The GLEAMing of the first supermassive black holes: III. Radio sources with ultra-faint host galaxies
Bibliographic record
Abstract
Abstract We present deep near-infrared $K_\textrm{s}$ -band imaging for 35 of the 53 sources from the high-redshift ( $z \gt 2$ ) radio galaxy candidate sample defined in Broderick et al. (2022, PASA, 39, e061). These images were obtained using the High-Acuity WidefieldK-band Imager (HAWK-I) on the Very Large Telescope. Host galaxies are detected for 27 of the sources, with $K_\textrm{s} \approx 21.6$ –23.0 mag (2 $^{\prime\prime}$ diameter apertures; AB). The remaining eight targets are not detected to a median $3\unicode{x03C3}$ depth of $K_\textrm{s} \approx 23.3$ mag (2 $^{\prime\prime}$ diameter apertures). We examine the radio and near-infrared flux densities of the 35 sources, comparing them to the known $z \gt 3$ powerful radio galaxies with 500-MHz radio luminosities $L_{500\,\textrm{MHz}} \gt 10^{27}$ W Hz $^{-1}$ . By plotting 150-MHz flux density versus $K_\textrm{s}$ -band flux density, we find that, similar to the sources from the literature, these new targets have large radio to near-infrared flux density ratios, but extending the distribution to fainter flux densities. Five of the eight HAWK-I deep non-detections have a median $3\unicode{x03C3}$ lower limit of $K_\textrm{s} \gtrsim 23.8$ mag (1 $.\!^{\prime\prime}$ 5 diameter apertures); these five targets, along with a further source from Broderick et al. (2022, PASA, 39, e061) with a deep non-detection ( $K_\textrm{s} \gtrsim 23.7$ mag; $3\unicode{x03C3}$ ; 2 $^{\prime\prime}$ diameter aperture) in the Southern H-ATLAS Regions $K_\textrm{s}$ -band Survey, are considered candidates to be ultra-high-redshift ( $z \gt 5$ ) radio galaxies. The extreme radio to near-infrared flux density ratios ( $\gt 10^5$ ) for these six sources are comparable to TN J0924 $-$ 2201, GLEAM J0856 $+$ 0223 and TGSS J1530 $+$ 1049, the three known powerful radio galaxies at $z \gt 5$ . For a selection of galaxy templates with different stellar masses, we show that $z \gtrsim 4.2$ is a plausible scenario for our ultra-high-redshift candidates if the stellar mass $M_\textrm{*} \gtrsim 10^{10.5}$ M $_\odot$ . In general, the 35 targets studied have properties consistent with the previously known class of infrared-faint radio sources. We also discuss the prospects for finding more UHzRG candidates from wide and deep near-infrared surveys.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".