To high redshift and low mass: exploring the emergence of quenched galaxies and their environments at $3<z<6$ in the ultra-deep JADES MIRI F770W parallel

We present the robust selection of quiescent (QG) and post-starburst (PSB) galaxies using ultra-deep NIRCam and MIRI imaging from the JWST Advanced Deep Extragalactic Survey (JADES). Key to this is MIRI 7.7$μ$m imaging which breaks the degeneracy between old stellar populations and dust attenuation at $3<z<6$ by providing rest-frame $J$-band. Using this, we identify 23 passively evolving galaxies in UVJ color space in a mass-limited (log $M_{\star}/M_{\odot}\geq8.5$) sample over 8.8 arcmin$^2$. Evaluation of this selection with and without 7.7$\,μ$m shows that dense wavelength coverage with NIRCam ($8-11$ bands including $1-4$ medium-bands) can compensate for lacking the $J-$band anchor, meaning that robust selection of high-redshift QGs is possible with NIRCam alone. Our sample is characterized by rapid quenching timescales ($\sim100-600$ Myr) with formation redshifts $z_{\rm f}\lesssim8.5$ and includes a potential record-holding massive QG at $z_{\rm phot}=5.33_{-0.17}^{+0.16}$ and two QGs with evidence for significant residual dust content ($A_{\rm V}\sim1-2$). In addition, we present a large sample of 12 log $M_{\star}/M_{\odot}=8.5-9.5$ PSBs, demonstrating that UVJ selection can be extended to low mass. Analysis of the environment of our sample reveals that the group known as the Cosmic Rose contains a massive QG and a dust-obscured star-forming galaxy (a so-called Jekyll and Hyde pair) plus three additional QGs within $\sim20$ kpc. Moreover, the Cosmic Rose is part of a larger overdensity at $z\sim3.7$ which contains 7/12 of our low-mass PSBs. Another 4 low-mass PSBs are members of an overdensity at $z\sim3.4$; this result strongly indicates low-mass PSBs are preferentially associated with overdense environments at $z>3$.