3,275 research outputs found
The Bose-Einstein Correlations and the strong coupling constant at low energies
It is shown that , the strong coupling constant, can be
determined in the non-perturbative regime from Bose-Einstein correlations
(BEC). The obtained is in agreement with the prescriptions dealt
with in the Analytic Perturbative Theory approach. It also extrapolates
smoothly to the standard perturbative at higher energies. Our
results indicate that BEC dimension can be considered as an alternative
approach to the short range measure between hadrons.Comment: 7 pages, 4 figure
Experience with selected physical methods to characterize the suitability of growing media for plant growth
Halo Mass Profiles and Low Surface Brightness Galaxies Rotation Curves
A recent study has claimed that the rotation curve shapes and mass densities
of Low Surface Brightness (LSB) galaxies are largely consistent with
CDM predictions, in contrast to a large body of observational work. I
demonstrate that the method used to derive this conclusion is incapable of
distinguishing the characteristic steep CDM mass-density distribution from the
core-dominated mass-density distributions found observationally: even
core-dominated pseudo-isothermal haloes would be inferred to be consistent with
CDM. This method can therefore make no definitive statements on the
(dis)agreement between the data and CDM simulations. After introducing an
additional criterion that does take the slope of the mass-distribution into
account I find that only about a quarter of the LSB galaxies investigated are
possibly consistent with CDM. However, for most of these the fit parameters are
so weakly constrained that this is not a strong conclusion. Only 3 out of 52
galaxies have tightly constrained solutions consistent with CDM. Two
of these galaxies are likely dominated by stars, leaving only one possible dark
matter dominated, CDM-consistent candidate, forming a mere 2 per cent of the
total sample. These conclusions are based on comparison of data and simulations
at identical radii and fits to the entire rotation curves. LSB galaxies that
are consistent with CDM simulations, if they exist, seem to be rare indeed.Comment: Accepted for publication in Astrophysical Journa
The First CO Map of a Low Surface Brightness Galaxy
Using the Owens Valley Radio Observatory Millimeter-Wavelength Array (OVRO)
we have obtained the first CO map of a low surface brightness (LSB) galaxy. The
studied galaxy, UGC 01922, was chosen for these observations because both of
its previous CO detection with the IRAM 30m telescope and its classification as
a Malin 1 `cousin' - an LSB galaxy with M_HI > 10^10 Msol. The OVRO map
detected approximately 65% of the CO(1-0) flux found earlier with the single
dish measurements, giving a detected gas mass equivalent to M_H2 = 1.1X10^9
Msol. The integrated gas peak lies at the center of the galaxy and coincides
with both the optical and 1.4 GHz continuum emission peaks. The molecular gas
extends well beyond the OVRO beam size (~4'' or 3 kpc), covering ~25% of the
optical bulge. In all, perhaps the most remarkable aspect of this map is its
unexceptional appearance. Given that it took over ten years to successfully
detect molecular gas in any low surface brightness system, it is surprising
that the appearance and distribution of UGC 01922's CO is similar to what would
be expected for a high surface brightness galaxy in the same morphological
class.Comment: 5 pages, including 3 figures and 3 tables. also available online at
http://www.gb.nrao.edu/~koneil. Accepted by ApJ
A practical and low cost microbiotest to assess the phytotoxic potential of growing media and soil
For routine toxicity testing of composts and growing media, two different types of assays are usually applied. One approach is the use of growing trials in pots with various mixtures of the material. In extract-based tests, seeds are germinated in petri dishes and exposed to an exudate from the material to be tested. In this study, one of these methods, the Phytotoxkit microbiotest, was compared to the standard phytotoxicity test with Lactuca sativa as used by the RHP foundation. The Phytotoxkit test was performed in transparent test containers which allow for direct observation and length measurements of the seedlings by means of image analysis. Two dicotyles (Lepidium sativum and Sinapis alba) and one monocotyle (Sorghum saccharatum) were used. When measuring a presumably phytotoxic bark, in comparison with a reference bark, the Phytotoxkit showed a seedling length inhibition of 60Âż80% for the dicotyles and less than 20% for the monocotyle after three days. The RHP growing trial showed 30% weight inhibition of the lettuce after two weeks of plant growth when comparing the same barks in mixtures. This preliminary comparison showed that the Phytotoxkit microbiotest is a quick and practical bioassay with a high resolution which has a potential to become an international standard
Mass Density Profiles of LSB Galaxies
We derive the mass density profiles of dark matter halos that are implied by
high spatial resolution rotation curves of low surface brightness galaxies. We
find that at small radii, the mass density distribution is dominated by a
nearly constant density core with a core radius of a few kpc. For rho(r) ~ r^a,
the distribution of inner slopes a is strongly peaked around a = -0.2. This is
significantly shallower than the cuspy a < -1 halos found in CDM simulations.
