Physical properties of jets in low-luminosity radio sources

We present the results of fitting Bicknell's semiempirical turbulent jet model to a sample of 23 jets taken from the B2 extragalactic radio sources studied in detail using the VLA (Fanti et al.). We find that the model fits are generally very reasonable (especially for the smoother jets) and that the single most important parameter in the fits is the ratio of galaxy virial temperature to interstellar medium temperature. We find a distribution for this parameter which is consistent with the distribution found by Thomas et al. for an independent sample of X-ray-emitting ellipticals. The core radii (similar to 1 kpc) inferred from the fits are typical of those found for cD galaxies. In most cases, where we have two jets within the same galaxy the inferred galaxy atmosphere parameters are almost identical. All jets are initially light with respect to the interstellar medium (ISM) and eventually approach density equilibrium through entrainment. The Mach numbers for most jets are in the range from 1 to 3. However, we can identify a high-Mach number subsample for which the Mach numbers could be as high as 10. Significantly these jets are lighter, better collimated, and more powerful than the rest of the sample, supporting the notion that the transition from class I to class 11 radio sources represents in large part, a transition from low- to high-Mach number jets. The velocities of all the jets in the sample range between similar to 1000-10,000 km s(-1) with the high-Mach number subsample having velocities at the upper end of this range. The jet velocities are consistent with the energy budget in each source (except one), with the qualification that the velocities of some low-velocity jets may be underestimated. It is also possible that these particular sources are approximately in radiative equilibrium. We estimate the mass-to-light ratios for the parent galaxies and find a mean value (for H-o = 100) of 24 +/- 5, somewhat higher than the usual core mass-to-light value of 14. However, these values need to be reassessed in the light of higher quality photometric and spectroscopic data.