PHANGS-JWST First Results: Dust embedded star clusters in NGC 7496 selected via 3.3 μ\mum PAH emission

The earliest stages of star formation occur enshrouded in dust and are not observable in the optical. Here we leverage the extraordinary new high-resolution infrared imaging from JWST to begin the study of dust-embedded star clusters in nearby galaxies throughout the local volume. We present a technique for identifying dust-embedded clusters in NGC 7496 (18.7 Mpc), the first galaxy to be observed by the PHANGS-JWST Cycle 1 Treasury Survey. We select sources that have strong 3.3$\mu$m PAH emission based on a $\rm F300M-F335M$ color excess, and identify 67 candidate embedded clusters. Only eight of these are found in the PHANGS-HST optically-selected cluster catalog and all are young (six have SED-fit ages of $\sim1$ Myr). We find that this sample of embedded cluster candidates may significantly increase the census of young clusters in NGC 7496 from the PHANGS-HST catalog -- the number of clusters younger than $\sim$2 Myr could be increased by a factor of two. Candidates are preferentially located in dust lanes, and are coincident with peaks in PHANGS-ALMA CO (2-1) maps. We take a first look at concentration indices, luminosity functions, SEDs spanning from 2700A to 21$\mu$m, and stellar masses (estimated to be between $\sim10^4-10^5 M_{\odot}$). The methods tested here provide a basis for future work to derive accurate constraints on the physical properties of embedded clusters, characterize the completeness of cluster samples, and expand analysis to all 19 galaxies in the PHANGS-JWST sample, which will enable basic unsolved problems in star formation and cluster evolution to be addressed.Comment: 12 pages, 6 figures; accepted for publication in ApJL as part of PHANGS-JWST First Results Special Issu

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures; https://iopscience.iop.org/article/10.1088/1538-3873/acb29

L'origine des galaxies à raies d'émission en doubles-pics

A central aspect in understanding how galaxies evolved over cosmic time is to characterise their mass growth. Galaxy merger, in particular, play an important role, since they can transform the galaxy's morphology and fuel star formation. Since galaxy mergers can rapidly relax after colliding or cannot be identified as such due to a lack of resolution, detection methods are crucial to study them.double-peak emission-line galaxies have been used extensively in order to identify dual active galactic nuclei which are late stages of galaxy mergers.In this thesis, a more general discussion on the phenomenon of double-peak emission-line galaxies is presented. To this end, a double-peak galaxy sample consisting of 5,663 galaxies is selected from the Sloan Digital Sky Survey and the properties are studied in detail. To get a deeper understanding in the underlying mechanisms, double-peak signatures arising in disc models and simulations of isolated galaxies and galaxy mergers are analysed.Smaller sub samples of double-peak galaxies, showing both, significant activities of the super-massive black hole and enhanced star formation are discussed separately as they present a peculiar merger sample. To further understand the connection between star formation and double-peak emission-line galaxies molecular gas observations, conducted with the IRAM 30m telescope, are presented and analysed.In conclusion, there is a clear favouring of bar structures and minor mergers, which can explain the observed double-peak signatures and are also consistent with the characteristics found. This thesis shows that double-peak emission-line galaxies are an important aspect for high redshift observations and present a potential method of identifying galaxy mergers in larger upcoming surveys.Compréhension de leur évolution au cours du temps cosmique. Les fusions de galaxies jouent un rôle particulièrement important car elles peuvent transformer la morphologie des galaxies et alimenter leur formation d'étoiles. Comme les galaxies issues d'une fusion peuvent atteindre un état dynamique stabilisé rapidement après une fusion ou qu'il se peut qu'elle ne soient pas identifiées comme issues d'une fusion en raison d'un manque de résolution, les méthodes de détection sont cruciales pour les étudier. Les galaxies à raies d'émission doubles ont été beaucoup utilisées afin d'identifier les noyaux actifs de galaxies doubles qui correspondent à des étapes tardives des fusions de galaxies. Dans cette thèse, une discussion plus générale sur le phénomène des galaxies à raies d'émission à doubles-pics est présentée. À cette fin, un échantillon de galaxies à doubles-pics composé de 5663 galaxies est sélectionné dans le Sloan Digital Sky Survey et ses propriétés sont étudiées en détail.Afin de mieux comprendre les mécanismes sous-jacents, les signatures de doubles-pics apparaissant dans les modèles de disques et les simulations de galaxies isolées et de fusions de galaxies sont analysées. Des sous-échantillons plus petits de galaxies à doubles-pics, montrant à la fois des activités significatives du trou noir super-massif et une formation d'étoiles accrue, sont discutés séparément car ils représentent un échantillon particulier de fusions. Pour mieux comprendre le lien entre la formation d'étoiles et les galaxies à raies d'émission à doubles-pics, des observations de gaz moléculaire, réalisées avec le télescope de 30m de l'IRAM, sont présentées et analysées. En conclusion, les barres et les fusions mineures sont nettement privilégiées comme explications des signatures à doubles-pics car cohérentes avec les caractéristiques trouvées.Cette thèse montre que les galaxies à raies d'émission à doubles-pics sont un aspect important pour les observations à haut redshift et représentent une méthode potentielle d'identification des fusions de galaxies dans les grands relevés à venir