While the observed distribution of alpha does have a tail towards such extreme
values, the derived value of alpha is found to depend on the spatial resolution
of the rotation curves: a ~ -1 is found only for the least well resolved
galaxies. Even for these galaxies, our data are also consistent with constant
density cores (a = 0) of modest (~ 1 kpc) core radius, which can give the
illusion of steep cusps when insufficiently resolved. Consequently, there is no
clear evidence for a cuspy halo in any of the low surface brightness galaxies
observed.Comment: To be published in ApJ Letters. 6 pages. Uses aastex and
emulateapj5.sty Typo in Eq 1 fixe
The bimodal spiral galaxy surface brightness distribution
We have assessed the significance of Tully and Verheijen's (1997) bimodal
Ursa Major Cluster spiral galaxy near-infrared surface brightness distribution,
focussing on whether this bimodality is simply an artifact of small number
statistics. A Kolmogorov-Smirnov style of significance test shows that the
total distribution is fairly represented by a single-peaked distribution, but
that their isolated galaxy subsample (with no significant neighbours within a
projected distance of around 80 kpc) is bimodal at the 96 per cent level. We
have also investigated the assumptions underlying the isolated galaxy surface
brightness distribution, finding that the (often large) inclination corrections
used in the construction of this distribution reduce the significance of the
bimodality. We conclude that the Ursa Major Cluster dataset is insufficient to
establish the presence of a bimodal near-infrared surface brightness
distribution: an independent sample of around 100 isolated, low inclination
galaxies is required to establish bimodality at the 99 per cent level.Comment: 5 pages LaTeX; 2 embedded figures; re-submitted to MNRAS after
replying to referee's comment
Further Discoveries of 12CO in Low Surface Brightness Galaxies
Using the IRAM 30m telescope we have obtained seven new, deep CO J(1-0) and
J(2-1) observations of low surface brightness (LSB) galaxies. Five of the
galaxies have no CO detected to extremely low limits (0.1-0.4 K km/s at
J(1-0)), while two of the galaxies, UGC 01922 and UGC 12289, have clear
detections in both line transitions. When these observations are combined with
all previous CO observations taken of LSB systems, we compile a total of 34
observations, in which only 3 galaxies have had detections of their molecular
gas. Comparing the LSB galaxies with and without CO detections to a sample of
high surface brightness (HSB) galaxies with CO observations indicates that it
is primarily the low density of baryonic matter within LSB galaxies which is
causing their low CO fluxes. Finally, we note that one of the massive LSB
galaxies studied in this project, UGC 06968 (a Malin-1 `cousin'), has upper
limits placed on both M_H2 and M_H2/M_HI which are 10-20 times lower than the
lowest values found for any galaxy (LSB or HSB) with similar global properties.
This may be due to an extremely low temperature and metallicity within UGC
06968, or simply due to the CO distribution within the galaxy being too diffuse
to be detected by the IRAM beam.Comment: 18 pages, 8 figures, 4 tables. Accepted by Ap
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