| 1. |
- Rodríguez, M. Jimena, et al.
(författare)
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PHANGS–JWST First Results : Dust-embedded Star Clusters in NGC 7496 Selected via 3.3 μm PAH Emission
- 2023
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 944:2
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Tidskriftsartikel (refereegranskat)abstract
- 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 μm PAH emission based on a 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 ∼1 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 ∼2 Myr could be increased by a factor of 2. Candidates are preferentially located in dust lanes and are coincident with the peaks in the PHANGS-ALMA CO (2–1) maps. We take a first look at concentration indices, luminosity functions, SEDs spanning from 2700 Å to 21 μm, and stellar masses (estimated to be between ∼104 and 105 M⊙). 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.
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| 2. |
- Schinnerer, Eva, et al.
(författare)
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PHANGS-JWST First Results : Rapid Evolution of Star Formation in the Central Molecular Gas Ring of NGC 1365
- 2023
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 944:2
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale bars can fuel galaxy centers with molecular gas, often leading to the development of dense ringlike structures where intense star formation occurs, forming a very different environment compared to galactic disks. We pair ∼0.″3 (30 pc) resolution new JWST/MIRI imaging with archival ALMA CO(2-1) mapping of the central ∼5 kpc of the nearby barred spiral galaxy NGC 1365 to investigate the physical mechanisms responsible for this extreme star formation. The molecular gas morphology is resolved into two well-known bright bar lanes that surround a smooth dynamically cold gas disk (R gal ∼ 475 pc) reminiscent of non-star-forming disks in early-type galaxies and likely fed by gas inflow triggered by stellar feedback in the lanes. The lanes host a large number of JWST-identified massive young star clusters. We find some evidence for temporal star formation evolution along the ring. The complex kinematics in the gas lanes reveal strong streaming motions and may be consistent with convergence of gas streamlines expected there. Indeed, the extreme line widths are found to be the result of inter-“cloud” motion between gas peaks; ScousePy decomposition reveals multiple components with line widths of 〈σ CO,scouse〉 ≈ 19 km s−1 and surface densities of 〈 Σ H 2 , scouse 〉 ≈ 800 M ⊙ pc − 2 , similar to the properties observed throughout the rest of the central molecular gas structure. Tailored hydrodynamical simulations exhibit many of the observed properties and imply that the observed structures are transient and highly time-variable. From our study of NGC 1365, we conclude that it is predominantly the high gas inflow triggered by the bar that is setting the star formation in its CMZ.
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| 3. |
- Thilker, David A., et al.
(författare)
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PHANGS–JWST First Results : The Dust Filament Network of NGC 628 and Its Relation to Star Formation Activity
- 2023
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 944:2
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Tidskriftsartikel (refereegranskat)abstract
- PHANGS–JWST mid-infrared (MIR) imaging of nearby spiral galaxies has revealed ubiquitous filaments of dust emission in intricate detail. We present a pilot study to systematically map the dust filament network (DFN) at multiple scales between 25 and 400 pc in NGC 628. MIRI images at 7.7, 10, 11.3, and 21 μm of NGC 628 are used to generate maps of the filaments in emission, while PHANGS–HST B-band imaging yields maps of dust attenuation features. We quantify the correspondence between filaments traced by MIR thermal continuum/polycyclic aromatic hydrocarbon (PAH) emission and filaments detected via extinction/scattering of visible light; the fraction of MIR flux contained in the DFN; and the fraction of H ii regions, young star clusters, and associations within the DFN. We examine the dependence of these quantities on the physical scale at which the DFN is extracted. With our highest-resolution DFN maps (25 pc filament width), we find that filaments in emission and attenuation are cospatial in 40% of sight lines, often exhibiting detailed morphological agreement; that ∼30% of the MIR flux is associated with the DFN; and that 75%–80% of the star formation in H ii regions and 60% of the mass in star clusters younger than 5 Myr are contained within the DFN. However, the DFN at this scale is anticorrelated with looser associations of stars younger than 5 Myr identified using PHANGS–HST near-UV imaging. We discuss the impact of these findings on studies of star formation and the interstellar medium, and the broad range of new investigations enabled by multiscale maps of the DFN.
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| 4. |
- Liu, Daizhong, et al.
(författare)
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PHANGS–JWST First Results : Stellar-feedback-driven Excitation and Dissociation of Molecular Gas in the Starburst Ring of NGC 1365?
