PHANGS–JWST First Results: Rapid Evolution of Star Formation in the Central Molecular Gas Ring of NGC 1365

Sandström

Rosolowsky

et al. 2023

ApJL

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We compare mid-infrared (mid-IR), extinction-corrected Hα, and CO (2–1) emission at 70–160 pc resolution in the first four PHANGS–JWST targets. We report correlation strengths, intensity ratios, and power-law fits relating emission in JWST’s F770W, F1000W, F1130W, and F2100W bands to CO and Hα. At these scales, CO and Hα each correlate strongly with mid-IR emission, and these correlations are each stronger than the one relating CO to Hα emission. This reflects that mid-IR emission simultaneously acts as a dust column density tracer, leading to a good match with the molecular-gas-tracing CO, and as a heating tracer, leading to a good match with the Hα. By combining mid-IR, CO, and Hα at scales where the overall correlation between cold gas and star formation begins to break down, we are able to separate these two effects. We model the mid-IR above I ν = 0.5 MJy sr−1 at F770W, a cut designed to select regions where the molecular gas dominates the interstellar medium (ISM) mass. This bright emission can be described to first order by a model that combines a CO-tracing component and an Hα-tracing component. The best-fitting models imply that ∼50% of the mid-IR flux arises from molecular gas heated by the diffuse interstellar radiation field, with the remaining ∼50% associated with bright, dusty star-forming regions. We discuss differences between the F770W, F1000W, and F1130W bands and the continuum-dominated F2100W band and suggest next steps for using the mid-IR as an ISM tracer.

Section: Data Selectionmentioning

confidence: 99%

PHANGS–JWST First Results: Mid-infrared Emission Traces Both Gas Column Density and Heating at 100 pc Scales

Sandström

Rosolowsky

et al. 2023

ApJL

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“…This ends up covering a region of ∼15″ in diameter (∼1.3 kpc in these targets). Some other bright sources in the center of NGC 1365 are also saturated and not included in this analysis, though these are further explored in Schinnerer et al (2023) and Liu et al (2023).…”

Section: Compact Source Identification and Photometrymentioning

confidence: 99%

“…Based on our CIGALE fits, we see only a few high-mass clusters (>10 4 M e ) in NGC 1365 that are deeply embedded (below the black dashed line). These objects are explored more in Whitmore et al (2023), Schinnerer et al (2023), andLiu et al (2023). For low mid-IR luminosities, all of the young (<10 Myr) embedded sources have SED fits that also find lowmass measurements (M < 10 3 M e ), reaching levels where stochastic sampling of the IMF can become important (da Silva et al 2012) and a cluster may not form stars with significant ionizing flux.…”

Section: A Dearth Of Embedded Sourcesmentioning

confidence: 99%

PHANGS–JWST First Results: The 21 μm Compact Source Population

Hassani

Rosolowsky

et al. 2023

ApJL

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We use PHANGS–James Webb Space Telescope (JWST) data to identify and classify 1271 compact 21 μm sources in four nearby galaxies using MIRI F2100W data. We identify sources using a dendrogram-based algorithm, and we measure the background-subtracted flux densities for JWST bands from 2 to 21 μm. Using the spectral energy distribution (SED) in JWST and HST bands plus ALMA and MUSE/VLT observations, we classify the sources by eye. Then we use this classification to define regions in color–color space and so establish a quantitative framework for classifying sources. We identify 1085 sources as belonging to the ISM of the target galaxies with the remainder being dusty stars or background galaxies. These 21 μm sources are strongly spatially associated with H ii regions (>92% of sources), while 74% of the sources are coincident with a stellar association defined in the HST data. Using SED fitting, we find that the stellar masses of the 21 μm sources span a range of 102–104 M ⊙ with mass-weighted ages down to 2 Myr. There is a tight correlation between attenuation-corrected Hα and 21 μm luminosity for L ν,F2100W > 1019 W Hz−1. Young embedded source candidates selected at 21 μm are found below this threshold and have M ⋆ < 103 M ⊙.

“…Hoyer et al (2023) studied the nuclear star cluster in NGC 628 and the nature of the mid-infrared structure surrounding it. Schinnerer et al (2023) showed that massive, dusty clusters can provide a sensitive diagnostic of the very dusty star-forming environments in nuclear regions when comparing ALMA data and simulations. Some of the clusters detected in the PHANGS-JWST survey push current stellar and dust models used by CIGALE to their limits due to their very young ages, high dust content, and/or low mass.…”

Section: Constraining the Natal Cluster Mass Function And Clustermentioning

confidence: 99%

“…The PHANGS-JWST first results on stellar clusters illustrate the potential (and challenges) in using the data at their highest resolution (which at 2 μm surpasses the resolution of HST optical imaging) to develop catalogs of embedded star clusters, augment the PHANGS-HST star cluster and association catalogs 81 with photometry from 2 to 21 μm, and measure their physical properties through SED fitting (Whitmore et al 2023b;Hoyer et al 2023;Rodriguez et al 2023). Catalogs of compact sources in the MIRI bands can be produced to identify larger star-forming regions on scales comparable to the H II regions observed with MUSE and the giant molecular clouds resolved by ALMA (Hassani et al 2023;Schinnerer et al 2023). As PHANGS-JWST analysis matures, it will be possible to develop complete catalogs of dust-enshrouded and visible stellar populations across multiple physics scales (Larson et al 2022), which include physical properties such as mass, age, and dust reddening, via SED fitting, which is able 79 CANFAR PHANGS-JWST Treasury Survey Data publication: doi:10.11570/22.0082.…”

Section: Data Productsmentioning

confidence: 99%

The PHANGS–JWST Treasury Survey: Star Formation, Feedback, and Dust Physics at High Angular Resolution in Nearby GalaxieS

Lee

Sandström

et al. 2023

ApJL

Self Cite

The PHANGS collaboration has been building a reference data set for the multiscale, multiphase study of star formation and the interstellar medium (ISM) in nearby galaxies. With the successful launch and commissioning of JWST, we can now obtain high-resolution infrared imaging to probe the youngest stellar populations and dust emission on the scales of star clusters and molecular clouds (∼5–50 pc). In Cycle 1, PHANGS is conducting an eight-band imaging survey from 2 to 21 μm of 19 nearby spiral galaxies. Optical integral field spectroscopy, CO(2–1) mapping, and UV-optical imaging for all 19 galaxies have been obtained through large programs with ALMA, VLT-MUSE, and Hubble. PHANGS–JWST enables a full inventory of star formation, accurate measurement of the mass and age of star clusters, identification of the youngest embedded stellar populations, and characterization of the physical state of small dust grains. When combined with Hubble catalogs of ∼10,000 star clusters, MUSE spectroscopic mapping of ∼20,000 H ii regions, and ∼12,000 ALMA-identified molecular clouds, it becomes possible to measure the timescales and efficiencies of the earliest phases of star formation and feedback, build an empirical model of the dependence of small dust grain properties on local ISM conditions, and test our understanding of how dust-reprocessed starlight traces star formation activity, all across a diversity of galactic environments. Here we describe the PHANGS–JWST Treasury survey, present the remarkable imaging obtained in the first few months of science operations, and provide context for the initial results presented in the first series of PHANGS–JWST publications.