ABSTRACT
In the hierarchical view of star formation, giant molecular clouds (GMCs) undergo fragmentation to form small-scale structures made up of stars and star clusters. Here we study the ...connection between young star clusters and cold gas across a range of extragalactic environments by combining the high resolution (1″) PHANGS–ALMA catalogue of GMCs with the star cluster catalogues from PHANGS–HST. The star clusters are spatially matched with the GMCs across a sample of 11 nearby star-forming galaxies with a range of galactic environments (centres, bars, spiral arms, etc.). We find that after 4 − 6 Myr the star clusters are no longer associated with any gas clouds. Additionally, we measure the autocorrelation of the star clusters and GMCs as well as their cross-correlation to quantify the fractal nature of hierarchical star formation. Young (≤10 Myr) star clusters are more strongly autocorrelated on kpc and smaller spatial scales than the $\gt \, 10$ Myr stellar populations, indicating that the hierarchical structure dissolves over time.
ABSTRACT
The spatial distribution of metals reflects, and can be used to constrain, the processes of chemical enrichment and mixing. Using PHANGS-MUSE optical integral field spectroscopy, we measure ...the gas-phase oxygen abundances (metallicities) across 7138 H ii regions in a sample of eight nearby disc galaxies. In Paper I, we measure and report linear radial gradients in the metallicities of each galaxy, and qualitatively searched for azimuthal abundance variations. Here, we examine the 2D variation in abundances once the radial gradient is subtracted, Δ(O/H), in order to quantify the homogeneity of the metal distribution and to measure the mixing scale over which H ii region metallicities are correlated. We observe low (0.03–0.05 dex) scatter in Δ(O/H) globally in all galaxies, with significantly lower (0.02–0.03 dex) scatter on small (<600 pc) spatial scales. This is consistent with the measurement uncertainties, and implies the 2D metallicity distribution is highly correlated on scales of ≲600 pc. We compute the two-point correlation function for metals in the disc in order to quantify the scale lengths associated with the observed homogeneity. This mixing scale is observed to correlate better with the local gas velocity dispersion (of both cold and ionized gas) than with the star formation rate. Selecting only H ii regions with enhanced abundances relative to a linear radial gradient, we do not observe increased homogeneity on small scales. This suggests that the observed homogeneity is driven by the mixing introducing material from large scales rather than by pollution from recent and on-going star formation.
Abstract
Determining how the galactic environment, especially the high gas densities and complex dynamics in bar-fed galaxy centers, alters the star formation efficiency (SFE) of molecular gas is ...critical to understanding galaxy evolution. However, these same physical or dynamical effects also alter the emissivity properties of CO, leading to variations in the CO-to-H
2
conversion factor (
α
CO
) that impact the assessment of the gas column densities and thus of the SFE. To address such issues, we investigate the dependence of
α
CO
on the local CO velocity dispersion at 150 pc scales using a new set of dust-based
α
CO
measurements and propose a new
α
CO
prescription that accounts for CO emissivity variations across galaxies. Based on this prescription, we estimate the SFE in a sample of 65 galaxies from the PHANGS–Atacama Large Millimeter/submillimeter Array survey. We find increasing SFE toward high-surface-density regions like galaxy centers, while using a constant or metallicity-based
α
CO
results in a more homogeneous SFE throughout the centers and disks. Our prescription further reveals a mean molecular gas depletion time of 700 Myr in the centers of barred galaxies, which is overall three to four times shorter than in nonbarred galaxy centers or the disks. Across the galaxy disks, the depletion time is consistently around 2–3 Gyr, regardless of the choice of
α
CO
prescription. All together, our results suggest that the high level of star formation activity in barred centers is not simply due to an increased amount of molecular gas, but also to an enhanced SFE compared to nonbarred centers or disk regions.
