Deep NIR spectrum of the Orion Bar PDR

IGRINS has high spectral resolution (R~45000) and instantaneous broad wavelength coverage (1.45-2.45{mu}m), enabling us to detect 87 emission lines from rovibrationally excited molecular hydrogen (H_2_) that arise from transitions out of 69 upper rovibration levels of the electronic ground state.

These levels cover a large range of rotational and vibrational quantum numbers and excitation energies, making them excellent probes of the excitation mechanisms of H_2_ and physical conditions within the PDR. The Orion Bar PDR is thought to consist of cooler high density clumps or filaments (T=50-250K, n_H_=10^5^-10^7^cm^-3^) embedded in a warmer lower density medium (T=250-1000K, n_H_=10^4^-10^5^cm^-3^). We fit a grid of constant temperature and density Cloudy models, which recreate the observed H_2_ level populations well, to constrain the temperature to a range of 600-650 K and the density to n_H_=2.5x10^3^-10^4^cm^-3^.