Abstract:
A comparative study of Weingartner and Draine (2001) (hereinafter referred as WD) and Bakes and Tielens (1994) (hereinafter referred as BT) models of photoelectric heating effiencies of gas shows that for neutral medium WD model of photoelectric heating dominates over the BT model but in a medium where grains are positively charged BT is higher by many factors as compared to WD. WD model predicts a maximum photoelectric heating efficiency of the gas epsilon ~ 0.029 and a maximum line intensity ratio of [CII] emission to that of total FIR emission ~2.5 x 10-2 . Ingalls et al. (2002) and Juvela et al. (2003) observed almost the same values for epsilon and intensity ratios for high latitude clouds. Intensity of interstellar radiation field G0 is estimated from the observed line intensities of CII and CO emissions for number of galactic and extragalactic photodissociation regions. It is found that G0 is highly correlated with the observed intensity of FIR with an intercept equal to 1.23 x 10-4 (ergs cm-2s-1sr-1), which is almost same as the ISRF of Habing (1968). This shows that ISRF photons absorbed by the dust grains are reradiated fully in the near -IR and far -IR
