Empirical determinations of key physical parameters related to classical double radio sources

Lin Wan, Ruth A. Daly, Erick J. Guerra

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26 Scopus citations


Multifrequency radio observations of the radio bridge of a powerful classical double radio source can be used to determine the beam power of the jets emanating from the active galactic nucleus (AGN), the total time the source will actively produce jets that power large-scale radio emission, the thermal pressure of the medium in the vicinity of the radio source, and the total mass, including dark matter, of the galaxy or cluster of galaxies traced by the ambient gas that surrounds the radio source. The theoretical constructs that allow a determination of each of these quantities using radio observations are presented and discussed. Empirical determinations of each of these quantities are obtained and analyzed for 22 radio sources; Cygnus A is one of the sources in the sample, but it is not used, or needed, to normalize any of these quantities. A sample of 14 radio galaxies and eight radio-loud quasars with redshifts between 0 and 2 was studied in detail; each source has enough radio information to be able to determine each of the physical parameters listed above. The beam power was determined for each beam of each AGN (so there are two numbers for each source); these AGNs are highly symmetric in terms of beam powers. Typical beam powers are about 1045 ergs s-1. No strong correlation is seen between the beam power and the core-hot spot separation, which suggests that the beam power is roughly constant over the lifetime of a source. The beam power increases with redshift, which is significant after excluding correlations between the radio power and redshift. The relationship between beam power and radio power is not well constrained by the current data. The characteristic or total time the AGN will actively produce a collimated outflow is estimated. Typical total lifetimes are ∼ (107-108) yr. Total source lifetimes decrease with redshift. This decrease in total lifetime with increasing redshift can explain the decrease in the average source size (hot spot-hot spot separation) with redshift. Thus, high-redshift sources are smaller because they have shorter lifetimes; note that higher redshift sources grow more rapidly than low-redshift sources. A new method of estimating the thermal pressure of the ambient gas in the vicinity of a powerful classical double radio source is presented. This new estimate is independent of synchrotron and inverse Compton aging arguments, and depends only upon the properties of the radio lobe and the shape of the radio bridge. A detailed radio map of the radio bridge at a single radio frequency can be used to estimate the thermal pressure of the ambient gas. Thermal pressures on the order of 10-10 dynes cm-2, typical of gas in low-redshift clusters of galaxies, are found for the environments of the sources studied here. It is shown that appreciable amounts of cosmic microwave background diminution (the Sunyaev-Zeldovich effect) are expected from many of these clusters. This could be detected at high frequency where the emission from the radio sources is weak. The total gravitational mass of the host cluster of galaxies is estimated using the composite pressure profile and the equation of hydrostatic equilibrium for cluster gas. Total masses, and mass-density profiles, similar to those of low-redshift clusters of galaxies, are obtained. Thus, some clusters of galaxies, or cores of clusters, exist at redshifts of 1-2. The redshift evolution of the cluster mass is not well determined at present. The current data do not indicate any negative evolution of the cluster mass, which may have implications for models of evolution of structure in the universe.

Original languageEnglish (US)
Pages (from-to)671-685
Number of pages15
JournalAstrophysical Journal
Issue number2 PART 1
StatePublished - Dec 1 2000

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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