NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-25 T06:39:12 PDT
Help | Comment | NED Home

For refcode 1991ApJ...382..475A:
Retrieve 8 NED objects in this reference.
Please click here for ADS abstract

NED Abstract

Copyright by American Astronomical Society. Reproduced by permission
1991ApJ...382..475A THE RELATIONSHIP BETWEEN THE CARBON MONOXIDE INTENSITY AND THE RADIO CONTINUUM EMISSION IN SPIRAL GALAXIES DAVID S. ADLER, RONALD J. ALLEN, AND K. Y. Lo Received 1991 March 18; accepted 1991 June 4 ABSTRACT The relationship between the velocity-integrated CO emission and the nonthermal radio continuum brightness in the disks of normal spiral galaxies is examined on a variety of length scales. On a global scale, the total CO intensity correlates strongly with the total radio continuum flux density for a sample of 31 galaxies. On scales of ~> 2 kpc in the disk of individual galaxies, we find that the ratio I_CO_/^T_20_ remains fairly constant over the entire disk as well as from galaxy to galaxy. For the eight spirals in our sample, the disk-averaged values of I_CO_/I_20_ range from 0.6-2.4, with the average over all eight galaxies being <I_CO_/T_20_> = 1.3 +/- 0.6. However, studies of giant molecular cloud complexes in the arms of nearby galaxies indicate that the relationship ceases to be constant on smaller (<~1-2 kpc) scales, with the CO dominating the ratio. We conclude that what these various length scales actually trace are differences in the primary heating mechanism of the gas in the beam. The observed relationship between CO and nonthermal radio continuum emission can be explained by assuming that molecular gas in galactic disks is heated primarily by cosmic rays. We use the observed relationship to show that the brightness of synchrotron emission is proportional to ^0.4-0.9^_cr_ in galactic disks. Finally, we conclude that while in a general sense star formation is undoubtedly the primary source of energy that causes the relationship to exist, the details of the specific mechanism(s) at work are complicated by the very different scale heights and (small-scale) spatial distributions of the CO and nonthermal radio continuum emission. Subject headings: galaxies: interstellar matter - interstellar: molecules - radio sources: galaxies
Retrieve 8 NED objects in this reference.
Please click here for ADS abstract

Back to NED Home