Towards 21-cm intensity mapping at <i>z</i> = 2.28 with uGMRT using the tapered gridded estimator – III. Foreground removal
Bibliographic record
Abstract
ABSTRACT Neutral hydrogen (${\rm H\, \small {I}}$) 21-cm intensity mapping (IM) is a promising probe of the large-scale structures in the Universe. However, a few orders of magnitude brighter foregrounds obscure the IM signal. Here, we use the tapered gridded estimator to estimate the multifrequency angular power spectrum Cℓ(Δν) from a $24.4\hbox{-} \rm {MHz}$ bandwidth upgraded Giant Metrewave Radio Telescope Band 3 data at $432.8\ \rm {MHz}$. In Cℓ(Δν) foregrounds remain correlated across the entire Δν range, whereas the 21-cm signal is localized within Δν ≤ [Δν] (typically, 0.5–1 MHz). Assuming the range Δν &gt; [Δν] to have minimal 21-cm signal, we use Cℓ(Δν) in this range to model the foregrounds. This foreground model is extrapolated to Δν ≤ [Δν], and subtracted from the measured Cℓ(Δν). The residual [Cℓ(Δν)]res in the range Δν ≤ [Δν] is used to constrain the 21-cm signal, compensating for the signal loss from foreground subtraction. [Cℓ(Δν)]res is found to be noise-dominated without any trace of foregrounds. Using [Cℓ(Δν)]res, we constrain the 21-cm brightness temperature fluctuations Δ2(k), and obtain the 2σ upper limit $\Delta _{\rm UL}^2(k)\le (18.07)^2\ \rm {mK^2}$ at $k=0.247\ \rm {Mpc}^{-1}$. We further obtain the 2σ upper limit $[\Omega _{{\rm H\, \small {I}}}b_{{\rm H\, \small {I}}}]_{\rm UL}\le 0.022$, where $\Omega _{{\rm H\, \small {I}}}$ and $b_{{\rm H\, \small {I}}}$ are the comoving ${\rm H\, \small {I}}$ density and bias parameters, respectively. Although the upper limit is nearly 10 times larger than the expected 21-cm signal, it is 3 times tighter over previous works using foreground avoidance on the same data.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".