Engineering topics

Garwood, Robert W.

Publications and source records attributed to Garwood, Robert W..

4 records

NASA NTRS1989

The mass spectrum of interstellar clouds

The abundances of diffuse clouds and molecular clouds in the inner Galaxy and at the solar circle are compared. Using results of recent low-latitude 21 cm absorption studies, the number of diffuse clouds per kiloparsec along the line of sight is derived as a function of the cloud column density, under two assumptions relating cloud densities and temperatures. The density of clouds is derived as a function of cloud mass. The results are consistent with a single, continuous mass spectrum for interstellar clouds from less than 1 solar mass to 1,000,000 solar masses, with perhaps a change of slope at masses where the atomic and molecular mass fractions are roughly equal.

Dickey, John M.↗

NASA NTRS1989

Cold atomic gas in the inner Galaxy

A new set of 21 cm H I absorption spectra were obtained toward 21 compact continuum sources in the Galactic plane is presented. The 21 cm line velocity-averaged absorption coefficient as a function of Galactocentric distance is calculated. The result for distances within 2 kpc of the sun agrees with the local value found from absorption toward pulsars of 5-7 km/s/kpc. Overall, the absorption coefficient decreases to about half of its local value inside a Galactocentric radius of about 4 kpc. This decrease is shown to be primarily due to an increase in the mean line-of-sight distance between absorbing atomic clouds. Thus, the cool phase of the atomic gas is less abundant in the inner Galaxy than at the solar circle. The absorption spectra are similar in appearance to existing (C-12)O spectra. The spectral regions which show H I absorption also show CO emission.

Garwood, Robert W.↗

NASA NTRS1987

Arecibo observations of IRAS galaxies at 21 and 18 centimeters

Arecibo observations at 21 cm and 18 cm of a sample of galaxies selected for their intense far-infrared (FIR) emission are reported. The objective was to search for H I absorption and OH maser emission. No new cases were found. The significance of this null result is discussed both in terms of spatial distribution of the interstellar gas and dust and in terms of the continuum luminosity of the nucleus. Nevertheless, the H I profiles are extraordinary in that most are convex (single peak). This may suggest disruption of the disk rotation system in some cases. Little correlation is found between the hydrogen mass of these galaxies and their FIR luminosity. Comparison of these quantities suggests that the dust in these galaxies is under conditions very different from the solar neighborhood. Much more of the FIR emission apparently comes from H II regions than in normal galaxies. There is an excellent correlation between IR flux and radio continuum flux. The ratio of these two is the same as for normal spirals, which is surprising considering the many variables which could change this ratio.

Garwood, Robert W.↗

NASA NTRS1987

The correlation between far-IR and radio continuum emission from spiral galaxies

A sample of 30 galaxies selected for their intense IRAS flux at 60 and 100 micron using the Arecibo telescope at 21 cm to measure the continuum and HI line luminosities were observed. The centimeter wave continuum correlates very well with the far-infrared flux, with a correlation coefficient as high as that found for other samples, and the same ratio between FIR and radio luminosities. Weaker correlations are seen between the FIR and optical luminosity and between the FIR and radio continuum. There is very little correlation between the FIR and the HI mass deduced from the integral of the 21 cm line. The strength of the radio continuum correlation suggests that there is little contribution to either the radio and FIR from physical processes not affecting both. If they each reflect time integrals of the star formation rate then the time constants must be similar, or the star formation rate must change slowly in these galaxies.

Dickey, John M.↗