147 research outputs found
On the ages of bright galaxies Myr after the Big Bang: insights into star formation activity at with JWST
With JWST, new opportunities to study the formation and evolution of galaxies
in the early Universe are now emerging. Spitzer constraints on rest-optical
properties of galaxies demonstrated the power of using stellar
masses and star formation histories (SFHs) of galaxies to indirectly infer the
star formation history of the Universe. However, only the brightest individual
objects at could be detected with Spitzer, making it difficult to
robustly constrain past activity at . Here, we leverage the
greatly improved rest-optical sensitivity of JWST at to constrain
the ages and SFHs of eleven UV-bright () galaxies
selected to lie at , then investigate implications for star
formation activity at . We infer the properties of individual
objects in our sample with two spectral energy distribution modelling codes,
then infer a distribution of ages for bright galaxies. We
find a median age of Myr, younger than that inferred at
with a similar analysis, which is consistent with an evolution towards larger
specific star formation rates at early times. The age distribution suggests
that only percent of bright galaxies would be
similarly luminous at , implying that the number density of
bright galaxies declines by approximately an order of magnitude between and . This evolution is challenging to reconcile with some
early JWST results suggesting that the abundance of bright galaxies does not
significantly decrease towards very early times, but we suggest this tension
may be eased if young stellar populations form on top of older stellar
components, or if bright galaxies at are observed during a burst of
star formation.Comment: 13 pages, 9 figure
Searching for Extremely Blue UV Continuum Slopes at in JWST/NIRCam Imaging: Implications for Stellar Metallicity and Ionizing Photon Escape in Early Galaxies
The ultraviolet (UV) continuum slope ( where f) of galaxies is sensitive to a variety of properties, from the
metallicity and age of the stellar population to the attenuation from dust
through the galaxy. Considerable attention has focused on identifying
reionization-era galaxies with very blue UV slopes (). Not only do
such systems provide a signpost of low metallicity stars, but they also
identify galaxies that likely have ionizing photons leaking from their HII
regions as such blue UV slopes can only be seen if the reddening effect of
nebular continuum has been diminished. In this paper we present a search for
reionization-era galaxies with very blue UV colors in recent JWST/NIRCam
imaging of the EGS field. We characterize UV slopes for a large sample of
galaxies, finding a median value of . Three of the
lower luminosity (M) and lower stellar mass
(5-6M) systems exhibit both extremely blue UV slopes
( to ) and rest-optical photometry indicating weak nebular
line emission. Each system is very compact (r260 pc) with very high star
formation rate surface densities. We model the SEDs with a suite of BEAGLE
models with varying levels of ionizing photon escape. The SEDs cannot be
reproduced with our fiducial (f=0) or alpha enhanced
(Z) models. The combined blue UV slopes and weak nebular
emission are best-fit by models with significant ionizing photon escape from
HII regions (f=0.6-0.8) and extremely low metallicity massive
stars (Z=0.01-0.06 Z). The discovery of these galaxies highlights
the potential for JWST to identify large numbers of candidate Lyman Continuum
leaking galaxies in the reionization era and suggests low metallicity stellar
populations may be veryComment: 11 pages, 8 figures, 2 tables; Submitted to Ap
A JWST/NIRCam Study of Key Contributors to Reionization: The Star-forming and Ionizing Properties of UV-faint Galaxies
Spitzer/IRAC imaging has revealed that the brightest galaxies
often exhibit young ages and strong nebular line emission, hinting at high
ionizing efficiency among early galaxies. However, IRAC's limited sensitivity
has long hindered efforts to study the fainter, more numerous population often
thought largely responsible for reionization. Here we use CEERS JWST/NIRCam
data to characterize 116 UV-faint (median M)
galaxies. The SEDs are typically dominated by young (10-50 Myr), low-mass
() stellar populations, and we find no need for
extremely high stellar masses (). Considering previous
studies of UV-bright (M) galaxies, we find evidence
for a strong (5-10) increase in specific star formation rate toward
lower luminosities (median sSFR=103 Gyr in CEERS). The larger sSFRs
imply a more dominant contribution from OB stars in the relatively numerous
UV-faint population, perhaps suggesting that these galaxies are very efficient
ionizing agents (median erg Hz). In spite of their
much larger sSFRs, we find no significant increase in [OIII]H EWs
towards fainter M (median 780 ). If confirmed,
this may indicate that a substantial fraction of our CEERS galaxies possess
extremely low metallicities (3% ) where [OIII] emission is
suppressed. Alternatively, high ionizing photon escape fractions or bursty star
formation histories can also weaken the nebular lines in a subset of our CEERS
galaxies. While the majority of our objects are very blue (median
), we identify a significant tail of very dusty galaxies
() at 0.5 which may contribute significantly
to the star formation rate density.Comment: Accepted in MNRAS. Updated to use the most recent NIRCam zeropoints.
