195 research outputs found
Transport of Antimony Processing Wastes in the Prospect Creek Drainage, Western Montana
We investigated the hydrogeologic behavior of the United States Antimony Corporation\u27s 1O-acre waste impoundment. We found that waste fluids from the impoundment contribute measurable concentrations of antimony, sulfate, and sodium to the underlying ground water system. The concentrations and transport of these contaminants are strongly influenced by large fluctuations in the water table beneath the disposal impoundments. Water table fluctuations are, in turn, driven by seasonally variable ground water recharge from Prospect Creek.
Prospect Creek carries a measurable dissolved antimony load attributable to the impoundment site. We found this flux to be maximized under high spring streamflow conditions. Under the conditions studied, the discharged antimony is unlikely to significantly degrade the mainstem Clark Fork River. However, we have estimated the impounded wastes contain up to 100,000 pounds of water- soluble antimony, and under the existing hydrologic conditions they will continue to provide the alluvial ground water system and Prospect Creek with a low-grade source of this metal
Power measures derived from the sequential query process
We study a basic sequential model for the discovery of winning coalitions in
a simple game, well known from its use in defining the Shapley-Shubik power
index. We derive in a uniform way a family of measures of collective and
individual power in simple games, and show that, as for the Shapley-Shubik
index, they extend naturally to measures for TU-games. In particular, the
individual measures include all weighted semivalues.
We single out the simplest measure in our family for more investigation, as
it is new to the literature as far as we know. Although it is very different
from the Shapley value, it is closely related in several ways, and is the
natural analogue of the Shapley value under a nonstandard, but natural,
definition of simple game. We illustrate this new measure by calculating its
values on some standard examples.Comment: 13 pages, to appear in Mathematical Social Science
The Rest-Frame Optical Properties of z~3 Galaxies
We present the results of a near-infrared imaging survey of z~3 Lyman Break
Galaxies (LBGs). The survey covers a total of 30 arcmin^2 and includes 118
photometrically selected LBGs with K_s band measurements, 63 of which also have
J band measurements, and 81 of which have spectroscopic redshifts. Using the
distribution of optical {\cal R} magnitudes from previous work and {\cal R}-K_s
colors for this sub-sample, we compute the rest-frame optical luminosity
function of LBGs. At the brightest magnitudes, where it is fairly well
constrained, this luminosity function strikingly exceeds locally determined
optical luminosity functions. The V-band luminosity density of only the
observed bright end of the z~3 LBG luminosity function already approaches that
of all stars in the local universe. For the 81 galaxies with measured
redshifts, we investigate the range of LBG stellar populations implied by the
photometry which generally spans the range 900--5500 AA in the rest-frame.
While there are only weak constraints on the parameters for most of the
individual galaxies, there are strong trends in the sample as a whole. A
unified scenario which accounts for the observed trends in bright LBGs is one
in which a relatively short period of very rapid star-formation (hundreds of
M_sun/yr) lasts for roughly 50--100 Myr, after which both the extinction and
star-formation rate are considerably reduced and stars are formed at a more
quiescent, but still rapid, rate for at least a few hundred Myr. In our sample,
a considerable fraction (~20%) of the LBGs have best-fit star-formation ages ~>
1 Gyr, implied stellar masses of ~> 10^10 M_sun, and are still forming stars at
\~30 M_sun/yr.Comment: 61 pages including 19 figures. Accepted for publication in Ap
Deep Observations of Lyman Break Galaxies
We summarise the main results of recent work on the Lyman break galaxy
population which takes advantage of newly commissioned instrumentation on the
VLT and Keck telescopes to push the detection of these objects to new
wavelengths and more sensitive limits. We focus in particular on near-infrared
observations targeted at detecting emission lines of [O II], [O III], and
H-beta and on the first tentative detection of Lyman continuum emission from
star forming galaxies at z = 3.Comment: 9 pages, LaTeX, 6 Postscript Figures. To appear in the Proceedings of
the ESO Symposium: Deep Fields, ed. S. Cristiani (Berlin: Springer
Lyman Alpha Imaging of a Proto-Cluster Region at <z>=3.09
We present very deep imaging observations, through a narrow-band filter tuned
to Lyman alpha at , of a volume containing a significant over-density
of galaxies at this redshift previously discovered in our survey for
continuum-selected Lyman break galaxies (LBGs). The new observations are used
in conjunction with our spectroscopic results on LBGs to compare the
effectiveness of continuum and emission line searches for star forming galaxies
at high redshift, and to extend the search for members of the structure at =
3.09 to much fainter continuum luminosities. We find that only 20-25 percent of