L'origine des galaxies à raies d'émission en doubles-pics

A central aspect in understanding how galaxies evolved over cosmic time is to characterise their mass growth. Galaxy merger, in particular, play an important role, since they can transform the galaxy's morphology and fuel star formation. Since galaxy mergers can rapidly relax after colliding or cannot be identified as such due to a lack of resolution, detection methods are crucial to study them.double-peak emission-line galaxies have been used extensively in order to identify dual active galactic nuclei which are late stages of galaxy mergers.In this thesis, a more general discussion on the phenomenon of double-peak emission-line galaxies is presented. To this end, a double-peak galaxy sample consisting of 5,663 galaxies is selected from the Sloan Digital Sky Survey and the properties are studied in detail. To get a deeper understanding in the underlying mechanisms, double-peak signatures arising in disc models and simulations of isolated galaxies and galaxy mergers are analysed.Smaller sub samples of double-peak galaxies, showing both, significant activities of the super-massive black hole and enhanced star formation are discussed separately as they present a peculiar merger sample. To further understand the connection between star formation and double-peak emission-line galaxies molecular gas observations, conducted with the IRAM 30m telescope, are presented and analysed.In conclusion, there is a clear favouring of bar structures and minor mergers, which can explain the observed double-peak signatures and are also consistent with the characteristics found. This thesis shows that double-peak emission-line galaxies are an important aspect for high redshift observations and present a potential method of identifying galaxy mergers in larger upcoming surveys.Compréhension de leur évolution au cours du temps cosmique. Les fusions de galaxies jouent un rôle particulièrement important car elles peuvent transformer la morphologie des galaxies et alimenter leur formation d'étoiles. Comme les galaxies issues d'une fusion peuvent atteindre un état dynamique stabilisé rapidement après une fusion ou qu'il se peut qu'elle ne soient pas identifiées comme issues d'une fusion en raison d'un manque de résolution, les méthodes de détection sont cruciales pour les étudier. Les galaxies à raies d'émission doubles ont été beaucoup utilisées afin d'identifier les noyaux actifs de galaxies doubles qui correspondent à des étapes tardives des fusions de galaxies. Dans cette thèse, une discussion plus générale sur le phénomène des galaxies à raies d'émission à doubles-pics est présentée. À cette fin, un échantillon de galaxies à doubles-pics composé de 5663 galaxies est sélectionné dans le Sloan Digital Sky Survey et ses propriétés sont étudiées en détail.Afin de mieux comprendre les mécanismes sous-jacents, les signatures de doubles-pics apparaissant dans les modèles de disques et les simulations de galaxies isolées et de fusions de galaxies sont analysées. Des sous-échantillons plus petits de galaxies à doubles-pics, montrant à la fois des activités significatives du trou noir super-massif et une formation d'étoiles accrue, sont discutés séparément car ils représentent un échantillon particulier de fusions. Pour mieux comprendre le lien entre la formation d'étoiles et les galaxies à raies d'émission à doubles-pics, des observations de gaz moléculaire, réalisées avec le télescope de 30m de l'IRAM, sont présentées et analysées. En conclusion, les barres et les fusions mineures sont nettement privilégiées comme explications des signatures à doubles-pics car cohérentes avec les caractéristiques trouvées.Cette thèse montre que les galaxies à raies d'émission à doubles-pics sont un aspect important pour les observations à haut redshift et représentent une méthode potentielle d'identification des fusions de galaxies dans les grands relevés à venir

