NGC 4438 and its environment at radio wavelengths
Bibliographic record
Abstract
We present multifrequency radio continuum and H i observations of NGC 4438, the highly disturbed, active galaxy in the Virgo cluster, with the Very Large Array (VLA) and the Giant Metrewave Radio Telescope (GMRT). High-resolution observations of the central 1 kpc with the VLA at 4860 and 8460 MHz show the presence of an inverted-spectrum radio nucleus located between the highly asymmetric lobes of radio emission. This demonstrates that these lobes which are seen in radio continuum, Hα and X-ray wavelengths and are located at ∼230 and 730 pc from the nucleus arise due to an active galactic nucleus rather than a compact nuclear starburst. The low-frequency radio continuum observations made with the GMRT detect the extended emission on the western side of the galaxy whose spectral index is flatter at higher frequencies and suggests that it is a mixture of thermal and non-thermal emission. The H i observations show an elongated structure which is displaced by ∼4.1 kpc on the western side of NGC 4438 and has a size of ∼9.8 kpc and a mass of 1.8 × 108 M⊙. The velocity field suggests systematic rotation, consistent with earlier observations. These observations also detect H i emission from the disc of the galaxy with a mass of 1.2 × 108 M⊙. We detect a faint H i tail towards the north of NGC 4438 close to a stellar tail seen earlier in deep optical observations. This H i tail has a total extent of ∼50 kpc and a mass of 1.4 × 108 M⊙ if it is at the distance of NGC 4438. The velocity of the H i tail is ∼−10 km s−1 similar to that of H i emission from IC 3355, but the possibility that the tail could be foreground Galactic emission cannot be ruled out. We discuss the different structures in light of different models which have been suggested for this disturbed galaxy, namely ram pressure stripping, tidal and interstellar medium (ISM)–ISM interactions.
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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 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".