4,240 research outputs found
The Properties of Satellite Galaxies in External Systems. I. Morphology and Structural Parameters
We present the first results of an ongoing project to study the
morphological, kinematical, dynamical, and chemical properties of satellite
galaxies of external giant spiral galaxies. The sample of objects has been
selected from the catalogue by Zaritsky et al. (1997). The paper analyzes the
morphology and structural parameters of a subsample of 60 such objects. The
satellites span a great variety of morphologies and surface brightness
profiles. About two thirds of the sample are spirals and irregulars, the
remaining third being early-types. Some cases showing interaction between pairs
of satellites are presented and briefly discussed.Comment: Accepted for publication in Astrophys. Journal Supp. Se
Re-description of Togwoteeus biceps (Arachnida, Opiliones, Sclerosomatidae) with notes on its morphology, karyology and phenology.
The harvestman genus Togwoteeus Roewer 1952 is monotypic. Its only species, T. biceps
(Thorell 1877), is known from throughout western Canada and USA and is newly recorded from California,
Nebraska, Nevada, Oregon, South Dakota, and Utah. This species occurs below 500 m and at the
highest elevation (4100 m) of any recorded harvestman in North America. It ranges from about 33-54°
N and exhibits considerable variation in its morphological measurements. Twenty-seven such measurements
are summarized for 80 males and 74 females. Ultrastructural details of the integument, appendages
and genital organs are presented. The karyotype is 2n = 22 for both sexes. All chromosomes are metacentric
and obvious sex chromosomes were not detected. Immature T. biceps overwinter and reach adulthood
in late spring or early summer. Adults die by late fall
A Hubble Space Telescope Snapshot Survey of Dynamically Close Galaxy Pairs in the CNOC2 Redshift Survey
We compare the structural properties of two classes of galaxies at
intermediate redshift: those in dynamically close galaxy pairs, and those which
are isolated. Both samples are selected from the CNOC2 Redshift Survey, and
have redshifts in the range 0.1 < z <0.6. Hubble Space Telescope WFPC2 images
were acquired as part of a snapshot survey, and were used to measure bulge
fraction and asymmetry for these galaxies. We find that paired and isolated
galaxies have identical distributions of bulge fractions. Conversely, we find
that paired galaxies are much more likely to be asymmetric (R_T+R_A >= 0.13)
than isolated galaxies. Assuming that half of these pairs are unlikely to be
close enough to merge, we estimate that 40% +/- 11% of merging galaxies are
asymmetric, compared with 9% +/- 3% of isolated galaxies. The difference is
even more striking for strongly asymmetric (R_T+R_A >= 0.16) galaxies: 25% +/-
8% for merging galaxies versus 1% +/- 1% for isolated galaxies. We find that
strongly asymmetric paired galaxies are very blue, with rest-frame B-R colors
close to 0.80, compared with a mean (B-R)_0 of 1.24 for all paired galaxies. In
addition, asymmetric galaxies in pairs have strong [OII]3727 emission lines. We
conclude that close to half of the galaxy pairs in our sample are in the
process of merging, and that most of these mergers are accompanied by triggered
star formation.Comment: Accepted for publication in the Astronomical Journal. 40 pages,
including 15 figures. For full resolution version, please see
http://www.trentu.ca/physics/dpatton/hstpairs
Radiation to supraclavicular and internal mammary lymph nodes in breast cancer increases the risk of stroke
The aim of this study was to assess whether adjuvant treatment of breast cancer (BC) affects the risk of stroke, and to explore radiation targets and fraction doses regarding risk and location of stroke. In a Swedish BC cohort diagnosed during 1970–2003, we carried out a nested case–control study of stroke after BC, with relevant details extracted from medical records. The odds ratio (OR) for radiotherapy (RT) vs that of no RT did not differ between cases and controls (OR=0.85; confidence interval, CI=0.6–1.3). Radiotherapy to internal mammary chain (IMC) and supraclavicular (SCL) lymph nodes vs that of no RT was associated with a higher, although not statistically significant, risk of stroke (OR=1.3; CI=0.8–2.2). In a pooled analysis, RT to IMC and SCL vs the pooled group of no RT and RT to breast/chest wall/axilla (but not IMC and SCL), showed a significant increase of stroke (OR=1.8; CI=1.1–2.8). There were no associations between cancer laterality, targets of RT, and location of stroke. The radiation targets, IMC and SCL, showed a statistically significant trend for an increased risk of stroke with daily fraction dose. Our finding of a target-specific increased risk of stroke and a dose-response relationship for daily fraction dose, indicate that there may be a causal link between RT to the IMC and SCL and risk of stroke
