Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOn the cosmological evolution of the FRII radio source population
112
0
0.0
(
0
)
Authors
Christian R. Kaiser
Ask ChatGPT about the research
No Arabic abstract
We present an analytical model for the cosmological evolution of the FRII source population. Based on an earlier model for the intrinsic radio luminosity - linear size evolution of these objects, we construct theoretical source samples. The source distributions in the radio power - linear size plane of these samples are then compared with that of an observed flux-limited sample. We find that the source parameters determining the radio luminosity of FRII objects can not be independent of each other. The best-fitting models predict the jet power to be correlated either with the life time of the source or with the shape of the density distribution of the source environment. The latter case is consistent with the observed tendency of the most luminous radio sources at high redshift to be located in richer and more extended environments than their low redshift counterparts. We also find evidence for a class of FRII sources distinctly different from the main population. These sources are extremely old and/or are located in very underdense environments. The luminosity function of FRII sources resulting from the model is in good agreement with previous results for high luminosity sources. The apparent luminosity evolution of the radio luminosity function is not reproduced because of the high flux limit of the used comparison sample. The cosmological evolution of the median linear size of FRII sources is found to be mild.
rate research
Read More
The time evolution of giant (D>1 Mpc) lobe-dominated galaxies is analysed on the basis of dynamical evolution of the entire FRII-type population.
In this paper we show normalized differential source counts n(S) at 408 MHz and 1.4 GHz of radio sources separately for FRI and FRII classes with extended and compact morphologies. The maps from the FIRST, NVSS, and WENSS surveys are used to define the source morphology and flux density. The counts provide a basis for a direct test as well as constraining the cosmological evolution of powerful extragalactic radio sources in terms of the dual-population model (Jackson & Wall 1999), where radio sources of Fanaroff-Riley (1974) types I and II are regarded as two physically separate types of active galactic nuclei (AGN). The predicted count values are compared with the observational data to find the best fits for the evolution and beaming parameters, and to further refine the model.
A catalogue of 14453 radio-loud AGN with 1.4 GHz fluxes above 3.5 mJy in the redshift range 0.4<z<0.8, has been constructed from the cross-correlation of the NVSS and FIRST radio surveys with the MegaZ-LRG catalogue of luminous red galaxies derived from Sloan Digital Sky Survey imaging data. New techniques were developed for extending the cross-correlation algorithm to FIRST detections that are below the nominal 1 mJy S/N limit of the catalogued sources. We estimate a reliability of ~98.3%, and completeness level (for LRGS) of about 95% for our new catalogue. We present a new determination of the luminosity function of radio AGN at z~0.55 and compare this to the luminosity function of nearby (z~0.1) radio sources from the SDSS main survey. The comoving number density of radio AGN with luminosities less than 10^{25} W Hz^{-1} increases by a factor ~1.5 between z=0.1 and z=0.55. At higher lumiosities, this factor increases sharply, reaching values of more than 10 at radio luminosities larger than 10^{26} W Hz^{-1}. We then study how the relation between radio AGN and their host galaxies evolves with redshift. Our main conclusion is that the fraction of radio-loud AGN increases towards higher redshift in all massive galaxies, but the evolution is particularly strong for the lower mass galaxies in our sample. These trends may be understood if there are two classes of radio galaxies (likely associated with the radio and quasar mode dichotomy) that have different fuelling/triggering mechanisms and hence evolve in different ways.
The time evolution of `fiducial radio sources derived from fitting the dynamical model of Kaiser et al. (1997) is compared with the observational data for the `clan sources found in the sample of giant and normal-size FRII-type sources published Paper I (Machalski et al. 2004). Each `clan comprises 3, 4 or 5 sample sources having similar values of the two basic physical parameters: the jet power Q_{0} and central density of the galaxy nucleus rho_{0} (determined in Paper I) but different ages, radio luminosities and axial ratios. These sources are considered as the `same source observed at different epochs of its lifetime and used to fit the evolutionary luminosity-size (P-D) and energy density-total energy (u_{c}-E_{tot}) tracks derived from the model for a `fiducial source with Q0 and rho_{0} equal to the means of relevant values obtained for the `clan members, as well as to constrain the evolutionary model of the source dynamics used. In the result we find that (i) The best fit is achieved when the Kaiser et al.s model is modified by allowing an evolution of the sources cocoon axial ratio with time as suggested by Blundell et al. (1999). (ii) A slow acceleration of the average expansion speed of the cocoon along the jet axis is suggested by the `clan sources. We argue that this acceleration, although minor, may be real and some supporting arguments come from the well known hydrodynamical considerations.
Compact Symmetric Objects (CSOs) show radio features such as jets, lobes, hot spots that are contained within the central 1 kpc region of their host galaxy. Thus, they are thought to be among the progenitors of large-scale radio galaxies. A debate on whether the CSOs are compact primarily because they are young or because they are surrounded by a dense medium impacting their expansion is ongoing. Until now, attempts to discriminate between the environmental and genuine youthfulness scenarios have been inconclusive. We present a study of three CSOs selected on the basis of their puzzling X-ray absorbing properties in prior Beppo-SAX and/or Chandra X-ray Observatory data. Our new XMM-Newton observations unambiguously confirm the nature of their X-ray absorbers. Furthermore, for the first time, our X-ray data reveal the existence of a population of CSOs with intrinsic hydrogen column density $N_H > 10^{23}$ cm$^{-2}$ that is different from the population of X-ray unabsorbed CSOs. The two groups appear to be separated in the linear size vs. radio power plane. This finding suggests that a dense medium in X-ray obscured CSOs may be able to confine the radio jets. Alternatively, X-ray obscured CSOs could be seen as radio brighter than their unobscured counterparts either because they reside in a dense environment or because they have larger jet powers. Our results help constrain the origin of the X-ray emission and the location and size of the X-ray obscurer in CSOs, and indicate that the environment may play a key role during the initial expansion of a radio source.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