Abstract
We present the radio properties of 66 spectroscopically confirmed normal star-forming galaxies (SFGs) at 4.4 <
z
< 5.9 in the COSMOS field that were C
ii
-detected in the Atacama Large ...Millimeter/submillimeter Array Large Program to INvestigate C
ii
at Early times (ALPINE). We separate these galaxies (“C
ii
-detected-all”) into lower-redshift (“C
ii
-detected-lz”; 〈
z
〉 = 4.5) and higher-redshift (“C
ii
-detected-hz”; 〈
z
〉 = 5.6) subsamples, and stack multiwavelength imaging for each subsample from X-ray to radio bands. A radio signal is detected in the stacked 3 GHz images of the C
ii
-detected-all and lz samples at ≳3
σ
. We find that the infrared–radio correlation of our sample, quantified by
q
TIR
, is lower than the local relation for normal SFGs at a ∼3
σ
significance level, and is instead broadly consistent with that of bright submillimeter galaxies at 2 <
z
< 5. Neither of these samples show evidence of dominant active galactic nucleus activity in their stacked spectral energy distributions (SEDs), UV spectra, or stacked X-ray images. Although we cannot rule out the possible effects of the assumed spectral index and applied infrared SED templates in causing these differences, at least partially, the lower obscured fraction of star formation than at lower redshift can alleviate the tension between our stacked
q
TIR
s and those of local normal SFGs. It is possible that the dust buildup, which primarily governs the infrared emission, in addition to older stellar populations, has not had enough time to occur fully in these galaxies, whereas the radio emission can respond on a more rapid timescale. Therefore, we might expect a lower
q
TIR
to be a general property of high-redshift SFGs.
Abstract
We present new 0.3–21
μ
m photometry of SN 2021aefx in the spiral galaxy NGC 1566 at +357 days after
B
-band maximum, including the first detection of any Type Ia supernova (SN Ia) at >15
μ
...m. These observations follow earlier JWST observations of SN 2021aefx at +255 days after the time of maximum brightness, allowing us to probe the temporal evolution of the emission properties. We measure the fraction of flux emerging at different wavelengths and its temporal evolution. Additionally, the integrated 0.3–14
μ
m decay rate of Δ
m
0.3–14
= 1.35 ± 0.05 mag/100 days is higher than the decline rate from the radioactive decay of
56
Co of ∼1.2 mag/100 days. The most plausible explanation for this discrepancy is that flux is shifting to >14
μ
m, and future JWST observations of SNe Ia will be able to directly test this hypothesis. However, models predicting nonradiative energy loss cannot be excluded with the present data.
The PHANGS-MUSE survey Emsellem, Eric; Schinnerer, Eva; Santoro, Francesco ...
Astronomy and astrophysics (Berlin),
03/2022, Letnik:
659
Journal Article
Recenzirano
Odprti dostop
We present the PHANGS-MUSE survey, a programme that uses the MUSE integral field spectrograph at the ESO VLT to map 19 massive (9.4 < log(M⋆/M⊙)< 11.0) nearby (D ≲ 20 Mpc) star-forming disc ...galaxies. The survey consists of 168 MUSE pointings (1′ by 1′ each) and a total of nearly 15 × 106 spectra, covering ∼1.5 × 106 independent spectra. PHANGS-MUSE provides the first integral field spectrograph view of star formation across different local environments (including galaxy centres, bars, and spiral arms) in external galaxies at a median resolution of 50 pc, better than the mean inter-cloud distance in the ionised interstellar medium. This ‘cloud-scale’ resolution allows detailed demographics and characterisations of H II regions and other ionised nebulae. PHANGS-MUSE further delivers a unique view on the associated gas and stellar kinematics and provides constraints on the star-formation history. The PHANGS-MUSE survey is complemented by dedicated ALMA CO(2–1) and multi-band HST observations, therefore allowing us to probe the key stages of the star-formation process from molecular clouds to H II regions and star clusters. This paper describes the scientific motivation, sample selection, observational strategy, data reduction, and analysis process of the PHANGS-MUSE survey. We present our bespoke automated data-reduction framework, which is built on the reduction recipes provided by ESO but additionally allows for mosaicking and homogenisation of the point spread function. We further present a detailed quality assessment and a brief illustration of the potential scientific applications of the large set of PHANGS-MUSE data products generated by our data analysis framework. The data cubes and analysis data products described in this paper represent the basis for the first PHANGS-MUSE public data release and are available in the ESO archive and via the Canadian Astronomy Data Centre.