The influence of nitrogen and phosphorus ferilization on nutrient status and profitability of Bromegrass on Ida soils
This study was undertaken to determine the profitability and the feasibility of fertilizing bromegrass for grazing in the Monona-Ida-Hamburg soil association area. This area is well adapted to growing forage crops. Because of the high content of calcium and potassium, alfalfa grows well if phosphorus is applied. Bromegrass is able in some way to get nitrogen from alfalfa, and the two crops grow well together. The bloat danger in pasturing alfalfa or bromegrass-alfalfa mixtures, however, is well known to cattlemen in the area. Many believe the cost of nitrogen fertilizer to maintain productivity of bromegrass pastures is less than the cost of losses from bloat on bromegrass-alfalfa pastures.
The profitability of fertilizing bromegrass stands is examined in Part I of the study. The feasibility is examined in Part II. In Part I, returns at three levels of nitrogen cost and beef price and at three conversion ratios of forage to beef are calculated on the basis of experimental yields
A Physically-Motivated Photometric Calibration of M Dwarf Metallicity
The location of M dwarfs in the V-K_s--M_Ks color-magnitude diagram (CMD) has
been shown to correlate with metallicity. We demonstrate that previous
empirical photometric calibrations of M dwarf metallicity exploiting this
correlation systematically underestimate or overestimate metallicity at the
extremes of their range. We improve upon previous calibrations in three ways.
We use both a volume-limited and kinematically-matched sample of F and G dwarfs
from the Geneva-Copehnagen Survey (GCS) to infer the mean metallicity of M
dwarfs in the Solar Neighborhood, we use theoretical models of M dwarf
interiors and atmospheres to determine the effect of metallicity on M dwarfs in
the V-K_s--M_Ks CMD, and we base our final calibration purely on
high-resolution spectroscopy of FGK primaries with M dwarf companions. As a
result, we explain an order of magnitude more of the variance in the
calibration sample than previous photometric calibrations. We
non-parametrically quantify the significance of the observation that M dwarfs
that host exoplanets are preferentially in a region of the V-K_s--M_Ks plane
populated by metal-rich M dwarfs. We find that the probability p that
planet-hosting M dwarfs are distributed across the V-K_s--M_Ks CMD in the same
way as field M dwarfs is p = 0.06 +/- 0.008. Interestingly, the subsample of M
dwarfs that host Neptune and sub-Neptune mass planets may also be
preferentially located in the region of the V-K_s--M_Ks plane populated by
high-metallicity M dwarfs. The probability of this occurrence by chance is p =
0.40 +/- 0.02, and this observation hints that low-mass planets may be more
likely to be found around metal-rich M dwarfs. An increased rate of low-mass
planet occurrence around metal-rich M dwarfs would be a natural consequence of
the core-accretion model of planet formation. (abridged)Comment: 10 pages, 4 figures, and 1 table in A&A format; accepted for
publication in A&
The Relationship Between Stellar Light Distributions of Galaxies and their Formation Histories
A major problem in extragalactic astronomy is the inability to distinguish in
a robust, physical, and model independent way how galaxy populations are
related to each other and to their formation histories. A similar, but
distinct, and also long standing question is whether the structural appearances
of galaxies, as seen through their stellar light distributions, contain enough
physical information to offer this classification. We argue through the use of
240 images of nearby galaxies that three model independent parameters measured
on a single galaxy image reveal its major ongoing and past formation modes, and
can be used as a robust classification system. These parameters quantitatively
measure: the concentration (C), asymmetry (A) and clumpiness (S) of a galaxy's
stellar light distribution. When combined into a three dimensional `CAS' volume
all major classes of galaxies in various phases of evolution are cleanly
