139 research outputs found
Direct observation of active material concentration gradients and crystallinity breakdown in LiFePO4 electrodes during charge/discharge cycling of lithium batteries
The phase changes that occur during discharge of an electrode comprised of LiFePO4, carbon, and PTFE binder have been studied in lithium half cells by using X-ray diffraction measurements in reflection geometry. Differences in the state of charge between the front and the back of LiFePO4 electrodes have been visualized. By modifying the X-ray incident angle the depth of penetration of the X-ray beam into the electrode was altered, allowing for the examination of any concentration gradients that were present within the electrode. At high rates of discharge the electrode side facing the current collector underwent limited lithium insertion while the electrode as a whole underwent greater than 50% of discharge. This behavior is consistent with depletion at high rate of the lithium content of the electrolyte contained in the electrode pores. Increases in the diffraction peak widths indicated a breakdown of crystallinity within the active material during cycling even during the relatively short duration of these experiments, which can also be linked to cycling at high rate
JWST NIRCam + NIRSpec: Interstellar medium and stellar populations of young galaxies with rising star formation and evolving gas reservoirs
We present an interstellar medium and stellar population analysis of three spectroscopically confirmed z > 7 galaxies in the Early Release Observations JWST/NIRCam and JWST/NIRSpec data of the SMACS J0723.3-7327 cluster. We use the Bayesian spectral energy distribution-fitting code PROSPECTOR with a flexible star formation history (SFH), a variable dust attenuation law, and a self-consistent model of nebular emission (continuum and emission lines). Importantly, we self-consistently fit both the emission line fluxes from JWST/NIRSpec and the broad-band photometry from JWST/NIRCam, taking into account slit-loss effects. We find that these three z=7.6-8.5 galaxies (M-* approximate to 10(8) M-circle dot) are young with rising SFHs and mass-weighted ages of 3-4 Myr, though we find indications for underlying older stellar populations. The inferred gas-phase metallicities broadly agree with the direct metallicity estimates from the auroral lines. The galaxy with the lowest gas-phase metallicity (Z(gas) = 0.06 Z(circle dot)) has a steeply rising SFH, is very compact ( <0.2 kpc), and has a high star formation rate surface density (Sigma(SFR) approximate to 22 M-circle dot yr(-1) kpc(-2)), consistent with rapid gas accretion. The two other objects with higher gas-phase metallicities show more complex multicomponent morphologies on kpc scales, indicating that their recent increase in star formation rate is driven by mergers or internal, gravitational instabilities. We discuss effects of assuming different SFH priors or only fitting the photometric data. Our analysis highlights the strength and importance of combining JWST imaging and spectroscopy for fully assessing the nature of galaxies at the earliest epochs
A Massive, Cooling-Flow-Induced Starburst in the Core of a Highly Luminous Galaxy Cluster
In the cores of some galaxy clusters the hot intracluster plasma is dense
enough that it should cool radiatively in the cluster's lifetime, leading to
continuous "cooling flows" of gas sinking towards the cluster center, yet no
such cooling flow has been observed. The low observed star formation rates and
cool gas masses for these "cool core" clusters suggest that much of the cooling
must be offset by astrophysical feedback to prevent the formation of a runaway
cooling flow. Here we report X-ray, optical, and infrared observations of the
galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an
exceptionally luminous (L_2-10 keV = 8.2 x 10^45 erg/s) galaxy cluster which
hosts an extremely strong cooling flow (dM/dt = 3820 +/- 530 Msun/yr). Further,
the central galaxy in this cluster appears to be experiencing a massive
starburst (740 +/- 160 Msun/yr), which suggests that the feedback source
responsible for preventing runaway cooling in nearby cool core clusters may not
yet be fully established in SPT-CLJ2344-4243. This large star formation rate
implies that a significant fraction of the stars in the central galaxy of this
cluster may form via accretion of the intracluster medium, rather than the
current picture of central galaxies assembling entirely via mergers.Comment: 11 pages, 3 figures, 1 table. Supplemental material contains 15
additional pages. Published in Natur
Color and stellar population gradients in galaxies. Correlation with mass
We analyze the color gradients (CGs) of ~50000 nearby SDSS galaxies. From
synthetic spectral models based on a simplified star formation recipe, we
derive the mean spectral properties, and explain the observed radial trends of
the color as gradients of the stellar population age and metallicity (Z). The
most massive ETGs (M_* > 10^{11} Msun) have shallow CGs in correspondence of
shallow (negative) Z gradients. In the stellar mass range 10^(10.3-10.5) < M_*
< 10^(11) Msun, the Z gradients reach their minimum of ~ -0.5 dex^{-1}. At M_*
~ 10^{10.3-10.5} Msun, color and Z gradient slopes suddenly change. They turn
out to anti-correlate with the mass, becoming highly positive at the very low
masses. We have also found that age gradients anti-correlate with Z gradients,
as predicted by hierarchical cosmological simulations for ETGs. On the other
