English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Ultra Steep Spectrum (USS) radio sources have been successfully used toselect powerful radio sources at high redshifts (z>~2). Typically restricted tolarge-sky surveys and relatively bright radio flux densities, it has graduallybecome possible to extend the USS search to sub-mJy levels, thanks to therecent appearance of sensitive low-frequency radio facilities. Here a firstdetailed analysis of the nature of the faintest USS sources is presented. Byusing Giant Metrewave Radio Telescope and Very Large Array radio observationsof the Lockman Hole at 610 MHz and 1.4 GHz, a sample of 58 USS sources, with610 MHz integrated fluxes above 100 microJy, is assembled. Deep infrared dataat 3.6 and 4.5 micron from the Spitzer Extragalactic Representative VolumeSurvey (SERVS) is used to reliably identify counterparts for 48 (83%) of thesesources, showing an average total magnitude of [3.6](AB)=19.8 mag.Spectroscopic redshifts for 14 USS sources, together with photometric redshiftestimates, improved by the use of the deep SERVS data, for a further 19objects, show redshifts ranging from z=0.1 to z=2.8, peaking at z~0.6 andtailing off at high redshifts. The remaining 25 USS sources, with no redshiftestimate, include the faintest [3.6] magnitudes, with 10 sources undetected at3.6 and 4.5 micron (typically [3.6]>22-23 mag, from local measurements), whichsuggests the likely existence of higher redshifts among the sub-mJy USSpopulation. The comparison with the Square Kilometre Array Design StudiesSimulated Skies models indicate that Fanaroff-Riley type I radio sources andradio-quiet Active Galactic Nuclei may constitute the bulk of the faintest USSpopulation, and raises the possibility that the high efficiency of the USStechnique for the selection of high redshift sources remains even at thesub-mJy level.

Ultra Steep Spectrum radio sources in the Lockman Hole: SERVS identifications and redshift distribution at the faintest radio fluxes