3,370 research outputs found
Geochemical Evidence for Vertical Migration of Deep Formation Fluids through the Baton Rouge -Denham Springs Fault System
Accumulations of brackish groundwater exist across south Louisiana within the shallow, south-dipping Pleistocene to Upper Miocene Baton Rouge Aquifer System (BRAS). This research investigates the source of brackish groundwater through geochemical analysis of representative groundwater samples by comparing the following geochemical ratios along with other trace elements. Low Bromide (Br)/Chloride (Cl) and Potassium (K) /Cl ratios, high Sodium (Na) /Cl ratios, trace Magnesium (Mg) concentrations, and low Strontium (Sr) 87/Sr86 in brackish waters from the BRAS are inconsistent with in situ saline water from marine formation fluids of similar age. The ratios are consistent with in situ saline-water sources from Lower Miocene or Paleogene formation fluids from dissolved recrystallized halite. Deep formation fluids have interacted with Louann Salt diapirs underlying the BRAS area, dissolving halite, and are shown to have moved up fault planes and entered shallow aquifers to mix with the in situ groundwaters
A High Signal-to-Noise Ratio Composite Spectrum of Gamma-ray Burst Afterglows
We present a composite spectrum of 60 long duration gamma-ray burst (GRB)
afterglows with redshifts in the range 0.35<z<6.7 observed with low resolution
optical spectra. The composite spectrum covers the wavelength range 700-6600 A
in the rest frame and has a mean signal-to-noise ratio of 150 per 1 A pixel and
reaches a maximum of ~300 in the range 2500-3500 A. Equivalent widths are
measured from metal absorption lines from the Lya line to ~5200 A, and
associated metal and hydrogen lines are identified between the Lyman break and
Lya line. The average transmission within the Lyman forest is consistent with
that found along quasar lines of sight. We find a temporal variation in fine
structure lines when dividing the sample into bursts observed within 2 hours
from their trigger and those observed later. Other lines in the predominantly
neutral gas show variations too, but this is most likely a random effect caused
by weighting of individual strong absorption lines and which mimics a temporal
variation. Bursts characterized with high or low prompt GRB energy release
produce afterglows with similar absorption line strengths, and likewise for
bursts with bright or faint optical afterglows. Bursts defined as dark from
their optical to X-ray spectral index have stronger absorption lines relative
to the optically bright bursts. The composite spectrum has strong CaII and MgII
absorption lines as commonly found in dusty galaxies, however, we find no
evidence for dust or a significant molecular content based on the non-detection
of diffuse interstellar bands. Compared to starburst galaxy spectra, the GRB
composite has much stronger fine structure lines, while metal absorption lines
are weaker.Comment: Accepted for publication in ApJ, 24 page
Low-ionization Line Emission from Starburst Galaxies: A New Probe of Galactic-Scale Outflows
We study the kinematically narrow, low-ionization line emission from a
bright, starburst galaxy at z = 0.69 using slit spectroscopy obtained with
Keck/LRIS. The spectrum reveals strong absorption in MgII and FeII resonance
transitions with Doppler shifts of -200 to -300 km/s, indicating a cool gas
outflow. Emission in MgII near and redward of systemic velocity, in concert
with the observed absorption, yields a P Cygni-like line profile similar to
those observed in the Ly alpha transition in Lyman Break Galaxies. Further, the
MgII emission is spatially resolved, and extends significantly beyond the
emission from stars and HII regions within the galaxy. Assuming the emission
has a simple, symmetric surface brightness profile, we find that the gas
extends to distances > ~7 kpc. We also detect several narrow FeII*
fine-structure lines in emission near the systemic velocity, arising from
energy levels which are radiatively excited directly from the ground state. We
suggest that the MgII and FeII* emission is generated by photon scattering in
the observed outflow, and emphasize that this emission is a generic prediction
of outflows. These observations provide the first direct constraints on the
minimum spatial extent and morphology of the wind from a distant galaxy.