- 2023
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 944:2
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Tidskriftsartikel (refereegranskat)abstract
- We compare embedded young massive star clusters (YMCs) to (sub-)millimeter line observations tracing the excitation and dissociation of molecular gas in the starburst ring of NGC 1365. This galaxy hosts one of the strongest nuclear starbursts and richest populations of YMCs within 20 Mpc. Here we combine near-/mid-IR PHANGS–JWST imaging with new Atacama Large Millimeter/submillimeter Array multi-J CO (1–0, 2–1 and 4–3) and [C ı] (1–0) mapping, which we use to trace CO excitation via R42 = ICO(4−3)/ICO(2−1) and R21 = ICO(2−1)/ICO(1−0) and dissociation via RCICO = I[CI](1−0)/ICO(2−1) at 330 pc resolution. We find that the gas flowing into the starburst ring from northeast to southwest appears strongly affected by stellar feedback, showing decreased excitation (lower R42) and increased signatures of dissociation (higher RCICO) in the downstream regions. There, radiative-transfer modeling suggests that the molecular gas density decreases and temperature and [CI/CO] abundance ratio increase. We compare R42 and RCICO with local conditions across the regions and find that both correlate with near-IR 2 μm emission tracing the YMCs and with both polycyclic aromatic hydrocarbon (11.3 μm) and dust continuum (21 μm) emission. In general, RCICO exhibits ∼0.1 dex tighter correlations than R42, suggesting C ı to be a more sensitive tracer of changing physical conditions in the NGC 1365 starburst than CO (4–3). Our results are consistent with a scenario where gas flows into the two arm regions along the bar, becomes condensed/shocked, forms YMCs, and then these YMCs heat and dissociate the gas.
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| 5. |
- Scheuermann, Fabian, et al.
(författare)
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Stellar associations powering H ii regions - I. Defining an evolutionary sequence
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 522:2, s. 2369-2383
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Tidskriftsartikel (refereegranskat)abstract
- Connecting the gas in H II regions to the underlying source of the ionizing radiation can help us constrain the physical processes of stellar feedback and how H II regions evolve over time. With PHANGS-MUSE, we detect nearly 24 000 H II regions across 19 galaxies and measure the physical properties of the ionized gas (e.g. metallicity, ionization parameter, and density). We use catalogues of multiscale stellar associations from PHANGS-HST to obtain constraints on the age of the ionizing sources. We construct a matched catalogue of 4177 H II regions that are clearly linked to a single ionizing association. A weak anticorrelation is observed between the association ages and the H a equi v alent width EW (H a), the H a/ FUV flux ratio, and the ionization parameter, log q . As all three are expected to decrease as the stellar population ages, this could indicate that we observe an evolutionary sequence. This interpretation is further supported by correlations between all three properties. Interpreting these as evolutionary tracers, we find younger nebulae to be more attenuated by dust and closer to giant molecular clouds, in line with recent models of feedback-regulated star formation. We also observe strong correlations with the local metallicity variations and all three proposed age tracers, suggestive of star formation preferentially occurring in locations of locally enhanced metallicity. Overall, EW (H a) and log q show the most consistent trends and appear to be most reliable tracers for the age of an H II region.
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| 6. |
- Larson, Kirsten L., et al.
(författare)
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Multiscale stellar associations across the star formation hierarchy in PHANGS-HST nearby galaxies : methodology and properties
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 523:4, s. 6061-6081
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Tidskriftsartikel (refereegranskat)abstract
- We develop a method to identify and determine the physical properties of stellar associations using Hubble Space Telescope (HST) NUV−U−B−V−I imaging of nearby galaxies from the Physics at High Angular Resolution in Nearby GalaxieS with the Hubble Space Telescope (PHANGS–HST) survey. We apply a watershed algorithm to density maps constructed from point source catalogues Gaussian smoothed to multiple physical scales from 8 to 64 pc. We develop our method on two galaxies that span the distance range in the PHANGS–HST sample: NGC 3351 (10 Mpc) and NGC 1566 (18 Mpc). We test our algorithm with different parameters such as the choice of detection band for the point source catalogue (NUV or V), source density image filtering methods, and absolute magnitude limits. We characterize the properties of the resulting multiscale associations, including sizes, number of tracer stars, number of associations, and photometry, as well as ages, masses, and reddening from spectral energy distribution fitting. Our method successfully identifies structures that occupy loci in the UBVI colour–colour diagram consistent with previously published catalogues of clusters and associations. The median ages of the associations increase from log(age/yr) = 6.6 to log(age/yr) = 6.9 as the spatial scale increases from 8 to 64 pc for both galaxies. We find that the youngest stellar associations, with ages <3 Myr, indeed closely trace H II regions in H α imaging, and that older associations are increasingly anticorrelated with the H α emission. Owing to our new method, the PHANGS–HST multiscale associations provide a far more complete census of recent star formation activity than found with previous cluster and compact association catalogues.
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| 7. |
- Adamo, Angela, et al.
