Sgr B2 Herschel/SPIRE-FTS and IRAM 30m maps

The extended [CI] emission arises from a pervasive component of neutral gas with n_H_~10^3cm^-3^. The high ionization rates, produced by enhanced cosmic-ray (CR) fluxes, drive the gas heating to T_k_~40-60K. The mid-J CO emission arises from a similarly extended but more pressurized gas component (P_th_/k~10^7^K/cm^3^).

Specific regions of enhanced SiO emission and high CO-to-FIR intensity ratios (>10^-3^) show mid-J CO emission compatible with shock models. A major difference compared to more quiescent star-forming clouds in the disk of our Galaxy is the extended nature of the SiO and N_2_H^+^ emission in Sgr B2. This can be explained by the presence of cloud-scale shocks, induced by cloud-cloud collisions and stellar feedback, and the much higher CR ionization rate (>10^-15^s^-1^) leading to overabundant H_3_^+^ and N_2_H^+^.

Hence, Sgr B2 hosts a more extreme environment than star-forming regions in the disk of the Galaxy. As a usual template for extra- galactic comparisons, Sgr B2 shows more similarities to ultra luminous infrared galaxies such as Arp 220, including a "deficit" in the [CI]/FIR and [NII]/FIR intensity ratios, than to pure starburst galaxies such as M82. However, it is the extended cloud environment, rather than the cores, that serves as a useful template when telescopes do not resolve such extended regions in galaxies.