374 research outputs found
The Hubble Legacy Archive NICMOS Grism Data
The Hubble Legacy Archive (HLA) aims to create calibrated science data from
the Hubble Space Telescope archive and make them accessible via user-friendly
and Virtual Observatory (VO) compatible interfaces. It is a collaboration
between the Space Telescope Science Institute (STScI), the Canadian Astronomy
Data Centre (CADC) and the Space Telescope - European Coordinating Facility
(ST-ECF). Data produced by the Hubble Space Telescope (HST) instruments with
slitless spectroscopy modes are among the most difficult to extract and
exploit. As part of the HLA project, the ST-ECF aims to provide calibrated
spectra for objects observed with these HST slitless modes. In this paper, we
present the HLA NICMOS G141 grism spectra. We describe in detail the
calibration, data reduction and spectrum extraction methods used to produce the
extracted spectra. The quality of the extracted spectra and associated direct
images is demonstrated through comparison with near-IR imaging catalogues and
existing near-IR spectroscopy. The output data products and their associated
metadata are publicly available through a web form at http://hla.stecf.org and
via VO interfaces. In total, 2470 spectra of 1923 unique targets are included
in the current release.Comment: 18 pages, 21 figures, accepted for publication in Astronomy &
Astrophysic
The impact of dark matter cusps and cores on the satellite galaxy population around spiral galaxies
(Abridged) We use N-body simulations to study the effects that a divergent
(i.e. "cuspy") dark matter (DM) profile introduces on the tidal evolution of
dwarf spheroidal galaxies (dSphs). Our models assume cosmologically-motivated
initial conditions where dSphs are DM-dominated systems on eccentric orbits
about a host galaxy composed of a dark halo and a baryonic disc. We find that
the resilience of dSphs to tidal stripping is extremely sensitive to the halo
cuspiness; whereas dwarfs with a cored profile can be easily destroyed by the
host disc, those with cusps always retain a bound remnant. For a given halo
profile the evolution of the structural parameters as driven by tides is
controlled solely by the total amount of mass lost. This information is used to
construct a semi-analytic code that simulates the hierarchical build-up of
spiral galaxies assuming different halo profiles and disc masses. We find that
tidal encounters with discs tend to decrease the average mass of satellites at
all galactocentric radii. Interestingly, satellites accreted before
re-ionization (z>6), which may be singled out by anomalous metallicity
patterns, survive only if haloes are cuspy. We show that the size-mass relation
established from Milky Way (MW) dwarfs strongly supports the presence of cusps
in the majority of these systems, as cored models systematically underestimate
the masses of the known Ultra-Faint dSphs. Our models also indicate that a
massive M31 disc may explain why many of its dSphs fall below the size-mass
relationship derived from MW dSphs. We use our models to constrain the mass
threshold below which star formation is suppressed in DM haloes, finding that
luminous satellites must be accreted with masses above 10^8--10^9 M_sol in
order to explain the size-mass relation observed in MW dwarfs.Comment: 17 pages, 14 figures, MNRAS accepted after minor revisio
The VO: A Powerful Tool for Global Astronomy
Since its inception in the early 2000's, the Virtual Observatory (VO), developed as a collaboration of many national and international projects, has become a major factor in the discovery and dissemination of astronomical information worldwide. The International Virtual Observatory Alliance (IVOA) has been coordinating all these efforts worldwide to ensure a common VO framework that enables transparent access to and interoperability of astronomy resources (data and software) around the world. The VO is not a magic solution to all astronomy data management challenges but it does bring useful solutions in many areas borne out by the fact that VO interfaces are broadly found in astronomy's major data centres and projects worldwide. Astronomy data centres have been building VO services on top of their existing data services to increase interoperability with other VO-compliant data resources to take advantage of the continuous and increasing development of VO applications. VO applications have made multi-instrument and multi-wavelength science, a difficult and fruitful part of astronomy, somewhat easier. More recently, several major new astronomy projects have been directly adopting VO standards to build their data management infrastructure, giving birth to ‘VO built-in' archives. Embracing the VO framework from the beginning brings the double gain of not needing to reinvent the wheel and ensuring from the start interoperability with other astronomy VO resources. Some of the IVOA standards are also starting to be used by neighbour disciplines like planetary sciences. There is still quite a lot to be done on the VO, in particular tackling the upcoming big data challenge and how to find interoperable solutions to the new data analysis paradigm of bringing and running the software close to the data. We report on the current status and also desire to encourage others to adopt VO technology and engage them in the effort of developing the VO. Thus, we wish to ensure that the VO standards fit new astronomy projects requirements and needs
HIV-1 DNA predicts disease progression and post-treatment virological control.