The origin of double-peak emission-line Galaxies

Compréhension de leur évolution au cours du temps cosmique. Les fusions de galaxies jouent un rôle particulièrement important car elles peuvent transformer la morphologie des galaxies et alimenter leur formation d'étoiles. Comme les galaxies issues d'une fusion peuvent atteindre un état dynamique stabilisé rapidement après une fusion ou qu'il se peut qu'elle ne soient pas identifiées comme issues d'une fusion en raison d'un manque de résolution, les méthodes de détection sont cruciales pour les étudier. Les galaxies à raies d'émission doubles ont été beaucoup utilisées afin d'identifier les noyaux actifs de galaxies doubles qui correspondent à des étapes tardives des fusions de galaxies. Dans cette thèse, une discussion plus générale sur le phénomène des galaxies à raies d'émission à doubles-pics est présentée. À cette fin, un échantillon de galaxies à doubles-pics composé de 5663 galaxies est sélectionné dans le Sloan Digital Sky Survey et ses propriétés sont étudiées en détail.Afin de mieux comprendre les mécanismes sous-jacents, les signatures de doubles-pics apparaissant dans les modèles de disques et les simulations de galaxies isolées et de fusions de galaxies sont analysées. Des sous-échantillons plus petits de galaxies à doubles-pics, montrant à la fois des activités significatives du trou noir super-massif et une formation d'étoiles accrue, sont discutés séparément car ils représentent un échantillon particulier de fusions. Pour mieux comprendre le lien entre la formation d'étoiles et les galaxies à raies d'émission à doubles-pics, des observations de gaz moléculaire, réalisées avec le télescope de 30m de l'IRAM, sont présentées et analysées. En conclusion, les barres et les fusions mineures sont nettement privilégiées comme explications des signatures à doubles-pics car cohérentes avec les caractéristiques trouvées.Cette thèse montre que les galaxies à raies d'émission à doubles-pics sont un aspect important pour les observations à haut redshift et représentent une méthode potentielle d'identification des fusions de galaxies dans les grands relevés à venir.A central aspect in understanding how galaxies evolved over cosmic time is to characterise their mass growth. Galaxy merger, in particular, play an important role, since they can transform the galaxy's morphology and fuel star formation. Since galaxy mergers can rapidly relax after colliding or cannot be identified as such due to a lack of resolution, detection methods are crucial to study them.double-peak emission-line galaxies have been used extensively in order to identify dual active galactic nuclei which are late stages of galaxy mergers.In this thesis, a more general discussion on the phenomenon of double-peak emission-line galaxies is presented. To this end, a double-peak galaxy sample consisting of 5,663 galaxies is selected from the Sloan Digital Sky Survey and the properties are studied in detail. To get a deeper understanding in the underlying mechanisms, double-peak signatures arising in disc models and simulations of isolated galaxies and galaxy mergers are analysed.Smaller sub samples of double-peak galaxies, showing both, significant activities of the super-massive black hole and enhanced star formation are discussed separately as they present a peculiar merger sample. To further understand the connection between star formation and double-peak emission-line galaxies molecular gas observations, conducted with the IRAM 30m telescope, are presented and analysed.In conclusion, there is a clear favouring of bar structures and minor mergers, which can explain the observed double-peak signatures and are also consistent with the characteristics found. This thesis shows that double-peak emission-line galaxies are an important aspect for high redshift observations and present a potential method of identifying galaxy mergers in larger upcoming surveys