side, LTGs have gradients which systematically decrease with mass (and are
always more negative than in ETGs), consistently with the expectation from gas
infall and SN feedback scenarios. Z is found to be the main driver of the trend
of color gradients, especially for LTGs, but age gradients are not negligible
and seem to play a significant role too. We have been able to highlight that
older galaxies have systematically shallower age and Z gradients than younger
ones. Our results for high-mass galaxies are in perfect agreement with
predictions based on the merging scenario, while the evolution of LTGs and
younger and less massive ETGs seems to be mainly driven by infall and SN
feedback. (Abridged)Comment: 20 pages, 16 figures, accepted for publication on MNRAS. This version
includes revisions after the referee's report
Discovery and properties of the earliest galaxies with confirmed distances
© 2023 Springer Nature Limited. This is the accepted manuscript version of an article which has been published in final form at 10.1038/s41550-023-01921-1Surveys with James Webb Space Telescope (JWST) have discovered candidate galaxies in the first 400 Myr of cosmic time. The properties of these distant galaxies provide initial conditions for understanding early galaxy formation and cosmic reionisation. Preliminary indications have suggested these candidate galaxies may be more massive and abundant than previously thought. However, without spectroscopic confirmation of their distances to constrain their intrinsic brightnesses, their inferred properties remain uncertain. Here we report on four galaxies located in the JWST Advanced Deep Extragalactic Survey (JADES) Near-Infrared Camera (NIRCam) imaging with photometric redshifts subsequently confirmed by JADES JWST Near- Infrared Spectrograph (NIRSpec) observations. These galaxies include the first redshift systems both discovered and spectroscopically confirmed by JWST. Using stellar population modelling, we find the galaxies typically contain a hundred million solar masses in stars, in stellar populations that are less than one hundred million years old. The moderate star formation rates and compact sizes suggest elevated star formation rate surface densities, a key indicator of their formation pathways. Taken together, these measurements show that the first galaxies contributing to cosmic reionisation formed rapidly and with intense internal radiation fields.Peer reviewe
Stellar mass-to-light ratio gradients in galaxies: correlations with mass
We analyze the stellar mass-to-light ratio (M/L) gradients in a large sample
of local galaxies taken from the Sloan Digital Sky Survey, spanning a wide
range of stellar masses and morphological types. As suggested by the well known
relationship between M/L ratios and colors, we show that M/L gradients are
strongly correlated with colour gradients, which we trace to the effects of age
variations. Stellar M/L gradients generally follow patterns of variation with
stellar mass and galaxy type that were previous found for colour and metallicty
gradients. In late-type galaxies M/L gradients are negative, steepening with
increasing mass. In early-type galaxies M/L gradients are shallower while
presenting a two-fold trend: they decrease with mass up to a characteristic
mass of \M* \sim 10^10.3 M_sun and increase at larger masses. We compare our
findings with other analyses and discuss some implications for galaxy formation
and for dark matter estimates.Comment: 9 pages, 3 figures, 3 tables, accepted for publication on MNRA
ACCESS IV: The quenching of star formation in a cluster population of dusty S0s
We present an analysis of the mid-infrared (MIR) colours of 165 70um-detected
galaxies in the Shapley supercluster core (SSC) at z=0.048 using panoramic
Spitzer/MIPS 24 and 70um imaging. While the bulk of galaxies show f70/f24
colours typical of local star-forming galaxies, we identify a significant
sub-population of 23 70micron-excess galaxies, whose MIR colours (f70/f24>25)
are much redder and cannot be reproduced by any of the standard model infrared
SEDs. These galaxies are found to be strongly concentrated towards the cores of
the five clusters that make up the SSC, and also appear rare among local field
galaxies, confirming them as a cluster-specific phenomenon. Their optical
spectra and lack of significant UV emission imply little or no ongoing star
formation, while fits to their panchromatic SEDs require the far-IR emission to
come mostly from a diffuse dust component heated by the general interstellar
radiation field rather than ongoing star formation. Most of these
70micron-excess galaxies are identified as ~L* S0s with smooth profiles. We
find that almost every cluster galaxy in the process of star-formation
quenching is already either an S0 or Sa, while we find no passive galaxies of
class Sb or later. Hence the formation of passive early-type galaxies in
cluster cores must involve the prior morphological transformation of late-type
spirals into Sa/S0s, perhaps via pre-processing or the impact of cluster tidal
fields, before a subsequent quenching of star formation once the lenticular
encounters the dense environment of the cluster core. In the cases of many
cluster S0s, this phase of star-formation quenching is characterised by an
excess of 70um emission, indicating that the cold dust content is declining at
a slower rate than star formation.Comment: 17 pages, 12 figures. Accepted for publication in MNRA
The star formation history of BCGs to z = 1.8 from the SpARCS/SWIRE survey : evidence for significant in situ star formation at high redshift
