Showing papers by "Charles H. Townes published in 1989"

158µm [CII] Mapping of the Galactic Center Molecular Clouds

Abstract: We have made 55″ resolution maps of the 158 µm [CII] emission line in the region of the curved, thermal filaments and the +20/+50 kms-1 molecular clouds in Sgr A. The [CII] emission is spatially well correlated with the radio continuum in the filaments. The large intensity of the [CII] radiation excludes shocks as the origin of the ionization and we conclude that the curved filaments are most likely photo-ionized HII regions at the surface of dense molecular clouds. Our [CII] maps of the +20/+50 kms-1 clouds indicate that the +50 kms-1cloud is close to ( 30pc).

The Galactic center.

Abstract: Over the last two decades, the refinement of radio and infrared techniques, as well as work in space, have provided a remarkable amount of information about the center of our galaxy. Much of it fits into a more or less understandable and increasingly well-defined pattern. However, some of this information seems to represent phenomena we do not yet understand, and still other measurements appear to challenge us with inconsistencies. Much of the material to be presented at this conference represents new results which will add both to our information and our understanding. It is hoped this first discussion will properly introduce the overall subject, paying particular attention to those areas which are still puzzling or under debate. Because of the wealth of material, the complexity of the subject, and my own limitations, not all of the many important points and questions will be treated, nor treated equally. Fortunately, the many gaps which I must leave will be filled by others, since there are review talks on most of the various, more specific aspects of the field.

Infrared Long Baseline Interferometry

Abstract: During the last few years, two new instruments using long baseline interferometry have been constructed for high angular resolution astronomy in the mid-infrared spectral region (8–12 μm). One called SOIRDETE-Synthese d’Overture en InfraRouge a DEux TElescopes—was built by J. Gay and his collaborators at CERGA. SOIRDETE has a fixed E-W 15 m baseline and two 1 m diameter telescopes of conventional design. This instrument obtains interference fringes by adjusting an optical-precision delay line in discrete steps to compen-sate for the geometrical delay of the projected baseline. The interference fringe from the source is detected using HgCdTe photodiodes. Because the instrumental delay has discrete steps a time-domain interferogram is created. This interferogram, upon Fourier transformation to the frequency domain, yields information about the spectral characteristics of the source. First fringes have recently been obtained with this instrument (Gay, 1988).

[CII] line emission from spiral galaxies

Abstract: We have measured 158 μm [CII] line emission from a sample of thirteen gas rich galaxies. The new data are combined with the previous sample of six infrared bright galaxies of Crawford et al. 1985. The [CII] line is bright in all of the galaxies detected amounting to between .1 and 2% of the total nuclear far-infrared (FIR) luminosity, and is therefore one of the primary gas coolants in these regions. The [CII] emission arises from warm (T-300 K), dense (NH∼103→104cm−3) photodissociated gas at the interface regions between giant molecular clouds and ionized gas regions, and is a very sensitive indicator of starformation activity. The integrated [CII] to the 12CO line intensity ratio is constant for starburst galaxies and star formation regions in our own galaxy. This suggests that much of the observed 12CO line radiation from starburst galaxies arises in the warm, (Tex>50 K), molecular gas immediately interior to these photodissociation regions, and not from the cold disk molecular cloud component as is commonly assumed. For the non-starburst galaxies in our sample, the line intensity ratio varies significantly from galaxy to galaxy but is always significantly less than the starburst value, in support of this model. The integrated line intensity ratios may thus be used as a sensitive probe of the physical conditions of the molecular gas in galaxies.