L'origine des galaxies à raies d'émission en doubles-pics

A central aspect in understanding how galaxies evolved over cosmic time is to characterise their mass growth. Galaxy merger, in particular, play an important role, since they can transform the galaxy's morphology and fuel star formation. Since galaxy mergers can rapidly relax after colliding or cannot be identified as such due to a lack of resolution, detection methods are crucial to study them.double-peak emission-line galaxies have been used extensively in order to identify dual active galactic nuclei which are late stages of galaxy mergers.In this thesis, a more general discussion on the phenomenon of double-peak emission-line galaxies is presented. To this end, a double-peak galaxy sample consisting of 5,663 galaxies is selected from the Sloan Digital Sky Survey and the properties are studied in detail. To get a deeper understanding in the underlying mechanisms, double-peak signatures arising in disc models and simulations of isolated galaxies and galaxy mergers are analysed.Smaller sub samples of double-peak galaxies, showing both, significant activities of the super-massive black hole and enhanced star formation are discussed separately as they present a peculiar merger sample. To further understand the connection between star formation and double-peak emission-line galaxies molecular gas observations, conducted with the IRAM 30m telescope, are presented and analysed.In conclusion, there is a clear favouring of bar structures and minor mergers, which can explain the observed double-peak signatures and are also consistent with the characteristics found. This thesis shows that double-peak emission-line galaxies are an important aspect for high redshift observations and present a potential method of identifying galaxy mergers in larger upcoming surveys.Compréhension de leur évolution au cours du temps cosmique. Les fusions de galaxies jouent un rôle particulièrement important car elles peuvent transformer la morphologie des galaxies et alimenter leur formation d'étoiles. Comme les galaxies issues d'une fusion peuvent atteindre un état dynamique stabilisé rapidement après une fusion ou qu'il se peut qu'elle ne soient pas identifiées comme issues d'une fusion en raison d'un manque de résolution, les méthodes de détection sont cruciales pour les étudier. Les galaxies à raies d'émission doubles ont été beaucoup utilisées afin d'identifier les noyaux actifs de galaxies doubles qui correspondent à des étapes tardives des fusions de galaxies. Dans cette thèse, une discussion plus générale sur le phénomène des galaxies à raies d'émission à doubles-pics est présentée. À cette fin, un échantillon de galaxies à doubles-pics composé de 5663 galaxies est sélectionné dans le Sloan Digital Sky Survey et ses propriétés sont étudiées en détail.Afin de mieux comprendre les mécanismes sous-jacents, les signatures de doubles-pics apparaissant dans les modèles de disques et les simulations de galaxies isolées et de fusions de galaxies sont analysées. Des sous-échantillons plus petits de galaxies à doubles-pics, montrant à la fois des activités significatives du trou noir super-massif et une formation d'étoiles accrue, sont discutés séparément car ils représentent un échantillon particulier de fusions. Pour mieux comprendre le lien entre la formation d'étoiles et les galaxies à raies d'émission à doubles-pics, des observations de gaz moléculaire, réalisées avec le télescope de 30m de l'IRAM, sont présentées et analysées. En conclusion, les barres et les fusions mineures sont nettement privilégiées comme explications des signatures à doubles-pics car cohérentes avec les caractéristiques trouvées.Cette thèse montre que les galaxies à raies d'émission à doubles-pics sont un aspect important pour les observations à haut redshift et représentent une méthode potentielle d'identification des fusions de galaxies dans les grands relevés à venir

