993 research outputs found
A Catalog of Diffuse X-ray-Emitting Features within 20 pc of Sgr A*: Twenty Pulsar Wind Nebulae?
We present a catalog of 34 diffuse features identified in X-ray images of the
Galactic center taken with the Chandra X-ray Observatory. Several of the
features have been discussed in the literature previously, including 7 that are
associated with a complex of molecular clouds that exhibits fluorescent line
emission, 4 that are superimposed on the supernova remnant Sgr A East, 2 that
are coincident with radio features that are thought to be the shell of another
supernova remnant, and one that is thought to be a pulsar wind nebula only a
few arcseconds in projection from Sgr A*. However, this leaves 20 features that
have not been reported previously. Based on the weakness of iron emission in
their spectra, we propose that most of them are non-thermal. One long, narrow
feature points toward Sgr A*, and so we propose that this feature is a jet of
synchrotron-emitting particles ejected from the supermassive black hole. For
the others, we show that their sizes (0.1-2 pc in length for D=8 kpc), X-ray
luminosities (between 10^32 and 10^34 erg/s, 2-8 keV), and spectra (power laws
with Gamma=1-3) are consistent with those of pulsar wind nebulae. Based on the
star formation rate at the Galactic center, we expect that ~20 pulsars have
formed in the last 300 kyr, and could be producing pulsar wind nebulae. Only
one of the 19 candidate pulsar wind nebulae is securely detected in an archival
radio image of the Galactic center; the remainder have upper limits
corresponding to L_R<la10^31 erg/s. These radio limits do not strongly
constrain their natures, which underscores the need for further multi-
wavelength studies of this unprecedented sample of Galactic X-ray emitting
structures.Comment: 14 pages, 8 figures, 5 in color. Submitted to Ap
Analysis of the Spatial Distribution of Galaxies by Multiscale Methods
Galaxies are arranged in interconnected walls and filaments forming a cosmic
web encompassing huge, nearly empty, regions between the structures. Many
statistical methods have been proposed in the past in order to describe the
galaxy distribution and discriminate the different cosmological models. We
present in this paper results relative to the use of new statistical tools
using the 3D isotropic undecimated wavelet transform, the 3D ridgelet transform
and the 3D beamlet transform. We show that such multiscale methods produce a
new way to measure in a coherent and statistically reliable way the degree of
clustering, filamentarity, sheetedness, and voidedness of a datasetComment: 26 pages, 20 figures. Submitted to EURASIP Journal on Applied Signal
Processing (special issue on "Applications of Signal Processing in
Astrophysics and Cosmology"
Plasma and Warm Dust in the Collisional Ring Galaxy VIIZw466 from VLA and ISO Observations
We present the first mid-infrared (Mid-IR) (m) and radio
continuum (20,~6 and 3.6 cm) observations of the star-forming
collisional ring galaxy VII Zw 466 and its host group made with the Infrared
Space Observatory and the NRAO Very Large Array. A search was also made for CO
line emission in two of the galaxies with the Onsala 20m radio telescope and
upper limits were placed on the mass of molecular gas in those galaxies. The
ring galaxy is believed to owe its morphology to a slightly off-center
collision between an `intruder' galaxy and a disk. An off-center collision is
predicted to generate a radially expanding density wave in the disk which
should show large azimuthal variations in overdensity, and have observational
consequences. The radio continuum emission shows the largest asymmetry,
exhibiting a crescent-shaped distribution consistent with either the trapping
of cosmic-ray particles in the target disk, or an enhanced supernova rate in
the compressed region. On the other hand, the ISO observations (especially
those made at m) show a more scattered distribution, with
emission centers associated with powerful star formation sites distributed more
uniformly around the ring. Low-signal to noise observations at
m show possible emission inside the ring, with little emission
directly associated with the \ion{H}{2} regions. The observations emphasize the
complex relationship between the generation of radio emission and the
development of star formation even in relatively simple and well understood
collisional scenarios.Comment: Accepted for publication in The Astrophysical Journal, 23 pages + 6
PS figure
A 12um ISOCAM Survey of the ESO-Sculptor Field: Data Reduction and Analysis
We present a detailed reduction of a mid-infrared 12um (LW10 filter) ISOCAM
open time observation performed on the ESO-Sculptor Survey field (Arnouts et
al. 1997). A complete catalogue of 142 sources (120 galaxies and 22 stars),
detected with high significance (equivalent to 5sigma), is presented above an
integrated flux density of 0.24mJy. Star/galaxy separation is performed by a
detailed study of colour-colour diagrams. The catalogue is complete to 1mJy and
below this flux density the incompleteness is corrected using two independent
methods. The first method uses stars and the second uses optical counterparts
of the ISOCAM galaxies; these methods yield consistent results. We also apply
an empirical flux density calibration using stars in the field. For each star,
the 12um flux density is derived by fitting optical colours from a multi-band
chi^2 to stellar templates (BaSel-2.0) and using empirical optical-IR
colour-colour relations. This article is a companion analysis to
Rocca-Volmerange 2007 et al. where the 12um faint galaxy counts are presented
and analysed by galaxy type with the evolutionary code PEGASE.3.Comment: 12 pages, 7 figures, figure 1 modified from journal version for size,
accepted for publication in A&A, includes psfig.st
Do maternal environmental conditions during reproductive development induce genotypic selection in Picea abies?
