50 research outputs found
Rest-frame UV and optical emission line diagnostics of ionized gas properties: a test case in a star-forming knot of a lensed galaxy at z similar to 1.7
We examine the diagnostic power of rest-frame ultraviolet (UV) nebular emission lines, and
compare them to more commonly used rest-frame optical emission lines, using the test case
of a single star-forming knot of the bright lensed galaxy RCSGA 032727–132609 at redshift
z ∼ 1.7. This galaxy has complete coverage of all the major rest-frame UV and optical emission
lines from Magellan/MagE and Keck/NIRSPEC. Using the full suite of diagnostic lines, we
infer the physical properties: nebular electron temperature (Te), electron density (ne), oxygen
abundance (log (O/H), ionization parameter [log (q), and interstellar medium (ISM) pressure
(log (P/k)]. We examine the effectiveness of the different UV, optical, and joint UV–optical
spectra in constraining the physical conditions. Using UV lines alone we can reliably estimate
log (q), but the same is difficult for log (O/H). UV lines yield a higher (∼1.5 dex) log (P/k) than
the optical lines, as the former probes a further inner nebular region than the latter. For this
comparison, we extend the existing Bayesian inference code IZI, adding to it the capability
to infer ISM pressure simultaneously with metallicity and ionization parameter. This work
anticipates future rest-frame UV spectral data sets from the James Webb Space Telescope
(JWST) at high redshift and from the Extremely Large Telescope (ELT) at moderate redshift.Parts of this research were conducted by the Australian Research
Council Centre of Excellence for All Sky Astrophysics in 3
Dimensions (ASTRO 3D), through project number CE170100013.
LJK gratefully acknowledges the support of an ARC Laureate
Fellowship (FL150100113). CF acknowledges funding provided by
the Australian Research Council (Discovery Projects DP150104329
and DP170100603, and Future Fellowship FT180100495), and
the Australia-Germany Joint Research Cooperation Scheme (UADAAD). GB is supported by CONICYT/ FONDECYT, Programa
de Iniciacion, Folio 11150220
CLASSY VIII: Exploring the Source of Ionization with UV ISM diagnostics in local High- Analogs
In the current JWST era, rest-frame UV spectra play a crucial role in
enhancing our understanding of the interstellar medium (ISM) and stellar
properties of the first galaxies in the epoch of reionization (EoR, ).
Here, we compare well-known and reliable optical diagrams sensitive to the main
ionization source (i.e., star formation, SF; active galactic nuclei, AGN;
shocks) to UV counterparts proposed in the literature - the so-called ``UV-BPT
diagrams'' - using the HST COS Legacy Archive Spectroscopic SurveY (CLASSY),
the largest high-quality, high-resolution and broad-wavelength range atlas of
far-UV spectra for 45 local star-forming galaxies. In particular, we explore
where CLASSY UV line ratios are located in the different UV diagnostic plots,
taking into account state-of-the-art photoionization and shock models and, for
the first time, the measured ISM and stellar properties (e.g., gas-phase
metallicity, ionization parameter, carbon abundance, stellar age). We find that
the combination of C III] 1907,9 He II and O III]
1666 can be a powerful tool to separate between SF, shocks and AGN at
sub-solar metallicities. We also confirm that alternative diagrams without O
III] 1666 still allow us to define a SF-locus with some caveats.
Diagrams including C IV 1548,51 should be taken with caution
given the complexity of this doublet profile. Finally, we present a discussion
detailing the ISM conditions required to detect UV emission lines, visible only
in low gas-phase metallicity (12+log(O/H) ) and high ionization
parameter (log() ) environments. Overall, CLASSY and our UV
toolkit will be crucial in interpreting the spectra of the earliest galaxies
that JWST is currently revealing.Comment: 31 pages, submitted to ApJ, comments welcom
X-ray Spectral Properties of the BAT AGN Sample
The 9-month Swift Burst Alert Telescope (BAT) catalog provides the first
unbiased (log N_H = 0.03) AGN. In this paper, we
present the collected X-ray properties (0.3 - 12keV) for the 153 AGN detected.