There are no significant changes to the conclusions relative to v
Gene Selection for Multiclass Prediction by Weighted Fisher Criterion
Gene expression profiling has been widely used to study molecular signatures of many diseases and to develop molecular diagnostics for disease prediction. Gene selection, as an important step for improved diagnostics, screens tens of thousands of genes and identifies a small subset that discriminates between disease types. A two-step gene selection method is proposed to identify informative gene subsets for accurate classification of multiclass phenotypes. In the first step, individually discriminatory genes (IDGs) are identified by using one-dimensional weighted Fisher criterion (wFC). In the second step, jointly discriminatory genes (JDGs) are selected by sequential search methods, based on their joint class separability measured by multidimensional weighted Fisher criterion (wFC). The performance of the selected gene subsets for multiclass prediction is evaluated by artificial neural networks (ANNs) and/or support vector machines (SVMs). By applying the proposed IDG/JDG approach to two microarray studies, that is, small round blue cell tumors (SRBCTs) and muscular dystrophies (MDs), we successfully identified a much smaller yet efficient set of JDGs for diagnosing SRBCTs and MDs with high prediction accuracies (96.9% for SRBCTs and 92.3% for MDs, resp.). These experimental results demonstrated that the two-step gene selection method is able to identify a subset of highly discriminative genes for improved multiclass prediction
Impact of alirocumab/evolocumab on lipoprotein (a) concentrations in patients with familial hypercholesterolaemia: a systematic review and meta-analysis of randomized controlled trials
Introduction: Familial hypercholesterolaemia (FH) is a common hereditary genetic disorder, characterized by elevated circulating low-density lipoprotein cholesterol (LDL-C) and lipoprotein (a) [Lp(a)] concentrations, leading to atherosclerotic cardiovascular disease (ASCVD). Two types of proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors — alirocumab and evolocumab — are efficient drugs in the treatment of FH, which can effectively reduce Lp(a) levels.
Material and methods: Embase, MEDLINE, and PubMed up to November 2022 were searched for randomized clinical trials (RCTs) evaluating the effect of alirocumab/evolocumab and placebo treatment on plasma Lp(a) levels in FH. Statistics were analysed by Review Manager (RevMan 5.3) and Stata 15.1.
Results: Eleven RCTs involved a total of 2408 participants. Alirocumab/evolocumab showed a significant efficacy in reducing Lp(a) [weighted mean difference (WMD): –20.10%, 95% confidence interval (CI): –25.59% to –14.61%] compared with placebo. In the drug type subgroup analyses, although the efficacy of evolocumab was slightly low (WMD: –19.98%, 95% CI: –25.23% to –14.73%), there was no difference with alirocumab (WMD: –20.54%, 95% CI: –30.07% to –11.02%). In the treatment duration subgroup analyses, the efficacy of the 12-week duration group (WMD: –17.61%, 95% CI: –23.84% to –11.38%) was lower than in the group of ≥ 24 weeks’ duration (WMD: –22.81%, 95% CI: –31.56% to –14.07%). In the participants’ characteristics subgroup analyses, the results showed that no differential effect of alirocumab/evolocumab therapy on plasma Lp(a) concentrations was observed (heterozygous FH [HeFH] WMD: –20.07%, 95% CI: –26.07% to –14.08%; homozygous FH [HoFH] WMD: –20.04%, 95% CI: –36.31% to –3.77%). Evaluation of all-cause adverse events (AEs) between alirocumab/evolocumab groups and placebo groups [relative risk (RR): 1.05, 95% CI: 0.98–1.12] implied no obvious difference between the 2 groups.
Conclusions: Anti-PCSK9 drugs (alirocumab and evolocumab) may be effective as therapy for reducing serum Lp(a) levels in FH, and no differences were observed in treatment durations, participant characteristics, and other aspects of the 2 types of PCSk9 inhibitors.
However, further experimental studies and RCTs are warranted to clarify the mechanism of PSCK9 inhibitors to lowering Lp(a) concentrations in FH
Metal-Enriched Neutral Gas Reservoir around a Strongly-lensed, Low-mass Galaxy at Identified by JWST/NIRISS and VLT/MUSE
Direct observations of low-mass, low-metallicity galaxies at
provide an indispensable opportunity for detailed inspection of the ionization
radiation, gas flow, and metal enrichment in sources similar to those that
reionized the Universe. Combining the James Webb Space Telescope (JWST),
VLT/MUSE, and ALMA, we present detailed observations of a strongly lensed,
low-mass ( ) galaxy at (also see
Vanzella et al. 2022). We identify strong narrow nebular emission, including
CIV , HeII , OIII]
, [NeIII] , [OII] , and
Balmer series of Hydrogen from this galaxy, indicating a metal-poor HII region
() powered by massive stars. Further, we detect a
metal-enriched damped Ly system (DLA) associated with the galaxy with
the HI column density of cm. The
metallicity of the associated DLA may reach the super solar metallicity
(). Moreover, thanks to JWST and gravitational lensing, we
present the resolved UV slope () map at the spatial resolution of
pc at , with steep UV slopes reaching
around three star-forming clumps. Combining with low-redshift analogs, our
observations suggest that low-mass, low-metallicity galaxies, which dominate
reionization, could be surrounded by a high covering fraction of the
metal-enriched, neutral-gaseous clouds. This implies that the metal enrichment
of low-mass galaxies is highly efficient, and further support that in low-mass
galaxies, only a small fraction of ionizing radiation can escape through the
interstellar or circumgalactic channels with low column-density neutral gas.Comment: 4 pages, 1 table; submitted to the ApJL; welcome comment
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