Probing Halos of Galaxies at Very Large Radii Using Background QSOs
Bibliographic record
Abstract
Gaseous halos of nine nearby galaxies (with redshifts cz < 6000 km s -1 ) were probed at large galactocentric radii using background quasars observed with the Hubble Space Telescope Goddard High Resolution Spectrograph and the Space Telescope Imaging Spectrograph. The projected quasar-galaxy separations range from 55 to 387 h kpc. Lyα absorption lines were successfully detected in the spectra of five quasars, at impact parameters of up to ~170 h kpc from the center of the nearby galaxy, and in each case at wavelengths consistent with the galaxy's redshift. Our observations include the lowest redshift Lyα lines detected to date. H I velocity fields were obtained at the Very Large Array for three of the galaxies in our sample (in one case the velocity field was available from the literature) to derive their rotation curves. When comparing the inner rotation curves of the galaxies with the velocity at large radius provided by the Lyα line, it is apparent that it is very difficult to explain the observed Lyα velocity as due to gas in an extended rotating disk. In most cases, one would need to invoke large warps in the outer gas disks and also thick gas disks to reconcile the observed velocities with the predicted ones. Indeed, in one case, the Lyα line velocity indicates, in fact, counterrotation with respect to the inner disk rotation. In light of these results, we conclude that in a typical galaxy there is no longer detectable atomic gas corotating in an extended disk at radii greater than 35α -1 , where α -1 is the stellar disk exponential scale length. The cosmic web is the most likely origin for the detected Lyα lines. Our observations confirm the recent Bowen et al. correlation of equivalent widths with the local volume density of galaxies around the sight line, and the observed equivalent widths of the lines are consistent with expectations of the cosmic web.
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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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".