798 research outputs found
Do the low PN velocity dispersions around elliptical galaxies imply that these lack dark matter?
While kinematical modelling of the low PN velocity dispersions observed in
the outer regions of elliptical galaxies suggest a lack of dark matter around
these galaxies, we report on an analysis of a suite of -body simulations
(with gas) of major mergers of spiral galaxies embedded in dark matter halos,
and find that the outer velocity dispersions are as low as observed for the
PNe. The inconsistency between our dynamical modelling and previous kinematical
modelling is caused by very radial stellar orbits and projection effects when
viewing face-on oblate ellipticals. Our simulations (weakly) suggest the youth
of PNe around ellipticals, and we propose that the universality of the PN
luminosity function may be explained if the bright PNe in ellipticals are
formed after the regular accretion of very low mass gas-rich galaxies.Comment: Contributed talk at meeting, "Planetary Nebulae as astronomical
tools", Gdansk, Poland, June-July 2005, ed. R. Szczerba, G. Stasi\'nska, and
S. K. G\'orny, AIP Conference Proceedings, Melville, New York, 2005. 4 or 5
pages, 6 figure
Lost and found dark matter in elliptical galaxies
The kinematical properties of elliptical galaxies formed during the mergers
of equal mass, stars+gas+dark matter spiral galaxies are compared to the
observed low velocity dispersions found for planetary nebulae on the outskirts
of ellipticals, which have been interpreted as pointing to a lack of dark
matter in ellipticals (which poses a problem for the standard model of galaxy
formation). We find that the velocity dispersion profiles of the stars in the
simulated ellipticals match well the observed ones. The low outer stellar
velocity dispersions are mainly caused by the radial orbits of the outermost
stars, which, for a given binding energy must have low angular momentum to
reach their large radial distances, usually driven out along tidal tails.Comment: Talk presented at 21st IAP meeting, Mass Profiles andShapes of
Cosmological Structures. Ed. G. A. Mamon, F. Combes, C. Deffayet & B. Fort
(Paris: EDP), 4 pages, 3 figures (4 plots
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
Bacillary angiomatosis in HIV-infected patients - An epidemiological and clinical study
Background: No data were available on the epidemiological and clinical characteristics of bacillary angiomatosis (BA) in Germany. Objective:To determine epidemiological and clinical data on HIV-associated BA. Methods: A chart review of all BA cases between 1990 and 1998 was performed in 23 German AIDS treatment units. Results: A total of 21 cases of BA was diagnosed. During th is period, the participating HIV centers treated about 17,000 HIV-infected patients. As a result, a BA prevalence of 1.2 cases/1,000 patients can be assumed. 19 BA were localized in the skin; in 5 cases bones and in 4 cases the liver were involved. Out of 20 patients who received antibiotic therapy, 13 had complete remission. The median time of duration up to complete remission was 32 days (9-82), During the follow-up of the 20 patients, 7 relapses were observed, Conclusion: BA is a rare HIV-associated disease with a prevalence of 1,2 cases/1,000 patients in the presented study. Copyright (C) 2000 S. Karger AG, Basel
Kinematic deprojection and mass inversion of spherical systems of known velocity anisotropy
Traditionally, the mass / velocity anisotropy degeneracy (MAD) inherent in
the spherical, stationary, non-streaming Jeans equation has been handled by
assuming a mass profile and fitting models to the observed kinematical data.
Here, the opposite approach is considered: the equation of anisotropic
kinematic projection is inverted for known arbitrary anisotropy to yield the
space radial velocity dispersion profile in terms of an integral involving the
radial profiles of anisotropy and isotropic dynamical pressure. Then, through
the Jeans equation, the mass profile is derived in terms of double integrals of
observable quantities. Single integral formulas for both deprojection and mass
inversion are provided for several simple anisotropy models (isotropic, radial,
circular, general constant, Osipkov-Merritt, Mamon-Lokas and
Diemand-Moore-Stadel). Tests of the mass inversion on NFW models with these
anisotropy models yield accurate results in the case of perfect observational
data, and typically better than 70% (in 4 cases out of 5) accurate mass
profiles for the sampling errors expected from current observational data on
clusters of galaxies. For the NFW model with mildly increasing radial
anisotropy, the mass is found to be insensitive to the adopted anisotropy
profile at 7 scale radii and to the adopted anisotropy radius at 3 scale radii.