Estimates of these parameters are crucial for understanding the impact of
outflows in driving galaxy evolution.Comment: Submitted to ApJL. 6 pages, 4 figures. Uses emulateapj forma
The SDSS Damped Lya Survey: Data Release 1
We present the results from an automated search for damped Lya (DLA) systems
in the quasar spectra of Data Release 1 from the Sloan Digital Sky Survey
(SDSS-DR1). At z~2.5, this homogeneous dataset has greater statistical
significance than the previous two decades of research. We derive a statistical
sample of 71 damped Lya systems (>50 previously unpublished) at z>2.1 and
measure HI column densities directly from the SDSS spectra. The number of DLA
systems per unit redshift is consistent with previous measurements and we
expect our survey has >95% completeness. We examine the cosmological baryonic
mass density of neutral gas Omega_g inferred from the damped Lya systems from
the SDSS-DR1 survey and a combined sample drawn from the literature. Contrary
to previous results, the Omega_g values do not require a significant correction
from Lyman limit systems at any redshift. We also find that the Omega_g values
for the SDSS-DR1 sample do not decline at high redshift and the combined sample
shows a (statistically insignificant) decrease only at z>4. Future data
releases from SDSS will provide the definitive survey of DLA systems at z~2.5
and will significantly reduce the uncertainty in Omega_g at higher redshift.Comment: 12 pages, includes color figures. Accepted to PASP, April 20 200
Metallicities, dust and molecular content of a QSO-Damped Lyman-{\alpha} system reaching log N (H i) = 22: An analog to GRB-DLAs
We present the elemental abundance and H2 content measurements of a Damped
Lyman-{\alpha} (DLA) system with an extremely large H i column density, log N(H
i) (cm-2) = 22.0+/-0.10, at zabs = 3.287 towards the QSO SDSS J 081634+144612.
We measure column densities of H2, C i, C i^*, Zn ii, Fe ii, Cr ii, Ni ii and
Si ii from a high signal-to-noise and high spectral resolution VLT-UVES
spectrum. The overall metallicity of the system is [Zn/H] = -1.10 +/- 0.10
relative to solar. Two molecular hydrogen absorption components are seen at z =
3.28667 and 3.28742 (a velocity separation of \approx 52 km s-1) in rotational
levels up to J = 3. We derive a total H2 column density of log N(H2) (cm-2) =
18.66 and a mean molecular fraction of f = 2N(H2)/[2N(H2) + N(H i)] =
10-3.04+/-0.37, typical of known H2-bearing DLA systems. From the observed
abundance ratios we conclude that dust is present in the Interstellar Medium
(ISM) of this galaxy, with a enhanced abundance in the H2-bearing clouds.
However, the total amount of dust along the line of sight is not large and does
not produce any significant reddening of the background QSO. The physical
conditions in the H2-bearing clouds are constrained directly from the column
densities of H2 in different rotational levels, C i and C i^* . The kinetic
temperature is found to be T = 75 K and the particle density lies in the range
nH = 50-80 cm-3 . The neutral hydrogen column density of this DLA is similar to
the mean H i column density of DLAs observed at the redshift of {\gamma}-ray
bursts (GRBs). We explore the relationship between GRB-DLAs and high column
density end of QSO-DLAs finding that the properties (metallicity and depletion)
of DLAs with log N(H i) > 21.5 in the two populations do not appear to be
significantly different
Measurement of the Spatial Cross-Correlation Function of Damped Lyman Alpha Systems and Lyman Break Galaxies
We present the first spectroscopic measurement of the spatial
cross-correlation function between damped Lyman alpha systems (DLAs) and Lyman
break galaxies (LBGs). We obtained deep u'BVRI images of nine QSO fields with
11 known z ~ 3 DLAs and spectroscopically confirmed 211 R < 25.5
photometrically selected z > 2 LBGs. We find strong evidence for an overdensity
of LBGs near DLAs versus random, the results of which are similar to that of
LBGs near other LBGs. A maximum likelihood cross-correlation analysis found the
best fit correlation length value of r_0 = 2.9^(+1.4)_(-1.5) h^(-1)Mpc using a
fixed value of gamma = 1.6. The implications of the DLA-LBG clustering
amplitude on the average dark matter halo mass of DLAs are discussed.Comment: 12 pages, 2 figures, accepted for publication in Astrophysical
Journal Letter
Street Tree Resource Evaluation and Education Trust (STREET)
An educational and applied research project, Street Tree Resource Evaluation and Education Trust (STREET), was conducted to train Master Gardener volunteers to identify and inventory Bucyrus street trees, to educate city government and citizens on street tree benefits, to secure funding and city approval for new street tree planting, and to compare citizen and landscape contractor tree planting by tree planting depth. Outcomes of STREET included: identification and inventory of 1,797 street trees, grant funding of $5000, 194 new trees planted, and citizen tree planting depth higher than tree professionals
On the Incidence of C IV Absorbers Along the Sightlines to Gamma-Ray Bursts
We report on the statistics of strong (W_r > 0.15 A) C IV absorbers at
z=1.5-3.5 toward high-redshift gamma-ray bursts (GRBs). In contrast with a
recent survey for strong Mg II absorption systems at z < 2, we find that the
number of C IV absorbers per unit redshift dN/dz does not show a significant
deviation from previous surveys using quasi-stellar objects (QSOs) as
background sources. We find that the number density of C IV toward GRBs is
dN/dz(z~1.5)= 2.2 +2.8/-1.4, dN/dz(z~2.5)= 2.3 +1.8/-1.1 and dN/dz(z~3.5)= 1.1
+2.6/-0.9. These numbers are consistent with previous C IV surveys using QSO
spectra. Binning the entire dataset, we set a 95% c.l. upper limit to the
excess of C IV absorbers along GRB sightlines at twice the incidence observed
along QSO sightlines. Furthermore, the distribution of equivalent widths of the
GRB and QSO samples are consistent with being drawn from the same parent
population. Although the results for Mg II and C IV absorbers along GRB
sightlines appear to contradict one another, we note that the surveys are
nearly disjoint: the C IV survey corresponds to higher redshift and more highly
ionized gas than the Mg II survey. Nevertheless, analysis on larger statistical
samples may constrain properties of the galaxies hosting these metals (e.g.