In HIV-1 infection, a population of latently infected cells facilitates viral persistence despite antiretroviral therapy (ART). With the aim of identifying individuals in whom ART might induce a period of viraemic control on stopping therapy, we hypothesised that quantification of the pool of latently infected cells in primary HIV-1 infection (PHI) would predict clinical progression and viral replication following ART. We measured HIV-1 DNA in a highly characterised randomised population of individuals with PHI. We explored associations between HIV-1 DNA and immunological and virological markers of clinical progression, including viral rebound in those interrupting therapy. In multivariable analyses, HIV-1 DNA was more predictive of disease progression than plasma viral load and, at treatment interruption, predicted time to plasma virus rebound. HIV-1 DNA may help identify individuals who could safely interrupt ART in future HIV-1 eradication trials
Simulation techniques for cosmological simulations
Modern cosmological observations allow us to study in great detail the
evolution and history of the large scale structure hierarchy. The fundamental
problem of accurate constraints on the cosmological parameters, within a given
cosmological model, requires precise modelling of the observed structure. In
this paper we briefly review the current most effective techniques of large
scale structure simulations, emphasising both their advantages and
shortcomings. Starting with basics of the direct N-body simulations appropriate
to modelling cold dark matter evolution, we then discuss the direct-sum
technique GRAPE, particle-mesh (PM) and hybrid methods, combining the PM and
the tree algorithms. Simulations of baryonic matter in the Universe often use
hydrodynamic codes based on both particle methods that discretise mass, and
grid-based methods. We briefly describe Eulerian grid methods, and also some
variants of Lagrangian smoothed particle hydrodynamics (SPH) methods.Comment: 42 pages, 16 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 12; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
The Additional Representative Images for Legacy (ARI-L) project for the ALMA Science Archive
The Additional Representative Images for Legacy (ARI-L) project is a European
Development project for ALMA Upgrade approved by the Joint ALMA Observatory
(JAO) and the European Southern Observatory (ESO), started in June 2019. It
aims to increase the legacy value of the ALMA Science Archive (ASA) by bringing
the reduction level of ALMA data from Cycles 2-4 close to that of data from
more recent Cycles processed for imaging with the ALMA Pipeline. As of mid-2021
more than 150000 images have been returned to the ASA for public use. At its
completion in 2022, the project will have provided enhanced products for at
least 70% of the observational data from Cycles 2-4 processable with the ALMA
Pipeline. In this paper we present the project rationale, its implementation,
and the new opportunities offered to ASA users by the ARI-L products. The ARI-L
cubes and images complement the much limited number of archival image products
generated during the data quality assurance stages (QA2), which cover only a
small fraction of the available data for those Cycles. ARI-L imaging products
are highly relevant for many science cases and significantly enhance the
possibilities for exploiting archival data. Indeed, ARI-L products facilitate
archive access and data usage for science purposes even for non-expert data
miners, provide a homogeneous view of all data for better dataset comparisons
and download selections, make the archive more accessible to visualization and
analysis tools, and enable the generation of preview images and plots similar
to those possible for subsequent Cycles.Comment: 15 pages. Accepted for publication in PAS
Indirect search for dark matter: prospects for GLAST
Possible indirect detection of neutralino, through its gamma-ray annihilation
product, by the forthcoming GLAST satellite from our galactic halo, M31, M87
and the dwarf galaxies Draco and Sagittarius is studied. Gamma-ray fluxes are
evaluated for the two representative energy thresholds, 0.1 GeV and 1.0 GeV, at
which the spatial resolution of GLAST varies considerably. Apart from dwarfs
which are described either by a modified Plummer profile or by a
tidally-truncated King profiles, fluxes are compared for halos with central
cusps and cores. It is demonstrated that substructures, irrespective of their
profiles, enhance the gamma-ray emission only marginally. The expected
gamma-ray intensity above 1 GeV at high galactic latitudes is consistent with
the residual emission derived from EGRET data if the density profile has a
central core and the neutralino mass is less than 50 GeV, whereas for a central
cusp only a substantial enhancement would explain the observations. From M31,
the flux can be detected above 0.1 GeV and 1.0 GeV by GLAST only if the
neutralino mass is below 300 GeV and if the density profile has a central cusp,
case in which a significant boost in the gamma-ray emission is produced by the
central black hole. For Sagittarius, the flux above 0.1 GeV is detectable by
GLAST provided the neutralino mass is below 50 GeV. From M87 and Draco the
fluxes are always below the sensitivity limit of GLAST.Comment: 14 Pages, 7 Figures, 3 Tables, version to appear on Physical Review
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