Not-so-little Red Dots: Two massive and dusty starbursts at z ∼ 5 − 7 pushing the limits of star formation discovered by JWST in the COSMOS-Web survey

= 5−7 in the first 0.28 deg2 of the COSMOS-Web survey. One object is spectroscopically confirmed 35 at zspec = 5.051, while the other has a robust zphot = 6.7 ± 0.3. Thanks to their extremely red 36 colors (F277W −F444W ∼ 1.7 mag), these galaxies satisfy the nominal color-selection for the widely37 studied “little red dot” (LRD) population with the exception of their spatially-resolved morphologies. 38 The morphology of our targets allows us to conclude that their red continuum is dominated by highly 39 obscured stellar emission and not by reddened nuclear activity. Using a variety of SED-fitting tools, we estimate the stellar masses to be log(M⋆) = 11.5+0.1 −0.1 M⊙ and log(M⋆) = 11.2+0.2 40 −0.2 M⊙, respectively, 41 with a red continuum emission dominated by a recent burst of star formation. We then compare their 42 number density to the halo mass function to infer stellar baryon fractions of ϵ⋆ ∼ 0.3 and ϵ⋆ ∼ 0.5. 43 Both are significantly higher than what is commonly observed in lower-z galaxies or more dust-obscured 44 galaxies at similar redshifts. With very bright ultra-high-z Lyman-Break Galaxies and some non-AGN Corresponding author: Fabrizio Gentile 45 dominated LRDs, such “extended” LRDs represent another population that may require very efficient 46 star formation at early times.