In forest trees, environmental conditions during reproduction can greatly
influence progeny performance. This phenomenon probably results from
adaptive phenotypic plasticity but also may be associated with genotypic
selection. In order to determine whether selective effects during the
reproduction are environment specific, single pair-crosses of Norway spruce
were studied in two contrasted maternal environments (warm and cold
conditions). One family expressed large and the other small phenotypic
differences between these crossing environments. The inheritance of genetic
polymorphism was analysed at the seed stage. Four parental genetic maps
covering 66 to 78% of the genome were constructed using 190 to 200 loci.
After correcting for multiple testing, there is no evidence of locus under
strong and repeatable selection. The maternal environment could thus only
induce limited genotypic-selection effects during reproductive steps, and
performance of progenies may be mainly affected by a long-lasting epigenetic
memory regulated by temperature and photoperiod prevailing during seed
production.L'environnement maternel induit-il une sélection génotypique
durant les différents stades de reproduction chez Picea
abies ?. Chez les arbres forestiers, les conditions environnementales durant la
reproduction peuvent influencer les performances des descendants. Ce
phénomène reflète probablement la plasticité
phénotypique, mais également il pourrait être associé à une
sélection génotypique. Afin de déterminer si des effets
sélectifs durant la reproduction sont spécifiques d'un environnement
donné, deux familles d'épicéa commun non apparentées ont
été obtenues par croisements dirigés dans deux environnements
maternels contrastés (conditions chaude et froide). La première
famille exprimait de larges différences phénotypiques entre les deux
environnements tandis que la seconde ne montrait pas de différence
significative. La transmission des polymorphismes génétiques a
été étudiée au stade de la graine. Quatre cartes
génétiques parentales couvrant 66 à 78 % du génome ont
été construites. Aucun effet de sélection n'a été mis en
évidence aux différents locus étudiés. L'environnement
maternel n'induirait donc que des effets de sélection génotypique
relativement faibles durant les stades de la reproduction. Les performances
des descendants seraient principalement affectées par une mémoire
épigénétique durable régulée par la température et
la photopériode régnant durant la production des graines
The application of a Trous wave filtering and Monte Carlo analysis on SECIS 2001 solar eclipse observations
8000 images of the Solar corona were captured during the June 2001 total
Solar eclipse. New software for the alignment of the images and an automated
technique for detecting intensity oscillations using multi scale wavelet
analysis were developed. Large areas of the images covered by the Moon and the
upper corona were scanned for oscillations and the statistical properties of
the atmospheric effects were determined. The a Trous wavelet transform was used
for noise reduction and Monte Carlo analysis as a significance test of the
detections. The effectiveness of those techniques is discussed in detail.Comment: 17 pages, 8 figures, accepted by Solar Physics Journal for
publication in Topical Issue: "Frontiers in Solar Image Processing
Embryological staging of the Zebra Finch, Taeniopygia guttata
Zebra Finches (Taeniopygia guttata) are the most commonly used laboratory songbird species, yet their embryological development has been poorly characterized. Most studies to date apply Hamburger and Hamilton stages derived from chicken development; however, significant differences in development between precocial and altricial species suggest that they may not be directly comparable. We provide the first detailed description of embryological development in the Zebra Finch under standard artificial incubation. These descriptions confirm that some of the features used to classify chicken embryos into stages are not applicable in an altricial bird such as the Zebra Finch. This staging protocol will help to standardize future studies of embryological development in the Zebra Finch. J. Morphol. 274:1090-1110, 2013. (c) 2013 Wiley Periodicals, Inc
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