115 research outputs found
The Neon Gap: Probing Ionization with Dwarf Galaxies at z~1
We present measurements of [NeIII]{\lambda}3869 emission in z~1 low-mass
galaxies taken from the Keck/DEIMOS spectroscopic surveys HALO7D and DEEPWinds.
We identify 167 individual galaxies with significant [NeIII] emission lines,
including 112 "dwarf" galaxies with log(M_{\star}/M_{\odot}) < 9.5, with 0.3 <
z < 1.4. We also measure [NeIII] emission from composite spectra derived from
all [OII]{\lambda}{\lambda}3727,3729 line emitters in this range. This provides
a unique sample of [NeIII]-emitters in the gap between well-studied emitters at
z = 0 and 2 < z < 3. To study evolution in ionization conditions in the ISM
over this time, we analyze the
log([NeIII]{\lambda}3869/[OII]{\lambda}{\lambda}3727,3729) ratio (Ne3O2) as a
function of the stellar mass and of the
log([OIII]{\lambda}{\lambda}4959,5007/[OII]{\lambda}{\lambda}3727,3729) ratio
(O32). We find that the typical star-forming dwarf galaxy at this redshift, as
measured from the composite spectra, shares the Ne3O2-M_{\star} relation with
local galaxies, but have higher O32 at given Ne3O2. This finding implies that
the ionization and metallicity characteristics of the z~1 dwarf population do
not evolve substantially from z~1 to z=0, suggesting that the known evolution
in those parameter from z~2 has largely taken place by z~1. Individual
[NeIII]-detected galaxies have emission characteristics situated between local
and z~2 galaxies, with elevated Ne3O2 and O32 emission potentially explained by
variations in stellar and nebular metallicity. We also compare our dwarf sample
to similarly low-mass z > 7 galaxies identified in JWST Early Release
Observations, finding four HALO7D dwarfs with similar size, metallicity, and
star formation properties.Comment: Accepted to ApJL, 16.01.202
Using willow riparian buffer strips for biomass production and riparian protection
Non-Peer ReviewedThere is increasing interest in the development of willow biomass as a renewable source of energy and woody lignocellulosic feedstock for bioproducts. Riparian buffers have been identified as an effective barrier to soil and nutrient movement from agricultural fields into watercourse. Willows are ideal riparian species in that they are well adapted to growing conditions in riparian zones and they vigorously re-grow following coppicing which allows them to be harvested for biomass in 3-4 year cycles. Characteristically riparian edges are highly productive due to water availability, therefore it is anticipated that willow biomass yield per unit area in riparian zones would be attractive. Research is being conducted to determine if using riparian buffer strips for willow biomass production provides energy alternatives and economic opportunities for land owners, but also leads to environmental benefits such as reduced erosion and nutrient leaching and preservation of water quality
Dwarf galaxies show little ISM evolution from to : a spectroscopic study of metallicity, star formation, and electron density
We present gas-phase metallicity measurements for 583 emission line galaxies
at , including 388 dwarf galaxies with , and explore the dependence of the metallicity on the stellar mass and
star formation properties of the galaxies. Metallicities are determined through
the measurement of emission lines in very deep (7 hr exposure)
Keck/DEIMOS spectra taken primarily from the HALO7D survey. We measure
metallicity with three strong-line calibrations (O3H, R23, and O3O2) for
the overall sample, as well as with the faint [Ne III]3869 and [O
III]4363 emission lines for 112 and 17 galaxies where robust
detections were possible. We construct mass-metallicity relations (MZR) for
each calibration method, finding MZRs consistent with other strong-line results
at comparable redshift, as well as with galaxies. We quantify the
intrinsic scatter in the MZR as a function of mass, finding it increases with
lower stellar mass. We also measure a weak but significant correlation between
increased MZR scatter and higher specific star formation rate. We find a weak
influence of SFR in the fundamental metallicity relation as well, with an SFR
coefficient of . Finally, we use the flux ratios of the [O
II]3727,3729 doublet to calculate gas electron density in
1000 galaxies with as a function of
redshift. We measure low electron densities ( cm) for
galaxies, again consistent with conditions, but measure higher
densities ( cm) at . These results all suggest that
there is little evolution in star-forming interstellar medium conditions from
to , confirmed with a more complete sample of low-mass galaxies
than has previously been available in this redshift range.Comment: 22 pages, 10 figures, accepted to Ap
First results from Faint Infrared Grism Survey (FIGS): first simultaneous detection of Lyman-alpha emission and Lyman break from a galaxy at z=7.51
Galaxies at high redshifts provide a valuable tool to study cosmic dawn, and
therefore it is crucial to reliably identify these galaxies. Here, we present
an unambiguous and first simultaneous detection of both the Lyman-alpha
emission and the Lyman break from a z = 7.512+/- 0.004 galaxy, observed in the
Faint Infrared Grism Survey (FIGS). These spectra, taken with G102 grism on
Hubble Space Telescope (HST), show a significant emission line detection (6
sigma) in multiple observational position angles (PA), with total integrated
Ly{\alpha} line flux of 1.06+/- 0.12 e10-17erg s-1cm-2. The line flux is nearly
a factor of four higher than the previous MOSFIRE spectroscopic observations of
faint Ly{\alpha} emission at {\lambda} = 1.0347{\mu}m, yielding z = 7.5078+/-
0.0004. This is consistent with other recent observations implying that
ground-based near-infrared spectroscopy underestimates total emission line
fluxes, and if confirmed, can have strong implications for reionization studies
that are based on ground-based Lyman-{\alpha} measurements. A 4-{\sigma}
detection of the NV line in one PA also suggests a weak Active Galactic Nucleus
(AGN), potentially making this source the highest-redshift AGN yet found. Thus,
this observation from the Hubble Space Telescope clearly demonstrates the
sensitivity of the FIGS survey, and the capability of grism spectroscopy to
