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

Abstract

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.

PHANGS–JWST First Results: The Influence of Stellar Clusters on Polycyclic Aromatic Hydrocarbons in Nearby Galaxies

“…The NIRCam mosaics use the F200M, F300M, F335M, and F360M filters and the MIRI mosaics use the F770W, F1000W, F1130W, and F2100W filters. The technical description and postprocessing of the NIRCam and MIRI imaging for the PHANGS-JWST program is described in Lee et al (2023).…”

“…In lieu of using the catalog of asymmetric and multipeaked Class 3 stellar associations, which is comparatively incomplete since the PHANGS-HST pipeline was optimized for detecting single-peaked compact clusters, we utilize the PHANGS-HST catalog of stellar associations. These stellar associations, which are less likely to be gravitationally bound than Class 1 and 2 compact clusters (Whitmore et al 2021), are derived from a watershed analysis that is based on V-band point-source detections and a 32 pc FWHM Gaussian smoothing, as presented in Lee et al (2023) and Larson et al (2022). The stellar masses and ages for the clusters and associations are based on spectral energy distribution fits to the five-band ultraviolet/optical PHANGS-HST data sets and span ∼10 2.8−6.0 M e and 1 Myr to 13 Gyr (see also Turner et al 2021).…”

“…(Hollenbach & Tielens 1997;Draine et al 2007;Tielens 2008;Wolfire et al 2022). We compare the theoretical predictions for PAH emission features with photometric observations from JWST for the Physics at High Angular resolution in Nearby Galaxies (PHANGS) program on nearby galaxies (Leroy et al 2021;Lee et al 2022Lee et al , 2023Emsellem et al 2022), using three filters with bandpasses that capture PAH emission features centered at 3.3, 7.7, and 11.2 μm. We specifically compare our observations with the predictions laid out in Draine et al (2021; see also Rigopoulou et al 2021) for a range of PAH ionization levels and size distributions in addition to a variety of interstellar radiation field intensities and ages of the stellar populations that drive the dust heating.…”

PHANGS–JWST First Results: The Dust Filament Network of NGC 628 and Its Relation to Star Formation Activity

“…NGC 628 is nearby (d = 9.84 ± 0.03 Mpc; Anand et al 2021aAnand et al , 2021b, star-forming (SFR = 1.8 ± 0.45 M e yr −1 ), massive (M * = 2.2 ± 0.56 × 10 10 M e ), and viewed at a low inclination (i ∼ 9°± 12°, Lang et al 2020). NGC 628 is part of a broader sample of 19 "main-sequence" star-forming galaxies for which systematic, uniform surveys with HST (Lee et al 2022), ALMA (Leroy et al 2021), VLT-MUSE (Emsellem et al 2022), and now JWST (Lee et al2023, this Issue) have been carried out by the PHANGS (Physics at High Angular resolution in Nearby GalaxieS) collaboration. 37…”

PHANGS–JWST First Results: Multiwavelength View of Feedback-driven Bubbles (the Phantom Voids) across NGC 628

“…In a companion Letter in this Issue, Watkins et al (2023) use a combination of JWST and Hubble Space Telescope (HST) observations to study the bubble population across the nearby (9.84 ± 0.63 Mpc; Anand et al 2021aAnand et al , 2021b, star-forming (1.8 ± 0.5 M e yr −1 ), face-on (i ∼9°; Lang et al 2020, and also see Blanc et al 2013), massive (M * = 10 10.3 M e , M H I = 10 9.7 M e , M H2 = 10 9.4 M e ; Walter et al 2008;Querejeta et al 2015;Leroy et al 2019Leroy et al , 2021a, spiral galaxy Messier 74 (also known as NGC 628 or the Phantom Galaxy). These authors manually identify bubbles using a combination of 7.7 μm JWST-MIRI observations (Lee et al 2023), B-band (438 nm) Physics at High Angular resolution in Nearby GalaxieS (PHANGS)-HST observations , and Very Large Telescope (VLT)-Multi Unit Spectroscopic Explorer (MUSE) Hα observations (Emsellem et al 2022). For each bubble, Watkins et al (2023) fit circular or elliptical apertures to the bubble boundaries (i.e., the shells) seen within this multiwavelength data set, and in doing so identify ∼1700 bubbles with radii ranging between 6 and 500 pc (e.g., left panel of Figure 1).…”