Speaker
Description
We introduced the Serendipitous H-ATLAS-fields Observations of Radio Extragalactic Sources (SHORES) survey, which targeted 29 fields in total intensity and polarisation within the Herschel-ATLAS Southern Galactic Field. Observations were performed with the Australia Telescope Compact Array in the 2 GHz band, with a central frequency of 2.1 GHz and 2 GHz total bandwidth. Two fields (Deep-1 and Deep-2) were observed to greater depth, while the remaining 27 shallower fields cover ∼26 deg², reaching a typical rms of σ ≲ 33 μJy in the central regions. The Deep-1 field reaches σ ∼ 9 μJy/beam, and Deep-2 ∼ 18 μJy/beam, with a combined coverage of ∼1 deg² at a mean sensitivity of ∼13 μJy/beam. Follow-up mosaics at 5.5, 7.25 and 9 GHz reach rms values of 28–39 μJy.
In the shallow component, 2294 sources were detected, with 95% completeness at 497 μJy and reliable counts down to 150 μJy. Thanks to the 6-km ATCA E-W configuration, we achieved angular resolutions of 3.2 × 7.2 arcsec, with 81% of sources remaining unresolved.
In the deep fields, we extracted 489 sources at 2.1 GHz, of which ∼100 are also detected at 5.5–9 GHz. Reliability reaches 95% at SNR ∼5, while completeness at 95% corresponds to 182 μJy (DEEP-1) and 198 μJy (DEEP-2). The spectral index distribution peaks at ⟨α⟩ ≈ –0.7 with σ ≈ 0.3, dominated by flat-to-steep spectrum sources, while peaked-spectrum sources account for ∼16%. About 20% of detections lack FIR counterparts and typically show steep spectra, consistent with a population of FIR-dark galaxies at z > 3. Among sources with H-ATLAS counterparts (∼19%), most exhibit qFIR > 1.7 and spectral indices typical of star-forming galaxies, indicating that star formation dominates below the mJy level.
Euclidean-normalised differential source counts were derived at 2.1 and 5.5 GHz. At 2.1 GHz, we confirm the transition from AGN to SFG dominance below ∼0.5 mJy, in agreement with models such as Mancuso et al. (2017). The 5.5–9 GHz counts provide the first direct constraints on the sub-mJy sky at these frequencies, showing an indication of flattening below ∼0.3 mJy.
These results demonstrate the value of deep, multi-frequency radio observations in well-characterised extragalactic fields. SHORES bridges the gap between wide-area shallow surveys and ultra-deep pencil-beam fields, offering new constraints on the relative contributions of star formation and AGN activity in preparation for SKA pathfinders and SKA surveys.
| Topics | Galaxy Evolution & AGN |
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