
TY  - JOUR
A1  - Murgia, Matteo 
T1  - Spectral Ages of CSOs and CSS Sources
JF  - Publications of the Astronomical Society of Australia
JO  - Publ. Astron. Soc.  Aust.
Y1  - 2003
VL  - 20
IS  - 1
SP  - 19
EP  - 24
KW  - radio continuum: galaxies &#8212; galaxies: evolution
UR  - https://doi.org/10.1071/AS02033 
N2  - This paper deals with the spectral ageing study of a representative sample of compact symmetric objects (CSOs) and compact steep spectrum (CSS) sources. Observations reveal a distinctive high-frequency steepening of the radio spectra of many of these sources. The existence of such a spectral feature is expected or may be naturally interpreted in terms of radiative ageing of synchrotron emitting electrons. The small angular size of CSS sources makes it relatively easy to measure their integrated spectra over a wide frequency range for a conspicuous number of objects. For those sources whose emission is dominated by the mini-lobes, the integrated spectra can be used to constrain the source age. Assuming equipartition magnetic fields, the spectral ages we found are in the range from 102 to 105&#32;yr. Multifrequency VLBA observations allow us to study the spectral properties of two CSOs: B1323&#43;321 and B1943&#43;546. The case of B1943&#43;546 is particularly interesting since for this source a kinematic age has been derived from the proper motion of the hot spots. We found that spectral and kinematic ages agree within a factor of 2. The overall results presented here confirm that the CSOs and CSS sources are indeed young objects. Finally, we show some examples of compact sources characterised by an extraordinary steep and curved spectrum. It is plausible that these are relic sources in which the injection of fresh electrons has ceased for a significant fraction of their lifetime. These observations may indicate either the presence of intermittent activity or a class of short-living objects. Throughout this paper we adopt H0&#32;=&#32;100&#32;h&#32;km&#32;s&#8211;1&#32;Mpc&#8211;1 and q0&#32;=&#32;0.5. 
ER  -