In addition, we examine the X-ray properties for a complete sample of
non-beamed sources, above the Galactic plane. Of these, 45% are best fit by
simple power law models while 55% require the more complex partial covering
model. One of our goals was to determine the fraction of "hidden" AGN, which we
define as sources with scattering fractions < 0.03 and ratios of soft to hard
X-ray flux < 0.04. We found that "hidden" AGN constitute a high percentage of
the sample (24%), proving that they are a very significant portion of local
AGN. Further, we find that the fraction of absorbed sources does increase at
lower unabsorbed 2-10 keV luminosities, as well as accretion rates. Some of the
most interesting results for the BAT AGN sample involve the host galaxy
properties. We found that 33% are hosted in peculiar/irregular galaxies and
only 5/74 hosted in ellipticals. Further, 54% are hosted in interacting/merger
galaxies. Finally, we present both the average X-ray spectrum (0.1-10 keV) and
log N-log S in the 2-10 keV band. With our average spectrum, we have the
remarkable result of reproducing the measured CXB X-ray power law slope of ~
1.4 (Marshall et al. 1980). From the log N-log S relationship, we show that we
are complete to log S < -11 in the 2-10 keV band. Both the collected X-ray
properties of our uniform sample and the log N-log S relationship will now
provide valuable input to X-ray background models for z ~ 0. (abridged)Comment: 40 pages, 4 tables, 19 figures (submitted to ApJ
The COS Legacy Archive Spectroscopy SurveY (CLASSY) Treasury Atlas
Far-ultraviolet (FUV; ~1200-2000 angstroms) spectra are fundamental to our
understanding of star-forming galaxies, providing a unique window on massive
stellar populations, chemical evolution, feedback processes, and reionization.
The launch of JWST will soon usher in a new era, pushing the UV spectroscopic
frontier to higher redshifts than ever before, however, its success hinges on a
comprehensive understanding of the massive star populations and gas conditions
that power the observed UV spectral features. This requires a level of detail
that is only possible with a combination of ample wavelength coverage,
signal-to-noise, spectral-resolution, and sample diversity that has not yet
been achieved by any FUV spectral database.
We present the COS Legacy Spectroscopic SurveY (CLASSY) treasury and its
first high level science product, the CLASSY atlas. CLASSY builds on the HST
archive to construct the first high-quality (S/N_1500 >~ 5/resel),
high-resolution (R~15,000) FUV spectral database of 45 nearby (0.002 < z <
0.182) star-forming galaxies. The CLASSY atlas, available to the public via the
CLASSY website, is the result of optimally extracting and coadding 170
archival+new spectra from 312 orbits of HST observations.
The CLASSY sample covers a broad range of properties including stellar mass
(6.2 < logM_star(M_sol) < 10.1), star formation rate (-2.0 < log SFR (M_sol/yr)
< +1.6), direct gas-phase metallicity (7.0 < 12+log(O/H) < 8.8), ionization
(0.5 < O_32 < 38.0), reddening (0.02 < E(B-V < 0.67), and nebular density (10 <
n_e (cm^-3) < 1120). CLASSY is biased to UV-bright star-forming galaxies,
resulting in a sample that is consistent with z~0 mass-metallicity
relationship, but is offset to higher SFRs by roughly 2 dex, similar to z >~2
galaxies. This unique set of properties makes the CLASSY atlas the benchmark
training set for star-forming galaxies across cosmic time.Comment: Accepted for publication in Ap
JWST reveals a possible galaxy merger in triply-lensed MACS0647JD
MACS0647JD is a triply-lensed galaxy originally discovered with
the Hubble Space Telescope. Here we report new JWST imaging, which clearly
resolves MACS0647JD as having two components that are either merging
galaxies or stellar complexes within a single galaxy. Both are very small, with
stellar masses and radii . The brighter
larger component "A" is intrinsically very blue (), likely due
to very recent star formation and no dust, and is spatially extended with an
effective radius . The smaller component "B" appears redder
(), likely because it is older () with mild dust
extinction (), and a smaller radius . We
identify galaxies with similar colors in a high-redshift simulation, finding
their star formation histories to be out of phase. With an estimated stellar
mass ratio of roughly 2:1 and physical projected separation ,
we may be witnessing a galaxy merger 400 million years after the Big Bang. We
also identify a candidate companion galaxy C away, likely
destined to merge with galaxies A and B. The combined light from galaxies A+B
is magnified by factors of 8, 5, and 2 in three lensed images JD1, 2, and
3 with F356W fluxes , , (AB mag 25.1, 25.6, 26.6).
