487 research outputs found
Gas temperature profiles in galaxy clusters with Swift XRT: observations and capabilities to map near R200
We investigate the possibility of using the X-ray telescope (XRT) on board
the Swift satellite to improve the current accuracy of the ICM temperature
measurements in the region close to the virial radius of nearby clusters. We
present the spectral analysis of the Swift XRT observations of 6 galaxy
clusters and their temperature profiles in the regions within 0.2-0.6 r200.
Four of them are nearby famous and very well studied objects (Coma, Abell 1795,
Abell 2029 and PKS0745-19). The remaining two, SWJ1557+35 and SWJ0847+13, at
redshift z=0.16 and z=0.36, were serendipitously observed by Swift-XRT. We
accurately quantify the temperature uncertainties, with particular focus on the
impact of the background scatter (both instrumental and cosmic). We extrapolate
these results and simulate a deep observation of the external region of Abell
1795 which is assumed here as a case study. In particular we calculate the
expected uncertainties in the temperature measurement as far as r200. We find
that, with a fairly deep observation (300 ks), the Swift XRT would be able to
measure the ICM temperature profiles in the external regions as far as the
virial radius, significantly improving the best accuracy among the previous
measurements. This can be achieved thanks to the unprecedented combination of
good PSF over the full field of view and very accurate control of the
instrumental background. Somehow unexpectedly we conclude that, among currently
operating telescope, the Swift-XRT is the only potentially able to improve the
current accuracy in plasma temperature measurement at the edges of the cluster
potential. This will be true until a newgeneration of low-background and large
field of view telescopes, aimed to the study of galaxy clusters, will operate.
These observations would be of great importance in developing the observing
strategy for suchmissions.Comment: Accepted for publication in A&A ;13 pages, 13 figure
Rapid Application of Space Effects for the Small Satellites Systems and Services Symposium
NASA Ames Research Center (ARC) has engaged Military Branches, the Department of Defense, and other Government Agencies in successful partnerships to design, develop, deliver and support various space effects capabilities and space vehicles on timeline of need. Contracts with Industry are in place to execute operational and enabler missions using physical and informational infrastructures including Responsive Manufacturing capabilities and Digital Assurance. The intent is to establish a secure, web-enabled "store front" for ordering and delivering any capabilities required as defined by the users and directed by NASA ARC and Partner Organizations. The capabilities are envisioned to cover a broad range and include 6U CubeSats, 50-100 kg Space Vehicles, Modular Space Vehicle architecture variations, as well as rapid payload integration on various Bus options. The paper will discuss the efforts underway to demonstrate autonomous manufacturing of low-volume, high-value assets, to validate the ability of autonomous digital techniques to provide Mission Assurance, and to demonstrate cost savings through the identification, characterization, and utilization of Responsive Space components. The culmination of this effort will be the integration of several 6U satellites and their launch in 2016
X-ray observations of the galaxy cluster Abell 2029 to the virial radius
We present Suzaku observations of the galaxy cluster Abell 2029, which
exploit Suzaku's low particle background to probe the ICM to radii beyond those
possible with previous observations (reaching out to the virial radius), and
with better azimuthal coverage. We find significant anisotropies in the
temperature and entropy profiles, with a region of lower temperature and
entropy occurring to the south east, possibly the result of accretion activity
in this direction. Away from this cold feature, the thermodynamic properties
are consistent with an entropy profile which rises, but less steeply than the
predictions of purely gravitational hierarchical structure formation. Excess
emission in the northern direction can be explained due to the overlap of the
emission from the outskirts of Abell 2029 and nearby Abell 2033 (which is at
slightly higher redshift). These observations suggest that the assumptions of
spherical symmetry and hydrostatic equilibrium break down in the outskirts of
galaxy clusters, which poses challenges for modelling cluster masses at large
radii and presents opportunities for studying the formation and accretion
history of clusters.Comment: 15 pages, 14 figures. Accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
Health workforce development: a needs assessment study in French speaking African countries