(författare)
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Star Clusters Near and Far Tracing Star Formation Across Cosmic Time
- 2020
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Ingår i: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 216:4
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Forskningsöversikt (refereegranskat)abstract
- Star clusters are fundamental units of stellar feedback and unique tracers of their host galactic properties. In this review, we will first focus on their constituents, i.e. detailed insight into their stellar populations and their surrounding ionised, warm, neutral, and molecular gas. We, then, move beyond the Local Group to review star cluster populations at various evolutionary stages, and in diverse galactic environmental conditions accessible in the local Universe. At high redshift, where conditions for cluster formation and evolution are more extreme, we are only able to observe the integrated light of a handful of objects that we believe will become globular clusters. We therefore discuss how numerical and analytical methods, informed by the observed properties of cluster populations in the local Universe, are used to develop sophisticated simulations potentially capable of disentangling the genetic map of galaxy formation and assembly that is carried by globular cluster populations.
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| 8. |
- Ballesteros-Paredes, Javier, et al.
(författare)
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From Diffuse Gas to Dense Molecular Cloud Cores
- 2020
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Ingår i: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 216:5
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Forskningsöversikt (refereegranskat)abstract
- Molecular clouds are a fundamental ingredient of galaxies: they are the channels that transform the diffuse gas into stars. The detailed process of how they do it is not completely understood. We review the current knowledge of molecular clouds and their substructure from scales similar to 1kpc down to the filament and core scale. We first review the mechanisms of cloud formation from the warm diffuse interstellar medium down to the cold and dense molecular clouds, the process of molecule formation and the role of the thermal and gravitational instabilities. We also discuss the main physical mechanisms through which clouds gather their mass, and note that all of them may have a role at various stages of the process. In order to understand the dynamics of clouds we then give a critical review of the widely used virial theorem, and its relation to the measurable properties of molecular clouds. Since these properties are the tools we have for understanding the dynamical state of clouds, we critically analyse them. We finally discuss the ubiquitous filamentary structure of molecular clouds and its connection to prestellar cores and star formation.
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| 9. |
- Chevance, Mélanie, et al.
(författare)
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The Molecular Cloud Lifecycle
- 2020
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Ingår i: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 216:4
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Forskningsöversikt (refereegranskat)abstract
- Giant molecular clouds (GMCs) and their stellar offspring are the building blocks of galaxies. The physical characteristics of GMCs and their evolution are tightly connected to galaxy evolution. The macroscopic properties of the interstellar medium propagate into the properties of GMCs condensing out of it, with correlations between e.g. the galactic and GMC scale gas pressures, surface densities and volume densities. That way, the galactic environment sets the initial conditions for star formation within GMCs. After the onset of massive star formation, stellar feedback from e.g. photoionisation, stellar winds, and supernovae eventually contributes to dispersing the parent cloud, depositing energy, momentum and metals into the surrounding medium, thereby changing the properties of galaxies. This cycling of matter between gas and stars, governed by star formation and feedback, is therefore a major driver of galaxy evolution. Much of the recent debate has focused on the durations of the various evolutionary phases that constitute this cycle in galaxies, and what these can teach us about the physical mechanisms driving the cycle. We review results from observational, theoretical, and numerical work to build a dynamical picture of the evolutionary lifecycle of GMC evolution, star formation, and feedback in galaxies.
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| 10. |
- Freeman, Pamela, et al.
(författare)
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The varying mass distribution of molecular clouds across M83
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 468:2, s. 1769-1781
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Tidskriftsartikel (refereegranskat)abstract
- The work of Adamo et al. showed that the mass distributions of young massive stellar clusters were truncated above a maximum-mass scale in the nearby galaxy M83 and that this truncation mass varies with the galactocentric radius. Here, we present a cloud-based analysis of Atacama Large Millimeter/submillimeter Array CO(1 -> 0) observations of M83 to search for such a truncation mass in the molecular cloud population. We identify a population of 873 molecular clouds in M83 that is largely similar to those found in the Milky Way and Local Group galaxies, though clouds in the centre of the galaxy show high surface densities and enhanced turbulence, as is common for clouds in high-density nuclear environments. Like the young massive clusters, we find a maximum-mass scale for the molecular clouds which decreases radially in the galaxy. We find that the most young massive cluster tracks the most massive molecular cloud with the cluster mass being 10(-2) times that of the most massive molecular cloud. Outside the nuclear region of M83 (R-g > 0.5 kpc), there is no evidence for changing internal conditions in the population of molecular clouds, with the average internal pressures, densities and free-fall times remaining constant for the cloud population over the galaxy. This result is consistent with the bound cluster formation efficiency depending only on the large-scale properties of the interstellar medium rather than the internal conditions of individual clouds.
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