666 research outputs found
Estimating Black Hole Masses in Triaxial Galaxies
Most of the super massive black hole mass estimates based on stellar
kinematics use the assumption that galaxies are axisymmetric oblate spheroids
or spherical. Here we use fully general triaxial orbit-based models to explore
the effect of relaxing the axisymmetric assumption on the previously studied
galaxies M32 and NGC 3379. We find that M32 can only be modeled accurately
using an axisymmetric shape viewed nearly edge-on and our black hole mass
estimate is identical to previous studies. When the observed 5 degrees
kinematical twist is included in our model of NGC 3379, the best shape is
mildly triaxial and we find that our best-fitting black hole mass estimate
doubles with respect to the axisymmetric model. This particular black hole mass
estimate is still within the errors of that of the axisymmetric model and
consistent with the M-sigma relationship. However, this effect may have a
pronounced impact on black hole demography, since roughly a third of the most
massive galaxies are strongly triaxial.Comment: Accepted for publication in MNRAS. 11 pages, 9 figures. PDFlate
Genetics of Uveal Melanoma and Cutaneous Melanoma: Two of a Kind?
Cutaneous melanoma and uveal melanoma both derive from melanocytes but show remarkable differences in tumorigenesis, mode of metastatic spread, genetic alterations, and therapeutic response. In this review we discuss the differences and similarities along with the genetic research techniques available and the contribution to our current understanding of melanoma. The several chromosomal aberrations already identified prove to be very strong predictors of decreased survival in CM and UM patients. Especially in UM, where the overall risk of metastasis is high (45%), genetic research might aid clinicians in selecting high-risk patients for future systemic adjuvant therapies
Immunoscintigraphy in axial spondyloarthritis : a new imaging modality for sacroiliac inflammation
Nuclear stellar discs in low-luminosity elliptical galaxies: NGC 4458 and NGC 4478
We present the detection of nuclear stellar discs in the low-luminosity
elliptical galaxies NGC 4458 and NGC 4478, which are known to host a
kinematically-decoupled core. Using archival HST imaging, and available
absorption line-strength index data based on ground-based spectroscopy, we
investigate the photometric parameters and the properties of the stellar
populations of these central structures. Their scale length, h, and face-on
central surface brightness, mu_0^c, fit on mu_0^c-h relation for galaxy discs.
For NGC 4458 these parameters are typical for nuclear discs, while the same
quantities for NGC 4478 lie between those of nuclear discs and the discs of
discy ellipticals. We present Lick/IDS absorption line-strength measurements of
Hbeta, Mgb, along the major and minor axes of the galaxies. We model these
data with simple stellar populations that account for the alpha/Fe
overabundance. The counter-rotating central disc of NGC 4458 is found to have
similar properties to the decoupled cores of bright ellipticals. This galaxy
has been found to be uniformly old despite being counter-rotating. In contrast,
the cold central disc of NGC 4478 is younger, richer in metals and less
overabundant than the main body of the galaxy. This points to a prolonged star
formation history, typical of an undisturbed disc-like, gas-rich (possibly
pre-enriched) structure.Comment: 11 pages, 8 figures, accepted for pubblication on MNRA
Living labs managing the intra-organizational knowledge exchange process when transitioning from closed to open innovation
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First Galaxy-Galaxy Lensing Measurement of Satellite Halo Mass in the CFHT Stripe-82 Survey
We select satellite galaxies from the galaxy group catalog constructed with
the SDSS spectroscopic galaxies and measure the tangential shear around these
galaxies with source catalog extracted from CFHT/MegaCam Stripe-82 Survey to
constrain the mass of subhalos associated with them. The lensing signal is
measured around satellites in groups with masses in the range [10^{13},
5x10^{14}]h^{-1}M_{sun}, and is found to agree well with theoretical
expectation. Fitting the data with a truncated NFW profile, we obtain an
average subhalo mass of log M_{sub}= 11.68 \pm 0.67 for satellites whose
projected distances to central galaxies are in the range [0.1, 0.3] h^{-1}Mpc,
and log M_{sub}= 11.68 \pm 0.76 for satellites with projected halo-centric
distance in [0.3, 0.5] h^{-1}Mpc. The best-fit subhalo masses are comparable to
the truncated subhalo masses assigned to satellite galaxies using abundance
matching and about 5 to 10 times higher than the average stellar mass of the
lensing satellite galaxies.Comment: 7 pages, 4 figures, accepted by MNRA
Natural Downsizing in Hierarchical Galaxy Formation
Stellar-population analyses of today's galaxies show "downsizing", where the
stars in more massive galaxies tend to have formed earlier and over a shorter
time span. We show that this phenomenon is not necessarily "anti-hierarchical"
but rather has its natural roots in the bottom-up clustering process of
dark-matter haloes. While the main progenitor does indeed show an opposite
effect, the integrated mass in all the progenitors down to a given minimum mass
shows a robust downsizing that is qualitatively similar to what has been
observed. These results are derived analytically from the standard extended
Press Schechter (EPS) theory, and are confirmed by merger trees based on EPS or
drawn from N-body simulations. The downsizing is valid for any minimum mass, as
long as it is the same for all haloes at any given time, but the effect is
weaker for smaller minimum mass. If efficient star formation is triggered by
atomic cooling, then a minimum halo mass arises naturally from the minimum
virial temperature for cooling, T~10^4 K, though for such a small minimum mass
the effect is weaker than observed. Baryonic feedback effects, which are
expected to stretch the duration of star formation in small galaxies and shut
it down in massive haloes at late epochs, are likely to play a subsequent role
in shaping up the final downsizing behaviour. Other appearances of downsizing,
such as the decline with time of the typical mass of star-forming galaxies, may
not be attributed to the gravitational clustering process but rather arise from
the gas processes.Comment: 16 pages, 16 figures; published in MNRAS; minor changes from first
versio
Internal alignments of red versus blue discs in dark matter haloes
Large surveys have shown that red galaxies are preferentially aligned with their haloes, while blue galaxies have a more isotropic distribution. Since haloes generally align with their filaments, this introduces a bias in the measurement of the cosmic shear from weak lensing. It is therefore vitally important to understand why this difference arises. We explore the stability of different disc orientations within triaxial haloes. We show that, in the absence of gas, the disc orientation is most stable when its spin is along the minor axis of the halo. Instead when gas cools on to a disc, it is able to form in almost arbitrary orientation, including off the main planes of the halo (but avoiding an orientation perpendicular to the halo's intermediate axis). Substructure helps gasless galaxies reach alignment with the halo faster, but has less effect on galaxies when gas is cooling on to the disc. Our results provide a novel and natural interpretation for why red, gas poor galaxies are preferentially aligned with their halo, while blue, star-forming, galaxies have nearly random orientations, without requiring a connection between galaxies' current star formation rate and their merger histor
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