In 2006, WHO alerted the world to a global health workforce crisis, demonstrated through critical shortages of health workers, primarily in Sub-Saharan Africa (WHO in World Health Report, 2006). The objective of our study was to assess, in a participative way, the educational needs for public health and health workforce development among potential trainees and training institutions in nine French-speaking African countries. A needs assessment was conducted in the target countries according to four approaches: (1) Review at national level of health challenges. (2) Semi-directed interviews with heads of relevant training institutions. (3) Focus group discussions with key-informants. (4) A questionnaire-based study targeting health professionals identified as potential trainees. A needs assessment showed important public health challenges in the field of health workforce development among the target countries (e.g. unequal HRH distribution in the country, ageing of HRH, lack of adequate training). It also showed a demand for education and training institutions that are able to offer a training programme in health workforce development, and identified training objectives and core competencies useful to potential employers and future trainees (e.g. leadership, planning/evaluation, management, research skill). In combining various approaches our study was able to show a general demand for health managers who are able to plan, develop and manage a nation's health workforce. It also identified specific competencies that should be developed through an education and training program in public health with a focus on health workforce developmen
GASP IV: A muse view of extreme ram-pressure stripping in the plane of the sky: the case of jellyfish galaxy JO204
In the context of the GAs Stripping Phenomena in galaxies with Muse (GASP)
survey, we present the characterization of JO204, a jellyfish galaxy in A957, a
relatively low-mass cluster with . This galaxy
shows a tail of ionized gas that extends up to 30 kpc from the main body in the
opposite direction of the cluster center. No gas emission is detected in the
galaxy outer disk, suggesting that gas stripping is proceeding outside-in. The
stellar component is distributed as a regular disk galaxy; the stellar
kinematics shows a symmetric rotation curve with a maximum radial velocity of
200km/s out to 20 kpc from the galaxy center. The radial velocity of the gas
component in the central part of the disk follows the distribution of the
stellar component; the gas kinematics in the tail retains the rotation of the
galaxy disk, indicating that JO204 is moving at high speed in the intracluster
medium. Both the emission and radial velocity maps of the gas and stellar
components indicate ram-pressure as the most likely primary mechanism for gas
stripping, as expected given that JO204 is close to the cluster center and it
is likely at the first infall in the cluster. The spatially resolved star
formation history of JO204 provides evidence that the onset of ram-pressure
stripping occurred in the last 500 Myr, quenching the star formation activity
in the outer disk, where the gas has been already completely stripped. Our
conclusions are supported by a set of hydrodynamic simulations.Comment: accepted for publication in Ap
GASP III. JO36: a case of multiple environmental effects at play?
The so-called jellyfish galaxies are objects exhibiting disturbed morphology,
mostly in the form of tails of gas stripped from the main body of the galaxy.
Several works have strongly suggested ram pressure stripping to be the
mechanism driving this phenomenon. Here, we focus on one of these objects,
drawn from a sample of optically selected jellyfish galaxies, and use it to
validate SINOPSIS, the spectral fitting code that will be used for the analysis
of the GASP (GAs Stripping Phenomena in galaxies with MUSE) survey, and study
the spatial distribution and physical properties of gas and stellar populations
in this galaxy. We compare the model spectra to those obtained with GANDALF, a
code with similar features widely used to interpret the kinematic of stars and
gas in galaxies from IFU data. We find that SINOPSIS can reproduce the
pixel-by-pixel spectra of this galaxy at least as good as GANDALF does,
providing reliable estimates of the underlying stellar absorption to properly
correct the nebular gas emission. Using these results, we find strong evidences
of a double effect of ram pressure exerted by the intracluster medium onto the
gas of the galaxy. A moderate burst of star formation, dating between 20 and
500 Myr ago and involving the outer parts of the galaxy more strongly than the
inner regions, was likely induced by a first interaction of the galaxy with the
intracluster medium. Stripping by ram pressure, plus probable gas depletion due