We present the results of an MIPS-24 ÎŒm study of the brightest cluster galaxies (BCGs) of 535 high-redshift galaxy clusters. The clusters are drawn from the Spitzer Adaptation of the Red-Sequence Cluster Survey, which effectively provides a sample selected on total stellar mass, over 0.2 12) increases rapidly with redshift. Above z ⌠1, an average of âŒ20% of the sample have 24 ÎŒm inferred infrared luminosities of LIR > 1012 Lo, while the fraction below z ⌠1 exhibiting such luminosities is <1%. The Spitzer-IRAC colors indicate the bulk of the 24 ÎŒm detected population is predominantly powered by star formation, with only 7/125 galaxies lying within the color region inhabited by active galactic nuclei (AGNs). Simple arguments limit the star formation activity to several hundred million years and this may therefore be indicative of the timescale for AGN feedback to halt the star formation. Below redshift z ⌠1, there is not enough star formation to significantly contribute to the overall stellar mass of the BCG population, and therefore BCG growth is likely dominated by dry mergers. Above z ⌠1, however, the inferred star formation would double the stellar mass of the BCGs and is comparable to the mass assembly predicted by simulations through dry mergers. We cannot yet constrain the process driving the star formation for the overall sample, though a single object studied in detail is consistent with a gas-rich merger.Peer reviewe
Planck 2013 results. XXIX. Planck catalogue of Sunyaev-Zeldovich sources
We describe the all-sky Planck catalogue of clusters and cluster candidates derived from Sunyaev-Zeldovich (SZ) effect detections using the first 15.5 months of Planck satellite observations. The catalogue contains 1227 entries, making it over six times the size of the Planck Early SZ (ESZ) sample and the largest SZ-selected catalogue to date. It contains 861 confirmed clusters, of which 178 have been confirmed as clusters, mostly through follow-up observations, and a further 683 are previously-known clusters. The remaining 366 have the status of cluster candidates, and we divide them into three classes according to the quality of evidence that they are likely to be true clusters. The Planck SZ catalogue is the deepest all-sky cluster catalogue, with redshifts up to about one, and spans the broadest cluster mass range from (0.1 to 1.6) Ă 1015 MĂąĆ âą. Confirmation of cluster candidates through comparison with existing surveys or cluster catalogues is extensively described, as is the statistical characterization of the catalogue in terms of completeness and statistical reliability. The outputs of the validation process are provided as additional information. This gives, in particular, an ensemble of 813 cluster redshifts, and for all these Planck clusters we also include a mass estimated from a newly-proposed SZ-mass proxy. A refined measure of the SZ Compton parameter for the clusters with X-ray counter-parts is provided, as is an X-ray flux for all the Planck clusters not previously detected in X-ray surveys.The development of Planck has been supported by: ESA; CNES and CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA); STFC and UKSA (UK); CSIC, MICINN and JA (Spain); Tekes, AoF and CSC (Finland); DLR and MPG (Germany); CSA (Canada); DTU Space (Denmark); SER/SSO (Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); and PRACE (EU).Peer Reviewe
Residual Cooling and Persistent Star Formation amid AGN Feedback in Abell 2597
New Chandra X-ray and Herschel FIR observations enable a multiwavelength
study of active galactic nucleus (AGN) heating and intracluster medium (ICM)
cooling in the brightest cluster galaxy of Abell 2597. The new Chandra
observations reveal the central < 30 kiloparsec X-ray cavity network to be more
extensive than previously thought, and associated with enough enthalpy to
theoretically inhibit the inferred classical cooling flow. Nevertheless, we
present new evidence, consistent with previous results, that a moderately
strong residual cooling flow is persisting at 4%-8% of the classically
predicted rates in a spatially structured manner amid the feedback-driven
excavation of the X-ray cavity network. New Herschel observations are used to
estimate warm and cold dust masses, a lower-limit gas-to-dust ratio, and a star
formation rate consistent with previous measurements. The cooling time profile
of the ambient X-ray atmosphere is used to map the locations of the
observational star formation entropy threshold as well as the theoretical
thermal instability threshold. Both lie just outside the < 30 kpc central
region permeated by X-ray cavities, and star formation as well as ionized and
molecular gas lie interior to both. The young stars are distributed in an
elongated region that is aligned with the radio lobes, and their estimated ages
are both younger and older than the X-ray cavity network, suggesting both
jet-triggered as well as persistent star formation over the current AGN
feedback episode. Bright X-ray knots that are coincident with extended Ly-alpha
and FUV continuum filaments motivate a discussion of structured cooling from
the ambient hot atmosphere along a projected axis that is perpendicular to
X-ray cavity and radio axis. We conclude that the cooling ICM is the dominant
contributor of the cold gas reservoir fueling star formation and AGN activity
in the Abell 2597 BCG.Comment: 20 pages, 7 figures; Accepted for publication in MNRA
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