219 research outputs found
The Properties of Field Elliptical Galaxies at Intermediate Redshift. I: Empirical Scaling Laws
We present measurements of the Fundamental Plane (FP) parameters (the
effective radius, the mean effective surface brightness, and the central
velocity dispersion) of six field elliptical galaxies at intermediate redshift.
The imaging is taken from the Medium Deep Survey of the Hubble Space Telescope,
while the kinematical data are obtained from long-slit spectroscopy using the
3.6-m ESO telescope. The Fundamental Plane appears well defined in the field
even at redshift 0.3. The data show a shift in the FP zero point with
respect to the local relation, possibly indicating modest evolution, consistent
with the result found for intermediate redshift cluster samples. The FP slopes
derived for our field data, plus other cluster ellipticals at intermediate
redshift taken from the literature, differ from the local ones, but are still
consistent with the interpretation of the FP as a result of homology, of the
virial theorem and of the existence of a relation between luminosity and mass,
. We also derive the surface brightness vs. effective
radius relation for nine galaxies with redshift up to , and data
from the literature; the evolution that can be inferred is consistent with what
is found using the FP.Comment: 17 pages, including 9 figures, MNRAS, accepte
Ellipticals with Kinematically-Distinct Cores: (V-I) Color Images with WFPC2
We have analysed HST/WFPC2 F555W and F814W images for fifteen elliptical
galaxies with kinematically-distinct cores. For each of them we have derived
surface brightness and isophotal parameter profiles in the two bands, color
maps, and radial profiles in (V-I). We have detected photometric evidence for
faint stellar disks, on scales of a few tens to a few arcseconds, in seven
galaxies, namely NGC 1427, 1439, 1700, 4365, 4406, 4494 and 5322. In NGC 1700,
the isophotes are slightly boxy at the scale of the counter-rotating component,
and disky at larger radii. We find no difference in (V-I) color greater than
0.02 mag between these disks and the surrounding galactic regions. Hence the
stellar populations in the kinematically distinct cores are not strongly
deviant from the population of the main body. For one galaxy, NGC 4365, the
innermost region is bluer than the surrounding regions. This area extends to
about 15pc, and contains a luminosity of 2.5x10^6 L. If interpreted as
a stellar population effect, an age difference of 3-4 Gyrs, or an
variation of about 0.2 dex, is derived. The nuclear intensity profiles
show a large variety: some galaxies have steep cusp profiles, others have
shallow cusps and a ``break radius''. The nuclear cusps of galaxies with
kinematically-distinct cores follow the same trends as the nuclei of normal
galaxies. We have not been able to identify a unique, qualifying feature in the
WFPC2 images which distinguish the galaxies with kinematically distinct cores
from the kinematically normal cores. [shortened]Comment: 56 pages, latex, 17 figures; figure 1 available upon request; ApJ,
481 in pres
On the Afterglow of the X-Ray Flash of July 23 2003: Photometric evidence for an off-axis Gamma-Ray Burst with an associated Supernova?
We present optical and near-infrared follow-up observations of the X-Ray
Flash (XRF) of July 23 2003. Our observations in the R-band cover the temporal
range from 4.2 h to 64 days after the high energy event. We also present the
results of multicolor imaging extending to the K-band on three epochs. The
lightcurve of the R-band afterglow the first week after the burst is similar to
the lightcurve for long duration Gamma-Ray Bursts (GRBs), i.e., a broken
power-law with a late time slope of alpha=-2.0 (F_nu propto t^alpha).
Furthermore, the spectral energy distribution (SED) has a power-law (F_nu
propto nu^beta) shape with slope beta=-1.0. However, the decay slope at t<1 day
is shallow, consistent with zero. This is in qualitative agreement with the
prediction that XRFs are off-axis classical GRBs. After the first week there is
a strong bump in the lightcurve, which peaks at around 16 days. The SED after
the peak becomes significantly redder. We discuss the possible interpretations
of this bump, and conclude that an underlying supernova is the most likely
explanation since no other model appears consistent with the evolution of the
SED. Finally, we present deep spectroscopy of the burst both in the afterglow
and in the bump phase. A firm upper limit of z=2.3 is placed on the redshift of
XRF030723 from the lack of Ly-alpha forest lines in the spectrum of the
afterglow. The lack of significant absorption and emission lines in either of
the two spectra excludes a spectroscopic redshift determination.Comment: 9 pages, 5 figures. Accepted for publication in Ap
Breast cancer incidence and overdiagnosis in Catalonia (Spain)
Introduction: Early detection of breast cancer (BC) with mammography may cause overdiagnosis and overtreatment, detecting tumors which would remain undiagnosed during a lifetime. The aims of this study were:
first, to model invasive BC incidence trends in Catalonia (Spain) taking into account reproductive and screening data; and second, to quantify the extent of BC overdiagnosis.
Methods: We modeled the incidence of invasive BC using a Poisson regression model. Explanatory variables were: age at diagnosis and cohort characteristics (completed fertility rate, percentage of women that use mammography at age 50, and year of birth). This model also was used to estimate the background incidence in the absence of screening. We used a probabilistic model to estimate the expected BC incidence if women in the population used
mammography as reported in health surveys. The difference between the observed and expected cumulative incidences provided an estimate of overdiagnosis.
Results: Incidence of invasive BC increased, especially in cohorts born from 1940 to 1955. The biggest increase was observed in these cohorts between the ages of 50 to 65 years, where the final BC incidence rates more than doubled the initial ones. Dissemination of mammography was significantly associated with BC incidence and overdiagnosis. Our estimates of overdiagnosis ranged from 0.4% to 46.6%, for women born around 1935 and 1950,
respectively.
Conclusions: Our results support the existence of overdiagnosis in Catalonia attributed to mammography usage, and the limited malignant potential of some tumors may play an important role. Women should be better informed about this risk. Research should be oriented towards personalized screening and risk assessment tools
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