to star formation, contributed to create a truncated ionized gas disk. The
presence of an extended stellar tail on only one side of the disk, points
instead to another kind of process, likely a gravitational interaction by a
fly-by or a close encounter with another galaxy in the cluster.Comment: ApJ in press, 26 pages, 18 figure
GASP XVIII: Star formation quenching due to AGN feedback in the central region of a jellyfish galaxy
We report evidence for star formation quenching in the central 8.6 kpc region
of the jellyfish galaxy JO201 which hosts an active galactic nucleus, while
undergoing strong ram pressure stripping. The ultraviolet imaging data of the
galaxy disk reveal a region with reduced flux around the center of the galaxy
and a horse shoe shaped region with enhanced flux in the outer disk. The
characterization of the ionization regions based on emission line diagnostic
diagrams shows that the region of reduced flux seen in the ultraviolet is
within the AGN-dominated area. The CO J map of the galaxy disk reveals
a cavity in the central region. The image of the galaxy disk at redder
wavelengths (9050-9250 \overset{\lower.5em\circ}{\mathrm{A}}) reveals the
presence of a stellar bar. The star formation rate map of the galaxy disk shows
that the star formation suppression in the cavity occurred in the last few
10 yr. We present several lines of evidence supporting the scenario that
suppression of star formation in the central region of the disk is most likely
due to the feedback from the AGN. The observations reported here make JO201 a
unique case of AGN feedback and environmental effects suppressing star
formation in a spiral galaxy.Comment: Author's accepted manuscrip
Unification of Gauge Couplings in the E(6)SSM
We argue that in the two-loop approximation gauge coupling unification in the
exceptional supersymmetric standard model can be achieved for any
phenomenologically reasonable value of strong gauge coupling at the electroweak
scale consistent with the experimentally measured central value.Comment: Parallel talk at SUSY09, Boston, USA, June 2009, 5 page
ORS Responsive Manufacturing 6U Spacecraft
The Operationally Responsive Space Office is developing a small satellite capability and small satellite design specifically for advanced manufacturing and assembly methods for a semi-automated assembly and test facility. Designing a small satellite to be assembled and tested with this novel and innovative approach enables reduced costs, schedule, and risk. This presentation will discuss the implementation, unique design features, lessons learned, and challenges associated with developing for this new rapid-assembly capability as well as the unique benefits and challenges of assembly and test using automated, robotic systems. The presentation will also include discussions of the role that design-for-manufacturing, modular open system architecture, componentized subsystems, and standardized interfaces each play in developing the spacecraft. Assembly processes, ground support interfaces, and other assembly, integration and test needs will also be discussed
X-ray observations of PKS 0745-191 at the virial radius: Are we there yet?
We wish to reassess the properties of the ICM at large radii in the galaxy
cluster PKS 0745-191 in light of the recent Suzaku measurements. We analyze an
archival 10.5 ksec ROSAT/PSPC observation to extract the surface-brightness
profile of PKS 0745-191 and infer the deprojected density profile. We then
compare the ROSAT surface-brightness profile with the Suzaku result. We perform
a mass analysis combining the ROSAT density profile and the published
temperature profiles from different instruments. We find that the ROSAT
surface-brightness profile is statistically inconsistent (7.7 sigma) with the
Suzaku result around and beyond the value of r200 estimated by Suzaku. We argue
that, thanks to its large field of view and low background, ROSAT/PSPC is to
the present day the most sensitive instrument to low surface-brightness X-ray
emission in the 0.4-2.0 keV band. We also note that the Suzaku temperature and
mass profiles are at odds with the results from at least two other satellites
(XMM-Newton and Swift). The difference in surface brightness between ROSAT and
Suzaku is most likely explained by the existence of additional foreground
components at the low Galactic latitude of the source, which were not taken
into account in the Suzaku background modeling. In light of our mass analysis,
we conclude that any estimate of the fraction of the virial radius reached by
X-ray measures is affected by systematic errors of the order of 25%. As a
result, the properties of the ICM at the virial radius are still uncertain, and
the Suzaku results should be considered with caution.Comment: 6 pages, 5 figures, accepted for publication in A&
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