25 research outputs found
Early results from GLASS-JWST. XXVII. The mass-metallicity relation in lensed field galaxies at cosmic noon with NIRISS
We present a measurement of the mass-metallicity relation (MZR) at cosmic
noon, using the JWST near-infrared wide-field slitless spectroscopy obtained by
the GLASS-JWST Early Release Science program. By combining the power of JWST
and the lensing magnification by the foreground cluster A2744, we extend the
measurements of the MZR to the dwarf mass regime at high redshifts. A sample of
50 galaxies with several emission lines is identified across two wide redshift
ranges of and in the stellar mass range of
. The observed slope of MZR is and at these two redshift ranges, respectively,
consistent with the slopes measured in field galaxies with higher masses. In
addition, we assess the impact of the morphological broadening on emission line
measurement by comparing two methods of using 2D forward modeling and line
profile fitting to 1D extracted spectra. We show that ignoring the
morphological broadening effect when deriving line fluxes from grism spectra
results in a systematic reduction of flux by on average. This
discrepancy appears to affect all the lines and thus does not lead to
significant changes in flux ratio and metallicity measurements. This assessment
of the morphological broadening effect using JWST data presents, for the first
time, an important guideline for future work deriving galaxy line fluxes from
wide-field slitless spectroscopy, such as Euclid, Roman, and the Chinese Space
Station Telescope.Comment: 19 pages, 6 figures, accepted for publication in ApJ
Early results from GLASS-JWST. XX: Unveiling a population of "red-excess'' galaxies in Abell2744 and in the coeval field
We combine JWST/NIRCam imaging and MUSE data to characterize the properties
of galaxies in different environmental conditions in the cluster Abell2744
() and in its immediate surroundings. We investigate how galaxy
colors, morphology and star forming fractions depend on wavelength and on
different parameterizations of environment. Our most striking result is the
discovery of a ``red-excess'' population in F200WF444W colors both in the
cluster regions and the field. These galaxies have normal F115WF150W colors,
but are up to 0.8 mag redder than red sequence galaxies in F200WF444W. They
also have rather blue rest frame BV colors. {Galaxies in the field and at
the cluster virial radius are overall characterized by redder colors, but
galaxies with the largest color deviations are found in the field and in the
cluster core. Several results} suggest that mechanisms taking place in these
regions might be more effective in producing these colors. Looking at their
morphology, many cluster galaxies show signatures consistent with ram pressure
stripping, while field galaxies have features resembling interactions and
mergers. Our hypothesis is that these galaxies are characterized by dust
enshrouded star formation: a JWST/NIRSpec spectrum for one of the galaxies is
dominated by a strong PAH at 3.3, suggestive of dust obscured star
formation. Larger spectroscopic samples are needed to understand if the color
excess is due exclusively to dust-obscured star formation, and the role of
environment in triggering it.Comment: ApJL in pres
Early Results from GLASS-JWST. XIX: A High Density of Bright Galaxies at in the Abell 2744 Region
We report the detection of a high density of redshift galaxies
behind the foreground cluster Abell 2744, selected from imaging data obtained
recently with NIRCam onboard {\it JWST} by three programs -- GLASS-JWST,
UNCOVER, and DDT\#2756. To ensure robust estimates of the lensing magnification
, we use an improved version of our model that exploits the first epoch of
NIRCam images and newly obtained MUSE spectra, and avoids regions with
where the uncertainty may be higher. We detect seven bright
galaxies with demagnified rest-frame mag,
over an area of sq. arcmin. Taking into account photometric
incompleteness and the effects of lensing on luminosity and cosmological
volume, we find that the density of galaxies in the field is
about () larger than the average at mag reported so far. The density is even higher when considering only
the GLASS-JWST data, which are the deepest and the least affected by
magnification and incompleteness. The GLASS-JWST field contains 5 out of 7
galaxies, distributed along an apparent filamentary structure of 2 Mpc in
projected length, and includes a close pair of candidates with mag having a projected separation of only 16 kpc. These findings suggest
the presence of a overdensity in the field. In addition to
providing excellent targets for efficient spectroscopic follow-up observations,
our study confirms the high density of bright galaxies observed in early {\it
JWST} observations, but calls for multiple surveys along independent lines of
sight to achieve an unbiased estimate of their average density and a first
estimate of their clustering.Comment: Accepted for publication in ApJL, 13 pages, 4 figure
Early results from GLASS-JWST. XIV: A spectroscopically confirmed protocluster 650 million years after the Big Bang
We present the spectroscopic confirmation of a protocluster at
behind the galaxy cluster Abell2744 (hereafter A2744-z7p9OD). Using JWST
NIRSpec, we find seven galaxies within a projected radius of 60kpc. Although
the galaxies reside in an overdensity around greater than a random
volume, they do not show strong Lyman-alpha emission. We place 2- upper
limits on the rest-frame equivalent width -AA. Based on the tight
upper limits to the Lyman-alpha emission, we constrain the volume-averaged
neutral fraction of hydrogen in the intergalactic medium to be (68% CI). Using an empirical - relation for
individual galaxies, we estimate that the total halo mass of the system is
. Likewise, the line of sight velocity