This anisotropic mass inversion method is a useful complementary tool to
analyze the mass and anisotropy profiles of spherical systems. It provides the
practical means to lift the MAD in quasi-spherical systems such as globular
clusters, round dwarf spheroidal and elliptical galaxies, as well as groups and
clusters of galaxies, when the anisotropy of the tracer is expected to be
linearly related to the slope of its density.Comment: Accepted in MNRAS. 19 pages. Minor changes from previous version:
Table 1 of nomenclature, some math simplifications, paragraph in Discussion
on alternative deprojection method by deconvolution. 19 pages. 6 figure
The effect of minihaloes on cosmic reionization
One of the most debated issues in the theoretical modeling of cosmic
reionization is the impact of small-mass gravitationally-bound structures. We
carry out the first numerical investigation of the role of such sterile
`minihaloes', which serve as self-shielding screens of ionizing photons.
Minihaloes are too small to be properly resolved in current large-scale
cosmological simulations, and thus we estimate their effects using a sub-grid
model, considering two cases that bracket their effect within this framework.
In the `extreme suppression' case in which minihalo formation ceases once a
region is partially ionized, their effect on cosmic reionization is modest,
reducing the volume-averaged ionization fraction by an overall factor of less
than 15%. In the other extreme, in which minihalo formation is never
suppressed, they delay complete reionization as much as Delta z~2, in rough
agreement with the results from a previous semi-analytical study by the
authors. Thus, depending on the details of the minihalo formation process,
their effect on the overall progress of reionization can range from modest to
significant, but the minihalo photon consumption is by itself insufficient to
force an extended reionization epoch.Comment: 9 pages, 2 figures, accepted for pubblication in MNRA
The Hubble Legacy Archive ACS Grism Data
A public release of slitless spectra, obtained with ACS/WFC and the G800L
grism, is presented. Spectra were automatically extracted in a uniform way from
153 archival fields (or "associations") distributed across the two Galactic
caps, covering all observations to 2008. The ACS G800L grism provides a
wavelength range of 0.55-1.00 \mu40 \ \AA / pixel\sim 80\ \AA32,149i_{\rm
AB}0.2-4.6$.Comment: Accepted for publication in Astronomy and Astrophysics; 29 pages, 16
Figures, 4 Tables in text and 3Tables in Appendi
Fibroblast growth factor receptor (FGFR) alterations in squamous differentiated bladder cancer: a putative therapeutic target for a small subgroup.
Although drugable fibroblast growth factor receptor (FGFR) alterations in squamous cell carcinomas (SCC) of various entities are well known, little is known about FGFR modifications in squamous differentiated bladder cancer. Therefore, our study evaluated FGFR1-3 alterations as a putative therapeutic target in this subgroup. We analyzed 73 squamous differentiated bladder cancers (n = 10 pT2, n = 55 pT3, n = 8 pT4) for FGFR1-3 protein expression, FGFR1-3 copy number variations, FGFR3 chromosomal rearrangements (fluorescence in situ hybridization (FISH)) and FGFR3 mutations (SNapShot analysis). Only single cases displayed enhanced protein expression, most frequently FGFR3 overexpression (9.4% (6/64)). FISH showed no amplifications of FGFR1, 2 or 3. Break apart events were only slightly above the cut off in 12.1% (8/66) of cases and no FGFR3-TACC3 rearrangements could be proven by qPCR. FGFR3 mutations (p.S249C) were found in 8.5% (6/71) of tumors and were significantly associated with FGFR3 protein overexpression (p < 0.001), and unfavourable clinical outcome (p = 0.001). Our findings are consistent with the results of the TCGA data set for the "squamous-like" subtype of bladder cancer (n = 85), which revealed reduced overall expression of FGFR1 and FGFR2 in tumors compared to normal tissue, while expression of FGFR3 remained high. In the TCGA "squamous-like" subtype FGFR3 mutations were found in 4.9% and correlated with high FGFR3 RNA expression. Mutations of FGFR1 and FGFR2 were less frequent (2.4% and 1.2%). Hence, our comprehensive study provides novel insights into a subgroup of squamous differentiated bladder tumors that hold clues for novel therapeutic regimens and may benefit from FGFR3-targeted therapies
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