Context. Dust reprocesses about half of the stellar radiation in galaxies. The thermal re-emission by dust of absorbed energy is considered to be driven merely by young stars so is often applied to ...tracing the star formation rate in galaxies. Recent studies have argued that the old stellar population might be responsible for a non-negligible fraction of the radiative dust heating. Aims. In this work, we aim to analyze the contribution of young (≲100 Myr) and old (~10 Gyr) stellar populations to radiative dust heating processes in the nearby grand-design spiral galaxy M 51 using radiative transfer modeling. High-resolution 3D radiative transfer (RT) models are required to describe the complex morphologies of asymmetric spiral arms and clumpy star-forming regions and to model the propagation of light through a dusty medium. Methods. In this paper, we present a new technique developed to model the radiative transfer effects in nearby face-on galaxies. We construct a high-resolution 3D radiative transfer model with the Monte-Carlo code SKIRT to account for the absorption, scattering, and non-local thermal equilibrium (NLTE) emission of dust in M 51. The 3D distribution of stars is derived from the 2D morphology observed in the IRAC 3.6 μm, GALEX FUV, Hα, and MIPS 24 μm wavebands, assuming an exponential vertical distribution with an appropriate scale height. The dust geometry is constrained through the far-ultraviolet (FUV) attenuation, which is derived from the observed total-infrared-to-far-ultraviolet luminosity ratio. The stellar luminosity, star formation rate, and dust mass have been scaled to reproduce the observed stellar spectral energy distribution (SED), FUV attenuation, and infrared SED. Results. The dust emission derived from RT calculations is consistent with far-infrared and submillimeter observations of M 51, implying that the absorbed stellar energy is balanced by the thermal re-emission of dust. The young stars provide 63% of the energy for heating the dust responsible for the total infrared emission (8−1000 μm), while 37% of the dust emission is governed through heating by the evolved stellar population. In individual wavebands, the contribution from young stars to the dust heating dominates at all infrared wavebands but gradually decreases towards longer infrared and submillimeter wavebands for which the old stellar population becomes a non-negligible source of heating. Upon extrapolation of the results for M 51, we present prescriptions for estimating the contribution of young stars to the global dust heating based on a tight correlation between the dust heating fraction and specific star formation rate.
Une dénutrition postnatale est fréquente chez le prématuré et source de retard de croissance extra-utérin (RCEU), lui-même suivi d’une croissance de rattrapage tardive (catch-up growth). Cette ...trajectoire non optimale de croissance précoce peut avoir un impact nocif sur le futur adulte en lien avec le concept de l’origine précoce des maladies de l’adulte (developmental origins of health and disease, DOHaD). La mise en place d’une nutrition optimale pour éviter un RCEU chez le prématuré est donc une priorité des néonatologistes. L’apport du lait maternel a été montré comme bénéfique chez les prématurés mais résulte souvent en un gain de poids sous-optimal qui peut s’expliquer par de grandes variations nutritionnelles dans la composition du lait maternel. Ainsi des informations précises sur la composition des laits maternels sont essentielles pour assurer aux enfants prématurés une croissance de qualité. Dans ce contexte, une signature la plus exhaustive possible du nutriome du lait maternel de prématuré d’une cohorte monocentrique observationnelle a été mise en relation avec la croissance staturo-pondérale des enfants prématurés durant leurs premières semaines de vie et jusqu’à leurs 2 ans d’âge corrigé.
La croissance des 138 enfants nés prématurés de la cohorte LACTACOL (Clinical Trial-NCT01493063) a été évaluée selon leur croissance hospitalière (différence de Z-score entre la sortie d’hospitalisation et la naissance, à l’aide de la courbe standard d’Olsen), et la qualité de croissance (Z-score de l’indice de masse corporelle et de masse maigre) à 2 ans d’âge corrigé. Un phénotypage à haut débit semi-quantitatif (métabolomique, lipidomique) combiné à des approches ciblées de mesures de familles de composés bioactifs par chromatographie liquide haute résolution couplée à la spectrométrie de masse en tandem a été réalisé sur 118 prélèvements (représentatifs de 24heures) de lait maternel de prématuré à la troisième semaine de lactation. La composition des laits maternels a été mise en relation avec les paramètres de croissance des enfants nés prématurés à l’aide d’outils statistiques univariés ou multivariés prenant en compte les facteurs confondants.
