259 research outputs found
A first look at JWST CEERS: massive quiescent galaxies from 3 < z < 5
We report a robust sample of 9 massive quiescent galaxies at redshift, , selected using the first data from the JWST CEERS programme. Three of these
galaxies are at , constituting the best evidence to date for
quiescent galaxies significantly before . These extreme galaxies have
stellar masses in the range logM, and formed
the bulk of their mass at , with two objects having star-formation
histories that suggest they had already reached logM
by . We report number densities for our sample, demonstrating that
previous work underestimated the number of quiescent galaxies at by
at least a factor of , due to a lack of ultra-deep imaging data at
m. This result deepens the existing tension between
observations and theoretical models, which already struggle to reproduce
previous estimates of quiescent galaxy number densities. Upcoming
wider-area JWST imaging surveys will provide larger samples of such galaxies,
as well as providing opportunities to search for quiescent galaxies at .
The galaxies we report are excellent potential targets for JWST NIRSpec
spectroscopy, which will be required to understand in detail their physical
properties, providing deeper insights into the processes responsible for
quenching star formation during the first billion years.Comment: 11 pages, 6 figures, submitted to MNRA
Timing the earliest quenching events with a robust sample of massive quiescent galaxies at 2 <z <5
We present a sample of 151 massive ()
quiescent galaxies at , based on a sophisticated Bayesian spectral
energy distribution fitting analysis of the CANDELS UDS and GOODS-South fields.
Our sample includes a robust sub-sample of 61 objects for which we confidently
exclude low-redshift and star-forming solutions. We identify 10 robust objects
at , of which 2 are at . We report formation redshifts, demonstrating
that the oldest objects formed at , however individual ages from our
photometric data have significant uncertainties, typically Gyr. We
demonstrate that the UVJ colours of the quiescent population evolve with
redshift at , becoming bluer and more similar to post-starburst galaxies
at lower redshift. Based upon this we construct a model for the time-evolution
of quiescent galaxy UVJ colours, concluding that the oldest objects are
consistent with forming the bulk of their stellar mass at and
quenching at . We report spectroscopic redshifts for two of our objects
at and , which exhibit extremely weak Ly emission in
ultra-deep VANDELS spectra. We calculate star-formation rates based on these
line fluxes, finding that these galaxies are consistent with our quiescent
selection criteria, provided their Ly escape fractions are and
per cent respectively. We finally report that our highest-redshift robust
object exhibits a continuum break at A in a spectrum from
VUDS, consistent with our photometric redshift of
. If confirmed as quiescent this object
would be the highest-redshift known quiescent galaxy. To obtain stronger
constraints on the times of the earliest quenching events, high-SNR
spectroscopy must be extended to quiescent objects.Comment: 14 pages, 8 figures, MNRAS accepte
Optical analysis of samarium doped sodium bismuth silicate glass
Samarium doped sodium bismuth silicate glass was synthesized using the melt quenching method. Detailed optical spectroscopic studies of the glassy material were carried out in the UV–Vis-NIR spectral range. Using the optical absorption spectra Judd-Ofelt (JO) parameters are derived. The calculated values of the JO parameters are utilized in evaluating the various radiative parameters such as electric dipole line strengths (Sed), radiative transition probabilities (Arad), radiative lifetimes (τrad), fluorescence branching ratios (β) and the integrated absorption cross- sections (σa) for stimulated emission from various excited states of Sm3 +‡ ion. The principal fluorescence transitions are identified by recording the fluorescence spectrum. Our analysis revealed that the novel glassy system has the optimum values for the key parameters viz. spectroscopic quality factor, optical gain, stimulated emission cross section and quantum efficiency, which are required for a high performance optical amplifier. Calculated chromaticity co-ordinates (0.61, 0.38) also confirm its application potential in display devices
Highly Efficient Near-IR Photoluminescence of Er3+ Immobilized in Mesoporous SBA-15
SiO2 mesoporous molecular sieve SBA-15 with the incorporation of erbium ions is studied as a novel type of nanoscopic composite photoluminescent material in this paper. To enhance the photoluminescence efficiency, two schemes have been used for the incorporation of Er3+ where (1) Er3+ is ligated with bis-(perfluoromethylsulfonyl)-aminate (PMS) forming Er(PMS)x-SBA-15 and (2) Yb3+ is codoped with Er3+ forming Yb-Er-SBA-15. As high as 11.17 × 10−21cm2 of fluorescent cross section at 1534 nm and 88 nm of “effective bandwidth” have been gained. It is a 29.3% boost in fluorescent cross section compared to what has been obtained in conventional silica. The upconversion coefficient in Yb-Er-SBA-15 is relatively small compared to that in other ordinary glass hosts. The increased fluorescent cross section and lowered upconversion coefficient could benefit for the high-gain optical amplifier. Finally, the Judd–Ofelt theory has also been used for the analyses of the optical spectra of Er(PMS)x-SBA-15
