Astronomy and Astrophysics – Astronomy
Scientific paper
May 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...463..191l&link_type=abstract
Astrophysical Journal v.463, p.191
Astronomy and Astrophysics
Astronomy
17
Infrared: Ism: Lines And Bands, Ism: Clouds, Ism: Individual Name: Orion, Ism: Individual Name: Rho Ophiuchi, Ism: Individual Ngc Number: Ngc 2024, Ism: Molecules, Molecular Processes
Scientific paper
We present observations of the 1.601 μm v = 6-4 Q(l), 2.121 μm V = 1-0 S(1), and 2.247 μm v = 2-1 S(l) lines of H2 from four galactic clouds: the Orion A and Orion B giant molecular clouds, the ρ Ophiuchi cloud, and the G236+39 interstellar cirrus cloud. We employed the University of Texas Near-Infrared Fabry-Perot Spectrometer to conduct the first survey of diffuse (≲10-5 ergs s-1 cm-2 sr-1)H2 emission from galactic clouds on multiparsec scales. The relative strengths of the H2 lines suggest that, on large scales, excitation of H2 via ultraviolet fluorescence is a common phenomenon. We compare the distribution and strength of the H2 emission to cospatial observations of the 158 am line of C+, the low rotational level lines of 13CO and 12CO, and the 60 and 100 μm continuum radiation. This comparative study shows that (1) ultraviolet-excited H2 and C+ correlate spatially, consistent with theoretical models of photon-dominated environments; (2) H2 emission arises from significant portions of CO clouds but can also extend into regions where much of the CO is dissociated; and (3) there is a significant correlation between the H2 line intensity and the far-infrared continuum, which we attribute to ultraviolet illumination of H2 and dust on cloud surfaces. We discuss the implications of this study for using CO and the far-infrared continuum to trace molecular gas, as well as for the future role of H2 as a complement to other large-scale probes of the dense interstellar medium.
Jaffe Daniel T.
Luhman Michael L.
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