MACS0647JD is significantly brighter than other galaxies recently discovered
at similar redshifts with JWST. Without magnification, it would have AB mag
27.3 (). With a high confidence level, we obtain a photometric
redshift of based on photometry measured in 6 NIRCam filters
spanning , out to rest-frame. JWST NIRSpec
observations planned for January 2023 will deliver a spectroscopic redshift and
a more detailed study of the physical properties of MACS0647JD.Comment: 27 pages, 14 figures, submitted to Natur
The James Webb Space Telescope Mission
Twenty-six years ago a small committee report, building on earlier studies,
expounded a compelling and poetic vision for the future of astronomy, calling
for an infrared-optimized space telescope with an aperture of at least .
With the support of their governments in the US, Europe, and Canada, 20,000
people realized that vision as the James Webb Space Telescope. A
generation of astronomers will celebrate their accomplishments for the life of
the mission, potentially as long as 20 years, and beyond. This report and the
scientific discoveries that follow are extended thank-you notes to the 20,000
team members. The telescope is working perfectly, with much better image
quality than expected. In this and accompanying papers, we give a brief
history, describe the observatory, outline its objectives and current observing
program, and discuss the inventions and people who made it possible. We cite
detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space
Telescope Overview, 29 pages, 4 figure
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb
Space Telescope (JWST), as determined from the six month commissioning period.
We summarize the performance of the spacecraft, telescope, science instruments,
and ground system, with an emphasis on differences from pre-launch
expectations. Commissioning has made clear that JWST is fully capable of
achieving the discoveries for which it was built. Moreover, almost across the
board, the science performance of JWST is better than expected; in most cases,
JWST will go deeper faster than expected. The telescope and instrument suite
have demonstrated the sensitivity, stability, image quality, and spectral range
that are necessary to transform our understanding of the cosmos through
observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures;
https://iopscience.iop.org/article/10.1088/1538-3873/acb29
Identifying the fitness costs of a pyrethroid-resistant genotype in the major arboviral vector Aedes aegypti
BACKGROUND: Effective vector control measures are essential in a world where many mosquito-borne diseases have no vaccines or drug therapies available. Insecticidal tools remain the mainstay of most vector-borne disease management programmes, although their use for both agricultural and public health purposes has resulted in selection for resistance. Despite this, little is known about the fitness costs associated with specific insecticide-resistant genotypes and their implications for the management of resistance. In Aedes aegypti, the primary vector of dengue, chikungunya, and Zika, the best-characterised resistance mechanisms are single-point mutations that protect the voltage-gated sodium channel from the action of pyrethroids. METHODS: We evaluated the fitness cost of two co-occurring, homozygous mutations (V1016G and S989P) by back-crossing a resistant strain of A. aegypti from Timor-Leste into a fully susceptible strain from Queensland. The creation of the backcross strain allowed us to isolate these kdr mutations in an otherwise susceptible genetic background. RESULTS: In comparison to the susceptible strain, the backcrossed colony exhibited longer larval development times (5\ua0days, P
The presence of knockdown resistance mutations reduces male mating competitiveness in the major arbovirus vector, Aedes aegypti.
BackgroundThe development of insecticide resistance in mosquitoes can have pleiotropic effects on key behaviours such as mating competition and host-location. Documenting these effects is crucial for understanding the dynamics and costs of insecticide resistance and may give researchers an evidence base for promoting vector control programs that aim to restore or conserve insecticide susceptibility.Methods and findingsWe evaluated changes in behaviour in a backcrossed strain of Aedes aegypti, homozygous for two knockdown resistance (kdr) mutations (V1016G and S989P) isolated in an otherwise fully susceptible genetic background. We compared biting activity, host location behaviours, wing beat frequency (WBF) and mating competition between the backcrossed strain, and the fully susceptible and resistant parental strains from which it was derived. The presence of the homozygous kdr mutations did not have significant effects on blood avidity, the time to locate a host, or WBF in females. There was, however, a significant reduction in mean WBF in males and a significant reduction in estimated male mating success (17.3%), associated with the isolated kdr genotype.ConclusionsOur results demonstrate a cost of insecticide resistance associated with an isolated kdr genotype and manifest as a reduction in male mating success. While there was no recorded difference in WBF between the females of our strains, the significant reduction in male WBF recorded in our backcrossed strain might contribute to mate-recognition and mating disruption. These consequences of resistance evolution, especially when combined with other pleiotropic fitness costs that have been previously described, may encourage reversion to susceptibility in the absence of insecticide selection pressures. This offers justification for the implementation of insecticide resistance management strategies based on the rotation or alternation of different insecticide classes in space and time