is uncertain, while in
the remaining 9/25 sources no CCCX is found. All the sources are embedded in a
diffuse soft X-ray component, generally on kpc-scales, which is in agreement
with the halo of the host galaxy and/or with the intracluster medium. The X-ray
spectra of the cores are described by a power law with photon indices Gamma=1.1
- 2.6. In 8 sources excess absorption over the Galactic value is detected, with
rest-frame column densities N_H^z ~ 10^20 - 10^21 cm^-2; thus, we confirm the
previous claim based on optical data that most FRI radio galaxies lack a
standard optically-thick torus. We find significant correlations between the
X-ray core luminosity and the radio and optical luminosities, suggesting that
at least a fraction of the X-ray emission originates in a jet; however, the
origin of the X-rays remains ambiguous. If the X-ray emission is entirely
attributed to an isotropic, accretion-related component, we find very small
Eddington ratios, L_bol/L_Edd ~ 10^-3 - 10^-8, and we calculate the radiative
efficiency to be eta ~ 10^-2 - 10^-6, based on the Bondi accretion rates from
the spatial analysis. This suggests that radiatively inefficient accretion
flows are present in the cores of low-power radio galaxies.Comment: 20 pages, 7 figures, accepted for publication in The Astrophysical
Journa
Antenatal atazanavir: a retrospective analysis of pregnancies exposed to atazanavir.
INTRODUCTION: There are few data regarding the tolerability, safety, or efficacy of antenatal atazanavir. We report our clinical experience of atazanavir use in pregnancy.
METHODS: A retrospective medical records review of atazanavir-exposed pregnancies in 12 London centres between 2004 and 2010.
RESULTS: There were 145 pregnancies in 135 women: 89 conceived whilst taking atazanavir-based combination antiretroviral therapy (cART), "preconception" atazanavir exposure; 27 started atazanavir-based cART as "first-line" during the pregnancy; and 29 "switched" to an atazanavir-based regimen from another cART regimen during pregnancy. Gastrointestinal intolerance requiring atazanavir cessation occurred in five pregnancies. Self-limiting, new-onset transaminitis was most common in first-line use, occurring in 11.0%. Atazanavir was commenced in five switch pregnancies in the presence of transaminitis, two of which discontinued atazanavir with persistent transaminitis. HIV-VL < 50 copies/mL was achieved in 89.3% preconception, 56.5% first-line, and 72.0% switch exposures. Singleton preterm delivery (<37 weeks) occurred in 11.7% preconception, 9.1% first-line, and 7.7% switch exposures. Four infants required phototherapy. There was one mother-to-child transmission in a poorly adherent woman.
CONCLUSIONS: These data suggest that atazanavir is well tolerated and can be safely prescribed as a component of combination antiretroviral therapy in pregnancy
Optical Morphologies of Millijansky Radio Galaxies Observed by HST and in the VLA FIRST Survey
We report on a statistical study of the 51 radio galaxies at the millijansky
flux level from the Faint Images of the Radio Sky at Twenty centimeters,
including their optical morphologies and structure obtained with the Hubble
Space Telescope. Our optical imaging is significantly deeper (~2 mag) than
previous studies with the superior angular resolution of space-based imaging.
We that find 8/51 (16%) of the radio sources have no optically identifiable
counterpart to AB~24 mag. For the remaining 43 sources, only 25 are
sufficiently resolved in the HST images to reliably assign a visual
classification: 15 (60%) are elliptical galaxies, 2 (8%) are late-type spiral
galaxies, 1 (4%) is an S0, 3 (12%) are point-like objects (quasars), and 4
(16%) are merger systems. We find a similar distribution of optical types with
measurements of the Sersic index. The optical magnitude distribution of these
galaxies peaks at I~20.7+-0.5 AB mag, which is ~3 mag brighter than the depth
of our typical HST field and is thus not due to the WFPC2 detection limit. This
supports the luminosity-dependent density evolutionary model, where the
majority of faint radio galaxies typically have L*-optical luminosities and a
median redshift of z~0.8 with a relatively abrupt redshift cut-off at z>~2. We
discuss our results in the context of the evolution of elliptical galaxies and
active galactic nuclei.Comment: 20 pages, 8 figures, 51 galaxy images, and 5 tables. Uses
emulateapj.cls and natbib.sty. Accepted to ApJS. High resolution images are
available upon reques
An Unusual Discontinuity in the X-ray Surface Brightness Profile of NGC 507: Evidence of an Abundance Gradient?