study the epoch of reionization.Comment: Published in ApJL; matches published versio
The Dwarf Galaxy Population at z ∼ 0.7: A Catalog of Emission Lines and Redshifts from Deep Keck Observations
We present a catalog of spectroscopically measured redshifts over
and emission line fluxes for 1440 galaxies. The majority (65\%) of the
galaxies come from the HALO7D survey, with the remainder from the DEEPwinds
program. This catalog includes redshifts for 646 dwarf galaxies with
. 810 catalog galaxies did not have previously
published spectroscopic redshifts, including 454 dwarf galaxies. HALO7D used
the DEIMOS spectrograph on the Keck II telescope to take very deep (up to 32
hours exposure, with a median of 7 hours) optical spectroscopy in the
COSMOS, EGS, GOODS-North, and GOODS-South CANDELS fields, and in some areas
outside CANDELS. We compare our redshift results to existing spectroscopic and
photometric redshifts in these fields, finding only a 1\% rate of discrepancy
with other spectroscopic redshifts. We measure a small increase in median
photometric redshift error (from 1.0\% to 1.3\%) and catastrophic outlier rate
(from 3.5\% to 8\%) with decreasing stellar mass. We obtained successful
redshift fits for 75\% of massive galaxies, and demonstrate a similar 70-75\%
successful redshift measurement rate in
galaxies, suggesting similar survey sensitivity in this low-mass range. We
describe the redshift, mass, and color-magnitude distributions of the catalog
galaxies, finding HALO7D galaxies representative of CANDELS galaxies up to
\textit{i}-band magnitudes of 25. The catalogs presented will enable studies of
star formation (SF), the mass-metallicity relation, SF-morphology relations,
and other properties of the dwarf galaxy population.Comment: 23 pages, 19 Figures, updated to version accepted by ApJ
Control of CD1d-restricted antigen presentation and inflammation by sphingomyelin.
Invariant natural killer T (iNKT) cells recognize activating self and microbial lipids presented by CD1d. CD1d can also bind non-activating lipids, such as sphingomyelin. We hypothesized that these serve as endogenous regulators and investigated humans and mice deficient in acid sphingomyelinase (ASM), an enzyme that degrades sphingomyelin. We show that ASM absence in mice leads to diminished CD1d-restricted antigen presentation and iNKT cell selection in the thymus, resulting in decreased iNKT cell levels and resistance to iNKT cell-mediated inflammatory conditions. Defective antigen presentation and decreased iNKT cells are also observed in ASM-deficient humans with Niemann-Pick disease, and ASM activity in healthy humans correlates with iNKT cell phenotype. Pharmacological ASM administration facilitates antigen presentation and restores the levels of iNKT cells in ASM-deficient mice. Together, these results demonstrate that control of non-agonistic CD1d-associated lipids is critical for iNKT cell development and function in vivo and represents a tight link between cellular sphingolipid metabolism and immunity
FIGS-Faint Infrared Grism Survey: Description and Data Reduction
The Faint Infrared Grism Survey (FIGS) is a deep Hubble Space Telescope (HST) WFC3/IR (Wide Field Camera 3 Infrared) slitless spectroscopic survey of four deep fields. Two fields are located in the Great Observatories Origins Deep Survey-North (GOODS-N) area and two fields are located in the Great Observatories Origins Deep Survey-South (GOODS-S) area. One of the southern fields selected is the Hubble Ultra Deep Field. Each of these four fields were observed using the WFC3/G102 grism (0.8 μm–1.15 μm continuous coverage) with a total exposure time of 40 orbits (≈100 kilo-seconds) per field. This reaches a continuum depth of AB magnitudes and probes emission lines to . This paper details the four FIGS fields and the overall observational strategy of the project. A detailed description of the Simulation Based Extraction (SBE) method used to extract and combine over 10,000 spectra of over 2000 distinct sources brighter than mag is provided. High fidelity simulations of the observations is shown to significantly improve the background subtraction process, the spectral contamination estimates, and the final flux calibration. This allows for the combination of multiple spectra to produce a final high quality, deep, 1D spectra for each object in the survey
Genome sequence of an Australian kangaroo, Macropus eugenii, provides insight into the evolution of mammalian reproduction and development.
BACKGROUND: We present the genome sequence of the tammar wallaby, Macropus eugenii, which is a member of the kangaroo family and the first representative of the iconic hopping mammals that symbolize Australia to be sequenced. The tammar has many unusual biological characteristics, including the longest period of embryonic diapause of any mammal, extremely synchronized seasonal breeding and prolonged and sophisticated lactation within a well-defined pouch. Like other marsupials, it gives birth to highly altricial young, and has a small number of very large chromosomes, making it a valuable model for genomics, reproduction and development. RESULTS: The genome has been sequenced to 2 × coverage using Sanger sequencing, enhanced with additional next generation sequencing and the integration of extensive physical and linkage maps to build the genome assembly. We also sequenced the tammar transcriptome across many tissues and developmental time points. Our analyses of these data shed light on mammalian reproduction, development and genome evolution: there is innovation in reproductive and lactational genes, rapid evolution of germ cell genes, and incomplete, locus-specific X inactivation. We also observe novel retrotransposons and a highly rearranged major histocompatibility complex, with many class I genes located outside the complex. Novel microRNAs in the tammar HOX clusters uncover new potential mammalian HOX regulatory elements. CONCLUSIONS: Analyses of these resources enhance our understanding of marsupial gene evolution, identify marsupial-specific conserved non-coding elements and critical genes across a range of biological systems, including reproduction, development and immunity, and provide new insight into marsupial and mammalian biology and genome evolution
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