COSMOS-3D: Diverse Environments and Hot-dust Signatures among Dusty Star-forming Galaxies at $z$ = 4.9-7.2

Dusty star-forming galaxies (DSFGs) are expected to trace early massive-halo assembly, but the connection between dust-obscured star formation, morphology, hot dust, and environment remains unclear at $z$>4. We combine JWST/NIRCam F444W grism spectroscopy from COSMOS-3D with MIRI F1000W/F2100W imaging and a mixed ALMA-selected and ALMA-followed dusty-galaxy sample from CRISTAL, CHAMPS, REBELS, and A3COSMOS to study 18 DSFGs or DSFG candidates at z=4.9-7.2. We compare their environments with the parent spectroscopically confirmed emission-line sample and the COSMOS-Web photo-z galaxy sample using separate and combined overdensity estimators. The parent narrow-line H$\alpha$ sample has a median observed, dust-uncorrected ${\mathrm{S}\mathrm{F}\mathrm{R}}_{\mathrm{H}\alpha }=11.7M_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$. Within R=0.5 pMpc, DSFGs have a median ${\delta }_{\mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}+\mathrm{p}\mathrm{h}\mathrm{o}\mathrm{t}}=0.92_{-0.16}^{+0.06}$, compared with $0.80_{-0.04}^{+0.05}$ for HAEs, with a stronger contrast on smaller scales. The strongest compact overdensities are associated with merger/interacting morphology: merging DSFGs reach ${\delta }_{\mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}+\mathrm{p}\mathrm{h}\mathrm{o}\mathrm{t}}=4.70_{-1.51}^{+1.61}$ within R=0.5 pMpc. In contrast, MIRI-bright DSFGs do not show an enhanced number of nearby visible H$\alpha$-emitting companions, and their F2100W fluxes are difficult to explain with the 3.3 $\mu$m PAH feature alone, suggesting an additional hot-dust component. These results are consistent with a possible phase-dependent picture in which the compact line-emitter core, merger-driven dusty phase, and MIRI-bright hot-dust phase need not be spatially or temporally identical during early structure growth.