all galaxies at a given UV continuum luminosity would be flagged as narrow-band
excess objects subject to the typical limits W_Lya > 80 Angstroms in the
observed frame. The density enhancement of strong Lyman alpha emitters in this
field is consistent with that inferred from the analysis of the spectroscopic
Lyman break galaxy sample in the same region (6+/-1), but extends to continuum
luminosities up to 2 magnitudes fainter. There is no evidence for a
significantly higher fraction of large Lyman alpha line equivalent widths at
faint continuum luminosities. By combining the 24 spectroscopic members of the
z=3.09 ``spike'' with the narrow-band candidates, we are able to produce a
sample of 162 objects which are either known or likely members of this large
structure. We have also discovered two extremely large and diffuse Lyman alpha
emitting ``blobs'', which have physical extents >100/h kpc and Lyman alpha line
fluxes 20-40 times larger than the typical line emitters at the same redshifts
in the field. The possible nature of the ``blobs'' is discussed. (abstract
abridged)Comment: To appear in the ApJ, 31 pages, aaste
On the Stellar Populations and Evolution of Star-Forming Galaxies at 6.3 < z < 8.6
We study the physical characteristics of galaxies at 6.3 < z < 8.6, selected
from deep near-infrared imaging with the Wide Field Camera 3 (WFC3) on board
the Hubble Space Telescope. Accounting for the photometric scatter using
simulations, galaxies at z ~ 7 have bluer UV colors compared to typical local
starburst galaxies at > 4 sigma confidence. Although these colors necessitate
young ages (<100 Myr), low or zero dust attenuation, and low metallicities,
these are explicable by normal (albeit unreddened) stellar populations, with no
evidence for near-zero metallicities and/or top-heavy initial mass functions.
The age of the Universe at these redshifts limits the amount of stellar mass in
late-type populations, and the WFC3 photometry implies galaxy stellar masses ~
10^8 - 10^9 Msol for Salpeter initial mass functions to a limiting magnitude of
M_1500 ~ -18. The masses of ``characteristic'' (L*) z > 7 galaxies are smaller
than those of L* Lyman break galaxies (LBGs) at lower redshifts, and are
comparable to less evolved galaxies selected on the basis of their Lyman alpha
emission at 3 < z < 6, implying that the 6.3 < z < 8.6 galaxies are the
progenitors of more evolved galaxies at lower redshifts. We estimate that Lyman
alpha emission is able to contribute to the observed WFC3 colors of galaxies at
these redshifts, with an estimated typical line flux of ~ 10^-18 erg s^-1
cm^-2, roughly a factor of four below currently planned surveys. The integrated
UV specific luminosity for the detected galaxies at z ~ 7 and z ~ 8 is within
factors of a few of that required to reionize the IGM assuming low clumping
factors, implying that in order to reionize the Universe galaxies at these
redshifts have a high ( ~ 50%) escape fraction of Lyman continuum photons,
possibly substantiated by the very blue colors of this population.Comment: Accepted to the Astrophysical Journal; replaced with accepted
version. Minor modifications to sample, conclusions are unchange
The Average Physical Properties and Star Formation Histories of the UV-Brightest Star-Forming Galaxies at z~3.7
[Abridged] We investigate the average physical properties and star formation
histories of the most UV-luminous star-forming galaxies at z~3.7. Our results
are derived from analyses of the average spectral energy distributions (SEDs),
constructed from stacked optical to infrared photometry, of a sample of the
1,902 most UV-luminous star-forming galaxies found in 5.3 square degrees of the
NOAO Deep Wide-Field Survey. We bin the sample according to UV luminosity, and
find that the shape of the average SED in the rest-frame optical and infrared
is fairly constant with UV luminosity: i.e., more UV luminous galaxies are, on
average, also more luminous at longer wavelengths. In the rest-UV, however, the
spectral slope (measured at 0.13-0.28 um) rises steeply with the median UV
luminosity from -1.8 at L L* to -1.2 in the brightest bin (L~4-5L*). We use
population synthesis analyses to derive the average physical properties of
these galaxies and find that: (1) L_UV, and thus star formation rates (SFRs),
scale closely with stellar mass such that more UV-luminous galaxies are also
more massive; (2) The median ages indicate that the stellar populations are
relatively young (200-400 Myr) and show little correlation with UV luminosity;
and (3) More UV-luminous galaxies are dustier than their less-luminous
counterparts, such that L~4-5L* galaxies are extincted up to A(1600)=2 mag
while L L* galaxies have A(1600)=0.7-1.5 mag. Based on these observations, we
argue that the average star formation histories of UV-luminous galaxies are
better described by models in which SFR increases with time in order to
simultaneously reproduce the tight correlation between the observed SFR and
stellar mass, and the universally young ages of these galaxies. We demonstrate
the potential of measurements of the SFR-M* relation at multiple redshifts to
discriminate between simple models of star formation histories.Comment: 14 pages, 7 figures. Accepted for publication in Astrophysical
Journa
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