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ABSTRACT In this paper, we study the filamentary substructure of 3.3 $$\mu$$m polycyclic aromatic hydrocarbon (PAH) emission from JWST/NIRCam observations in the base of the M 82 star-burst driven wind. We identify plume-like substructure within the PAH emission with widths of $$\sim$$50 pc. Several of those plumes extend to the edge of the field-of-view, and thus are at least 200–300 pc in length. In this region of the outflow, the vast majority ($$\sim$$70 per cent) of PAH emission is associated with the plumes. We show that those structures contain smaller scale ‘clouds’ with widths that are $$\sim$$5–15 pc, and they are morphologically similar to the results of ‘cloud-crushing’ simulations. We estimate the cloud-crushing time-scales of $$\sim$$0.5–3 Myr, depending on assumptions. We show this time-scale is consistent with a picture in which these observed PAH clouds survived break-out from the disc rather than being destroyed by the hot wind. The PAH emission in both the mid-plane and the outflow is shown to tightly correlate with that of Pa $$\alpha$$ emission (from Hubble Space Telescope data), at the scale of both plumes and clouds, though the ratio of PAH-to-Pa $$\alpha$$ increases at further distances from the mid-plane. Finally, we show that the outflow PAH emission reaches a local minimum in regions of the M 82 wind that are bright in X-ray emission. Our results are consistent cold gas in galactic outflows being launched via hierarchically structured plumes, and those small scale clouds are more likely to survive the wind environment when collected into the larger plume structure. 

Abstract We present a near-infrared (NIR) candidate star cluster catalog for the central kiloparsec of M82 based on new JWST NIRCam images. We identify star cluster candidates using the F250M filter, finding 1357 star cluster candidates with stellar masses >10⁴M_⊙. Compared to previous optical catalogs, nearly all (87%) of the candidates we identify are new. The star cluster candidates have a median intrinsic cluster radius of ≈1 pc and stellar masses up to 10⁶M_⊙. By comparing the color–color diagram to dust-freeyggdrasilstellar population models, we estimate that the star cluster candidates haveA_V∼ 3−24 mag, corresponding toA_2.5μm∼ 0.3−2.1 mag. There is still appreciable dust extinction toward these clusters into the NIR. We measure the stellar masses of the star cluster candidates, assuming ages of 0 and 8 Myr. The slope of the resulting cluster mass function isβ= 1.9 ± 0.2, in excellent agreement with studies of star clusters in other galaxies. 

Abstract We use 0.1″ observations from the Atacama Large Millimeter Array (ALMA), Hubble Space Telescope (HST), and JWST to study young massive clusters (YMCs) in their embedded “infant” phase across the central starburst ring in NGC 3351. Our new ALMA data reveal 18 bright and compact (sub-)millimeter continuum sources, of which 8 have counterparts in JWST images and only 6 have counterparts in HST images. Based on the ALMA continuum and molecular line data, as well as ancillary measurements for the HST and JWST counterparts, we identify 14 sources as infant star clusters with high stellar and/or gas masses (∼10⁵M_⊙), small radii (≲ 5 pc), large escape velocities (6–10 km s⁻¹), and short freefall times (0.5–1 Myr). Their multiwavelength properties motivate us to divide them into four categories, likely corresponding to four evolutionary stages from starless clumps to exposed Hiiregion–cluster complexes. Leveraging age estimates for HST-identified clusters in the same region, we infer an evolutionary timeline, ranging from ∼1–2 Myr before cluster formation as starless clumps, to ∼4–6 Myr after as exposed Hiiregion–cluster complexes. Finally, we show that the YMCs make up a substantial fraction of recent star formation across the ring, exhibit a nonuniform azimuthal distribution without a very coherent evolutionary trend along the ring, and are capable of driving large-scale gas outflows.