distinguished. We argue that these three parameters correlate with important
modes of galaxy evolution: star formation and major merging activity. This is
argued through the strong correlation of Halpha equivalent width and broad band
colors with the clumpiness parameter, the uniquely large asymmetries of 66
galaxies undergoing mergers, and the correlation of bulge to total light
ratios, and stellar masses, with the concentration index. As an obvious goal is
to use this system at high redshifts to trace evolution, we demonstrate that
these parameters can be measured, within a reasonable and quantifiable
uncertainty, with available data out to z ~ 3 using the Hubble Space Telescope
GOODS ACS and Hubble Deep Field images.Comment: ApJS, in press, 30 pages, Figures 15 and 16 are in color. For a full
resolution version, please go to http://www.astro.caltech.edu/~cc/cas.p
Galactic Extinction from Colors and Counts of Field Galaxies in WFPC2 Frames: An Application to GRB 970228
We develop the ``simulated extinction method'' to measure average foreground
Galactic extinction from field galaxy number-counts and colors. The method
comprises simulating extinction in suitable reference fields by changing the
isophotal detection limit. This procedure takes into account selection effects,
in particular, the change in isophotal detection limit (and hence in isophotal
magnitude completeness limit) with extinction, and the galaxy color--magnitude
relation.
We present a first application of the method to the HST WFPC2 images of the
gamma-ray burster GRB 970228. Four different WFPC2 high-latitude fields,
including the HDF, are used as reference to measure the average extinction
towards the GRB in the F606W passband. From the counts, we derive an average
extinction of A_V = 0.5 mag, but the dispersion of 0.4 mag between the
estimates from the different reference fields is significantly larger than can
be accounted by Poisson plus clustering uncertainties. Although the counts
differ, the average colors of the field galaxies agree well. The extinction
implied by the average color difference between the GRB field and the reference
galaxies is A_V = 0.6 mag, with a dispersion in the estimated extinction from
the four reference fields of only 0.1 mag. All our estimates are in good
agreement with the value of 0.81\pm0.27 mag obtained by Burstein & Heiles, and
with the extinction of 0.78\pm0.12 measured by Schlegel et al. from maps of
dust IR emission. However, the discrepancy between the widely varying counts
and the very stable colors in these high-latitude fields is worth
investigating.Comment: 14 pages, 2 figures; submitted to the Astrophysical Journa
The Anisotropic Distribution of Galactic Satellites
We present a study of the spatial distribution of subhalos in galactic dark
matter halos using dissipationless cosmological simulations of the concordance
LCDM model. We find that subhalos are distributed anisotropically and are
preferentially located along the major axes of the triaxial mass distributions
of their hosts. The Kolmogorov-Smirnov probability for drawing our simulated
subhalo sample from an isotropic distribution is P_KS \simeq 1.5 \times
10^{-4}. An isotropic distribution of subhalos is thus not the correct null
hypothesis for testing the CDM paradigm. The nearly planar distribution of
observed Milky Way (MW) satellites is marginally consistent (probability \simeq
0.02) with being drawn randomly from the subhalo distribution in our
simulations. Furthermore, if we select the subhalos likely to be luminous, we
find a distribution that is consistent with the observed MW satellites. In
fact, we show that subsamples of the subhalo population with a
centrally-concentrated radial distribution, similar to that of the MW dwarfs,
typically exhibit a comparable degree of planarity. We explore the origin of
the observed subhalo anisotropy and conclude that it is likely due to (1)
preferential accretion of subhalos along filaments, often closely aligned with
the major axis of the host halo, and (2) evolution of satellite orbits within
the prolate, triaxial potentials typical of CDM halos. Agreement between
predictions and observations requires the major axis of the outer dark matter
halo of the Milky Way to be nearly perpendicular to the disk. We discuss
possible observational tests of such disk-halo alignment with current large
galaxy surveys.Comment: 14 pages (including appendix), 9 figures. Accepted for Publication in
ApJ. Minor changes to reflect referee's comment
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