mass, dust content) and/or the coherence-length of the gas giving rise to the
metal-line absorption.Comment: Accepted version (for publication in ApJ), results unchanged, 18
pages, 3 tables, 5 figure
Evidence for Ubiquitous Collimated Galactic-Scale Outflows along the Star-Forming Sequence at z~0.5
We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption
line profiles in individual spectra of 105 galaxies at 0.3<z<1.4. The galaxies,
drawn from redshift surveys of the GOODS fields and the Extended Groth Strip,
fully sample the range in star formation rates (SFRs) occupied by the
star-forming sequence with stellar masses log M_*/M_sun > 9.5 at 0.3<z<0.7.
Using the Doppler shifts of the MgII and FeII absorption lines as tracers of
cool gas kinematics, we detect large-scale winds in 66+/-5% of the galaxies.
HST/ACS imaging and our spectral analysis indicate that the outflow detection
rate depends primarily on galaxy orientation: winds are detected in ~89% of
galaxies having inclinations (i) <30 degrees (face-on), while the wind
detection rate is only ~45% in objects having i>50 degrees (edge-on). Combined
with the comparatively weak dependence of the wind detection rate on intrinsic
galaxy properties, this suggests that biconical outflows are ubiquitous in
normal, star-forming galaxies at z~0.5. We find that the wind velocity is
correlated with host galaxy M_* at 3.4-sigma significance, while the equivalent
width of the flow is correlated with host galaxy SFR at 3.5-sigma significance,
suggesting that hosts with higher SFR may launch more material into outflows
and/or generate a larger velocity spread for the absorbing clouds. Assuming
that the gas is launched into dark matter halos with simple, isothermal density
profiles, the wind velocities measured for the bulk of the cool material
(~200-400 km/s) are sufficient to enable escape from the halo potentials only
for the lowest-M_* systems in the sample. However, the outflows typically carry
sufficient energy to reach distances of >50 kpc, and may therefore be a viable
source of cool material for the massive circumgalactic medium observed around
bright galaxies at z~0. [abridged]Comment: Submitted to ApJ. 61 pages, 25 figures, 4 tables, 4 appendices. Uses
emulateapj forma
Metallicity Evolution in the Early Universe
Observations of the damped Lya systems provide direct measurements on the
chemical enrichment history of neutral gas in the early universe. In this
Letter, we present new measurements for four damped Lya systems at high
redshift. Combining these data with [Fe/H] values culled from the literature,
we investigate the metallicity evolution of the universe from z~1.5-4.5.
Contrary to our expectations and the predictions of essentially every chemical
evolution model, the N(HI)-weighted mean [Fe/H] metallicity exhibits minimal
evolution over this epoch. For the individual systems, we report tentative
evidence for an evolution in the unweighted [Fe/H] mean and the scatter in
[Fe/H] with the higher redshift systems showing lower scatter and lower typical
[Fe/H] values. We also note that no damped Lya system has [Fe/H] < -2.7 dex.
Finally, we discuss the potential impact of small number statistics and dust on
our conclusions and consider the implications of these results on chemical
evolution in the early universe.Comment: 6 pages, 2 encapsulated figures, Latex2e, uses emulateapj.sty and
onecolfloat.sty. Accepted for publication in ApJ Letters: Feb 28, 200
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