We present results from a 45 ks Chandra/ACIS-I observation of the nearby
() NGC 507 group. The X-ray surface brightness profile of the outer
region of the group is well described by an isothermal -profile
consistent with earlier ROSAT observations. We find a sharp edge or
discontinuity in the radial surface brightness profile 55 kpc E and SE of NGC
507 covering a arc. At the sharpest part of the discontinuity,
the surface brightness declines by a factor of 2 over a distance of 6.9
kpc (). The inner and outer gas temperatures across the
discontinuity differ by only about 0.2 keV (interior and exterior gas
temperatures are 1.2 and 1.3 keV, respectively). Spectral analysis indicates
that there is a large gradient in the elemental abundance across the
discontinuity, and comparison with the low resolution NVSS radio maps suggests
that the discontinuity is aligned with a low surface brightness radio lobe. We
conclude that the appearance of this discontinuity is the result of the
transport of high abundance material from the center of the galaxy by the
expanding radio lobe, similar to structures seen in {\em Chandra} observations
of Perseus A and Hydra A.Comment: 15 pages, 6 figures, submitted to Astrophysical Journal Letter
The VLA-VIRMOS Deep Field I. Radio observations probing the microJy source population
We have conducted a deep survey (r.m.s noise 17 microJy) with the Very Large
Array (VLA) at 1.4 GHz, with a resolution of 6 arcsec, of a 1 square degree
region included in the VIRMOS VLT Deep Survey. In the same field we already
have multiband photometry down to I(AB)=25, and spectroscopic observations will
be obtained during the VIRMOS VLT survey. The homogeneous sensitivity over the
whole field has allowed to derive a complete sample of 1054 radio sources (5
sigma limit). We give a detailed description of the data reduction and of the
analysis of the radio observations, with particular care to the effects of
clean bias and bandwidth smearing, and of the methods used to obtain the
catalogue of radio sources. To estimate the effect of the resolution bias on
our observations we have modelled the effective angular-size distribution of
the sources in our sample and we have used this distribution to simulate a
sample of radio sources. Finally we present the radio count distribution down
to 0.08 mJy derived from the catalogue. Our counts are in good agreement with
the best fit derived from earlier surveys, and are about 50 % higher than the
counts in the HDF. The radio count distribution clearly shows, with extremely
good statistics, the change in the slope for the sub-mJy radio sources.Comment: 13 pages, Accepted for publication in Astronomy & Astrophysic
ROSAT-HRI investigation of the NGC 507 X-ray halo
We present an X-ray investigation of the elliptical galaxy NGC 507. We make
use of archival Rosat HRI, PSPC and Chandra data, to connect the large-scale
structure of the halo to the core morphology. Our analysis shows that the halo
core (r3 r_e) are characterised by different
dynamical properties and suggests a different origin of the two components. The
halo core has a complex morphology with a main X-ray emission peak, coincident
with the center of the optical galaxy, and several secondary peaks. The spatial
and spectral analysis of the central peak shows that this feature is produced
by denser hot gas in the galaxy core. Our data support the scenario where the
gas is kinetically heated by stellar mass losses. Comparison with previously
published studies suggest that the core of X-ray extended galaxies is
associated to the stellar distribution and has similar properties to the X-ray
halo of compact galaxies. The secondary peaks are due instead to interactions
between the radio-emitting plasma and the surrounding ISM. We found that the
energy input by the central radio source in the ISM may be large enough to
prevent gas from cooling. The total mass profile shows the presence of a dark
matter halo extending on cluster scales which is likely to be associated with
the whole cluster rather than with NGC 507. This structure is typical of many
X-ray bright Early-Type galaxies and may explain the spatial and spectral
differences with X-ray compact galaxies largely debated in literature. Finally
we discuss the nature of the point sources detected in the HRI FOV.Comment: AASTEX preprint format, 48 pages, 18 figures, 6 tables. A higher
quality copy with color figures can be found at
http://www.na.astro.it/~paolillo/papers/ngc507.ps.gz Accepted for publication
in Ap
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