Computer Science
Scientific paper
Mar 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999esasp.427..627l&link_type=abstract
The Universe as Seen by ISO. Eds. P. Cox & M. F. Kessler. ESA-SP 427., p. 627
Computer Science
Galactic Center, Star Formation
Scientific paper
We have used the Long Wavelength Spectrometer (LWS) aboard the Infrared Space Observatory in grating mode to map the far-infrared continuum emission (45-175 mic) toward several massive Giant Molecular Cloud (GMC) cores located near the Galactic center. These sources are observed in emission at far-infrared and submillimeter wavelengths (>100 mic). However, at mid-infrared wavelengths (<70 mic) they are seen in absorption against the general Galactic centre background. Gray-body fits to the observed far-infrared and submillimeter spectral energy distributions give low temperatures (about 13-20 K) for the bulk of the dust in all the sources. This indicates external heating of the dust by the diffuse ISRF and suggests that the cores do not harbor high-mass star-formation sites, in spite of their large molecular mass. In addition, the grain emissivity in these sources is a very steep function of frequency (β > 2.4). The high grain emissivity exponent is consistent with the presence of dust grains covered with thick ice mantles. Molecular line observations carried out with the Caltech Submillimeter Observatory (CSO) show a large velocity gradient across the most massive core, GCM0.25+0.11, indicative of streaming motions of the gas or of the presence of multiple, spatially overlapping velocity components. The observed gas kinematics may indicate that the GCM0.25+0.11 core is in an early stage of a cloud-cloud collision that may result in a future star formation episode. Recent MSX observations indicate that cold GMC cores similar to those studied with ISO are ubiquitous in the Galactic center and throughout the Galaxy. The observed intensities of the OI and CII fine structure lines imply a radiation field intensity of about 1000 times the standard ISRF intensity and a hydrogen density of about 1000 pccm\ for the diffuse gas component in the Galactic center.
Dowell Charles (Darren)
Li Yadong
Lis Darek C.
Menten Karl. M.
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