A DEEP SEARCH FOR EXTENDED RADIO CONTINUUM EMISSION FROM DWARF SPHEROIDAL GALAXIES: IMPLICATIONS FOR PARTICLE DARK MATTER
Bibliographic record
Abstract
We present deep radio observations of four nearby dwarf spheroidal (dSph) galaxies, designed to detect extended synchrotron emission resulting from weakly interacting massive particle (WIMP) dark matter annihilations in their halos. Models by Colafrancesco et al. (CPU07) predict the existence of angularly large, smoothly distributed radio halos in such systems, which stem from electron and positron annihilation products spiraling in a turbulent magnetic field. We map a total of 40.5 deg 2 around the Draco, Ursa Major II, Coma Berenices, and Willman 1 dSphs with the Green Bank Telescope (GBT) at 1.4 GHz to detect this annihilation signature, greatly reducing discrete-source confusion using the NVSS catalog. We achieve a sensitivity of σ sub ≲ 7 mJy beam −1 in our discrete source-subtracted maps, implying that the NVSS is highly effective at removing background sources from GBT maps. For Draco we obtained approximately concurrent Very Large Array observations to quantify the variability of the discrete source background, and find it to have a negligible effect on our results. We construct radial surface brightness profiles from each of the subtracted maps, and jackknife the data to quantify the significance of the features therein. At the ∼10' resolution of our observations, foregrounds contribute a standard deviation of 1.8 mJy beam −1 ⩽ σ ast ⩽ 5.7 mJy beam −1 to our high-latitude maps, with the emission in Draco and Coma dominated by foregrounds. On the other hand, we find no significant emission in the Ursa Major II and Willman 1 fields, and explore the implications of non-detections in these fields for particle dark matter using the fiducial models of CPU07. For a WIMP mass M χ = 100 GeV annihilating into final states and B = 1 μG, upper limits on the annihilation cross-section for Ursa Major II and Willman I are log (〈σ v 〉 χ , cm 3 s −1 ) ≲ −25 for the preferred set of charged particle propagation parameters adopted by CPU07; this is comparable to that inferred at γ-ray energies from the two-year Fermi Large Area Telescope data. We discuss three avenues for improving the constraints on 〈σ v 〉 χ presented here, and conclude that deep radio observations of dSphs are highly complementary to indirect WIMP searches at higher energies.
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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 | 0.000 |
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".