  The carbonaceous macromolecules imprinting in astronomical spectra the
numerous absorptions called Diffuse Interstellar Bands (DIBs) are omnipresent
in the Galaxy and beyond and represent a considerable reservoir of organic
matter. However, their chemical formulae, formation and destruction sites
remain open questions. Their spatial distribution and the local relation to
other interstellar species is paramount to unravel their role in the lifecycle
of organic matter. Volume density maps bring local instead of line-of-sight
distributed information, and allow for new diagnostics. We present the first
large-scale volume (3D) density map of a DIB carrier and compare it with an
equivalent map of interstellar dust. The DIB carrier map is obtained through
hierarchical inversion of about 202,000 measurements of the 8621 nm DIB
obtained with the Gaia-RVS instrument. It covers about 4000 pc around the Sun
in the Galactic plane. A dedicated interstellar dust map is built based on
extinction towards the same target stars. At the 50 pc resolution of the maps,
the 3D DIB distribution is found remarkably similar in shape to the 3D
distribution of dust. On the other hand, the DIB-to-dust local density ratio
increases in low-dust areas. It is also increasing away from the disk, however,
the minimum ratio is found to be shifted above the Plane to Z = +50pc. Finally,
the average ratio is also surprisingly found to increase away from the Galactic
Center. We suggest that the three latter trends may be indications of a
dominant contribution of material from the carbon-rich category of dying giant
stars to the formation of the carriers. Our suggestion is based on recent
catalogues of AGB stars and estimates of their mass fluxes of C-rich and O-rich
ejecta.