Des premières analyses discriminantes par la méthode des moindres carrés (PLS-DA) montrent une signature spécifique du lipidome du lait maternel associée au groupe d’enfants prématurés appartenant au tertile haut de croissance hospitalière. Parmi les variables les plus discriminantes, des analyses de la variance (Anova) montrent que les laits maternels associés à des enfants présentant un delta-Z score pondéral postnatal compris entre −0,31 et 2,10 sont des laits riches en choline (sous forme libre ou incorporée dans des glycéro-phosphocholines et sphingomyélines) et en certains céramides. Parmi les composés polaires, ce sont les laits les plus riches en composés insulino-trophiques, dont les acides aminés à chaînes branchées, qui sont associés aux prématurés présentant une croissance pondérale optimale en cours d’hospitalisation. Les enfants prématurés ayant reçu un lait enrichi en glycine et en bétaïne, deux composés impliqués dans la synthèse d’un antioxydant majoritaire, le glutathion, et en acides aminés qui jouent un rôle majeur dans la maturation du tube digestif (glutamine, arginine, proline) sont ceux qui appartiennent au tertile haut du Z-score d’indice de masse corporelle à 2 ans (compris entre 0,16 et 1,82). Une analyse de type AoV-PLS/LDA (Analyse discriminante linéaire) couplée à une régression multiple linéaire (MLR) devrait permettre de sélectionner des biomarqueurs du lait maternel prédictifs de la croissance postnatale et à 2 ans des enfants nés prématurés.
Cette étude montre l’intérêt des approches intégratives de phénotypage par chromatographie liquide haute résolution couplée à la spectrométrie de masse combinée à des outils de statistiques exploratoires et prédictifs pour améliorer les connaissances sur la composition du lait maternel et à plus long terme, orienter les pratiques nutritionnelles des enfants nés prématurés en vue d’optimiser la qualité de leur croissance.
Localization of peptidases in lactococci Tan, P.S.T. (University of Groningen, Haren, The Netherlands); Chapot-Chartier, M.P; Pos, K.M ...
Applied and Environmental Microbiology,
(Jan 1992), 19920101, 1992, 1992-Jan, 1992-01-00, Letnik:
58, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The localization of two aminopeptidases, an X-prolyl-dipeptidyl aminopeptidase, an endopeptidase, and a tripeptidase in Lactococcus lactis was studied. Polyclonal antibodies raised against each ...purified peptides are specific and do not cross-react with other peptidases. Experiments were performed by immunoblotting after cell fractionation and by electron microscopy of immunogold-labeled peptidases. All peptidases were found to be intracellular. However, immunogold studies showed a peripheral labeling of the X-prolyl-dipeptidyl aminopeptidase, the tripeptidase, and the endopeptidase. This peripheral location was further supported by the detection of these three enzymes in cell membrane fractions in which none of the two aminopeptidases was present
This study illustrated the effect of controlled oxygenation on diacetyl production by citrate-utilizing Lactococcus lactis ssp. lactis CNRZ 483. Effects of soluble oxygen concentrations at 21 and 50% ...of the medium saturation and pressurization of the reactor under 1 and 2atm (atmospheres) of oxygen were tested. Oxygen had a slightly negative effect on the growth of L. lactis ssp. lactis CNRZ 483. In contrast, oxygen had a substantial effect on diacetyl production. Under nitrogen, the maximal concentration of diacetyl in the medium was 0.015mM; diacetyl maxima were 0.13 and 0.26mM when soluble oxygen concentrations were 21 and 5096, respectively. Diacetyl production reached a maximum of 0.39 and 0.45mM when oxygen pressures of the culture were 1 and 2atm, respectively. The effect of oxygen on lactate dehydrogenase activity and on chemical decarboxylation of α-acetolactate explained the higher diacetyl production.
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