|9th of January 2017|
|Giga-hertz Peaked Spectrum (GPS) sources: new results|
|by Phil Edwards (CASS)|
Giga-hertz Peaked Spectrum (GPS) sources are, as their name suggests,
radio sources that have a pronounced peak in their spectrum when flux
density is plotted as a function of frequency. In addition to this
defining characteristic, GPS sources generally have low levels of
polarised flux density, and display low levels of variability with
time. These characteristics differentiate persistent GPS sources from
others which may have a peaked spectrum for only a relatively short
period of time (months to years). Genuine GPS sources are of interest as there
is evidence to suggest they are relatively young radio galaxies. |
A set of multi-frequency, multi-epoch observations made with the ATCA resulted in the identification of 9 new candidate GPS sources. The Long Baseline Array was used to image several of these candidates on the parsec (several light-year) scale at 4.8 GHz, using the Australia Telescope Compact Array (ATCA), Mopra 22m, Parkes 64m, and Hobart 26m telescopes.
The image above is of PKS 1831-711 (J1837-7108), which is clearly resolved into two components separated by 13 milli-arcseconds (a projected separation of about 30 light-years), with the brighter component being about twice as bright as the fainter, and with the fainter component being more extended. Comparison with the earlier ATCA data reveals the source has brightened significantly over several years, suggesting that the peaked spectrum seen earlier was an ephemeral stage in the source evolution. This is consistent with the image above having a bright core (hosting the supermassive black hole at the centre of the galaxy) and a one-sided jet directed towards our line of sight. (The grey ellipse at the bottom depicts the synthesized beam-shape for this observation.)
This images and others from this project are presented in a paper by Edwards & Tingay published in the Publications of the Astronomical Society of Australia (arXiv:1701.01172).