762 research outputs found
On the Metallicity-Color Relations and Bimodal Color Distributions in Extragalactic Globular Cluster Systems
We perform a series of numerical experiments to study how the nonlinear
metallicity--color relations predicted by different stellar population models
affect the color distributions observed in extragalactic globular cluster
systems. % We present simulations in the bandpasses based on five
different sets of simple stellar population (SSP) models. The presence of
photometric scatter in the colors is included as well. % We find that unimodal
metallicity distributions frequently ``project'' into bimodal color
distributions. The likelihood of this effect depends on both the mean and
dispersion of the metallicity distribution, as well as of course on the SSP
model used for the transformation. % Adopting the Teramo-SPoT SSP models for
reference, we find that optical--to--near-IR colors should be favored with
respect to other colors to avoid the bias effect in globular cluster color
distributions discussed by \citet{yoon06}. In particular, colors such as \vh\
or \vk are more robust against nonlinearity of the metallicity--color relation,
and an observed bimodal distribution in such colors is more likely to indicate
a true underlying bimodal metallicity distribution. Similar conclusions come
from the simulations based on different SSP models, although we also identify
exceptions to this result.Comment: ApJ accepte
Trends in illegal wildlife trade: Analyzing personal baggage seizure data in the Pacific Northwest.
This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.The illegal import of wildlife and wildlife products is a growing concern, and the U.S. is one of the world’s leading countries in the consumption and transit of illegal wildlife and their derivatives. Yet, few U.S. studies have analyzed the illegal wildlife trade (IWT) on a national or local scale. Moreover, to our knowledge, no studies have specifically examined the trends associated with IWT moving through personal baggage. This work aimed to better understand the magnitude of illegal wildlife importation into U.S. ports of entry by determining trends associated with illegal wildlife products from personal baggage seizures, using the Pacific Northwest (PNW) as a specific case study. To identify the most influential factors determining the numbers and types of personal baggage seizures into PNW, we analyzed 1,731 records between 1999 and 2016 from the Fish and Wildlife Service’s (FWS) Law Enforcement Management Information System (LEMIS) database. We found five significant contributors: taxonomic classification of wildlife, categorical import date, wildlife product, source region, and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) status. While wildlife seizures across taxonomic categories have generally decreased in the PNW since 2008, other findings provide a reason for concern. More specifically, mammals were identified as the largest animal group of seized wildlife, and temporal trends indicate increases in seizures for this and several other taxonomic groups. Many of the seizures originated from overseas, with East Asia serving as the largest source. Our PNW case study can be a model for how large-scale geographical seizure data can be used to inform about the major factors that have historically and presently contribute to IWT, with conservation implications globally.ECU Open Access Publishing Support Fun
Global Patterns of Lightning Properties Derived by LIS
The Lightning Imaging Sensor LIS aboard the TRMM satellite provides unmatched empirical data of the global lightning distribution (up to approx.35deg S/N) since end of 1997. Climatological flash rate densities derived from LIS are standard references, e.g. for flash rate parameterizations used in GCMs. It is known that flash characteristics are quite variable, and that various quantities (like the flash energy or the NOx production per flash) vary considerably, statistically as well as systematically on regional and seasonal scales. LIS provides information beyond flash counts, in particular radiance and flash footprint. Here we present an analysis of global patterns of various lightning properties derived from LIS, in relation to the number of flashes. These normalized flash characteristics show consistent spatial patterns of regions with "strong" versus regions with "weak" lightning. Most striking is a clear land-ocean contrast, with oceanic flashes being "stronger" than continental flashes. But also