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

Abstract

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 ⊙.

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

“…Given that the attenuation filament mask remains constant in comparison to F770W and F2100W, this could suggest that either we are sensitivity limited for F2100W or the filamentary emission detected in 21 μm imaging is less consistently recovered into coherent structures. The latter interpretation is supported by mask inspection in the figures of the Appendix and by the fact that the morphology of the F2100W image is more dominated by compact sources (e.g., IR-bright starforming regions; see Hassani et al 2023, this Issue) than F770W, F1000W, and F1130W. This serves as a reminder that we are tracing warm (140 K) dust at 21 μm, whereas the dust attenuation provides a more complete inventory with respect to dust over a wide range of (cooler) temperatures.…”

PHANGS–JWST First Results: Mapping the 3.3 μm Polycyclic Aromatic Hydrocarbon Vibrational Band in Nearby Galaxies with NIRCam Medium Bands

“…The data are radially binned as described in Section 4.1, with the addition of masking out radial ranges affected by saturation for the F1130W filter. We masked the inner 7 5 radius region, which extends to the radius where the PSF for the bright central source drops to 10 −3 of its peak value (see Hassani et al 2023 for further details). This corresponds to a cut at <0.04r 25 (<1.4 kpc) for NGC 1365 and <0.08r 25 (<0.7 kpc) for NGC 7496.…”

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

“…The photometry of sources with poor ramp fits is likely underestimated (Section 4.1). Hassani et al (2023) produced bespoke masks to flag diffraction spikes due to the AGN in NGC 1365 and NGC 7496, but as better PSF estimates become available, subtracting such features from the image should become an option. Liu et al (2023) presented the first efforts at recovering the fluxes of sources with saturated pixels and poor ramp fits by using PSF matching in the outskirts of the source.…”

“…While the highest surface brightness features are apparent in the Spitzer imaging, the JWST imaging shows the pervasiveness of the network deep into the interarm regions and morphological details that suggest that the multiscale impact of star formation feedback on the ISM is ubiquitous. With the PHANGS-JWST imaging, we will now be able to develop catalogs of these structures and characterize their ensemble properties (e.g., Hassani et al 2023;Rodriguez et al 2023;Thilker et al 2023;Watkins et al 2023) even with the lowest-resolution image at 21 μm.…”