SIMBAD references

We report on the first X-ray Chandra observations of a sample of seven low-luminosity compact sources, which belong to a class of young compact steep spectrum (CSS) radio sources. Four of these have been detected, while the other three have upper limit estimations for X-ray flux; one CSS galaxy is associated with an X-ray cluster. We have used the new observations, together with the observational data for known strong CSS and gigahertz-peaked spectrum (GPS) objects and large-scale Fanaroff-Riley types I and II objects (FR I and II), to study the relation between morphology, X-ray properties and excitation modes in radio-loud active galactic nuclei (AGNs). We have found the following. (i) The low-power objects fit well with the already established X-ray-radio luminosity correlation for AGNs and occupy the space among FR I objects, which are weaker in X-rays. (ii) The high-excitation and low-excitation galaxies occupy a distinct locus in the radio/X-ray luminosity plane, notwithstanding their evolutionary stage. This is in agreement with the postulated different origins of the X-ray emission in these two groups of objects. (iii) We have tested the AGN evolution models by comparing the radio/X-ray luminosity ratio with the size of the sources and, indirectly, with their age. We conclude that the division for two different X-ray emission modes, which originate in the base of the relativistic jet (FR Is) or in the accretion disc (FR IIs) is already present among the younger compact AGNs. (iv) Finally, we have found that the CSS sources are less obscured than the more compact GPS objects in X-rays. However, the anticorrelation between X-ray column density and radio size does not hold for the whole sample of GPS and CSS objects.