over continents, flash strength shows systematic variations. Highest continental values are found over the US, while values over South America and India are quite low. These regional variations cannot be simply parameterized as function of latitude. Information on spatial patterns of mean flash "strength", though rather qualitative up to now, is potentially a valuable input for improving empirical parameterizations based on flash counts (like precipitation or lightning NOx). Further investigation is in progress to come to a more physical and quantitative understanding of the spatial patterns of the different LIS properties. In particular, it has to be checked how far they could be related to established lightning properties (like energy or the fraction of intra-cloud to cloud-to-ground flashes) or to meteorological quantities (like CAPE)
Comment on 'Current Budget of the Atmospheric Electric Global Circuit'
In this paper, three major issues relevant to Kasemir's new model will be addressed. The first concerns Kasemir's assertion that there are significant differences between the potentials associated with the new model and the conventional model. A recalculation of these potentials reveals that both models provide equivalent results for the potential difference between the Earth and ionosphere. The second issue to be addressed is Kasemir's assertion that discrepancies in the electric potentials associated with both models can be attributed to modeling the Earth as a sphere, instead of as a planar surface. A simple analytical comparison will demonstrate that differences in the equations for the potentials of the atmosphere derived with a spherical and a planar Earth are negligible for applications to global current flow. Finally, the third issue to be discussed is Kasemir's claim that numerous aspects of the conventional model are incorrect, including the role of the ionosphere in global current flow as well as the significance of cloud-to-ground lightning in supplying charge to the global circuit. In order to refute these misconceptions, it will be shown that these aspects related to the flow of charge in the atmosphere are accurately described by the conventional model of the global circuit
The SBF Survey of Galaxy Distances. II. Local and Large-Scale Flows
We present analysis of local large scale flows using the Surface Brightness
Fluctuation (SBF) Survey for the distances to 300 early-type galaxies. Our
models of the distribution function of mean velocity and velocity dispersion at
each point in space include a uniform thermal velocity dispersion and spherical
attractors whose position, amplitude, and radial shape are free to vary. Our
fitting procedure performs a maximum likelihood fit of the model to the
observations. We obtain a Hubble constant of Ho = 77 +/- 4 +/- 7 km/s/Mpc, but
a uniform Hubble flow is not acceptable fit to the data. Inclusion of two
attractors, one of whose fit location coincides with the Virgo cluster and the
other whose fit location is slightly beyond the Centaurus clusters nearly
explain the peculiar velocities, but the quality of the fit can be further
improved by the addition of a quadrupole correction to the Hubble flow.
Although the dipole and quadrupole may be genuine manifestations of more
distant density fluctuations, we find evidence that they are more likely due to
non-spherical attractors. We find no evidence for bulk flows which include our
entire survey volume (R < 3000 km/s); our volume is at rest with respect to the
CMB. The fits to the attractors both have isothermal radial profiles (v ~ 1/r)
over a range of overdensity between about 10 and 1, but fall off more steeply
at larger radius. The best fit value for the small scale, cosmic thermal
velocity is 180 +/- 14 km/s.Comment: 37 pages, AASTeX Latex, including 30 Postscript figures, submitted to
Astrophysical Journal, July 2, 199
An Old Cluster in NGC 6822
We present spectroscopy of two clusters in the dwarf irregular galaxy NGC
6822. From these we deduce an age for Cluster VII of 11 Gyr and [Fe/H] = -1.95
+/- 0.15 dex. Cluster VII appears to be an analog of the metal-poor galactic
globular clusters. Cluster VI is found to be much younger and more metal rich,
with an age of approximately 2 Gyr. Its derived metallicity, [Fe/H], of
approximately -1.0 dex is comparable to that of the gas seen today in NGC 6822.
The existence of a metal-poor old cluster in NGC 6822 rules out models for the
chemical evolution of this galaxy with significant prompt initial enhancement.