Ultimate merging at z ∼ 0.1

International audienceWe present a study of 58 double-peaked emission line galaxies for which one of the components is suppressed in [OIII]λ5008 or is significantly weaker than the other one. Accordingly, the two components are classified differently in the BPT diagram. We show that the strong [OIII] component coincides with the stellar velocity and the suppressed component is off-centred in 66% of the galaxies, while in 12% of them it is the opposite. The analysis of their morphology reveals that about half of the sample is composed of S0, and the rest is composed of mergers and late-type galaxies in equal measure. We discuss the hypothesis that these characteristics exclude rotating discs and suggest different stages of merging. It is possible that the number of mergers is underestimated if the double nuclei are not resolved. Tidal features are detected in the outskirts of some S0 galaxies. This high fraction of S0 is surprising, as in addition most of the galaxies are isolated and the others are in small groups. All these galaxies that host an AGN component are massive, lie on the star forming sequence, and exhibit an enhanced star formation at their centre. While we cannot exclude outflows, these galaxies exhibit spectra that do not correspond to usual outflow observations characterised by high gas velocities, and the standard deviations of the two peaks are comparable. In parallel, these characteristics are compatible with ultimate stages of galaxy merging, where the two nuclei are either too close to be detected, or dynamical disturbances might be present in post-mergers like massive S0 galaxies

Testing He ii Emission from Wolf–Rayet Stars as a Dust Attenuation Measure in Eight Nearby Star-forming Galaxies

The ability to determine galaxy properties such as masses, ages, and star formation rates robustly is critically limited by the ability to measure dust attenuation accurately. Dust reddening is often characterized by comparing observations to models of either nebular recombination lines or the UV continuum. Here, we use a new technique to measure dust reddening by exploiting the He ii λ 1640 and λ 4686 emission lines originating from the stellar winds of Wolf–Rayet stars. The intrinsic line ratio is determined by atomic physics, enabling an estimate of the stellar reddening similar to how the Balmer lines probe gas-emission reddening. The He ii line ratio is measured from UV and optical spectroscopy using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope for eight nearby galaxies hosting young massive star clusters. We compare our results to dust reddening values estimated from UV spectral slopes and from Balmer line ratios and find tentative evidence for systematic differences. The reddening derived from the He ii lines tends to be higher, whereas that from the UV continuum tends to be lower. A larger sample size is needed to confirm this trend. If confirmed, this may indicate an age sequence probing different stages of dust clearing. Broad He ii lines have also been detected in galaxies more distant than in our sample, providing the opportunity to estimate the dust reddening of the youngest stellar populations out to distances of ∼100 Mpc

The origin of double-peak emission-line galaxies: Rotating discs, bars, or galaxy mergers?

Emission lines with a double-peak (DP) shape, detected in the centre of galaxies, have been extensively used in the past to identify peculiar kinematics such as dual active galactic nuclei (AGNs), outflows, or mergers. With a more general approach considering a large DP galaxy sample selected from the Sloan Digital Sky Survey (SDSS), a connection to minor merger galaxies with ongoing star formation was suggested. To gain a better understanding of different mechanisms creating a DP signature, in this paper, we explore synthetic SDSS spectroscopic observations computed from disc models and simulations. We show how a DP signature is connected to the central part of the rotation curve of galaxies, which is mostly shaped by the stellar bulge. We, furthermore, find that bars can create strong DP emission-line signatures when viewed along their major axis. Major mergers can form a central rotating disc in late post-coalescence merger stages (1 Gyr after the final coalescence), which creates a DP signature. Minor mergers tend to show a DP feature with no correlation to the galaxy inclination within 350 Myr after the final coalescence. Comparisons of these scenarii with observations disfavour major mergers, since they show predominantly elliptical and only a few S0 morphologies. Furthermore, at such a late merger stage, the enhanced star formation is most likely faded. Bars and minor mergers, on the other hand, can be compared quite well with the observations. Both observations coincide with increased star formation found in observations, and minor mergers in particular do not show any dependency with the observation direction. However, observations resolving the galaxy kinematics spatially are needed to distinguish between the discussed possibilities. More insight into the origin of DP will be gained by a broader comparison with cosmological simulations. The understanding of the DP origin can provide important tools to study the mass growth of galaxies in future high redshift surveys