Open AccessOverpressured emission‐line clouds in the haloes of powerful radio galaxies
Author(s) -
Robinson T. G.,
Tadhunter C. N.,
Dyson J. E.
Publication year - 2002
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2002.05318.x
Subject(s) - physics , astrophysics , doubly ionized oxygen , radio galaxy , galaxy , photoionization , line (geometry) , emission spectrum , active galactic nucleus , astronomy , ionization , spectral line , ion , geometry , mathematics , quantum mechanics
We present accurate measurements of the physical conditions in five powerful radio galaxies, as derived from deep, long‐slit spectroscopic observations. All five objects show prominent extended line emission, and have X‐ray luminosities similar to those of isolated elliptical galaxies. The data are high enough quality that the electron density and temperature can be measured at several positions across the emission‐line nebulae. We subtract a model continuum comprising a combination of a 15‐Gyr stellar template, a young stellar template and a power law, so as to be better able to measure faint diagnostic lines. Electron temperatures measured from the [O iii ](4959+5007)/4363 line ratio are in the range 10 000< T e <20 000 K , whilst [S ii ](6716/6731) densities fall between 100–500 cm ‐3 . Using these values, we find pressures within the line‐emitting clouds a factor of 10–100 times higher than expected for pressure balance with the hot X‐ray haloes of the host galaxies. Previous studies of sources that show significant evidence of jet–cloud interactions, both in terms of their kinematics and ionization, have concluded that the overpressure is a result of the warm, line‐emitting gas being compressed by the radio cocoon; however, there is no evidence that the radio jet is influencing the emission‐line regions in four of our five objects. We suggest that it is plausible that the line‐emitting clouds have not yet relaxed into pressure equilibrium from their initial photoionization by the central active galactic nucleus.