We find that a star formation rate which is constant with time and is within a
factor of two of the present star formation rate can reproduce the two points
on the age-metallicity relationship for NGC 6822 over the past 10 Gyr defined
by these two clusters.Comment: 8 pages; accepted for publication in A
Slow, Steady-State Transport with "Loading" and Bulk Reactions: the Mixed Ionic Conductor LaCuO
We consider slow, steady transport for the normal state of the superconductor
LaCuO in a one-dimensional geometry, with surface fluxes
sufficiently general to permit oxygen to be driven into the sample (``loaded'')
either by electrochemical means or by high oxygen partial pressure. We include
the bulk reaction OO, where neutral atoms () go into ions
() and holes (). For slow, steady transport, the transport equations
simplify because the bulk reaction rate density and the bulk loading rates
then are uniform in space and time. All three fluxes must be
specified at each surface, which for a uniform current density corresponds
to five independent fluxes. These fluxes generate two types of static modes at
each surface and a bulk response with a voltage profile that varies
quadratically in space, characterized by and the total oxygen flux
(neutral plus ion) at each surface. One type of surface mode is associated with
electrical screening; the other type is associated both with diffusion and
drift, and with chemical reaction (the {\it diffusion-reaction mode}). The
diffusion-reaction mode is accompanied by changes in the chemical potentials
, and by reactions and fluxes, but it neither carries current (J=0) nor
loads the system chemically (). Generation of the diffusion-reaction
mode may explain the phenomenon of ``turbulence in the voltage'' often observed
near the electrodes of other mixed ionic electronic conductors (MIECs).Comment: 11 pages, 1 figur
Imprints of Environment on Cluster and Field Late-type Galaxies at z~1
We present a comparison of late-type galaxies (Sa and later) in intermediate
redshift clusters and the field using ACS imaging of four cluster fields:
CL0152-1357, CL1056-0337 (MS1054), CL1604+4304, and CL1604+4321. Concentration,
asymmetry, and clumpiness parameters are calculated for each galaxy in blue
(F606W or F625W) and red (F775W or F814W) filters. Galaxy half-light radii,
disk scale lengths, color gradients, and overall color are compared. We find
marginally significant differences in the asymmetry distributions of spiral and
irregular galaxies in the X-ray luminous and X-ray faint clusters. The massive
clusters contain fewer galaxies with large asymmetries. The physical sizes of
the cluster and field populations are similar; no significant differences are
found in half-light radii or disk scale lengths. The most significant
difference is in rest-frame color. Late-type cluster galaxies are
significantly redder, magnitudes at rest-frame , than their
field counterparts. Moreover, the intermediate-redshift cluster galaxies tend
to have blue inward color gradients, in contrast to the field galaxies, but
similar to late-type galaxies in low redshift clusters. These blue inward color
gradients are likely to be the result of enhanced nuclear star formation rates
relative to the outer disk. Based on the significant rest-frame color
difference, we conclude that late-type cluster members at are not a
pristine infalling field population; some difference in past and/or current
star formation history is already present. This points to high redshift
``groups'', or filaments with densities similar to present-day groups, as the
sites where the first major effects of environment are imprinted.Comment: updated titl
Star Formation at z~6: The UDF-Parallel ACS Fields
We report on the i-dropouts detected in two exceptionally deep ACS fields
(B_{435}, V_{606}, i_{775}, and z_{850} with 10 sigma limits of 28.8, 29.0,
28.5, and 27.8, respectively) taken in parallel with the UDF NICMOS
observations. Using an i-z>1.4 cut, we find 30 i-dropouts over 21 arcmin^2 down
to z_AB=28.1, or 1.4 i-dropouts arcmin^{-2}, with significant field-to-field
variation (as expected from cosmic variance). This extends i-dropout searches
some ~0.9^m further down the luminosity function than was possible in the GOODS
field, netting a ~7x increase in surface density. An estimate of the size
evolution for UV bright objects is obtained by comparing the composite radial
flux profile of the bright i-dropouts (z<27.2) with scaled versions of the
HDF-N + HDF-S U-dropouts. The best-fit is found with a (1+z)^{-1.57_{-0.53}
^{+0.50}} scaling in size (for fixed luminosity), extending lower redshift
(1<z<5) trends to z~6. Adopting this scaling and the brighter i-dropouts from
both GOODS fields, we make incompleteness estimates and construct a z~6 LF in
the rest-frame continuum UV (~1350 A) over a 3.5 magnitude baseline, finding a
shape consistent with that found at lower redshift. To evaluate the evolution
in the LF from z~3.8, we make comparisons against different scalings of a lower
redshift B-dropout sample. Though a strong degeneracy is found between
luminosity and density evolution, our best-fit model scales as (1+z)^{-2.8} in
number and (1+z)^0.1 in luminosity, suggesting a rest-frame continuum UV
luminosity density at z~6 which is just 0.38_{-0.07} ^{+0.09}x that at z~3.8.
Our inclusion of size evolution makes the present estimate lower than previous
z~6 estimates.Comment: 5 pages, 5 figures, accepted for publication in the Astrophysical
Journal Letters, labelling to the left-hand axis of Figure 4 correcte
- …