Preparation of name and address data for record linkage using hidden Markov models
BACKGROUND: Record linkage refers to the process of joining records that relate to the same entity or event in one or more data collections. In the absence of a shared, unique key, record linkage involves the comparison of ensembles of partially-identifying, non-unique data items between pairs of records. Data items with variable formats, such as names and addresses, need to be transformed and normalised in order to validly carry out these comparisons. Traditionally, deterministic rule-based data processing systems have been used to carry out this pre-processing, which is commonly referred to as "standardisation". This paper describes an alternative approach to standardisation, using a combination of lexicon-based tokenisation and probabilistic hidden Markov models (HMMs). METHODS: HMMs were trained to standardise typical Australian name and address data drawn from a range of health data collections. The accuracy of the results was compared to that produced by rule-based systems. RESULTS: Training of HMMs was found to be quick and did not require any specialised skills. For addresses, HMMs produced equal or better standardisation accuracy than a widely-used rule-based system. However, acccuracy was worse when used with simpler name data. Possible reasons for this poorer performance are discussed. CONCLUSION: Lexicon-based tokenisation and HMMs provide a viable and effort-effective alternative to rule-based systems for pre-processing more complex variably formatted data such as addresses. Further work is required to improve the performance of this approach with simpler data such as names. Software which implements the methods described in this paper is freely available under an open source license for other researchers to use and improve
The VANDELS survey:the star-formation histories of massive quiescent galaxies at 1.0 <z <1.3
We present a Bayesian full-spectral-fitting analysis of 75 massive () UVJ-selected galaxies at redshifts of ,
combining extremely deep rest-frame ultraviolet spectroscopy from VANDELS with
multi-wavelength photometry. By the use of a sophisticated physical plus
systematic uncertainties model, constructed within the Bagpipes code, we place
strong constraints on the star-formation histories (SFHs) of individual
objects. We firstly constrain the stellar mass vs stellar age relationship,
finding a steep trend towards earlier average formation with increasing stellar
mass of Gyr per decade in mass, although this shows
signs of flattening at . We show that this is consistent
with other spectroscopic studies from . This relationship places
strong constraints on the AGN-feedback models used in cosmological simulations.
We demonstrate that, although the relationships predicted by Simba and
IllustrisTNG agree well with observations at , they are too shallow at
, predicting an evolution of Gyr per decade in mass. Secondly, we
consider the connections between green-valley, post-starburst and quiescent
galaxies, using our inferred SFH shapes and the distributions of galaxy
physical properties on the UVJ diagram. The majority of our lowest-mass
galaxies () are consistent with formation in recent
(), intense starburst events, with timescales of Myr. A
second class of objects experience extended star-formation epochs before
rapidly quenching, passing through both green-valley and post-starburst phases.
The most massive galaxies in our sample are extreme systems: already old by
, they formed at and quenched by . However, we find evidence
for their continued evolution through both AGN and rejuvenated star-formation
activity.Comment: 25 pages, 13 figures, MNRAS accepte
The VANDELS ESO public spectroscopic survey
VANDELS is a uniquely deep spectroscopic survey of high-redshift galaxies with the VIMOS spectrograph on ESO’s Very Large Telescope (VLT). The survey has obtained ultradeep optical (0.48 < λ < 1.0 μ m) spectroscopy of ≃2100 galaxies within the redshift interval 1.0 ≤ z ≤ 7.0, over a total area of ≃0.2 deg2 centred on the CANDELS Ultra Deep Survey and Chandra Deep Field South fields. Based on accurate photometric redshift pre-selection, 85 per cent of the galaxies targeted by VANDELS were selected to be at z ≥ 3. Exploiting the red sensitivity of the refurbished VIMOS spectrograph, the fundamental aim of the survey is to provide the high-signal-to-noise ratio spectra necessary to measure key physical properties such as stellar population ages, masses, metallicities, and outflow velocities from detailed absorption-line studies. Using integration times calculated to produce an approximately constant signal-to-noise ratio (20 < tint< 80 h), the VANDELS survey targeted: (a) bright star-forming galaxies at 2.4 ≤ z ≤ 5.5, (b) massive quiescent galaxies at 1.0 ≤ z ≤ 2.5, (c) fainter star-forming galaxies at 3.0 ≤ z ≤ 7.0, and (d) X-ray/Spitzer-selected active galactic nuclei and Herschel-detected galaxies. By targeting two extragalactic survey fields with superb multiwavelength imaging data, VANDELS will produce a unique legacy data set for exploring the physics underpinning high-redshift galaxy evolution. In this paper, we provide an overview of the VANDELS survey designed to support the science exploitation of the first ESO public data release, focusing on the scientific motivation, survey design, and target selection
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