dispersion is estimated to be km/s. Using an empirical relation,
we estimate the present-day halo mass of A2744-z7p9OD to be
, comparable to the Coma cluster. A2744-z7p9OD is
the highest redshift spectroscopically confirmed protocluster to date,
demonstrating the power of JWST to investigate the connection between
dark-matter halo assembly and galaxy formation at very early times with
medium-deep observations at hrs total exposure time. Follow-up
spectroscopy of the remaining photometric candidates of the overdensity will
further refine the features of this system and help characterize the role of
such overdensities in cosmic reionization.Comment: The title has been updated to reflect the published numbering; a
minor change has been made to Figure 1 with regard to the MSA shutters on the
rgb stamp image. NASA press release article can be found at:
https://www.nasa.gov/feature/goddard/2023/webb-reveals-early-universe-prequel-to-huge-galaxy-cluste
A shot in the Dark (Ages): a faint galaxy at confirmed with JWST
The appearance of galaxies over the first billion years after the Big Bang is
believed to be responsible for the last dramatic change in the state of the
Universe. Ultraviolet photons from galaxies within this time period - the Epoch
of Reionization - ionized intergalactic Hydrogen, rendering the Universe
transparent to UV radiation and ending the so-called cosmic Dark Ages, sometime
after redshift . The majority of ionizing photons in the first few
hundred Myrs of cosmic history are thought to derive from galaxies
significantly fainter than the characteristic luminosity . These faint
galaxies are thought to be surrounded by sufficient neutral gas to prevent the
escape of the Lyman- photons that would allow confirmation with current
observatories. Here we demonstrate the power of the recently commissioned James
Webb Space Telescope to transform our understanding of the sources of
reionization, by reporting the first spectroscopic confirmation of a very low
luminosity () galaxy at , observed 480 Myr after the
Big Bang, via the detection of the Lyman-break and redward continuum with the
NIRSpec and NIRCam instruments. The galaxy JD1 is gravitationally magnified by
a factor of by the foreground cluster A2744. The power of JWST and
lensing allows us to peer deeper than ever before into the cosmic Dark Ages,
revealing the compact (150 pc) and complex morphology and physical
properties of an ultrafaint galaxy ().Comment: Submitted to Nature. 34 pages, 4 main figures, 1 supplementary
figure, 2 supplementary tables. Comments are welcom
The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance.
Investment in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing in Africa over the past year has led to a major increase in the number of sequences that have been generated and used to track the pandemic on the continent, a number that now exceeds 100,000 genomes. Our results show an increase in the number of African countries that are able to sequence domestically and highlight that local sequencing enables faster turnaround times and more-regular routine surveillance. Despite limitations of low testing proportions, findings from this genomic surveillance study underscore the heterogeneous nature of the pandemic and illuminate the distinct dispersal dynamics of variants of concern-particularly Alpha, Beta, Delta, and Omicron-on the continent. Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve while the continent faces many emerging and reemerging infectious disease threats. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century
The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance
INTRODUCTION
Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic.
RATIONALE
We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs).
RESULTS
Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants.
CONCLUSION
Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century
A geostatistical analysis of multiscale metallicity variations in galaxies [II]: Predicting the metallicities of Hii and diffuse ionised gas regions via universal kriging
The metallicity of diffuse ionised gas (DIG) cannot be determined using
strong emission line diagnostics, which are calibrated to calculate the
metallicity of Hii regions. Because of this, resolved metallicity maps from
integral field spectroscopy (IFS) data remain largely incomplete. In this paper
(the second of a series), we introduce the geostatistical technique of
universal kriging, which allows the complete 2D metallicity distribution of a
galaxy to be reconstructed from metallicities measured at Hii regions,
accounting for spatial correlations between nearby data points. We apply this
method to construct high-fidelity metallicity maps of the local spiral galaxy
NGC 5236 using data from the TYPHOON/PrISM survey. We find significant
correlation in the metallicity of Hii regions separated by up to 0.4-1.2 kpc.
Predictions constructed using this method were tested using cross-validation in
Hii regions, and we show that they outperform significantly interpolation based
on metallicity gradients. Furthermore, we apply kriging to predict the
metallicities in regions dominated by DIG emission, considering seven
additional spiral galaxies with high resolution (<100pc) metallicity maps. We
compare kriging maps to DIG metallicities computed with novel ionisation
corrections, and find that such corrections introduce a systematic offset of up
to dex for any individual galaxy, with a scatter of 0.02-0.07 dex for
the sample. Overall we recommend universal kriging, together with a calibrated
geostatistical model, as the superior method for inferring the metallicities of
DIG-dominated regions in local spiral galaxies, demonstrating further the
potential of applying geostatistical methods to spatially resolved galaxy
observations.Comment: 26 pages, 11 figures, including 2 appendices. Accepted for
publication in MNRA