\justify We have analyzed the temperature , velocity and density of H _ { 2 } gas in NGC 7023 with a high-resolution near-infrared spectrum of the northwestern filament of the reflection nebula .
By observing NGC 7023 in the H and K bands at R \simeq 45,000 with the Immersion GRating INfrared Spectrograph ( IGRINS ) , we detected 68 H _ { 2 } emission lines within the 1 \arcsec \times 15 \arcsec slit .
The diagnostic ratios of 2-1 S ( 1 ) /1-0 S ( 1 ) is 0.41 - 0.56 .
In addition , the estimated ortho-to-para ratios ( OPR ) is 1.63 - 1.82 , indicating that the H _ { 2 } emission transitions in the observed region arises mostly from gas excited by UV fluorescence .
Gradients in the temperature , velocity , and OPR within the observed area imply motion of the photodissociation region ( PDR ) relative to the molecular cloud .
In addition , we derive the column density of H _ { 2 } from the observed emission lines and compare these results with PDR models in the literature covering a range of densities and incident UV field intensities .
The notable difference between PDR model predictions and the observed data , in high rotational J levels of \nu = 1 , is that the predicted formation temperature for newly-formed H _ { 2 } should be lower than that of the model predictions .
To investigate the density distribution , we combine pixels in 1 \arcsec \times 1 \arcsec areas and derive the density distribution at the 0.002 pc scale .
The derived gradient of density suggests that NGC 7023 has a clumpy structure , including a high clump density of \sim 10 ^ { 5 } cm ^ { -3 } with a size smaller than \sim 5 \times 10 ^ { -3 } pc embedded in lower density regions of 10 ^ { 3 } - 10 ^ { 4 } cm ^ { -3 } .