3600-24700{AA} deep X-shooter spectrum of HH 1

We observe atomic fine structure lines, HI and HeI recombination lines and H_2_ ro-vibrational lines (more than 500 detections in total). Line emission was analyzed by means of Non-local Thermal Equilibiurm codes to derive the electron temperature and density, and for the first time we are able to accurately probe different physical regimes behind a dissociative shock.

We find a temperature stratification in the range 4000K/80000K, and a significant correlation between temperature and ionization energy. Two density regimes are identified for the ionized gas, a more tenuous, spatially broad component (density ~10^3^/cm^3^), and a more compact component (density>=10^5^/cm^3^) likely associated with the hottest gas. A further neutral component is also evidenced, having a temperature <~10000K and a density >10^4^/cm^3^.