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Arxiv: Hidden Gems on a Ring: Infant Massive Clusters and Their Formation Timeline Unveiled by ALMA, HST, and JWST in NGC 3351 Published: 1/25/2024 9:00:00 PM Updated: 4/10/2024 10:42:07 PM

Paper abstract: We study young massive clusters (YMCs) in their embedded "infant" phase with~0.\!^{\prime\prime}1 ALMA, HST, and JWST observations targeting thecentral starburst ring in NGC 3351, a nearby Milky Way analog galaxy. Our newALMA data reveal 18 bright and compact (sub-)millimeter continuum sources, ofwhich 8 have counterparts in JWST images and only 6 have counterparts in HSTimages. Based on the ALMA continuum and molecular line data, as well asancillary measurements for the HST and JWST counterparts, we identify 14sources as infant star clusters with high stellar and/or gas masses({~}10^5\;\mathrm{M_\odot}), small radii ({<~}\,5\;\mathrm{pc}),large escape velocities (6{-}10\;\mathrm{km/s}), and short free-fall times(0.5{-}1\;\mathrm{Myr}). Their multiwavelength properties motivate us todivide them into four categories, likely corresponding to four evolutionarystages from starless clumps to exposed HII region-cluster complexes. Leveragingage estimates for HST-identified clusters in the same region, we infer anevolutionary timeline going from ~1-2 Myr before cluster formation asstarless clumps, to ~4-6 Myr after as exposed HII region-clustercomplexes. Finally, we show that the YMCs make up a substantial fraction ofrecent star formation across the ring, exhibit an non-uniform azimuthaldistribution without a very coherent evolutionary trend along the ring, and arecapable of driving large-scale gas outflows.