Molecular emission from interstellar shocks

In this dissertation, the author has studied the shock-excited molecular regions associated with several supernova remnants (SNRs) and protostellar outflows (Herbig-Haro objects), using spectroscopic observations obtained by several space observatories including Spitzer, Herschel, and the Infrared Space Observatory ( ISO), together with photometric data extracted from the Spitzer's archive.;The H2 S(0) to S(7) spectral line maps obtained for the six sources are used to map the physical parameters within these regions, which yield estimated densities n(H2) in the range 2 -- 4 x 103 cm--3. The excitation of higher-lying transitions including H2 S(9) to S(12) and high- J CO pure rotational lines, however, require environments several times denser. The inconsistency among the best-fit densities estimated from different species can be explained by density fluctuations within the observed regions. The clouds may be composed of both moderate density gas with n(H2) ∼ 103 cm--3 and dense cores with n(H2) ∼ 105 -- 106 cm--3.;The best-fit parameters for SNRs and Herbig-Haro objects do not differ significantly between the two classes of sources, except that for the SNRs the ortho-to-para ratio (OPR) of hot gas (T > 1000 K) is close to the LTE value 3, while for HH 7 and HH 54 even the hottest gas exhibits an OPR smaller than 3; the author interprets this difference as resulting from environmental differences between these classes of source, molecular material near SNRs being subject to stronger photodissociation that results in faster para-to-ortho conversion.;The author has also analysed the Spitzer observations of hydrogen deuteride (HD) detected from the same shock-heated regions associated with the supernova remnant IC 443C and with the Herbig-Haro objects HH 7 and HH 54. The derived HD abundance relative to H2 is found to be quite sensitive to the assumed excitation conditions in the emitting gas. Assuming that HD accounts for all gas-phase deuterium in the emitting material, and using all the available spectroscopic data to constrain the excitation conditions, the gas-phase deuterium abundances are estimated as 0.95+0.54-0.27 x 10--5 and 0.87+0.31-0.27 x 10--5 (statistical errors only) for IC 443C and HH 54 respectively, which corresponds to destruction factors of deuterium due to astration < 3 if a portion of D is depleted on the dust, and is consistent with the current Galactic star formation models.;With the most recent spectroscopic maps of CO and atomic lines obtained by Herschel, the author finds that the CO high-lying transitions in W28 emerge from the same shocked component that emits H2 rotational lines. The CO lower-J lines (from J = 3 -- 2 to J = 7 -- 6) detected by ground-based facilities appear to have non-negligible contributions from cooler components, which help to constrain the lower temperature cut-off for the shocked gas > 200 K. If the H2 and CO emissions arise from the same gas density component in W28, the best-fit CO abundance relative to H2 is obtained as 1.05 x 10--4, which corresponds to a C depletion factor of ∼ 0.23 (77% of carbon trapped in grains) or larger if there exists a small amount of atomic C and C+ generated by UV photodissociation. For 3C 391, in contrast, the morphology of CO high-J line emissions is correlated equally well with those of the H2 rotational line maps and of the [OI] and [CII] fine structure lines. It implies that the CO emissions in 3C 391 may also have contributions from the [CII] (158 mum) emitting regions where the gas may be partially dissociated. The excitation conditions for CO and H2 emissions in W28 both indicate that the emitting region is cooler (with less hot gas) than that in 3C 391 and NGC 2071.